summaryrefslogtreecommitdiffstats
path: root/fs/btrfs/backref.c
blob: 79336fa853db363c5543d2b880a9290a99ce41ff (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2011 STRATO.  All rights reserved.
 */

#include <linux/mm.h>
#include <linux/rbtree.h>
#include <trace/events/btrfs.h>
#include "ctree.h"
#include "disk-io.h"
#include "backref.h"
#include "ulist.h"
#include "transaction.h"
#include "delayed-ref.h"
#include "locking.h"
#include "misc.h"
#include "tree-mod-log.h"
#include "fs.h"
#include "accessors.h"
#include "extent-tree.h"
#include "relocation.h"
#include "tree-checker.h"

/* Just arbitrary numbers so we can be sure one of these happened. */
#define BACKREF_FOUND_SHARED     6
#define BACKREF_FOUND_NOT_SHARED 7

struct extent_inode_elem {
	u64 inum;
	u64 offset;
	u64 num_bytes;
	struct extent_inode_elem *next;
};

static int check_extent_in_eb(struct btrfs_backref_walk_ctx *ctx,
			      const struct btrfs_key *key,
			      const struct extent_buffer *eb,
			      const struct btrfs_file_extent_item *fi,
			      struct extent_inode_elem **eie)
{
	const u64 data_len = btrfs_file_extent_num_bytes(eb, fi);
	u64 offset = key->offset;
	struct extent_inode_elem *e;
	const u64 *root_ids;
	int root_count;
	bool cached;

	if (!ctx->ignore_extent_item_pos &&
	    !btrfs_file_extent_compression(eb, fi) &&
	    !btrfs_file_extent_encryption(eb, fi) &&
	    !btrfs_file_extent_other_encoding(eb, fi)) {
		u64 data_offset;

		data_offset = btrfs_file_extent_offset(eb, fi);

		if (ctx->extent_item_pos < data_offset ||
		    ctx->extent_item_pos >= data_offset + data_len)
			return 1;
		offset += ctx->extent_item_pos - data_offset;
	}

	if (!ctx->indirect_ref_iterator || !ctx->cache_lookup)
		goto add_inode_elem;

	cached = ctx->cache_lookup(eb->start, ctx->user_ctx, &root_ids,
				   &root_count);
	if (!cached)
		goto add_inode_elem;

	for (int i = 0; i < root_count; i++) {
		int ret;

		ret = ctx->indirect_ref_iterator(key->objectid, offset,
						 data_len, root_ids[i],
						 ctx->user_ctx);
		if (ret)
			return ret;
	}

add_inode_elem:
	e = kmalloc(sizeof(*e), GFP_NOFS);
	if (!e)
		return -ENOMEM;

	e->next = *eie;
	e->inum = key->objectid;
	e->offset = offset;
	e->num_bytes = data_len;
	*eie = e;

	return 0;
}

static void free_inode_elem_list(struct extent_inode_elem *eie)
{
	struct extent_inode_elem *eie_next;

	for (; eie; eie = eie_next) {
		eie_next = eie->next;
		kfree(eie);
	}
}

static int find_extent_in_eb(struct btrfs_backref_walk_ctx *ctx,
			     const struct extent_buffer *eb,
			     struct extent_inode_elem **eie)
{
	u64 disk_byte;
	struct btrfs_key key;
	struct btrfs_file_extent_item *fi;
	int slot;
	int nritems;
	int extent_type;
	int ret;

	/*
	 * from the shared data ref, we only have the leaf but we need
	 * the key. thus, we must look into all items and see that we
	 * find one (some) with a reference to our extent item.
	 */
	nritems = btrfs_header_nritems(eb);
	for (slot = 0; slot < nritems; ++slot) {
		btrfs_item_key_to_cpu(eb, &key, slot);
		if (key.type != BTRFS_EXTENT_DATA_KEY)
			continue;
		fi = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
		extent_type = btrfs_file_extent_type(eb, fi);
		if (extent_type == BTRFS_FILE_EXTENT_INLINE)
			continue;
		/* don't skip BTRFS_FILE_EXTENT_PREALLOC, we can handle that */
		disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
		if (disk_byte != ctx->bytenr)
			continue;

		ret = check_extent_in_eb(ctx, &key, eb, fi, eie);
		if (ret == BTRFS_ITERATE_EXTENT_INODES_STOP || ret < 0)
			return ret;
	}

	return 0;
}

struct preftree {
	struct rb_root_cached root;
	unsigned int count;
};

#define PREFTREE_INIT	{ .root = RB_ROOT_CACHED, .count = 0 }

struct preftrees {
	struct preftree direct;    /* BTRFS_SHARED_[DATA|BLOCK]_REF_KEY */
	struct preftree indirect;  /* BTRFS_[TREE_BLOCK|EXTENT_DATA]_REF_KEY */
	struct preftree indirect_missing_keys;
};

/*
 * Checks for a shared extent during backref search.
 *
 * The share_count tracks prelim_refs (direct and indirect) having a
 * ref->count >0:
 *  - incremented when a ref->count transitions to >0
 *  - decremented when a ref->count transitions to <1
 */
struct share_check {
	struct btrfs_backref_share_check_ctx *ctx;
	struct btrfs_root *root;
	u64 inum;
	u64 data_bytenr;
	u64 data_extent_gen;
	/*
	 * Counts number of inodes that refer to an extent (different inodes in
	 * the same root or different roots) that we could find. The sharedness
	 * check typically stops once this counter gets greater than 1, so it
	 * may not reflect the total number of inodes.
	 */
	int share_count;
	/*
	 * The number of times we found our inode refers to the data extent we
	 * are determining the sharedness. In other words, how many file extent
	 * items we could find for our inode that point to our target data
	 * extent. The value we get here after finishing the extent sharedness
	 * check may be smaller than reality, but if it ends up being greater
	 * than 1, then we know for sure the inode has multiple file extent
	 * items that point to our inode, and we can safely assume it's useful
	 * to cache the sharedness check result.
	 */
	int self_ref_count;
	bool have_delayed_delete_refs;
};

static inline int extent_is_shared(struct share_check *sc)
{
	return (sc && sc->share_count > 1) ? BACKREF_FOUND_SHARED : 0;
}

static struct kmem_cache *btrfs_prelim_ref_cache;

int __init btrfs_prelim_ref_init(void)
{
	btrfs_prelim_ref_cache = kmem_cache_create("btrfs_prelim_ref",
					sizeof(struct prelim_ref),
					0,
					SLAB_MEM_SPREAD,
					NULL);
	if (!btrfs_prelim_ref_cache)
		return -ENOMEM;
	return 0;
}

void __cold btrfs_prelim_ref_exit(void)
{
	kmem_cache_destroy(btrfs_prelim_ref_cache);
}

static void free_pref(struct prelim_ref *ref)
{
	kmem_cache_free(btrfs_prelim_ref_cache, ref);
}

/*
 * Return 0 when both refs are for the same block (and can be merged).
 * A -1 return indicates ref1 is a 'lower' block than ref2, while 1
 * indicates a 'higher' block.
 */
static int prelim_ref_compare(struct prelim_ref *ref1,
			      struct prelim_ref *ref2)
{
	if (ref1->level < ref2->level)
		return -1;
	if (ref1->level > ref2->level)
		return 1;
	if (ref1->root_id < ref2->root_id)
		return -1;
	if (ref1->root_id > ref2->root_id)
		return 1;
	if (ref1->key_for_search.type < ref2->key_for_search.type)
		return -1;
	if (ref1->key_for_search.type > ref2->key_for_search.type)
		return 1;
	if (ref1->key_for_search.objectid < ref2->key_for_search.objectid)
		return -1;
	if (ref1->key_for_search.objectid > ref2->key_for_search.objectid)
		return 1;
	if (ref1->key_for_search.offset < ref2->key_for_search.offset)
		return -1;
	if (ref1->key_for_search.offset > ref2->key_for_search.offset)
		return 1;
	if (ref1->parent < ref2->parent)
		return -1;
	if (ref1->parent > ref2->parent)
		return 1;

	return 0;
}

static void update_share_count(struct share_check *sc, int oldcount,
			       int newcount, struct prelim_ref *newref)
{
	if ((!sc) || (oldcount == 0 && newcount < 1))
		return;

	if (oldcount > 0 && newcount < 1)
		sc->share_count--;
	else if (oldcount < 1 && newcount > 0)
		sc->share_count++;

	if (newref->root_id == sc->root->root_key.objectid &&
	    newref->wanted_disk_byte == sc->data_bytenr &&
	    newref->key_for_search.objectid == sc->inum)
		sc->self_ref_count += newref->count;
}

/*
 * Add @newref to the @root rbtree, merging identical refs.
 *
 * Callers should assume that newref has been freed after calling.
 */
static void prelim_ref_insert(const struct btrfs_fs_info *fs_info,
			      struct preftree *preftree,
			      struct prelim_ref *newref,
			      struct share_check *sc)
{
	struct rb_root_cached *root;
	struct rb_node **p;
	struct rb_node *parent = NULL;
	struct prelim_ref *ref;
	int result;
	bool leftmost = true;

	root = &preftree->root;
	p = &root->rb_root.rb_node;

	while (*p) {
		parent = *p;
		ref = rb_entry(parent, struct prelim_ref, rbnode);
		result = prelim_ref_compare(ref, newref);
		if (result < 0) {
			p = &(*p)->rb_left;
		} else if (result > 0) {
			p = &(*p)->rb_right;
			leftmost = false;
		} else {
			/* Identical refs, merge them and free @newref */
			struct extent_inode_elem *eie = ref->inode_list;

			while (eie && eie->next)
				eie = eie->next;

			if (!eie)
				ref->inode_list = newref->inode_list;
			else
				eie->next = newref->inode_list;
			trace_btrfs_prelim_ref_merge(fs_info, ref, newref,
						     preftree->count);
			/*
			 * A delayed ref can have newref->count < 0.
			 * The ref->count is updated to follow any
			 * BTRFS_[ADD|DROP]_DELAYED_REF actions.
			 */
			update_share_count(sc, ref->count,
					   ref->count + newref->count, newref);
			ref->count += newref->count;
			free_pref(newref);
			return;
		}
	}

	update_share_count(sc, 0, newref->count, newref);
	preftree->count++;
	trace_btrfs_prelim_ref_insert(fs_info, newref, NULL, preftree->count);
	rb_link_node(&newref->rbnode, parent, p);
	rb_insert_color_cached(&newref->rbnode, root, leftmost);
}

/*
 * Release the entire tree.  We don't care about internal consistency so
 * just free everything and then reset the tree root.
 */
static void prelim_release(struct preftree *preftree)
{
	struct prelim_ref *ref, *next_ref;

	rbtree_postorder_for_each_entry_safe(ref, next_ref,
					     &preftree->root.rb_root, rbnode) {
		free_inode_elem_list(ref->inode_list);
		free_pref(ref);
	}

	preftree->root = RB_ROOT_CACHED;
	preftree->count = 0;
}

/*
 * the rules for all callers of this function are:
 * - obtaining the parent is the goal
 * - if you add a key, you must know that it is a correct key
 * - if you cannot add the parent or a correct key, then we will look into the
 *   block later to set a correct key
 *
 * delayed refs
 * ============
 *        backref type | shared | indirect | shared | indirect
 * information         |   tree |     tree |   data |     data
 * --------------------+--------+----------+--------+----------
 *      parent logical |    y   |     -    |    -   |     -
 *      key to resolve |    -   |     y    |    y   |     y
 *  tree block logical |    -   |     -    |    -   |     -
 *  root for resolving |    y   |     y    |    y   |     y
 *
 * - column 1:       we've the parent -> done
 * - column 2, 3, 4: we use the key to find the parent
 *
 * on disk refs (inline or keyed)
 * ==============================
 *        backref type | shared | indirect | shared | indirect
 * information         |   tree |     tree |   data |     data
 * --------------------+--------+----------+--------+----------
 *      parent logical |    y   |     -    |    y   |     -
 *      key to resolve |    -   |     -    |    -   |     y
 *  tree block logical |    y   |     y    |    y   |     y
 *  root for resolving |    -   |     y    |    y   |     y
 *
 * - column 1, 3: we've the parent -> done
 * - column 2:    we take the first key from the block to find the parent
 *                (see add_missing_keys)
 * - column 4:    we use the key to find the parent
 *
 * additional information that's available but not required to find the parent
 * block might help in merging entries to gain some speed.
 */
static int add_prelim_ref(const struct btrfs_fs_info *fs_info,
			  struct preftree *preftree, u64 root_id,
			  const struct btrfs_key *key, int level, u64 parent,
			  u64 wanted_disk_byte, int count,
			  struct share_check *sc, gfp_t gfp_mask)
{
	struct prelim_ref *ref;

	if (root_id == BTRFS_DATA_RELOC_TREE_OBJECTID)
		return 0;

	ref = kmem_cache_alloc(btrfs_prelim_ref_cache, gfp_mask);
	if (!ref)
		return -ENOMEM;

	ref->root_id = root_id;
	if (key)
		ref->key_for_search = *key;
	else
		memset(&ref->key_for_search, 0, sizeof(ref->key_for_search));

	ref->inode_list = NULL;
	ref->level = level;
	ref->count = count;
	ref->parent = parent;
	ref->wanted_disk_byte = wanted_disk_byte;
	prelim_ref_insert(fs_info, preftree, ref, sc);
	return extent_is_shared(sc);
}

/* direct refs use root == 0, key == NULL */
static int add_direct_ref(const struct btrfs_fs_info *fs_info,
			  struct preftrees *preftrees, int level, u64 parent,
			  u64 wanted_disk_byte, int count,
			  struct share_check *sc, gfp_t gfp_mask)
{
	return add_prelim_ref(fs_info, &preftrees->direct, 0, NULL, level,
			      parent, wanted_disk_byte, count, sc, gfp_mask);
}

/* indirect refs use parent == 0 */
static int add_indirect_ref(const struct btrfs_fs_info *fs_info,
			    struct preftrees *preftrees, u64 root_id,
			    const struct btrfs_key *key, int level,
			    u64 wanted_disk_byte, int count,
			    struct share_check *sc, gfp_t gfp_mask)
{
	struct preftree *tree = &preftrees->indirect;

	if (!key)
		tree = &preftrees->indirect_missing_keys;
	return add_prelim_ref(fs_info, tree, root_id, key, level, 0,
			      wanted_disk_byte, count, sc, gfp_mask);
}

static int is_shared_data_backref(struct preftrees *preftrees, u64 bytenr)
{
	struct rb_node **p = &preftrees->direct.root.rb_root.rb_node;
	struct rb_node *parent = NULL;
	struct prelim_ref *ref = NULL;
	struct prelim_ref target = {};
	int result;

	target.parent = bytenr;

	while (*p) {
		parent = *p;
		ref = rb_entry(parent, struct prelim_ref, rbnode);
		result = prelim_ref_compare(ref, &target);

		if (result < 0)
			p = &(*p)->rb_left;
		else if (result > 0)
			p = &(*p)->rb_right;
		else
			return 1;
	}
	return 0;
}

static int add_all_parents(struct btrfs_backref_walk_ctx *ctx,
			   struct btrfs_root *root, struct btrfs_path *path,
			   struct ulist *parents,
			   struct preftrees *preftrees, struct prelim_ref *ref,
			   int level)
{
	int ret = 0;
	int slot;
	struct extent_buffer *eb;
	struct btrfs_key key;
	struct btrfs_key *key_for_search = &ref->key_for_search;
	struct btrfs_file_extent_item *fi;
	struct extent_inode_elem *eie = NULL, *old = NULL;
	u64 disk_byte;
	u64 wanted_disk_byte = ref->wanted_disk_byte;
	u64 count = 0;
	u64 data_offset;
	u8 type;

	if (level != 0) {
		eb = path->nodes[level];
		ret = ulist_add(parents, eb->start, 0, GFP_NOFS);
		if (ret < 0)
			return ret;
		return 0;
	}

