summaryrefslogtreecommitdiffstats
path: root/drivers/s390/block/dasd_eer.c
blob: 0c075d100252b73382f910a172edf91108e09cee (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
// SPDX-License-Identifier: GPL-2.0
/*
 *  Character device driver for extended error reporting.
 *
 *  Copyright IBM Corp. 2005
 *  extended error reporting for DASD ECKD devices
 *  Author(s): Stefan Weinhuber <wein@de.ibm.com>
 */

#define KMSG_COMPONENT "dasd-eckd"

#include <linux/init.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/device.h>
#include <linux/poll.h>
#include <linux/mutex.h>
#include <linux/err.h>
#include <linux/slab.h>

#include <linux/uaccess.h>
#include <linux/atomic.h>
#include <asm/ebcdic.h>

#include "dasd_int.h"
#include "dasd_eckd.h"

#ifdef PRINTK_HEADER
#undef PRINTK_HEADER
#endif				/* PRINTK_HEADER */
#define PRINTK_HEADER "dasd(eer):"

/*
 * SECTION: the internal buffer
 */

/*
 * The internal buffer is meant to store obaque blobs of data, so it does
 * not know of higher level concepts like triggers.
 * It consists of a number of pages that are used as a ringbuffer. Each data
 * blob is stored in a simple record that consists of an integer, which
 * contains the size of the following data, and the data bytes themselfes.
 *
 * To allow for multiple independent readers we create one internal buffer
 * each time the device is opened and destroy the buffer when the file is
 * closed again. The number of pages used for this buffer is determined by
 * the module parmeter eer_pages.
 *
 * One record can be written to a buffer by using the functions
 * - dasd_eer_start_record (one time per record to write the size to the
 *                          buffer and reserve the space for the data)
 * - dasd_eer_write_buffer (one or more times per record to write the data)
 * The data can be written in several steps but you will have to compute
 * the total size up front for the invocation of dasd_eer_start_record.
 * If the ringbuffer is full, dasd_eer_start_record will remove the required
 * number of old records.
 *
 * A record is typically read in two steps, first read the integer that
 * specifies the size of the following data, then read the data.
 * Both can be done by
 * - dasd_eer_read_buffer
 *
 * For all mentioned functions you need to get the bufferlock first and keep
 * it until a complete record is written or read.
 *
 * All information necessary to keep track of an internal buffer is kept in
 * a struct eerbuffer. The buffer specific to a file pointer is strored in
 * the private_data field of that file. To be able to write data to all
 * existing buffers, each buffer is also added to the bufferlist.
 * If the user does not want to read a complete record in one go, we have to
 * keep track of the rest of the record. residual stores the number of bytes
 * that are still to deliver. If the rest of the record is invalidated between
 * two reads then residual will be set to -1 so that the next read will fail.
 * All entries in the eerbuffer structure are protected with the bufferlock.
 * To avoid races between writing to a buffer on the one side and creating
 * and destroying buffers on the other side, the bufferlock must also be used
 * to protect the bufferlist.
 */

static int eer_pages = 5;
module_param(eer_pages, int, S_IRUGO|S_IWUSR);

struct eerbuffer {
	struct list_head list;
	char **buffer;
	int buffersize;
	int buffer_page_count;
	int head;
        int tail;
	int residual;
};

static LIST_HEAD(bufferlist);
static DEFINE_SPINLOCK(bufferlock);
static DECLARE_WAIT_QUEUE_HEAD(dasd_eer_read_wait_queue);

/*
 * How many free bytes are available on the buffer.
 * Needs to be called with bufferlock held.
 */
static int dasd_eer_get_free_bytes(struct eerbuffer *eerb)
{
	if (eerb->head < eerb->tail)
		return eerb->tail - eerb->head - 1;
	return eerb->buffersize - eerb->head + eerb->tail -1;
}

/*
 * How many bytes of buffer space are used.
 * Needs to be called with bufferlock held.
 */
static int dasd_eer_get_filled_bytes(struct eerbuffer *eerb)
{

	if (eerb->head >= eerb->tail)
		return eerb->head - eerb->tail;
	return eerb->buffersize - eerb->tail + eerb->head;
}

/*
 * The dasd_eer_write_buffer function just copies count bytes of data
 * to the buffer. Make sure to call dasd_eer_start_record first, to
 * make sure that enough free space is available.
 * Needs to be called with bufferlock held.
 */
static void dasd_eer_write_buffer(struct eerbuffer *eerb,
				  char *data, int count)
{

	unsigned long headindex,localhead;
	unsigned long rest, len;
	char *nextdata;

	nextdata = data;
	rest = count;
	while (rest > 0) {
 		headindex = eerb->head / PAGE_SIZE;
 		localhead = eerb->head % PAGE_SIZE;
		len = min(rest, PAGE_SIZE - localhead);
		memcpy(eerb->buffer[headindex]+localhead, nextdata, len);
		nextdata += len;
		rest -= len;
		eerb->head += len;
		if (eerb->head == eerb->buffersize)
			eerb->head = 0; /* wrap around */
		BUG_ON(eerb->head > eerb->buffersize);
	}
}

