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author | Qu Wenruo <wqu@suse.com> | 2023-02-07 12:26:13 +0800 |
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committer | David Sterba <dsterba@suse.com> | 2023-04-17 18:01:14 +0200 |
commit | 4ced85f81a7a67e190a4ff4e14d8cc04978a3767 (patch) | |
tree | 998d8a705b43d03ff29ceb975806a2f32ebdb004 /fs/btrfs/volumes.h | |
parent | be5c7edbfdf1112cbbdd15700f33f37b66fc8976 (diff) | |
download | linux-stable-4ced85f81a7a67e190a4ff4e14d8cc04978a3767.tar.gz linux-stable-4ced85f81a7a67e190a4ff4e14d8cc04978a3767.tar.bz2 linux-stable-4ced85f81a7a67e190a4ff4e14d8cc04978a3767.zip |
btrfs: reduce type width of btrfs_io_contexts
That structure is our ultimate object for all __btrfs_map_block()
related functions. We have some hard to understand members, like
tgtdev_map, but without any comments.
This patch will improve the situation:
- Add extra comments for num_stripes, mirror_num, num_tgtdevs and
tgtdev_map[]
Especially for the last two members, add a dedicated (thus very long)
comments for them, with example to explain it.
- Shrink those int members to u16.
In fact our on-disk format is only using u16 for num_stripes, thus
no need to use int at all.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/volumes.h')
-rw-r--r-- | fs/btrfs/volumes.h | 54 |
1 files changed, 49 insertions, 5 deletions
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h index 9f397b4c1b4f..da0f9a9eaf94 100644 --- a/fs/btrfs/volumes.h +++ b/fs/btrfs/volumes.h @@ -408,11 +408,55 @@ struct btrfs_io_context { u64 map_type; /* get from map_lookup->type */ struct bio *orig_bio; atomic_t error; - int max_errors; - int num_stripes; - int mirror_num; - int num_tgtdevs; - int *tgtdev_map; + u16 max_errors; + + /* + * The total number of stripes, including the extra duplicated + * stripe for replace. + */ + u16 num_stripes; + + /* + * The mirror_num of this bioc. + * + * This is for reads which use 0 as mirror_num, thus we should return a + * valid mirror_num (>0) for the reader. + */ + u16 mirror_num; + + /* + * The following two members are for dev-replace case only. + * + * @num_tgtdevs: Number of duplicated stripes which need to be + * written to replace target. + * Should be <= 2 (2 for DUP, otherwise <= 1). + * @tgtdev_map: The array indicates where the duplicated stripes + * are from. The size is the number of original + * stripes (num_stripes - num_tgtdevs). + * + * The @tgtdev_map[] array is mostly for RAID56 cases. + * As non-RAID56 stripes share the same contents of the mapped range, + * thus no need to bother where the duplicated ones are from. + * + * But for RAID56 case, all stripes contain different contents, thus + * we need a way to know the mapping. + * + * There is an example for the two members, using a RAID5 write: + * + * num_stripes: 4 (3 + 1 duplicated write) + * stripes[0]: dev = devid 1, physical = X + * stripes[1]: dev = devid 2, physical = Y + * stripes[2]: dev = devid 3, physical = Z + * stripes[3]: dev = devid 0, physical = Y + * + * num_tgtdevs = 1 + * tgtdev_map[0] = 0 <- Means stripes[0] is not involved in replace. + * tgtdev_map[1] = 3 <- Means stripes[1] is involved in replace, + * and it's duplicated to stripes[3]. + * tgtdev_map[2] = 0 <- Means stripes[2] is not involved in replace. + */ + u16 num_tgtdevs; + u16 *tgtdev_map; /* * logical block numbers for the start of each stripe * The last one or two are p/q. These are sorted, |