	/*
	 * 1. We normally enter this function with the path already pointing to
	 *    the first item to check. But sometimes, we may enter it with
	 *    slot == nritems.
	 * 2. We are searching for normal backref but bytenr of this leaf
	 *    matches shared data backref
	 * 3. The leaf owner is not equal to the root we are searching
	 *
	 * For these cases, go to the next leaf before we continue.
	 */
	eb = path->nodes[0];
	if (path->slots[0] >= btrfs_header_nritems(eb) ||
	    is_shared_data_backref(preftrees, eb->start) ||
	    ref->root_id != btrfs_header_owner(eb)) {
		if (ctx->time_seq == BTRFS_SEQ_LAST)
			ret = btrfs_next_leaf(root, path);
		else
			ret = btrfs_next_old_leaf(root, path, ctx->time_seq);
	}

	while (!ret && count < ref->count) {
		eb = path->nodes[0];
		slot = path->slots[0];

		btrfs_item_key_to_cpu(eb, &key, slot);

		if (key.objectid != key_for_search->objectid ||
		    key.type != BTRFS_EXTENT_DATA_KEY)
			break;

		/*
		 * We are searching for normal backref but bytenr of this leaf
		 * matches shared data backref, OR
		 * the leaf owner is not equal to the root we are searching for
		 */
		if (slot == 0 &&
		    (is_shared_data_backref(preftrees, eb->start) ||
		     ref->root_id != btrfs_header_owner(eb))) {
			if (ctx->time_seq == BTRFS_SEQ_LAST)
				ret = btrfs_next_leaf(root, path);
			else
				ret = btrfs_next_old_leaf(root, path, ctx->time_seq);
			continue;
		}
		fi = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
		type = btrfs_file_extent_type(eb, fi);
		if (type == BTRFS_FILE_EXTENT_INLINE)
			goto next;
		disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
		data_offset = btrfs_file_extent_offset(eb, fi);

		if (disk_byte == wanted_disk_byte) {
			eie = NULL;
			old = NULL;
			if (ref->key_for_search.offset == key.offset - data_offset)
				count++;
			else
				goto next;
			if (!ctx->skip_inode_ref_list) {
				ret = check_extent_in_eb(ctx, &key, eb, fi, &eie);
				if (ret == BTRFS_ITERATE_EXTENT_INODES_STOP ||
				    ret < 0)
					break;
			}
			if (ret > 0)
				goto next;
			ret = ulist_add_merge_ptr(parents, eb->start,
						  eie, (void **)&old, GFP_NOFS);
			if (ret < 0)
				break;
			if (!ret && !ctx->skip_inode_ref_list) {
				while (old->next)
					old = old->next;
				old->next = eie;
			}
			eie = NULL;
		}
next:
		if (ctx->time_seq == BTRFS_SEQ_LAST)
			ret = btrfs_next_item(root, path);
		else
			ret = btrfs_next_old_item(root, path, ctx->time_seq);
	}

	if (ret == BTRFS_ITERATE_EXTENT_INODES_STOP || ret < 0)
		free_inode_elem_list(eie);
	else if (ret > 0)
		ret = 0;

	return ret;
}

/*
 * resolve an indirect backref in the form (root_id, key, level)
 * to a logical address
 */
static int resolve_indirect_ref(struct btrfs_backref_walk_ctx *ctx,
				struct btrfs_path *path,
				struct preftrees *preftrees,
				struct prelim_ref *ref, struct ulist *parents)
{
	struct btrfs_root *root;
	struct extent_buffer *eb;
	int ret = 0;
	int root_level;
	int level = ref->level;
	struct btrfs_key search_key = ref->key_for_search;

	/*
	 * If we're search_commit_root we could possibly be holding locks on
	 * other tree nodes.  This happens when qgroups does backref walks when
	 * adding new delayed refs.  To deal with this we need to look in cache
	 * for the root, and if we don't find it then we need to search the
	 * tree_root's commit root, thus the btrfs_get_fs_root_commit_root usage
	 * here.
	 */
	if (path->search_commit_root)
		root = btrfs_get_fs_root_commit_root(ctx->fs_info, path, ref->root_id);
	else
		root = btrfs_get_fs_root(ctx->fs_info, ref->root_id, false);
	if (IS_ERR(root)) {
		ret = PTR_ERR(root);
		goto out_free;
	}

	if (!path->search_commit_root &&
	    test_bit(BTRFS_ROOT_DELETING, &root->state)) {
		ret = -ENOENT;
		goto out;
	}

	if (btrfs_is_testing(ctx->fs_info)) {
		ret = -ENOENT;
		goto out;
	}

	if (path->search_commit_root)
		root_level = btrfs_header_level(root->commit_root);
	else if (ctx->time_seq == BTRFS_SEQ_LAST)
		root_level = btrfs_header_level(root->node);
	else
		root_level = btrfs_old_root_level(root, ctx->time_seq);

	if (root_level + 1 == level)
		goto out;

	/*
	 * We can often find data backrefs with an offset that is too large
	 * (>= LLONG_MAX, maximum allowed file offset) due to underflows when
	 * subtracting a file's offset with the data offset of its
	 * corresponding extent data item. This can happen for example in the
	 * clone ioctl.
	 *
	 * So if we detect such case we set the search key's offset to zero to
	 * make sure we will find the matching file extent item at
	 * add_all_parents(), otherwise we will miss it because the offset
	 * taken form the backref is much larger then the offset of the file
	 * extent item. This can make us scan a very large number of file
	 * extent items, but at least it will not make us miss any.
	 *
	 * This is an ugly workaround for a behaviour that should have never
	 * existed, but it does and a fix for the clone ioctl would touch a lot
	 * of places, cause backwards incompatibility and would not fix the
	 * problem for extents cloned with older kernels.
	 */
	if (search_key.type == BTRFS_EXTENT_DATA_KEY &&
	    search_key.offset >= LLONG_MAX)
		search_key.offset = 0;
	path->lowest_level = level;
	if (ctx->time_seq == BTRFS_SEQ_LAST)
		ret = btrfs_search_slot(NULL, root, &search_key, path, 0, 0);
	else
		ret = btrfs_search_old_slot(root, &search_key, path, ctx->time_seq);

	btrfs_debug(ctx->fs_info,
		"search slot in root %llu (level %d, ref count %d) returned %d for key (%llu %u %llu)",
		 ref->root_id, level, ref->count, ret,
		 ref->key_for_search.objectid, ref->key_for_search.type,
		 ref->key_for_search.offset);
	if (ret < 0)
		goto out;

	eb = path->nodes[level];
	while (!eb) {
		if (WARN_ON(!level)) {
			ret = 1;
			goto out;
		}
		level--;
		eb = path->nodes[level];
	}

	ret = add_all_parents(ctx, root, path, parents, preftrees, ref, level);
out:
	btrfs_put_root(root);
out_free:
	path->lowest_level = 0;
	btrfs_release_path(path);
	return ret;
}

static struct extent_inode_elem *
unode_aux_to_inode_list(struct ulist_node *node)
{
	if (!node)
		return NULL;
	return (struct extent_inode_elem *)(uintptr_t)node->aux;
}

static void free_leaf_list(struct ulist *ulist)
{
	struct ulist_node *node;
	struct ulist_iterator uiter;

	ULIST_ITER_INIT(&uiter);
	while ((node = ulist_next(ulist, &uiter)))
		free_inode_elem_list(unode_aux_to_inode_list(node));

	ulist_free(ulist);
}

/*
 * We maintain three separate rbtrees: one for direct refs, one for
 * indirect refs which have a key, and one for indirect refs which do not
 * have a key. Each tree does merge on insertion.
 *
 * Once all of the references are located, we iterate over the tree of
 * indirect refs with missing keys. An appropriate key is located and
 * the ref is moved onto the tree for indirect refs. After all missing
 * keys are thus located, we iterate over the indirect ref tree, resolve
 * each reference, and then insert the resolved reference onto the
 * direct tree (merging there too).
 *
 * New backrefs (i.e., for parent nodes) are added to the appropriate
 * rbtree as they are encountered. The new backrefs are subsequently
 * resolved as above.
 */
static int resolve_indirect_refs(struct btrfs_backref_walk_ctx *ctx,
				 struct btrfs_path *path,
				 struct preftrees *preftrees,
				 struct share_check *sc)
{
	int err;
	int ret = 0;
	struct ulist *parents;
	struct ulist_node *node;
	struct ulist_iterator uiter;
	struct rb_node *rnode;

	parents = ulist_alloc(GFP_NOFS);
	if (!parents)
		return -ENOMEM;

	/*
	 * We could trade memory usage for performance here by iterating
	 * the tree, allocating new refs for each insertion, and then
	 * freeing the entire indirect tree when we're done.  In some test
	 * cases, the tree can grow quite large (~200k objects).
	 */
	while ((rnode = rb_first_cached(&preftrees->indirect.root))) {
		struct prelim_ref *ref;

		ref = rb_entry(rnode, struct prelim_ref, rbnode);
		if (WARN(ref->parent,
			 "BUG: direct ref found in indirect tree")) {
			ret = -EINVAL;
			goto out;
		}

		rb_erase_cached(&ref->rbnode, &preftrees->indirect.root);
		preftrees->indirect.count--;

		if (ref->count == 0) {
			free_pref(ref);
			continue;
		}

		if (sc && ref->root_id != sc->root->root_key.objectid) {
			free_pref(ref);
			ret = BACKREF_FOUND_SHARED;
			goto out;
		}
		err = resolve_indirect_ref(ctx, path, preftrees, ref, parents);
		/*
		 * we can only tolerate ENOENT,otherwise,we should catch error
		 * and return directly.
		 */
		if (err == -ENOENT) {
			prelim_ref_insert(ctx->fs_info, &preftrees->direct, ref,
					  NULL);
			continue;
		} else if (err) {
			free_pref(ref);
			ret = err;
			goto out;
		}

		/* we put the first parent into the ref at hand */
		ULIST_ITER_INIT(&uiter);
		node = ulist_next(parents, &uiter);
		ref->parent = node ? node->val : 0;
		ref->inode_list = unode_aux_to_inode_list(node);

		/* Add a prelim_ref(s) for any other parent(s). */
		while ((node = ulist_next(parents, &uiter))) {
			struct prelim_ref *new_ref;

			new_ref = kmem_cache_alloc(btrfs_prelim_ref_cache,
						   GFP_NOFS);
			if (!new_ref) {
				free_pref(ref);
				ret = -ENOMEM;
				goto out;
			}
			memcpy(new_ref, ref, sizeof(*ref));
			new_ref->parent = node->val;
			new_ref->inode_list = unode_aux_to_inode_list(node);
			prelim_ref_insert(ctx->fs_info, &preftrees->direct,
					  new_ref, NULL);
		}

		/*
		 * Now it's a direct ref, put it in the direct tree. We must
		 * do this last because the ref could be merged/freed here.
		 */
		prelim_ref_insert(ctx->fs_info, &preftrees->direct, ref, NULL);

		ulist_reinit(parents);
		cond_resched();
	}
out:
	/*
	 * We may have inode lists attached to refs in the parents ulist, so we
	 * must free them before freeing the ulist and its refs.
	 */
	free_leaf_list(parents);
	return ret;
}

/*
 * read tree blocks and add keys where required.
 */
static int add_missing_keys(struct btrfs_fs_info *fs_info,
			    struct preftrees *preftrees, bool lock)
{
	struct prelim_ref *ref;
	struct extent_buffer *eb;
	struct preftree *tree = &preftrees->indirect_missing_keys;
	struct rb_node *node;

	while ((node = rb_first_cached(&tree->root))) {
		struct btrfs_tree_parent_check check = { 0 };

		ref = rb_entry(node, struct prelim_ref, rbnode);
		rb_erase_cached(node, &tree->root);

		BUG_ON(ref->parent);	/* should not be a direct ref */
		BUG_ON(ref->key_for_search.type);
		BUG_ON(!ref->wanted_disk_byte);

		check.level = ref->level - 1;
		check.owner_root = ref->root_id;

		eb = read_tree_block(fs_info, ref->wanted_disk_byte, &check);
		if (IS_ERR(eb)) {
			free_pref(ref);
			return PTR_ERR(eb);
		}
		if (!extent_buffer_uptodate(eb)) {
			free_pref(ref);
			free_extent_buffer(eb);
			return -EIO;
		}

		if (lock)
			btrfs_tree_read_lock(eb);
		if (btrfs_header_level(eb) == 0)
			btrfs_item_key_to_cpu(eb, &ref->key_for_search, 0);
		else
			btrfs_node_key_to_cpu(eb, &ref->key_for_search, 0);
		if (lock)
			btrfs_tree_read_unlock(eb);
		free_extent_buffer(eb);
		prelim_ref_insert(fs_info, &preftrees->indirect, ref, NULL);
		cond_resched();
	}
	return 0;
}

/*
 * add all currently queued delayed refs from this head whose seq nr is
 * smaller or equal that seq to the list
 */
static int add_delayed_refs(const struct btrfs_fs_info *fs_info,
			    struct btrfs_delayed_ref_head *head, u64 seq,
			    struct preftrees *preftrees, struct share_check *sc)
{
	struct btrfs_delayed_ref_node *node;
	struct btrfs_key key;
	struct rb_node *n;
	int count;
	int ret = 0;

	spin_lock(&head->lock);
	for (n = rb_first_cached(&head->ref_tree); n; n = rb_next(n)) {
		node = rb_entry(n, struct btrfs_delayed_ref_node,
				ref_node);
		if (node->seq > seq)
			continue;

		switch (node->action) {
		case BTRFS_ADD_DELAYED_EXTENT:
		case BTRFS_UPDATE_DELAYED_HEAD:
			WARN_ON(1);
			continue;
		case BTRFS_ADD_DELAYED_REF:
			count = node->ref_mod;
			break;
		case BTRFS_DROP_DELAYED_REF:
			count = node->ref_mod * -1;
			break;
		default:
			BUG();
		}
		switch (node->type) {
		case BTRFS_TREE_BLOCK_REF_KEY: {
			/* NORMAL INDIRECT METADATA backref */
			struct btrfs_delayed_tree_ref *ref;
			struct btrfs_key *key_ptr = NULL;

			if (head->extent_op && head->extent_op->update_key) {
				btrfs_disk_key_to_cpu(&key, &head->extent_op->key);
				key_ptr = &key;
			}

			ref = btrfs_delayed_node_to_tree_ref(node);
			ret = add_indirect_ref(fs_info, preftrees, ref->root,
					       key_ptr, ref->level + 1,
					       node->bytenr, count, sc,
					       GFP_ATOMIC);
			break;
		}
		case BTRFS_SHARED_BLOCK_REF_KEY: {
			/* SHARED DIRECT METADATA backref */
			struct btrfs_delayed_tree_ref *ref;

			ref = btrfs_delayed_node_to_tree_ref(node);

			ret = add_direct_ref(fs_info, preftrees, ref->level + 1,
					     ref->parent, node->bytenr, count,
					     sc, GFP_ATOMIC);
			break;
		}
		case BTRFS_EXTENT_DATA_REF_KEY: {
			/* NORMAL INDIRECT DATA backref */
			struct btrfs_delayed_data_ref *ref;
			ref = btrfs_delayed_node_to_data_ref(node);

			key.objectid = ref->objectid;
			key.type = BTRFS_EXTENT_DATA_KEY;
			key.offset = ref->offset;

			/*
			 * If we have a share check context and a reference for
			 * another inode, we can't exit immediately. This is
			 * because even if this is a BTRFS_ADD_DELAYED_REF
			 * reference we may find next a BTRFS_DROP_DELAYED_REF
			 * which cancels out this ADD reference.
			 *
			 * If this is a DROP reference and there was no previous
			 * ADD reference, then we need to signal that when we
			 * process references from the extent tree (through
			 * add_inline_refs() and add_keyed_refs()), we should
			 * not exit early if we find a reference for another
			 * inode, because one of the delayed DROP references
			 * may cancel that reference in the extent tree.
			 */
			if (sc && count < 0)
				sc->have_delayed_delete_refs = true;

			ret = add_indirect_ref(fs_info, preftrees, ref->root,
					       &key, 0, node->bytenr, count, sc,
					       GFP_ATOMIC);
			break;
		}
		case BTRFS_SHARED_DATA_REF_KEY: {
			/* SHARED DIRECT FULL backref */
			struct btrfs_delayed_data_ref *ref;

			ref = btrfs_delayed_node_to_data_ref(node);

			ret = add_direct_ref(fs_info, preftrees, 0, ref->parent,
					     node->bytenr, count, sc,
					     GFP_ATOMIC);
			break;
		}
		default:
			WARN_ON(1);
		}
		/*
		 * We must ignore BACKREF_FOUND_SHARED until all delayed
		 * refs have been checked.
		 */
		if (ret && (ret != BACKREF_FOUND_SHARED))
			break;
	}
	if (!ret)
		ret = extent_is_shared(sc);

	spin_unlock(&head->lock);
	return ret;
}

/*
 * add all inline backrefs for bytenr to the list
 *
 * Returns 0 on success, <0 on error, or BACKREF_FOUND_SHARED.
 */
static int add_inline_refs(struct btrfs_backref_walk_ctx *ctx,
			   struct btrfs_path *path,
			   int *info_level, struct preftrees *preftrees,
			   struct share_check *sc)
{
	int ret = 0;
	int slot;
	struct extent_buffer *leaf;
	struct btrfs_key key;
	struct btrfs_key found_key;
	unsigned long ptr;
	unsigned long end;
	struct btrfs_extent_item *ei;
	u64 flags;
	u64 item_size;

	/*
	 * enumerate all inline refs
	 */
	leaf = path->nodes[0];
	slot = path->slots[0];

	item_size = btrfs_item_size(leaf, slot);
	BUG_ON(item_size < sizeof(*ei));

	ei = btrfs_item_ptr(leaf, slot, struct btrfs_extent_item);

	if (ctx->check_extent_item) {
		ret = ctx->check_extent_item(ctx->bytenr, ei, leaf, ctx->user_ctx);
		if (ret)
			return ret;
	}

	flags = btrfs_extent_flags(leaf, ei);
	btrfs_item_key_to_cpu(leaf, &found_key, slot);

	ptr = (unsigned long)(ei + 1);
	end = (unsigned long)ei + item_size;

	if (found_key.type == BTRFS_EXTENT_ITEM_KEY &&
	    flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
		struct btrfs_tree_block_info *info;

		info = (struct btrfs_tree_block_info *)ptr;
		*info_level = btrfs_tree_block_level(leaf, info);
		ptr += sizeof(struct btrfs_tree_block_info);
		BUG_ON(ptr > end);
	} else if (found_key.type == BTRFS_METADATA_ITEM_KEY) {
		*info_level = found_key.offset;
	} else {
		BUG_ON(!(flags & BTRFS_EXTENT_FLAG_DATA));
	}

	while (ptr < end) {
		struct btrfs_extent_inline_ref *iref;
		u64 offset;
		int type;

		iref = (struct btrfs_extent_inline_ref *)ptr;
		type = btrfs_get_extent_inline_ref_type(leaf, iref,
							BTRFS_REF_TYPE_ANY);
		if (type == BTRFS_REF_TYPE_INVALID)
			return -EUCLEAN;

		offset = btrfs_extent_inline_ref_offset(leaf, iref);

		switch (type) {
		case BTRFS_SHARED_BLOCK_REF_KEY:
			ret = add_direct_ref(ctx->fs_info, preftrees,
					     *info_level + 1, offset,
					     ctx->bytenr, 1, NULL, GFP_NOFS);
			break;
		case BTRFS_SHARED_DATA_REF_KEY: {
			struct btrfs_shared_data_ref *sdref;
			int count;

			sdref = (struct btrfs_shared_data_ref *)(iref + 1);
			count = btrfs_shared_data_ref_count(leaf, sdref);

			ret = add_direct_ref(ctx->fs_info, preftrees, 0, offset,
					     ctx->bytenr, count, sc, GFP_NOFS);
			break;
		}
		case BTRFS_TREE_BLOCK_REF_KEY:
			ret = add_indirect_ref(ctx->fs_info, preftrees, offset,
					       NULL, *info_level + 1,
					       ctx->bytenr, 1, NULL, GFP_NOFS);
			break;
		case BTRFS_EXTENT_DATA_REF_KEY: {
			struct btrfs_extent_data_ref *dref;
			int count;
			u64 root;

			dref = (struct btrfs_extent_data_ref *)(&iref->offset);
			count = btrfs_extent_data_ref_count(leaf, dref);
			key.objectid = btrfs_extent_data_ref_objectid(leaf,
								      dref);
			key.type = BTRFS_EXTENT_DATA_KEY;
			key.offset = btrfs_extent_data_ref_offset(leaf, dref);

			if (sc && key.objectid != sc->inum &&
			    !sc->have_delayed_delete_refs) {
				ret = BACKREF_FOUND_SHARED;
				break;
			}

			root = btrfs_extent_data_ref_root(leaf, dref);

			if (!ctx->skip_data_ref ||
			    !ctx->skip_data_ref(root, key.objectid, key.offset,
						ctx->user_ctx))
				ret = add_indirect_ref(ctx->fs_info, preftrees,
						       root, &key, 0, ctx->bytenr,
						       count, sc, GFP_NOFS);
			break;
		}
		default:
			WARN_ON(1);
		}
		if (ret)
			return ret;
		ptr += btrfs_extent_inline_ref_size(type);
	}

	return 0;
}

/*
 * add all non-inline backrefs for bytenr to the list
 *
 * Returns 0 on success, <0 on error, or BACKREF_FOUND_SHARED.
 */
static int add_keyed_refs(struct btrfs_backref_walk_ctx *ctx,
			  struct btrfs_root *extent_root,
			  struct btrfs_path *path,
			  int info_level, struct preftrees *preftrees,
			  struct share_check *sc)
{
	struct btrfs_fs_info *fs_info = extent_root->fs_info;
	int ret;
	int slot;
	struct extent_buffer *leaf;
	struct btrfs_key key;

	while (1) {
		ret = btrfs_next_item(extent_root, path);
		if (ret < 0)
			break;
		if (ret) {
			ret = 0;
			break;
		}

		slot = path->slots[0];
		leaf = path->nodes[0];
		btrfs_item_key_to_cpu(leaf, &key, slot);

		if (key.objectid != ctx->bytenr)
			break;
		if (key.type < BTRFS_TREE_BLOCK_REF_KEY)
			continue;
		if (key.type > BTRFS_SHARED_DATA_REF_KEY)
			break;

		switch (key.type) {
		case BTRFS_SHARED_BLOCK_REF_KEY:
			/* SHARED DIRECT METADATA backref */
			ret = add_direct_ref(fs_info, preftrees,
					     info_level + 1, key.offset,
					     ctx->bytenr, 1, NULL, GFP_NOFS);
			break;
		case BTRFS_SHARED_DATA_REF_KEY: {
			/* SHARED DIRECT FULL backref */
			struct btrfs_shared_data_ref *sdref;
			int count;

			sdref = btrfs_item_ptr(leaf, slot,
					      struct btrfs_shared_data_ref);
			count = btrfs_shared_data_ref_count(leaf, sdref);
			ret = add_direct_ref(fs_info, preftrees, 0,
					     key.offset, ctx->bytenr, count,
					     sc, GFP_NOFS);
			break;
		}
		case BTRFS_TREE_BLOCK_REF_KEY:
			/* NORMAL INDIRECT METADATA backref */
			ret = add_indirect_ref(fs_info, preftrees, key.offset,
					       NULL, info_level + 1, ctx->bytenr,
					       1, NULL, GFP_NOFS);
			break;
		case BTRFS_EXTENT_DATA_REF_KEY: {
			/* NORMAL INDIRECT DATA backref */
			struct btrfs_extent_data_ref *dref;
			int count;
			u64 root;

			dref = btrfs_item_ptr(leaf, slot,
					      struct btrfs_extent_data_ref);
			count = btrfs_extent_data_ref_count(leaf, dref);
			key.objectid = btrfs_extent_data_ref_objectid(leaf,
								      dref);
			key.type = BTRFS_EXTENT_DATA_KEY;
			key.offset = btrfs_extent_data_ref_offset(leaf, dref);

			if (sc && key.objectid != sc->inum &&
			    !sc->have_delayed_delete_refs) {
				ret = BACKREF_FOUND_SHARED;
				break;
			}

			root = btrfs_extent_data_ref_root(leaf, dref);

			if (!ctx->skip_data_ref ||
			    !ctx->skip_data_ref(root, key.objectid, key.offset,
						ctx->user_ctx))
				ret = add_indirect_ref(fs_info, preftrees, root,
						       &key, 0, ctx->bytenr,
						       count, sc, GFP_NOFS);
			break;
		}
		default:
			WARN_ON(1);
		}
		if (ret)
			return ret;

	}

	return ret;
}

/*
 * The caller has joined a transaction or is holding a read lock on the
 * fs_info->commit_root_sem semaphore, so no need to worry about the root's last
 * snapshot field changing while updating or checking the cache.
 */
static bool lookup_backref_shared_cache(struct btrfs_backref_share_check_ctx *ctx,
					struct btrfs_root *root,
					u64 bytenr, int level, bool *is_shared)
{
	const struct btrfs_fs_info *fs_info = root->fs_info;
	struct btrfs_backref_shared_cache_entry *entry;

	if (!current->journal_info)
		lockdep_assert_held(&fs_info->commit_root_sem);

	if (!ctx->use_path_cache)
		return false;

	if (WARN_ON_ONCE(level >= BTRFS_MAX_LEVEL))
		return false;

	/*
	 * Level -1 is used for the data extent, which is not reliable to cache
	 * because its reference count can increase or decrease without us
	 * realizing. We cache results only for extent buffers that lead from
	 * the root node down to the leaf with the file extent item.
	 */
	ASSERT(level >= 0);

	entry = &ctx->path_cache_entries[level];

	/* Unused cache entry or being used for some other extent buffer. */
	if (entry->bytenr != bytenr)
		return false;

	/*
	 * We cached a false result, but the last snapshot generation of the
	 * root changed, so we now have a snapshot. Don't trust the result.
	 */
	if (!entry->is_shared &&
	    entry->gen != btrfs_root_last_snapshot(&root->root_item))
		return false;

	/*
	 * If we cached a true result and the last generation used for dropping
	 * a root changed, we can not trust the result, because the dropped root
	 * could be a snapshot sharing this extent buffer.
	 */
	if (entry->is_shared &&
	    entry->gen != btrfs_get_last_root_drop_gen(fs_info))
		return false;

	*is_shared = entry->is_shared;
	/*
	 * If the node at this level is shared, than all nodes below are also
	 * shared. Currently some of the nodes below may be marked as not shared
	 * because we have just switched from one leaf to another, and switched
	 * also other nodes above the leaf and below the current level, so mark
	 * them as shared.
	 */
	if (*is_shared) {
		for (int i = 0; i < level; i++) {
			ctx->path_cache_entries[i].is_shared = true;
			ctx->path_cache_entries[i].gen = entry->gen;
		}
	}

	return true;
}

/*
 * The caller has joined a transaction or is holding a read lock on the
 * fs_info->commit_root_sem semaphore, so no need to worry about the root's last
 * snapshot field changing while updating or checking the cache.
 */
static void store_backref_shared_cache(struct btrfs_backref_share_check_ctx *ctx,
				       struct btrfs_root *root,
				       u64 bytenr, int level, bool is_shared)
{
	const struct btrfs_fs_info *fs_info = root->fs_info;
	struct btrfs_backref_shared_cache_entry *entry;
	u64 gen;

	if (!current->journal_info)
		lockdep_assert_held(&fs_info->commit_root_sem);

	if (!ctx->use_path_cache)
		return;

	if (WARN_ON_ONCE(level >= BTRFS_MAX_LEVEL))
		return;

	/*
	 * Level -1 is used for the data extent, which is not reliable to cache
	 * because its reference count can increase or decrease without us
	 * realizing. We cache results only for extent buffers that lead from
	 * the root node down to the leaf with the file extent item.
	 */
	ASSERT(level >= 0);

	if (is_shared)
		gen = btrfs_get_last_root_drop_gen(fs_info);
	else
		gen = btrfs_root_last_snapshot(&root->root_item);

	entry = &ctx->path_cache_entries[level];
	entry->bytenr = bytenr;
	entry->is_shared = is_shared;
	entry->gen = gen;

	/*
	 * If we found an extent buffer is shared, set the cache result for all
	 * extent buffers below it to true. As nodes in the path are COWed,
	 * their sharedness is moved to their children, and if a leaf is COWed,
	 * then the sharedness of a data extent becomes direct, the refcount of
	 * data extent is increased in the extent item at the extent tree.
	 */
	if (is_shared) {
		for (int i = 0; i < level; i++) {
			entry = &ctx->path_cache_entries[i];
			entry->is_shared = is_shared;
			entry->gen = gen;
		}
	}
}

/*
 * this adds all existing backrefs (inline backrefs, backrefs and delayed
 * refs) for the given bytenr to the refs list, merges duplicates and resolves
 * indirect refs to their parent bytenr.
 * When roots are found, they're added to the roots list
 *
 * @ctx:     Backref walking context object, must be not NULL.
 * @sc:      If !NULL, then immediately return BACKREF_FOUND_SHARED when a
 *           shared extent is detected.
 *
 * Otherwise this returns 0 for success and <0 for an error.
 *
 * FIXME some caching might speed things up
 */
static int find_parent_nodes(struct btrfs_backref_walk_ctx *ctx,
			     struct share_check *sc)
{
	struct btrfs_root *root = btrfs_extent_root(ctx->fs_info, ctx->bytenr);
	struct btrfs_key key;
	struct btrfs_path *path;
	struct btrfs_delayed_ref_root *delayed_refs = NULL;
	struct btrfs_delayed_ref_head *head;
	int info_level = 0;
	int ret;
	struct prelim_ref *ref;
	struct rb_node *node;
	struct extent_inode_elem *eie = NULL;
	struct preftrees preftrees = {
		.direct = PREFTREE_INIT,
		.indirect = PREFTREE_INIT,
		.indirect_missing_keys = PREFTREE_INIT
	};

	/* Roots ulist is not needed when using a sharedness check context. */
	if (sc)
		ASSERT(ctx->roots == NULL);

	key.objectid = ctx->bytenr;
	key.offset = (u64)-1;
	if (btrfs_fs_incompat(ctx->fs_info, SKINNY_METADATA))
		key.type = BTRFS_METADATA_ITEM_KEY;
	else
		key.type = BTRFS_EXTENT_ITEM_KEY;

	path = btrfs_alloc_path();
	if (!path)
		return -ENOMEM;
	if (!ctx->trans) {
		path->search_commit_root = 1;
		path->skip_locking = 1;
	}

	if (ctx->time_seq == BTRFS_SEQ_LAST)
		path->skip_locking = 1;

again:
	head = NULL;

	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
	if (ret < 0)
		goto out;
	if (ret == 0) {
		/* This shouldn't happen, indicates a bug or fs corruption. */
		ASSERT(ret != 0);
		ret = -EUCLEAN;
		goto out;
	}

	if (ctx->trans && likely(ctx->trans->type != __TRANS_DUMMY) &&
	    ctx->time_seq != BTRFS_SEQ_LAST) {
		/*
		 * We have a specific time_seq we care about and trans which
		 * means we have the path lock, we need to grab the ref head and
		 * lock it so we have a consistent view of the refs at the given
		 * time.
		 */
		delayed_refs = &ctx->trans->transaction->delayed_refs;
		spin_lock(&delayed_refs->lock);
		head = btrfs_find_delayed_ref_head(delayed_refs, ctx->bytenr);
		if (head) {
			if (!mutex_trylock(&head->mutex)) {
				refcount_inc(&head->refs);
				spin_unlock(&delayed_refs->lock);

				btrfs_release_path(path);

				/*
				 * Mutex was contended, block until it's
				 * released and try again
				 */
				mutex_lock(&head->mutex);
				mutex_unlock(&head->mutex);
				btrfs_put_delayed_ref_head(head);
				goto again;
			}
			spin_unlock(&delayed_refs->lock);
			ret = add_delayed_refs(ctx->fs_info, head, ctx->time_seq,
					       &preftrees, sc);
			mutex_unlock(&head->mutex);
			if (ret)
				goto out;
		} else {
			spin_unlock(&delayed_refs->lock);
		}
	}

	if (path->slots[0]) {
		struct extent_buffer *leaf;
		int slot;

		path->slots[0]--;
		leaf = path->nodes[0];
		slot = path->slots[0];
		btrfs_item_key_to_cpu(leaf, &key, slot);
		if (key.objectid == ctx->bytenr &&
		    (key.type == BTRFS_EXTENT_ITEM_KEY ||
		     key.type == BTRFS_METADATA_ITEM_KEY)) {
			ret = add_inline_refs(ctx, path, &info_level,
					      &preftrees, sc);
			if (ret)
				goto out;
			ret = add_keyed_refs(ctx, root, path, info_level,
					     &preftrees, sc);
			if (ret)
				goto out;
		}
	}

	/*
	 * If we have a share context and we reached here, it means the extent
	 * is not directly shared (no multiple reference items for it),
	 * otherwise we would have exited earlier with a return value of
	 * BACKREF_FOUND_SHARED after processing delayed references or while
	 * processing inline or keyed references from the extent tree.
	 * The extent may however be indirectly shared through shared subtrees
	 * as a result from creating snapshots, so we determine below what is
	 * its parent node, in case we are dealing with a metadata extent, or
	 * what's the leaf (or leaves), from a fs tree, that has a file extent
	 * item pointing to it in case we are dealing with a data extent.
	 */
	ASSERT(extent_is_shared(sc) == 0);

	/*
	 * If we are here for a data extent and we have a share_check structure
	 * it means the data extent is not directly shared (does not have
	 * multiple reference items), so we have to check if a path in the fs
	 * tree (going from the root node down to the leaf that has the file
	 * extent item pointing to the data extent) is shared, that is, if any
	 * of the extent buffers in the path is referenced by other trees.
	 */
	if (sc && ctx->bytenr == sc->data_bytenr) {
		/*
		 * If our data extent is from a generation more recent than the
		 * last generation used to snapshot the root, then we know that
		 * it can not be shared through subtrees, so we can skip
		 * resolving indirect references, there's no point in
		 * determining the extent buffers for the path from the fs tree
		 * root node down to the leaf that has the file extent item that
		 * points to the data extent.
		 */
		if (sc->data_extent_gen >
		    btrfs_root_last_snapshot(&sc->root->root_item)) {
			ret = BACKREF_FOUND_NOT_SHARED;
			goto out;
		}

		/*
		 * If we are only determining if a data extent is shared or not
		 * and the corresponding file extent item is located in the same
		 * leaf as the previous file extent item, we can skip resolving
		 * indirect references for a data extent, since the fs tree path
		 * is the same (same leaf, so same path). We skip as long as the
		 * cached result for the leaf is valid and only if there's only
		 * one file extent item pointing to the data extent, because in
		 * the case of multiple file extent items, they may be located
		 * in different leaves and therefore we have multiple paths.
		 */
		if (sc->ctx->curr_leaf_bytenr == sc->ctx->prev_leaf_bytenr &&
		    sc->self_ref_count == 1) {
			bool cached;
			bool is_shared;

			cached = lookup_backref_shared_cache(sc->ctx, sc->root,
						     sc->ctx->curr_leaf_bytenr,
						     0, &is_shared);
			if (cached) {
				if (is_shared)
					ret = BACKREF_FOUND_SHARED;
				else
					ret = BACKREF_FOUND_NOT_SHARED;
				goto out;
			}
		}
	}

	btrfs_release_path(path);

	ret = add_missing_keys(ctx->fs_info, &preftrees, path->skip_locking == 0);
	if (ret)
		goto out;

	WARN_ON(!RB_EMPTY_ROOT(&preftrees.indirect_missing_keys.root.rb_root));

	ret = resolve_indirect_refs(ctx, path, &preftrees, sc);
	if (ret)
		goto out;

	WARN_ON(!RB_EMPTY_ROOT(&preftrees.indirect.root.rb_root));

	/*
	 * This walks the tree of merged and resolved refs. Tree blocks are
	 * read in as needed. Unique entries are added to the ulist, and
	 * the list of found roots is updated.
	 *
	 * We release the entire tree in one go before returning.
	 */
	node = rb_first_cached(&preftrees.direct.root);
	while (node) {
		ref = rb_entry(node, struct prelim_ref, rbnode);
		node = rb_next(&ref->rbnode);
		/*
		 * ref->count < 0 can happen here if there are delayed
		 * refs with a node->action of BTRFS_DROP_DELAYED_REF.
		 * prelim_ref_insert() relies on this when merging
		 * identical refs to keep the overall count correct.
		 * prelim_ref_insert() will merge only those refs
		 * which compare identically.  Any refs having
		 * e.g. different offsets would not be merged,
		 * and would retain their original ref->count < 0.
		 */
		if (ctx->roots && ref->count && ref->root_id && ref->parent == 0) {
			/* no parent == root of tree */
			ret = ulist_add(ctx->roots, ref->root_id, 0, GFP_NOFS);
			if (ret < 0)
				goto out;
		}
		if (ref->count && ref->parent) {
			if (!ctx->skip_inode_ref_list && !ref->inode_list &&
			    ref->level == 0) {
				struct btrfs_tree_parent_check check = { 0 };
				struct extent_buffer *eb;

				check.level = ref->level;

				eb = read_tree_block(ctx->fs_info, ref->parent,
						     &check);
				if (IS_ERR(eb)) {
					ret = PTR_ERR(eb);
					goto out;
				}
				if (!extent_buffer_uptodate(eb)) {
					free_extent_buffer(eb);
					ret = -EIO;
					goto out;
				}

				if (!path->skip_locking)
					btrfs_tree_read_lock(eb);
				ret = find_extent_in_eb(ctx, eb, &eie);
				if (!path->skip_locking)
					btrfs_tree_read_unlock(eb);
				free_extent_buffer(eb);
				if (ret == BTRFS_ITERATE_EXTENT_INODES_STOP ||
				    ret < 0)
					goto out;
				ref->inode_list = eie;
				/*
				 * We transferred the list ownership to the ref,
				 * so set to NULL to avoid a double free in case
				 * an error happens after this.
				 */
				eie = NULL;
			}
			ret = ulist_add_merge_ptr(ctx->refs, ref->parent,
						  ref->inode_list,
						  (void **)&eie, GFP_NOFS);
			if (ret < 0)
				goto out;
			if (!ret && !ctx->skip_inode_ref_list) {
				/*
				 * We've recorded that parent, so we must extend
				 * its inode list here.
				 *
				 * However if there was corruption we may not
				 * have found an eie, return an error in this
				 * case.
				 */
				ASSERT(eie);
				if (!eie) {
					ret = -EUCLEAN;
					goto out;
				}
				while (eie->next)
					eie = eie->next;
				eie->next = ref->inode_list;
			}
			eie = NULL;
			/*
			 * We have transferred the inode list ownership from
			 * this ref to the ref we added to the 'refs' ulist.
			 * So set this ref's inode list to NULL to avoid
			 * use-after-free when our caller uses it or double
			 * frees in case an error happens before we return.
			 */
			ref->inode_list = NULL;
		}
		cond_resched();
	}

out:
	btrfs_free_path(path);

	prelim_release(&preftrees.direct);
	prelim_release(&preftrees.indirect);
	prelim_release(&preftrees.indirect_missing_keys);

	if (ret == BTRFS_ITERATE_EXTENT_INODES_STOP || ret < 0)
		free_inode_elem_list(eie);
	return ret;
}

/*
 * Finds all leaves with a reference to the specified combination of
 * @ctx->bytenr and @ctx->extent_item_pos. The bytenr of the found leaves are
 * added to the ulist at @ctx->refs, and that ulist is allocated by this
 * function. The caller should free the ulist with free_leaf_list() if
 * @ctx->ignore_extent_item_pos is false, otherwise a fimple ulist_free() is
 * enough.
 *
 * Returns 0 on success and < 0 on error. On error @ctx->refs is not allocated.
 */
int btrfs_find_all_leafs(struct btrfs_backref_walk_ctx *ctx)
{
	int ret;

	ASSERT(ctx->refs == NULL);

	ctx->refs = ulist_alloc(GFP_NOFS);
	if (!ctx->refs)
		return -ENOMEM;

	ret = find_parent_nodes(ctx, NULL);
	if (ret == BTRFS_ITERATE_EXTENT_INODES_STOP ||
	    (ret < 0 && ret != -ENOENT)) {
		free_leaf_list(ctx->refs);
		ctx->refs = NULL;
		return ret;
	}

	return 0;
}

/*
 * Walk all backrefs for a given extent to find all roots that reference this
 * extent. Walking a backref means finding all extents that reference this
 * extent and in turn walk the backrefs of those, too. Naturally this is a
 * recursive process, but here it is implemented in an iterative fashion: We
 * find all referencing extents for the extent in question and put them on a
 * list. In turn, we find all referencing extents for those, further appending
 * to the list. The way we iterate the list allows adding more elements after
 * the current while iterating. The process stops when we reach the end of the
 * list.
 *
 * Found roots are added to @ctx->roots, which is allocated by this function if
 * it points to NULL, in which case the caller is responsible for freeing it
 * after it's not needed anymore.
 * This function requires @ctx->refs to be NULL, as it uses it for allocating a
 * ulist to do temporary work, and frees it before returning.
 *
 * Returns 0 on success, < 0 on error.
 */
static int btrfs_find_all_roots_safe(struct btrfs_backref_walk_ctx *ctx)
{
	const u64 orig_bytenr = ctx->bytenr;
	const bool orig_skip_inode_ref_list = ctx->skip_inode_ref_list;
	bool roots_ulist_allocated = false;
	struct ulist_iterator uiter;
	int ret = 0;

	ASSERT(ctx->refs == NULL);

	ctx->refs = ulist_alloc(GFP_NOFS);
	if (!ctx->refs)
		return -ENOMEM;

	if (!ctx->roots) {
		ctx->roots = ulist_alloc(GFP_NOFS);
		if (!ctx->roots) {
			ulist_free(ctx->refs);
			ctx->refs = NULL;
			return -ENOMEM;
		}
		roots_ulist_allocated = true;
	}

	ctx->skip_inode_ref_list = true;

	ULIST_ITER_INIT(&uiter);
	while (1) {
		struct ulist_node *node;

		ret = find_parent_nodes(ctx, NULL);
		if (ret < 0 && ret != -ENOENT) {
			if (roots_ulist_allocated) {
				ulist_free(ctx->roots);
				ctx->roots = NULL;
			}
			break;
		}
		ret = 0;
		node = ulist_next(ctx->refs, &uiter);
		if (!node)
			break;
		ctx->bytenr = node->val;
		cond_resched();
	}

	ulist_free(ctx->refs);
	ctx->refs = NULL;
	ctx->bytenr = orig_bytenr;
	ctx->skip_inode_ref_list = orig_skip_inode_ref_list;

	return ret;
}

int btrfs_find_all_roots(struct btrfs_backref_walk_ctx *ctx,
			 bool skip_commit_root_sem)
{
	int ret;

	if (!ctx->trans && !skip_commit_root_sem)
		down_read(&ctx->fs_info->commit_root_sem);
	ret = btrfs_find_all_roots_safe(ctx);
	if (!ctx->trans && !skip_commit_root_sem)
		up_read(&ctx->fs_info->commit_root_sem);
	return ret;
}

struct btrfs_backref_share_check_ctx *btrfs_alloc_backref_share_check_ctx(void)
{
	struct btrfs_backref_share_check_ctx *ctx;

	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
	if (!ctx)
		return NULL;

	ulist_init(&ctx->refs);

	return ctx;
}

void btrfs_free_backref_share_ctx(struct btrfs_backref_share_check_ctx *ctx)
{
	if (!ctx)
		return;

	ulist_release(&ctx->refs);
	kfree(ctx);
}

/*
 * Check if a data extent is shared or not.
 *
 * @inode:       The inode whose extent we are checking.
 * @bytenr:      Logical bytenr of the extent we are checking.
 * @extent_gen:  Generation of the extent (file extent item) or 0 if it is
 *               not known.
 * @ctx:         A backref sharedness check context.
 *
 * btrfs_is_data_extent_shared uses the backref walking code but will short
 * circuit as soon as it finds a root or inode that doesn't match the
 * one passed in. This provides a significant performance benefit for
 * callers (such as fiemap) which want to know whether the extent is
 * shared but do not need a ref count.
 *
 * This attempts to attach to the running transaction in order to account for
 * delayed refs, but continues on even when no running transaction exists.
 *
 * Return: 0 if extent is not shared, 1 if it is shared, < 0 on error.
 */
int btrfs_is_data_extent_shared(struct btrfs_inode *inode, u64 bytenr,
				u64 extent_gen,
				struct btrfs_backref_share_check_ctx *ctx)
{
	struct btrfs_backref_walk_ctx walk_ctx = { 0 };
	struct btrfs_root *root = inode->root;
	struct btrfs_fs_info *fs_info = root->fs_info;
	struct btrfs_trans_handle *trans;
	struct ulist_iterator uiter;
	struct ulist_node *node;
	struct btrfs_seq_list elem = BTRFS_SEQ_LIST_INIT(elem);
	int ret = 0;
	struct share_check shared = {
		.ctx = ctx,
		.root = root,
		.inum = btrfs_ino(inode),
		.data_bytenr = bytenr,
		.data_extent_gen = extent_gen,
		.share_count = 0,
		.self_ref_count = 0,
		.have_delayed_delete_refs = false,
	};
	int level;
	bool leaf_cached;
	bool leaf_is_shared;

	for (int i = 0; i < BTRFS_BACKREF_CTX_PREV_EXTENTS_SIZE; i++) {
		if (ctx->prev_extents_cache[i].bytenr == bytenr)
			return ctx->prev_extents_cache[i].is_shared;
	}

	ulist_init(&ctx->refs);

	trans = btrfs_join_transaction_nostart(root);
	if (IS_ERR(trans)) {
		if (PTR_ERR(trans) != -ENOENT && PTR_ERR(trans) != -EROFS) {
			ret = PTR_ERR(trans);
			goto out;
		}
		trans = NULL;
		down_read(&fs_info->commit_root_sem);
	} else {
		btrfs_get_tree_mod_seq(fs_info, &elem);
		walk_ctx.time_seq = elem.seq;
	}

	ctx->use_path_cache = true;

	/*
	 * We may have previously determined that the current leaf is shared.
	 * If it is, then we have a data extent that is shared due to a shared
	 * subtree (caused by snapshotting) and we don't need to check for data
	 * backrefs. If the leaf is not shared, then we must do backref walking
	 * to determine if the data extent is shared through reflinks.
	 */
	leaf_cached = lookup_backref_shared_cache(ctx, root,
						  ctx->curr_leaf_bytenr, 0,
						  &leaf_is_shared);
	if (leaf_cached && leaf_is_shared) {
		ret = 1;
		goto out_trans;
	}

	walk_ctx.skip_inode_ref_list = true;
	walk_ctx.trans = trans;
	walk_ctx.fs_info = fs_info;
	walk_ctx.refs = &ctx->refs;

	/* -1 means we are in the bytenr of the data extent. */
	level = -1;
	ULIST_ITER_INIT(&uiter);
	while (1) {
		const unsigned long prev_ref_count = ctx->refs.nnodes;

		walk_ctx.bytenr = bytenr;
		ret = find_parent_nodes(&walk_ctx, &shared);
		if (ret == BACKREF_FOUND_SHARED ||
		    ret == BACKREF_FOUND_NOT_SHARED) {
			/* If shared must return 1, otherwise return 0. */
			ret = (ret == BACKREF_FOUND_SHARED) ? 1 : 0;
			if (level >= 0)
				store_backref_shared_cache(ctx, root, bytenr,
							   level, ret == 1);
			break;
		}
		if (ret < 0 && ret != -ENOENT)
			break;
		ret = 0;

		/*
		 * More than one extent buffer (bytenr) may have been added to
		 * the ctx->refs ulist, in which case we have to check multiple
		 * tree paths in case the first one is not shared, so we can not
		 * use the path cache which is made for a single path. Multiple
		 * extent buffers at the current level happen when:
		 *
		 * 1) level -1, the data extent: If our data extent was not
		 *    directly shared (without multiple reference items), then
		 *    it might have a single reference item with a count > 1 for
		 *    the same offset, which means there are 2 (or more) file
		 *    extent items that point to the data extent - this happens
		 *    when a file extent item needs to be split and then one
		 *    item gets moved to another leaf due to a b+tree leaf split
		 *    when inserting some item. In this case the file extent
		 *    items may be located in different leaves and therefore
		 *    some of the leaves may be referenced through shared
		 *    subtrees while others are not. Since our extent buffer
		 *    cache only works for a single path (by far the most common
		 *    case and simpler to deal with), we can not use it if we
		 *    have multiple leaves (which implies multiple paths).
		 *
		 * 2) level >= 0, a tree node/leaf: We can have a mix of direct
		 *    and indirect references on a b+tree node/leaf, so we have
		 *    to check multiple paths, and the extent buffer (the
		 *    current bytenr) may be shared or not. One example is
		 *    during relocation as we may get a shared tree block ref
		 *    (direct ref) and a non-shared tree block ref (indirect
		 *    ref) for the same node/leaf.
		 */
		if ((ctx->refs.nnodes - prev_ref_count) > 1)
			ctx->use_path_cache = false;

		if (level >= 0)
			store_backref_shared_cache(ctx, root, bytenr,
						   level, false);
		node = ulist_next(&ctx->refs, &uiter);
		if (!node)
			break;
		bytenr = node->val;
		if (ctx->use_path_cache) {
			bool is_shared;
			bool cached;

			level++;
			cached = lookup_backref_shared_cache(ctx, root, bytenr,
							     level, &is_shared);
			if (cached) {
				ret = (is_shared ? 1 : 0);
				break;
			}
		}
		shared.share_count = 0;
		shared.have_delayed_delete_refs = false;
		cond_resched();
	}

	/*
	 * If the path cache is disabled, then it means at some tree level we
	 * got multiple parents due to a mix of direct and indirect backrefs or
	 * multiple leaves with file extent items pointing to the same data
	 * extent. We have to invalidate the cache and cache only the sharedness
	 * result for the levels where we got only one node/reference.
	 */
	if (!ctx->use_path_cache) {
		int i = 0;

		level--;
		if (ret >= 0 && level >= 0) {
			bytenr = ctx->path_cache_entries[level].bytenr;
			ctx->use_path_cache = true;
			store_backref_shared_cache(ctx, root, bytenr, level, ret);
			i = level + 1;
		}

		for ( ; i < BTRFS_MAX_LEVEL; i++)
			ctx->path_cache_entries[i].bytenr = 0;
	}

	/*
	 * Cache the sharedness result for the data extent if we know our inode
	 * has more than 1 file extent item that refers to the data extent.
	 */
	if (ret >= 0 && shared.self_ref_count > 1) {
		int slot = ctx->prev_extents_cache_slot;

		ctx->prev_extents_cache[slot].bytenr = shared.data_bytenr;
		ctx->prev_extents_cache[slot].is_shared = (ret == 1);

		slot = (slot + 1) % BTRFS_BACKREF_CTX_PREV_EXTENTS_SIZE;
		ctx->prev_extents_cache_slot = slot;
	}

out_trans:
	if (trans) {
		btrfs_put_tree_mod_seq(fs_info, &elem);
		btrfs_end_transaction(trans);
	} else {
		up_read(&fs_info->commit_root_sem);
	}
out:
	ulist_release(&ctx->refs);
	ctx->prev_leaf_bytenr = ctx->curr_leaf_bytenr;

	return ret;
}

int btrfs_find_one_extref(struct btrfs_root *root, u64 inode_objectid,
			  u64 start_off, struct btrfs_path *path,
			  struct btrfs_inode_extref **ret_extref,
			  u64 *found_off)
{
	int ret, slot;
	struct btrfs_key key;
	struct btrfs_key found_key;
	struct btrfs_inode_extref *extref;
	const struct extent_buffer *leaf;
	unsigned long ptr;

	key.objectid = inode_objectid;
	key.type = BTRFS_INODE_EXTREF_KEY;
	key.offset = start_off;

	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
	if (ret < 0)
		return ret;

	while (1) {
		leaf = path->nodes[0];
		slot = path->slots[0];
		if (slot >= btrfs_header_nritems(leaf)) {
			/*
			 * If the item at offset is not found,
			 * btrfs_search_slot will point us to the slot
			 * where it should be inserted. In our case
			 * that will be the slot directly before the
			 * next INODE_REF_KEY_V2 item. In the case
			 * that we're pointing to the last slot in a
			 * leaf, we must move one leaf over.
			 */
			ret = btrfs_next_leaf(root, path);
			if (ret) {
				if (ret >= 1)
					ret = -ENOENT;
				break;
			}
			continue;
		}

		btrfs_item_key_to_cpu(leaf, &found_key, slot);

		/*
		 * Check that we're still looking at an extended ref key for
		 * this particular objectid. If we have different
		 * objectid or type then there are no more to be found
		 * in the tree and we can exit.
		 */
		ret = -ENOENT;
		if (found_key.objectid != inode_objectid)
			break;
		if (found_key.type != BTRFS_INODE_EXTREF_KEY)
			break;

		ret = 0;
		ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
		extref = (struct btrfs_inode_extref *)ptr;
		*ret_extref = extref;
		if (found_off)
			*found_off = found_key.offset;
		break;
	}

	return ret;
}

/*
 * this iterates to turn a name (from iref/extref) into a full filesystem path.
 * Elements of the path are separated by '/' and the path is guaranteed to be
 * 0-terminated. the path is only given within the current file system.
 * Therefore, it never starts with a '/'. the caller is responsible to provide
 * "size" bytes in "dest". the dest buffer will be filled backwards. finally,
 * the start point of the resulting string is returned. this pointer is within
 * dest, normally.
 * in case the path buffer would overflow, the pointer is decremented further
 * as if output was written to the buffer, though no more output is actually
 * generated. that way, the caller can determine how much space would be
 * required for the path to fit into the buffer. in that case, the returned
 * value will be smaller than dest. callers must check this!
 */
char *btrfs_ref_to_path(struct btrfs_root *fs_root, struct btrfs_path *path,
			u32 name_len, unsigned long name_off,
			struct extent_buffer *eb_in, u64 parent,
			char *dest, u32 size)
{
	int slot;
	u64 next_inum;
	int ret;
	s64 bytes_left = ((s64)size) - 1;
	struct extent_buffer *eb = eb_in;
	struct btrfs_key found_key;
	struct btrfs_inode_ref *iref;

	if (bytes_left >= 0)
		dest[bytes_left] = '\0';

	while (1) {
		bytes_left -= name_len;
		if (bytes_left >= 0)
			read_extent_buffer(eb, dest + bytes_left,
					   name_off, name_len);
		if (eb != eb_in) {
			if (!path->skip_locking)
				btrfs_tree_read_unlock(eb);
			free_extent_buffer(eb);
		}
		ret = btrfs_find_item(fs_root, path, parent, 0,
				BTRFS_INODE_REF_KEY, &found_key);
		if (ret > 0)
			ret = -ENOENT;
		if (ret)
			break;

		next_inum = found_key.offset;

		/* regular exit ahead */
		if (parent == next_inum)
			break;

		slot = path->slots[0];
		eb = path->nodes[0];
		/* make sure we can use eb after releasing the path */
		if (eb != eb_in) {
			path->nodes[0] = NULL;
			path->locks[0] = 0;
		}
		btrfs_release_path(path);
		iref = btrfs_item_ptr(eb, slot, struct btrfs_inode_ref);

		name_len = btrfs_inode_ref_name_len(eb, iref);
		name_off = (unsigned long)(iref + 1);

		parent = next_inum;
		--bytes_left;
		if (bytes_left >= 0)
			dest[bytes_left] = '/';
	}

	btrfs_release_path(path);

	if (ret)
		return ERR_PTR(ret);

	return dest + bytes_left;
}

/*
 * this makes the path point to (logical EXTENT_ITEM *)
 * returns BTRFS_EXTENT_FLAG_DATA for data, BTRFS_EXTENT_FLAG_TREE_BLOCK for
 * tree blocks and <0 on error.
 */
int extent_from_logical(struct btrfs_fs_info *fs_info, u64 logical,
			struct btrfs_path *path, struct btrfs_key *found_key,
			u64 *flags_ret)
{
	struct btrfs_root *extent_root = btrfs_extent_root(fs_info, logical);
	int ret;
	u64 flags;
	u64 size = 0;
	u32 item_size;
	const struct extent_buffer *eb;
	struct btrfs_extent_item *ei;
	struct btrfs_key key;

	if (btrfs_fs_incompat(fs_info, SKINNY_METADATA))
		key.type = BTRFS_METADATA_ITEM_KEY;
	else
		key.type = BTRFS_EXTENT_ITEM_KEY;
	key.objectid = logical;
	key.offset = (u64)-1;

	ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
	if (ret < 0)
		return ret;

	ret = btrfs_previous_extent_item(extent_root, path, 0);
	if (ret) {
		if (ret > 0)
			ret = -ENOENT;
		return ret;
	}
	btrfs_item_key_to_cpu(path->nodes[0], found_key, path->slots[0]);
	if (found_key->type == BTRFS_METADATA_ITEM_KEY)
		size = fs_info->nodesize;
	else if (found_key->type == BTRFS_EXTENT_ITEM_KEY)
		size = found_key->offset;

	if (found_key->objectid > logical ||
	    found_key->objectid + size <= logical) {
		btrfs_debug(fs_info,
			"logical %llu is not within any extent", logical);
		return -ENOENT;
	}

	eb = path->nodes[0];
	item_size = btrfs_item_size(eb, path->slots[0]);
	BUG_ON(item_size < sizeof(*ei));

	ei = btrfs_item_ptr(eb, path->slots[0], struct btrfs_extent_item);
	flags = btrfs_extent_flags(eb, ei);

	btrfs_debug(fs_info,
		"logical %llu is at position %llu within the extent (%llu EXTENT_ITEM %llu) flags %#llx size %u",
		 logical, logical - found_key->objectid, found_key->objectid,
		 found_key->offset, flags, item_size);

	WARN_ON(!flags_ret);
	if (flags_ret) {
		if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)
			*flags_ret = BTRFS_EXTENT_FLAG_TREE_BLOCK;
		else if (flags & BTRFS_EXTENT_FLAG_DATA)
			*flags_ret = BTRFS_EXTENT_FLAG_DATA;
		else
			BUG();
		return 0;
	}

	return -EIO;
}

/*
 * helper function to iterate extent inline refs. ptr must point to a 0 value
 * for the first call and may be modified. it is used to track state.
 * if more refs exist, 0 is returned and the next call to
 * get_extent_inline_ref must pass the modified ptr parameter to get the
 * next ref. after the last ref was processed, 1 is returned.
 * returns <0 on error
 */
static int get_extent_inline_ref(unsigned long *ptr,
				 const struct extent_buffer *eb,
				 const struct btrfs_key *key,
				 const struct btrfs_extent_item *ei,
				 u32 item_size,
				 struct btrfs_extent_inline_ref **out_eiref,
				 int *out_type)
{
	unsigned long end;
	u64 flags;
	struct btrfs_tree_block_info *info;

	if (!*ptr) {
		/* first call */
		flags = btrfs_extent_flags(eb, ei);
		if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
			if (key->type == BTRFS_METADATA_ITEM_KEY) {
				/* a skinny metadata extent */
				*out_eiref =
				     (struct btrfs_extent_inline_ref *)(ei + 1);
			} else {
				WARN_ON(key->type != BTRFS_EXTENT_ITEM_KEY);
				info = (struct btrfs_tree_block_info *)(ei + 1);
				*out_eiref =
				   (struct btrfs_extent_inline_ref *)(info + 1);
			}
		} else {
			*out_eiref = (struct btrfs_extent_inline_ref *)(ei + 1);
		}
		*ptr = (unsigned long)*out_eiref;
		if ((unsigned long)(*ptr) >= (unsigned long)ei + item_size)
			return -ENOENT;
	}

	end = (unsigned long)ei + item_size;
	*out_eiref = (struct btrfs_extent_inline_ref *)(*ptr);
	*out_type = btrfs_get_extent_inline_ref_type(eb, *out_eiref,
						     BTRFS_REF_TYPE_ANY);
	if (*out_type == BTRFS_REF_TYPE_INVALID)
		return -EUCLEAN;

	*ptr += btrfs_extent_inline_ref_size(*out_type);
	WARN_ON(*ptr > end);
	if (*ptr == end)
		return 1; /* last */

	return 0;
}

/*
 * reads the tree block backref for an extent. tree level and root are returned
 * through out_level and out_root. ptr must point to a 0 value for the first
 * call and may be modified (see get_extent_inline_ref comment).
 * returns 0 if data was provided, 1 if there was no more data to provide or
 * <0 on error.
 */
int tree_backref_for_extent(unsigned long *ptr, struct extent_buffer *eb,
			    struct btrfs_key *key, struct btrfs_extent_item *ei,
			    u32 item_size, u64 *out_root, u8 *out_level)
{
	int ret;
	int type;
	struct btrfs_extent_inline_ref *eiref;

	if (*ptr == (unsigned long)-1)
		return 1;

	while (1) {
		ret = get_extent_inline_ref(ptr, eb, key, ei, item_size,
					      &eiref, &type);
		if (ret < 0)
			return ret;

		if (type == BTRFS_TREE_BLOCK_REF_KEY ||
		    type == BTRFS_SHARED_BLOCK_REF_KEY)
			break;

		if (ret == 1)
			return 1;
	}

	/* we can treat both ref types equally here */
	*out_root = btrfs_extent_inline_ref_offset(eb, eiref);

	if (key->type == BTRFS_EXTENT_ITEM_KEY) {
		struct btrfs_tree_block_info *info;

		info = (struct btrfs_tree_block_info *)(ei + 1);
		*out_level = btrfs_tree_block_level(eb, info);
	} else {
		ASSERT(key->type == BTRFS_METADATA_ITEM_KEY);
		*out_level = (u8)key->offset;
	}

	if (ret == 1)
		*ptr = (unsigned long)-1;

	return 0;
}

static int iterate_leaf_refs(struct btrfs_fs_info *fs_info,
			     struct extent_inode_elem *inode_list,
			     u64 root, u64 extent_item_objectid,
			     iterate_extent_inodes_t *iterate, void *ctx)
{
	struct extent_inode_elem *eie;
	int ret = 0;

	for (eie = inode_list; eie; eie = eie->next) {
		btrfs_debug(fs_info,
			    "ref for %llu resolved, key (%llu EXTEND_DATA %llu), root %llu",
			    extent_item_objectid, eie->inum,
			    eie->offset, root);
		ret = iterate(eie->inum, eie->offset, eie->num_bytes, root, ctx);
		if (ret) {
			btrfs_debug(fs_info,
				    "stopping iteration for %llu due to ret=%d",
				    extent_item_objectid, ret);
			break;
		}
	}

	return ret;
}

/*
 * calls iterate() for every inode that references the extent identified by
 * the given parameters.
 * when the iterator function returns a non-zero value, iteration stops.
 */
int iterate_extent_inodes(struct btrfs_backref_walk_ctx *ctx,
			  bool search_commit_root,
			  iterate_extent_inodes_t *iterate, void *user_ctx)
{
	int ret;
	struct ulist *refs;
	struct ulist_node *ref_node;
	struct btrfs_seq_list seq_elem = BTRFS_SEQ_LIST_INIT(seq_elem);
	struct ulist_iterator ref_uiter;

	btrfs_debug(ctx->fs_info, "resolving all inodes for extent %llu",
		    ctx->bytenr);

	ASSERT(ctx->trans == NULL);
	ASSERT(ctx->roots == NULL);

	if (!search_commit_root) {
		struct btrfs_trans_handle *trans;

		trans = btrfs_attach_transaction(ctx->fs_info->tree_root);
		if (IS_ERR(trans)) {
			if (PTR_ERR(trans) != -ENOENT &&
			    PTR_ERR(trans) != -EROFS)
				return PTR_ERR(trans);
			trans = NULL;
		}
		ctx->trans = trans;
	}

	if (ctx->trans) {
		btrfs_get_tree_mod_seq(ctx->fs_info, &seq_elem);
		ctx->time_seq = seq_elem.seq;
	} else {
		down_read(&ctx->fs_info->commit_root_sem);
	}

	ret = btrfs_find_all_leafs(ctx);
	if (ret)
		goto out;
	refs = ctx->refs;
	ctx->refs = NULL;

	ULIST_ITER_INIT(&ref_uiter);
	while (!ret && (ref_node = ulist_next(refs, &ref_uiter))) {
		const u64 leaf_bytenr = ref_node->val;
		struct ulist_node *root_node;
		struct ulist_iterator root_uiter;
		struct extent_inode_elem *inode_list;

		inode_list = (struct extent_inode_elem *)(uintptr_t)ref_node->aux;

		if (ctx->cache_lookup) {
			const u64 *root_ids;
			int root_count;
			bool cached;

			cached = ctx->cache_lookup(leaf_bytenr, ctx->user_ctx,
						   &root_ids, &root_count);
			if (cached) {
				for (int i = 0; i < root_count; i++) {
					ret = iterate_leaf_refs(ctx->fs_info,
								inode_list,
								root_ids[i],
								leaf_bytenr,
								iterate,
								user_ctx);
					if (ret)
						break;
				}
				continue;
			}
		}

		if (!ctx->roots) {
			ctx->roots = ulist_alloc(GFP_NOFS);
			if (!ctx->roots) {
				ret = -ENOMEM;
				break;
			}
		}

		ctx->bytenr = leaf_bytenr;
		ret = btrfs_find_all_roots_safe(ctx);
		if (ret)
			break;

		if (ctx->cache_store)
			ctx->cache_store(leaf_bytenr, ctx->roots, ctx->user_ctx);

		ULIST_ITER_INIT(&root_uiter);
		while (!ret && (root_node = ulist_next(ctx->roots, &root_uiter))) {
			btrfs_debug(ctx->fs_info,
				    "root %llu references leaf %llu, data list %#llx",
				    root_node->val, ref_node->val,
				    ref_node->aux);
			ret = iterate_leaf_refs(ctx->fs_info, inode_list,
						root_node->val, ctx->bytenr,
						iterate, user_ctx);
		}
		ulist_reinit(ctx->roots);
	}

	free_leaf_list(refs);
out:
	if (ctx->trans) {
		btrfs_put_tree_mod_seq(ctx->fs_info, &seq_elem);
		btrfs_end_transaction(ctx->trans);
		ctx->trans = NULL;
	} else {
		up_read(&ctx->fs_info->commit_root_sem);
	}

	ulist_free(ctx->roots);
	ctx->roots = NULL;

	if (ret == BTRFS_ITERATE_EXTENT_INODES_STOP)
		ret = 0;

	return ret;
}

static int build_ino_list(u64 inum, u64 offset, u64 num_bytes, u64 root, void *ctx)
{
	struct btrfs_data_container *inodes = ctx;
	const size_t c = 3 * sizeof(u64);

	if (inodes->bytes_left >= c) {
		inodes->bytes_left -= c;
		inodes->val[inodes->elem_cnt] = inum;
		inodes->val[inodes->elem_cnt + 1] = offset;
		inodes->val[inodes->elem_cnt + 2] = root;
		inodes->elem_cnt += 3;
	} else {
		inodes->bytes_missing += c - inodes->bytes_left;
		inodes->bytes_left = 0;
		inodes->elem_missed += 3;
	}

	return 0;
}

int iterate_inodes_from_logical(u64 logical, struct btrfs_fs_info *fs_info,
				struct btrfs_path *path,
				void *ctx, bool ignore_offset)
{
	struct btrfs_backref_walk_ctx walk_ctx = { 0 };
	int ret;
	u64 flags = 0;
	struct btrfs_key found_key;
	int search_commit_root = path->search_commit_root;

	ret = extent_from_logical(fs_info, logical, path, &found_key, &flags);
	btrfs_release_path(path);
	if (ret < 0)
		return ret;
	if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)
		return -EINVAL;

	walk_ctx.bytenr = found_key.objectid;
	if (ignore_offset)
		walk_ctx.ignore_extent_item_pos = true;
	else
		walk_ctx.extent_item_pos = logical - found_key.objectid;
	walk_ctx.fs_info = fs_info;

	return iterate_extent_inodes(&walk_ctx, search_commit_root,
				     build_ino_list, ctx);
}

static int inode_to_path(u64 inum, u32 name_len, unsigned long name_off,
			 struct extent_buffer *eb, struct inode_fs_paths *ipath);

static int iterate_inode_refs(u64 inum, struct inode_fs_paths *ipath)
{
	int ret = 0;
	int slot;
	u32 cur;
	u32 len;
	u32 name_len;
	u64 parent = 0;
	int found = 0;
	struct btrfs_root *fs_root = ipath->fs_root;
	struct btrfs_path *path = ipath->btrfs_path;
	struct extent_buffer *eb;
	struct btrfs_inode_ref *iref;
	struct btrfs_key found_key;

	while (!ret) {
		ret = btrfs_find_item(fs_root, path, inum,
				parent ? parent + 1 : 0, BTRFS_INODE_REF_KEY,
				&found_key);

		if (ret < 0)
			break;
		if (ret) {
			ret = found ? 0 : -ENOENT;
			break;
		}
		++found;

		parent = found_key.offset;
		slot = path->slots[0];
		eb = btrfs_clone_extent_buffer(path->nodes[0]);
		if (!eb) {
			ret = -ENOMEM;
			break;
		}
		btrfs_release_path(path);

		iref = btrfs_item_ptr(eb, slot, struct btrfs_inode_ref);

		for (cur = 0; cur < btrfs_item_size(eb, slot); cur += len) {
			name_len = btrfs_inode_ref_name_len(eb, iref);
			/* path must be released before calling iterate()! */
			btrfs_debug(fs_root->fs_info,
				"following ref at offset %u for inode %llu in tree %llu",
				cur, found_key.objectid,
				fs_root->root_key.objectid);
			ret = inode_to_path(parent, name_len,
				      (unsigned long)(iref + 1), eb, ipath);
			if (ret)
				break;
			len = sizeof(*iref) + name_len;
			iref = (struct btrfs_inode_ref *)((char *)iref + len);
		}
		free_extent_buffer(eb);
	}

	btrfs_release_path(path);

	return ret;
}

static int iterate_inode_extrefs(u64 inum, struct inode_fs_paths *ipath)
{
	int ret;
	int slot;
	u64 offset = 0;
	u64 parent;
	int found = 0;
	struct btrfs_root *fs_root = ipath->fs_root;
	struct btrfs_path *path = ipath->btrfs_path;
	struct extent_buffer *eb;
	struct btrfs_inode_extref *extref;
	u32 item_size;
	u32 cur_offset;
	unsigned long ptr;

	while (1) {
		ret = btrfs_find_one_extref(fs_root, inum, offset, path, &extref,
					    &offset);
		if (ret < 0)
			break;
		if (ret) {
			ret = found ? 0 : -ENOENT;
			break;
		}
		++found;

		slot = path->slots[0];
		eb = btrfs_clone_extent_buffer(path->nodes[0]);
		if (!eb) {
			ret = -ENOMEM;
			break;
		}
		btrfs_release_path(path);

		item_size = btrfs_item_size(eb, slot);
		ptr = btrfs_item_ptr_offset(eb, slot);
		cur_offset = 0;

		while (cur_offset < item_size) {
			u32 name_len;

			extref = (struct btrfs_inode_extref *)(ptr + cur_offset);
			parent = btrfs_inode_extref_parent(eb, extref);
			name_len = btrfs_inode_extref_name_len(eb, extref);
			ret = inode_to_path(parent, name_len,
				      (unsigned long)&extref->name, eb, ipath);
			if (ret)
				break;

			cur_offset += btrfs_inode_extref_name_len(eb, extref);
			cur_offset += sizeof(*extref);
		}
		free_extent_buffer(eb);

		offset++;
	}

	btrfs_release_path(path);

	return ret;
}

/*
 * returns 0 if the path could be dumped (probably truncated)
 * returns <0 in case of an error
 */
static int inode_to_path(u64 inum, u32 name_len, unsigned long name_off,
			 struct extent_buffer *eb, struct inode_fs_paths *ipath)
{
	char *fspath;
	char *fspath_min;
	int i = ipath->fspath->elem_cnt;
	const int s_ptr = sizeof(char *);
	u32 bytes_left;

	bytes_left = ipath->fspath->bytes_left > s_ptr ?
					ipath->fspath->bytes_left - s_ptr : 0;

	fspath_min = (char *)ipath->fspath->val + (i + 1) * s_ptr;
	fspath = btrfs_ref_to_path(ipath->fs_root, ipath->btrfs_path, name_len,
				   name_off, eb, inum, fspath_min, bytes_left);
	if (IS_ERR(fspath))
		return PTR_ERR(fspath);

	if (fspath > fspath_min) {
		ipath->fspath->val[i] = (u64)(unsigned long)fspath;
		++ipath->fspath->elem_cnt;
		ipath->fspath->bytes_left = fspath - fspath_min;
	} else {
		++ipath->fspath->elem_missed;
		ipath->fspath->bytes_missing += fspath_min - fspath;
		ipath->fspath->bytes_left = 0;
	}

	return 0;
}

/*
 * this dumps all file system paths to the inode into the ipath struct, provided
 * is has been created large enough. each path is zero-terminated and accessed
 * from ipath->fspath->val[i].
 * when it returns, there are ipath->fspath->elem_cnt number of paths available
 * in ipath->fspath->val[]. when the allocated space wasn't sufficient, the
 * number of missed paths is recorded in ipath->fspath->elem_missed, otherwise,
 * it's zero. ipath->fspath->bytes_missing holds the number of bytes that would
 * have been needed to return all paths.
 */
int paths_from_inode(u64 inum, struct inode_fs_paths *ipath)
{
	int ret;
	int found_refs = 0;

	ret = iterate_inode_refs(inum, ipath);
	if (!ret)
		++found_refs;
	else if (ret != -ENOENT)
		return ret;

	ret = iterate_inode_extrefs(inum, ipath);
	if (ret == -ENOENT && found_refs)
		return 0;

	return ret;
}

struct btrfs_data_container *init_data_container(u32 total_bytes)
{
	struct btrfs_data_container *data;
	size_t alloc_bytes;

	alloc_bytes = max_t(size_t, total_bytes, sizeof(*data));
	data = kvmalloc(alloc_bytes, GFP_KERNEL);
	if (!data)
		return ERR_PTR(-ENOMEM);

	if (total_bytes >= sizeof(*data)) {
		data->bytes_left = total_bytes - sizeof(*data);
		data->bytes_missing = 0;
	} else {
		data->bytes_missing = sizeof(*data) - total_bytes;
		data->bytes_left = 0;
	}

	data->elem_cnt = 0;
	data->elem_missed = 0;

	return data;
}

/*
 * allocates space to return multiple file system paths for an inode.
 * total_bytes to allocate are passed, note that space usable for actual path
 * information will be total_bytes - sizeof(struct inode_fs_paths).
 * the returned pointer must be freed with free_ipath() in the end.
 */
struct inode_fs_paths *init_ipath(s32 total_bytes, struct btrfs_root *fs_root,
					struct btrfs_path *path)
{
	struct inode_fs_paths *ifp;
	struct btrfs_data_container *fspath;

	fspath = init_data_container(total_bytes);
	if (IS_ERR(fspath))
		return ERR_CAST(fspath);

	ifp = kmalloc(sizeof(*ifp), GFP_KERNEL);
	if (!ifp) {
		kvfree(fspath);
		return ERR_PTR(-ENOMEM);
	}

	ifp->btrfs_path = path;
	ifp->fspath = fspath;
	ifp->fs_root = fs_root;

	return ifp;
}

void free_ipath(struct inode_fs_paths *ipath)
{
	if (!ipath)
		return;
	kvfree(ipath->fspath);
	kfree(ipath);
}

struct btrfs_backref_iter *btrfs_backref_iter_alloc(struct btrfs_fs_info *fs_info)
{
	struct btrfs_backref_iter *ret;

	ret = kzalloc(sizeof(*ret), GFP_NOFS);
	if (!ret)
		return NULL;

	ret->path = btrfs_alloc_path();
	if (!ret->path) {
		kfree(ret);
		return NULL;
	}

	/* Current backref iterator only supports iteration in commit root */
	ret->path->search_commit_root = 1;
	ret->path->skip_locking = 1;
	ret->fs_info = fs_info;

	return ret;
}

int btrfs_backref_iter_start(struct btrfs_backref_iter *iter, u64 bytenr)
{
	struct btrfs_fs_info *fs_info = iter->fs_info;
	struct btrfs_root *extent_root = btrfs_extent_root(fs_info, bytenr);
	struct btrfs_path *path = iter->path;
	struct btrfs_extent_item *ei;
	struct btrfs_key key;
	int ret;

	key.objectid = bytenr;
	key.type = BTRFS_METADATA_ITEM_KEY;
	key.offset = (u64)-1;
	iter->bytenr = bytenr;

	ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
	if (ret < 0)
		return ret;
	if (ret == 0) {
		ret = -EUCLEAN;
		goto release;
	}
	if (path->slots[0] == 0) {
		WARN_ON(IS_ENABLED(CONFIG_BTRFS_DEBUG));
		ret = -EUCLEAN;
		goto release;
	}
	path->slots[0]--;

	btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
	if ((key.type != BTRFS_EXTENT_ITEM_KEY &&
	     key.type != BTRFS_METADATA_ITEM_KEY) || key.objectid != bytenr) {
		ret = -ENOENT;
		goto release;
	}
	memcpy(&iter->cur_key, &key, sizeof(key));
	iter->item_ptr = (u32)btrfs_item_ptr_offset(path->nodes[0],
						    path->slots[0]);
	iter->end_ptr = (u32)(iter->item_ptr +
			btrfs_item_size(path->nodes[0], path->slots[0]));
	ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
			    struct btrfs_extent_item);

	/*
	 * Only support iteration on tree backref yet.
	 *
	 * This is an extra precaution for non skinny-metadata, where
	 * EXTENT_ITEM is also used for tree blocks, that we can only use
	 * extent flags to determine if it's a tree block.
	 */
	if (btrfs_extent_flags(path->nodes[0], ei) & BTRFS_EXTENT_FLAG_DATA) {
		ret = -ENOTSUPP;
		goto release;
	}
	iter->cur_ptr = (u32)(iter->item_ptr + sizeof(*ei));

	/* If there is no inline backref, go search for keyed backref */
	if (iter->cur_ptr >= iter->end_ptr) {
		ret = btrfs_next_item(extent_root, path);

		/* No inline nor keyed ref */
		if (ret > 0) {
			ret = -ENOENT;
			goto release;
		}
		if (ret < 0)
			goto release;

		btrfs_item_key_to_cpu(path->nodes[0], &iter->cur_key,
				path->slots[0]);
		if (iter->cur_key.objectid != bytenr ||
		    (iter->cur_key.type != BTRFS_SHARED_BLOCK_REF_KEY &&
		     iter->cur_key.type != BTRFS_TREE_BLOCK_REF_KEY)) {
			ret = -ENOENT;
			goto release;
		}
		iter->cur_ptr = (u32)btrfs_item_ptr_offset(path->nodes[0],
							   path->slots[0]);
		iter->item_ptr = iter->cur_ptr;
		iter->end_ptr = (u32)(iter->item_ptr + btrfs_item_size(
				      path->nodes[0], path->slots[0]));
	}

	return 0;
release:
	btrfs_backref_iter_release(iter);
	return ret;
}

/*
 * Go to the next backref item of current bytenr, can be either inlined or
 * keyed.
 *
 * Caller needs to check whether it's inline ref or not by iter->cur_key.
 *
 * Return 0 if we get next backref without problem.
 * Return >0 if there is no extra backref for this bytenr.
 * Return <0 if there is something wrong happened.
 */
int btrfs_backref_iter_next(struct btrfs_backref_iter *iter)
{
	struct extent_buffer *eb = btrfs_backref_get_eb(iter);
	struct btrfs_root *extent_root;
	struct btrfs_path *path = iter->path;
	struct btrfs_extent_inline_ref *iref;
	int ret;
	u32 size;

	if (btrfs_backref_iter_is_inline_ref(iter)) {
		/* We're still inside the inline refs */
		ASSERT(iter->cur_ptr < iter->end_ptr);

		if (btrfs_backref_has_tree_block_info(iter)) {
			/* First tree block info */
			size = sizeof(struct btrfs_tree_block_info);
		} else {
			/* Use inline ref type to determine the size */
			int type;

			iref = (struct btrfs_extent_inline_ref *)
				((unsigned long)iter->cur_ptr);
			type = btrfs_extent_inline_ref_type(eb, iref);

			size = btrfs_extent_inline_ref_size(type);
		}
		iter->cur_ptr += size;
		if (iter->cur_ptr < iter->end_ptr)
			return 0;

		/* All inline items iterated, fall through */
	}

	/* We're at keyed items, there is no inline item, go to the next one */
	extent_root = btrfs_extent_root(iter->fs_info, iter->bytenr);
	ret = btrfs_next_item(extent_root, iter->path);
	if (ret)
		return ret;

	btrfs_item_key_to_cpu(path->nodes[0], &iter->cur_key, path->slots[0]);
	if (iter->cur_key.objectid != iter->bytenr ||
	    (iter->cur_key.type != BTRFS_TREE_BLOCK_REF_KEY &&
	     iter->cur_key.type != BTRFS_SHARED_BLOCK_REF_KEY))
		return 1;
	iter->item_ptr = (u32)btrfs_item_ptr_offset(path->nodes[0],
					path->slots[0]);
	iter->cur_ptr = iter->item_ptr;
	iter->end_ptr = iter->item_ptr + (u32)btrfs_item_size(path->nodes[0],
						path->slots[0]);
	return 0;
}

void btrfs_backref_init_cache(struct btrfs_fs_info *fs_info,
			      struct btrfs_backref_cache *cache, int is_reloc)
{
	int i;

	cache->rb_root = RB_ROOT;
	for (i = 0; i < BTRFS_MAX_LEVEL; i++)
		INIT_LIST_HEAD(&cache->pending[i]);
	INIT_LIST_HEAD(&cache->changed);
	INIT_LIST_HEAD(&cache->detached);
	INIT_LIST_HEAD(&cache->leaves);
	INIT_LIST_HEAD(&cache->pending_edge);
	INIT_LIST_HEAD(&cache->useless_node);
	cache->fs_info = fs_info;
	cache->is_reloc = is_reloc;
}

struct btrfs_backref_node *btrfs_backref_alloc_node(
		struct btrfs_backref_cache *cache, u64 bytenr, int level)
{
	struct btrfs_backref_node *node;

	ASSERT(level >= 0 && level < BTRFS_MAX_LEVEL);
	node = kzalloc(sizeof(*node), GFP_NOFS);
	if (!node)
		return node;

	INIT_LIST_HEAD(&node->list);
	INIT_LIST_HEAD(&node->upper);
	INIT_LIST_HEAD(&node->lower);
	RB_CLEAR_NODE(&node->rb_node);
	cache->nr_nodes++;
	node->level = level;
	node->bytenr = bytenr;

	return node;
}

struct btrfs_backref_edge *btrfs_backref_alloc_edge(
		struct btrfs_backref_cache *cache)
{
	struct btrfs_backref_edge *edge;

	edge = kzalloc(sizeof(*edge), GFP_NOFS);
	if (edge)
		cache->nr_edges++;
	return edge;
}

/*
 * Drop the backref node from cache, also cleaning up all its
 * upper edges and any uncached nodes in the path.
 *
 * This cleanup happens bottom up, thus the node should either
 * be the lowest node in the cache or a detached node.
 */
void btrfs_backref_cleanup_node(struct btrfs_backref_cache *cache,
				struct btrfs_backref_node *node)
{
	struct btrfs_backref_node *upper;
	struct btrfs_backref_edge *edge;

	if (!node)
		return;

	BUG_ON(!node->lowest && !node->detached);
	while (!list_empty(&node->upper)) {
		edge = list_entry(node->upper.next, struct btrfs_backref_edge,
				  list[LOWER]);
		upper = edge->node[UPPER];
		list_del(&edge->list[LOWER]);
		list_del(&edge->list[UPPER]);
		btrfs_backref_free_edge(cache, edge);

		/*
		 * Add the node to leaf node list if no other child block
		 * cached.
		 */
		if (list_empty(&upper->lower)) {
			list_add_tail(&upper->lower, &cache->leaves);
			upper->lowest = 1;
		}
	}

	btrfs_backref_drop_node(cache, node);
}

/*
 * Release all nodes/edges from current cache
 */
void btrfs_backref_release_cache(struct btrfs_backref_cache *cache)
{
	struct btrfs_backref_node *node;
	int i;

	while (!list_empty(&cache->detached)) {
		node = list_entry(cache->detached.next,
				  struct btrfs_backref_node, list);
		btrfs_backref_cleanup_node(cache, node);
	}

	while (!list_empty(&cache->leaves)) {
		node = list_entry(cache->leaves.next,
				  struct btrfs_backref_node, lower);
		btrfs_backref_cleanup_node(cache, node);
	}

	cache->last_trans = 0;

	for (i = 0; i < BTRFS_MAX_LEVEL; i++)
		ASSERT(list_empty(&cache->pending[i]));
	ASSERT(list_empty(&cache->pending_edge));
	ASSERT(list_empty(&cache->useless_node));
	ASSERT(list_empty(&cache->changed));
	ASSERT(list_empty(&cache->detached));
	ASSERT(RB_EMPTY_ROOT(&cache->rb_root));
	ASSERT(!cache->nr_nodes);
	ASSERT(!cache->nr_edges);
}

/*
 * Handle direct tree backref
 *
 * Direct tree backref means, the backref item shows its parent bytenr
 * directly. This is for SHARED_BLOCK_REF backref (keyed or inlined).
 *
 * @ref_key:	The converted backref key.
 *		For keyed backref, it's the item key.
 *		For inlined backref, objectid is the bytenr,
 *		type is btrfs_inline_ref_type, offset is
 *		btrfs_inline_ref_offset.
 */
static int handle_direct_tree_backref(struct btrfs_backref_cache *cache,
				      struct btrfs_key *ref_key,
				      struct btrfs_backref_node *cur)
{
	struct btrfs_backref_edge *edge;
	struct btrfs_backref_node *upper;
	struct rb_node *rb_node;

	ASSERT(ref_key->type == BTRFS_SHARED_BLOCK_REF_KEY);

	/* Only reloc root uses backref pointing to itself */
	if (ref_key->objectid == ref_key->offset) {
		struct btrfs_root *root;

		cur->is_reloc_root = 1;
		/* Only reloc backref cache cares about a specific root */
		if (cache->is_reloc) {
			root = find_reloc_root(cache->fs_info, cur->bytenr);
			if (!root)
				return -ENOENT;
			cur->root = root;
		} else {
			/*
			 * For generic purpose backref cache, reloc root node
			 * is useless.
			 */
			list_add(&cur->list, &cache->useless_node);
		}
		return 0;
	}

	edge = btrfs_backref_alloc_edge(cache);
	if (!edge)
		return -ENOMEM;

	rb_node = rb_simple_search(&cache->rb_root, ref_key->offset);
	if (!rb_node) {
		/* Parent node not yet cached */
		upper = btrfs_backref_alloc_node(cache, ref_key->offset,
					   cur->level + 1);
		if (!upper) {
			btrfs_backref_free_edge(cache, edge);
			return -ENOMEM;
		}

		/*
		 *  Backrefs for the upper level block isn't cached, add the
		 *  block to pending list
		 */
		list_add_tail(&edge->list[UPPER], &cache->pending_edge);
	} else {
		/* Parent node already cached */
		upper = rb_entry(rb_node, struct btrfs_backref_node, rb_node);
		ASSERT(upper->checked);
		INIT_LIST_HEAD(&edge->list[UPPER]);
	}
	btrfs_backref_link_edge(edge, cur, upper, LINK_LOWER);
	return 0;
}

/*
 * Handle indirect tree backref
 *
 * Indirect tree backref means, we only know which tree the node belongs to.
 * We still need to do a tree search to find out the parents. This is for
 * TREE_BLOCK_REF backref (keyed or inlined).
 *
 * @ref_key:	The same as @ref_key in  handle_direct_tree_backref()
 * @tree_key:	The first key of this tree block.
 * @path:	A clean (released) path, to avoid allocating path every time
 *		the function get called.
 */
static int handle_indirect_tree_backref(struct btrfs_backref_cache *cache,
					struct btrfs_path *path,
					struct btrfs_key *ref_key,
					struct btrfs_key *tree_key,
					struct btrfs_backref_node *cur)
{
	struct btrfs_fs_info *fs_info = cache->fs_info;
	struct btrfs_backref_node *upper;
	struct btrfs_backref_node *lower;
	struct btrfs_backref_edge *edge;
	struct extent_buffer *eb;
	struct btrfs_root *root;
	struct rb_node *rb_node;
	int level;
	bool need_check = true;
	int ret;

	root = btrfs_get_fs_root(fs_info, ref_key->offset, false);
	if (IS_ERR(root))
		return PTR_ERR(root);
	if (!test_bit(BTRFS_ROOT_SHAREABLE, &root->state))
		cur->cowonly = 1;

	if (btrfs_root_level(&root->root_item) == cur->level) {
		/* Tree root */
		ASSERT(btrfs_root_bytenr(&root->root_item) == cur->bytenr);
		/*
		 * For reloc backref cache, we may ignore reloc root.  But for
		 * general purpose backref cache, we can't rely on
		 * btrfs_should_ignore_reloc_root() as it may conflict with
		 * current running relocation and lead to missing root.
		 *
		 * For general purpose backref cache, reloc root detection is
		 * completely relying on direct backref (key->offset is parent
		 * bytenr), thus only do such check for reloc cache.
		 */
		if (btrfs_should_ignore_reloc_root(root) && cache->is_reloc) {
			btrfs_put_root(root);
			list_add(&cur->list, &cache->useless_node);
		} else {
			cur->root = root;
		}
		return 0;
	}

	level = cur->level + 1;

	/* Search the tree to find parent blocks referring to the block */
	path->search_commit_root = 1;
	path->skip_locking = 1;
	path->lowest_level = level;
	ret = btrfs_search_slot(NULL, root, tree_key, path, 0, 0);
	path->lowest_level = 0;
	if (ret < 0) {
		btrfs_put_root(root);
		return ret;
	}
	if (ret > 0 && path->slots[level] > 0)
		path->slots[level]--;

	eb = path->nodes[level];
	if (btrfs_node_blockptr(eb, path->slots[level]) != cur->bytenr) {
		btrfs_err(fs_info,
"couldn't find block (%llu) (level %d) in tree (%llu) with key (%llu %u %llu)",
			  cur->bytenr, level - 1, root->root_key.objectid,
			  tree_key->objectid, tree_key->type, tree_key->offset);
		btrfs_put_root(root);
		ret = -ENOENT;
		goto out;
	}
	lower = cur;

	/* Add all nodes and edges in the path */
	for (; level < BTRFS_MAX_LEVEL; level++) {
		if (!path->nodes[level]) {
			ASSERT(btrfs_root_bytenr(&root->root_item) ==
			       lower->bytenr);
			/* Same as previous should_ignore_reloc_root() call */
			if (btrfs_should_ignore_reloc_root(root) &&
			    cache->is_reloc) {
				btrfs_put_root(root);
				list_add(&lower->list, &cache->useless_node);
			} else {
				lower->root = root;
			}
			break;
		}

		edge = btrfs_backref_alloc_edge(cache);
		if (!edge) {
			btrfs_put_root(root);
			ret = -ENOMEM;
			goto out;
		}

		eb = path->nodes[level];
		rb_node = rb_simple_search(&cache->rb_root, eb->start);
		if (!rb_node) {
			upper = btrfs_backref_alloc_node(cache, eb->start,
							 lower->level + 1);
			if (!upper) {
				btrfs_put_root(root);
				btrfs_backref_free_edge(cache, edge);
				ret = -ENOMEM;
				goto out;
			}
			upper->owner = btrfs_header_owner(eb);
			if (!test_bit(BTRFS_ROOT_SHAREABLE, &root->state))
				upper->cowonly = 1;

			/*
			 * If we know the block isn't shared we can avoid
			 * checking its backrefs.
			 */
			if (btrfs_block_can_be_shared(root, eb))
				upper->checked = 0;
			else
				upper->checked = 1;

			/*
			 * Add the block to pending list if we need to check its
			 * backrefs, we only do this once while walking up a
			 * tree as we will catch anything else later on.
			 */
			if (!upper->checked && need_check) {
				need_check = false;
				list_add_tail(&edge->list[UPPER],
					      &cache->pending_edge);
			} else {
				if (upper->checked)
					need_check = true;
				INIT_LIST_HEAD(&edge->list[UPPER]);
			}
		} else {
			upper = rb_entry(rb_node, struct btrfs_backref_node,
					 rb_node);
			ASSERT(upper->checked);
			INIT_LIST_HEAD(&edge->list[UPPER]);
			if (!upper->owner)
				upper->owner = btrfs_header_owner(eb);
		}
		btrfs_backref_link_edge(edge, lower, upper, LINK_LOWER);

		if (rb_node) {
			btrfs_put_root(root);
			break;
		}
		lower = upper;
		upper = NULL;
	}
out:
	btrfs_release_path(path);
	return ret;
}

/*
 * Add backref node @cur into @cache.
 *
 * NOTE: Even if the function returned 0, @cur is not yet cached as its upper
 *	 links aren't yet bi-directional. Needs to finish such links.
 *	 Use btrfs_backref_finish_upper_links() to finish such linkage.
 *
 * @path:	Released path for indirect tree backref lookup
 * @iter:	Released backref iter for extent tree search
 * @node_key:	The first key of the tree block
 */
int btrfs_backref_add_tree_node(struct btrfs_backref_cache *cache,
				struct btrfs_path *path,
				struct btrfs_backref_iter *iter,
				struct btrfs_key *node_key,
				struct btrfs_backref_node *cur)
{
	struct btrfs_fs_info *fs_info = cache->fs_info;
	struct btrfs_backref_edge *edge;
	struct btrfs_backref_node *exist;
	int ret;

	ret = btrfs_backref_iter_start(iter, cur->bytenr);
	if (ret < 0)
		return ret;
	/*
	 * We skip the first btrfs_tree_block_info, as we don't use the key
	 * stored in it, but fetch it from the tree block
	 */
	if (btrfs_backref_has_tree_block_info(iter)) {
		ret = btrfs_backref_iter_next(iter);
		if (ret < 0)
			goto out;
		/* No extra backref? This means the tree block is corrupted */
		if (ret > 0) {
			ret = -EUCLEAN;
			goto out;
		}
	}
	WARN_ON(cur->checked);
	if (!list_empty(&cur->upper)) {
		/*
		 * The backref was added previously when processing backref of
		 * type BTRFS_TREE_BLOCK_REF_KEY
		 */
		ASSERT(list_is_singular(&cur->upper));
		edge = list_entry(cur->upper.next, struct btrfs_backref_edge,
				  list[LOWER]);
		ASSERT(list_empty(&edge->list[UPPER]));
		exist = edge->node[UPPER];
		/*
		 * Add the upper level block to pending list if we need check
		 * its backrefs
		 */
		if (!exist->checked)
			list_add_tail(&edge->list[UPPER], &cache->pending_edge);
	} else {
		exist = NULL;
	}

	for (; ret == 0; ret = btrfs_backref_iter_next(iter)) {
		struct extent_buffer *eb;
		struct btrfs_key key;
		int type;

		cond_resched();
		eb = btrfs_backref_get_eb(iter);

		key.objectid = iter->bytenr;
		if (btrfs_backref_iter_is_inline_ref(iter)) {
			struct btrfs_extent_inline_ref *iref;

			/* Update key for inline backref */
			iref = (struct btrfs_extent_inline_ref *)
				((unsigned long)iter->cur_ptr);
			type = btrfs_get_extent_inline_ref_type(eb, iref,
							BTRFS_REF_TYPE_BLOCK);
			if (type == BTRFS_REF_TYPE_INVALID) {
				ret = -EUCLEAN;
				goto out;
			}
			key.type = type;
			key.offset = btrfs_extent_inline_ref_offset(eb, iref);
		} else {
			key.type = iter->cur_key.type;
			key.offset = iter->cur_key.offset;
		}

		/*
		 * Parent node found and matches current inline ref, no need to
		 * rebuild this node for this inline ref
		 */
		if (exist &&
		    ((key.type == BTRFS_TREE_BLOCK_REF_KEY &&
		      exist->owner == key.offset) ||
		     (key.type == BTRFS_SHARED_BLOCK_REF_KEY &&
		      exist->bytenr == key.offset))) {
			exist = NULL;
			continue;
		}

		/* SHARED_BLOCK_REF means key.offset is the parent bytenr */
		if (key.type == BTRFS_SHARED_BLOCK_REF_KEY) {
			ret = handle_direct_tree_backref(cache, &key, cur);
			if (ret < 0)
				goto out;
			continue;
		} else if (unlikely(key.type == BTRFS_EXTENT_REF_V0_KEY)) {
			ret = -EINVAL;
			btrfs_print_v0_err(fs_info);
			btrfs_handle_fs_error(fs_info, ret, NULL);
			goto out;
		} else if (key.type != BTRFS_TREE_BLOCK_REF_KEY) {
			continue;
		}

		/*
		 * key.type == BTRFS_TREE_BLOCK_REF_KEY, inline ref offset
		 * means the root objectid. We need to search the tree to get
		 * its parent bytenr.
		 */
		ret = handle_indirect_tree_backref(cache, path, &key, node_key,
						   cur);
		if (ret < 0)
			goto out;
	}
	ret = 0;
	cur->checked = 1;
	WARN_ON(exist);
out:
	btrfs_backref_iter_release(iter);
	return ret;
}

/*
 * Finish the upwards linkage created by btrfs_backref_add_tree_node()
 */
int btrfs_backref_finish_upper_links(struct btrfs_backref_cache *cache,
				     struct btrfs_backref_node *start)
{
	struct list_head *useless_node = &cache->useless_node;
	struct btrfs_backref_edge *edge;
	struct rb_node *rb_node;
	LIST_HEAD(pending_edge);

	ASSERT(start->checked);

	/* Insert this node to cache if it's not COW-only */
	if (!start->cowonly) {
		rb_node = rb_simple_insert(&cache->rb_root, start->bytenr,
					   &start->rb_node);
		if (rb_node)
			btrfs_backref_panic(cache->fs_info, start->bytenr,
					    -EEXIST);
		list_add_tail(&start->lower, &cache->leaves);
	}

	/*
	 * Use breadth first search to iterate all related edges.
	 *
	 * The starting points are all the edges of this node
	 */
	list_for_each_entry(edge, &start->upper, list[LOWER])
		list_add_tail(&edge->list[UPPER], &pending_edge);

	while (!list_empty(&pending_edge)) {
		struct btrfs_backref_node *upper;
		struct btrfs_backref_node *lower;

		edge = list_first_entry(&pending_edge,
				struct btrfs_backref_edge, list[UPPER]);
		list_del_init(&edge->list[UPPER]);
		upper = edge->node[UPPER];
		lower = edge->node[LOWER];

		/* Parent is detached, no need to keep any edges */
		if (upper->detached) {
			list_del(&edge->list[LOWER]);
			btrfs_backref_free_edge(cache, edge);

			/* Lower node is orphan, queue for cleanup */
			if (list_empty(&lower->upper))
				list_add(&lower->list, useless_node);
			continue;
		}

		/*
		 * All new nodes added in current build_backref_tree() haven't
		 * been linked to the cache rb tree.
		 * So if we have upper->rb_node populated, this means a cache
		 * hit. We only need to link the edge, as @upper and all its
		 * parents have already been linked.
		 */
		if (!RB_EMPTY_NODE(&upper->rb_node)) {
			if (upper->lowest) {
				list_del_init(&upper->lower);
				upper->lowest = 0;
			}

			list_add_tail(&edge->list[UPPER], &upper->lower);
			continue;
		}

		/* Sanity check, we shouldn't have any unchecked nodes */
		if (!upper->checked) {
			ASSERT(0);
			return -EUCLEAN;
		}

		/* Sanity check, COW-only node has non-COW-only parent */
		if (start->cowonly != upper->cowonly) {
			ASSERT(0);
			return -EUCLEAN;
		}

		/* Only cache non-COW-only (subvolume trees) tree blocks */
		if (!upper->cowonly) {
			rb_node = rb_simple_insert(&cache->rb_root, upper->bytenr,
						   &upper->rb_node);
			if (rb_node) {
				btrfs_backref_panic(cache->fs_info,
						upper->bytenr, -EEXIST);
				return -EUCLEAN;
			}
		}

		list_add_tail(&edge->list[UPPER], &upper->lower);

		/*
		 * Also queue all the parent edges of this uncached node
		 * to finish the upper linkage
		 */
		list_for_each_entry(edge, &upper->upper, list[LOWER])
			list_add_tail(&edge->list[UPPER], &pending_edge);
	}
	return 0;
}

void btrfs_backref_error_cleanup(struct btrfs_backref_cache *cache,
				 struct btrfs_backref_node *node)
{
	struct btrfs_backref_node *lower;
	struct btrfs_backref_node *upper;
	struct btrfs_backref_edge *edge;

	while (!list_empty(&cache->useless_node)) {
		lower = list_first_entry(&cache->useless_node,
				   struct btrfs_backref_node, list);
		list_del_init(&lower->list);
	}
	while (!list_empty(&cache->pending_edge)) {
		edge = list_first_entry(&cache->pending_edge,
				struct btrfs_backref_edge, list[UPPER]);
		list_del(&edge->list[UPPER]);
		list_del(&edge->list[LOWER]);
		lower = edge->node[LOWER];
		upper = edge->node[UPPER];
		btrfs_backref_free_edge(cache, edge);

		/*
		 * Lower is no longer linked to any upper backref nodes and
		 * isn't in the cache, we can free it ourselves.
		 */
		if (list_empty(&lower->upper) &&
		    RB_EMPTY_NODE(&lower->rb_node))
			list_add(&lower->list, &cache->useless_node);

		if (!RB_EMPTY_NODE(&upper->rb_node))
			continue;

		/* Add this guy's upper edges to the list to process */
		list_for_each_entry(edge, &upper->upper, list[LOWER])
			list_add_tail(&edge->list[UPPER],
				      &cache->pending_edge);
		if (list_empty(&upper->upper))
			list_add(&upper->list, &cache->useless_node);
	}

	while (!list_empty(&cache->useless_node)) {
		lower = list_first_entry(&cache->useless_node,
				   struct btrfs_backref_node, list);
		list_del_init(&lower->list);
		if (lower == node)
			node = NULL;
		btrfs_backref_drop_node(cache, lower);
	}

	btrfs_backref_cleanup_node(cache, node);
	ASSERT(list_empty(&cache->useless_node) &&
	       list_empty(&cache->pending_edge));
}