/*
 * Needs to be called with bufferlock held.
 */
static int dasd_eer_read_buffer(struct eerbuffer *eerb, char *data, int count)
{

	unsigned long tailindex,localtail;
	unsigned long rest, len, finalcount;
	char *nextdata;

	finalcount = min(count, dasd_eer_get_filled_bytes(eerb));
	nextdata = data;
	rest = finalcount;
	while (rest > 0) {
 		tailindex = eerb->tail / PAGE_SIZE;
 		localtail = eerb->tail % PAGE_SIZE;
		len = min(rest, PAGE_SIZE - localtail);
		memcpy(nextdata, eerb->buffer[tailindex] + localtail, len);
		nextdata += len;
		rest -= len;
		eerb->tail += len;
		if (eerb->tail == eerb->buffersize)
			eerb->tail = 0; /* wrap around */
		BUG_ON(eerb->tail > eerb->buffersize);
	}
	return finalcount;
}

/*
 * Whenever you want to write a blob of data to the internal buffer you
 * have to start by using this function first. It will write the number
 * of bytes that will be written to the buffer. If necessary it will remove
 * old records to make room for the new one.
 * Needs to be called with bufferlock held.
 */
static int dasd_eer_start_record(struct eerbuffer *eerb, int count)
{
	int tailcount;

	if (count + sizeof(count) > eerb->buffersize)
		return -ENOMEM;
	while (dasd_eer_get_free_bytes(eerb) < count + sizeof(count)) {
		if (eerb->residual > 0) {
			eerb->tail += eerb->residual;
			if (eerb->tail >= eerb->buffersize)
				eerb->tail -= eerb->buffersize;
			eerb->residual = -1;
		}
		dasd_eer_read_buffer(eerb, (char *) &tailcount,
				     sizeof(tailcount));
		eerb->tail += tailcount;
		if (eerb->tail >= eerb->buffersize)
			eerb->tail -= eerb->buffersize;
	}
	dasd_eer_write_buffer(eerb, (char*) &count, sizeof(count));

	return 0;
};

/*
 * Release pages that are not used anymore.
 */
static void dasd_eer_free_buffer_pages(char **buf, int no_pages)
{
	int i;

	for (i = 0; i < no_pages; i++)
		free_page((unsigned long) buf[i]);
}

/*
 * Allocate a new set of memory pages.
 */
static int dasd_eer_allocate_buffer_pages(char **buf, int no_pages)
{
	int i;

	for (i = 0; i < no_pages; i++) {
		buf[i] = (char *) get_zeroed_page(GFP_KERNEL);
		if (!buf[i]) {
			dasd_eer_free_buffer_pages(buf, i);
			return -ENOMEM;
		}
	}
	return 0;
}

/*
 * SECTION: The extended error reporting functionality
 */

/*
 * When a DASD device driver wants to report an error, it calls the
 * function dasd_eer_write and gives the respective trigger ID as
 * parameter. Currently there are four kinds of triggers:
 *
 * DASD_EER_FATALERROR:  all kinds of unrecoverable I/O problems
 * DASD_EER_PPRCSUSPEND: PPRC was suspended
 * DASD_EER_NOPATH:      There is no path to the device left.
 * DASD_EER_STATECHANGE: The state of the device has changed.
 *
 * For the first three triggers all required information can be supplied by
 * the caller. For these triggers a record is written by the function
 * dasd_eer_write_standard_trigger.
 *
 * The DASD_EER_STATECHANGE trigger is special since a sense subsystem
 * status ccw need to be executed to gather the necessary sense data first.
 * The dasd_eer_snss function will queue the SNSS request and the request
 * callback will then call dasd_eer_write with the DASD_EER_STATCHANGE
 * trigger.
 *
 * To avoid memory allocations at runtime, the necessary memory is allocated
 * when the extended error reporting is enabled for a device (by
 * dasd_eer_probe). There is one sense subsystem status request for each
 * eer enabled DASD device. The presence of the cqr in device->eer_cqr
 * indicates that eer is enable for the device. The use of the snss request
 * is protected by the DASD_FLAG_EER_IN_USE bit. When this flag indicates
 * that the cqr is currently in use, dasd_eer_snss cannot start a second
 * request but sets the DASD_FLAG_EER_SNSS flag instead. The callback of
 * the SNSS request will check the bit and call dasd_eer_snss again.
 */

#define SNSS_DATA_SIZE 44

#define DASD_EER_BUSID_SIZE 10
struct dasd_eer_header {
	__u32 total_size;
	__u32 trigger;
	__u64 tv_sec;
	__u64 tv_usec;
	char busid[DASD_EER_BUSID_SIZE];
} __attribute__ ((packed));

/*
 * The following function can be used for those triggers that have
 * all necessary data available when the function is called.
 * If the parameter cqr is not NULL, the chain of requests will be searched
 * for valid sense data, and all valid sense data sets will be added to
 * the triggers data.
 */
static void dasd_eer_write_standard_trigger(struct dasd_device *device,
					    struct dasd_ccw_req *cqr,
					    int trigger)
{
	struct dasd_ccw_req *temp_cqr;
	int data_size;
	struct timespec64 ts;
	struct dasd_eer_header header;
	unsigned long flags;
	struct eerbuffer *eerb;
	char *sense;

	/* go through cqr chain and count the valid sense data sets */
	data_size = 0;
	for (temp_cqr = cqr; temp_cqr; temp_cqr = temp_cqr->refers)
		if (dasd_get_sense(&temp_cqr->irb))
			data_size += 32;

	header.total_size = sizeof(header) + data_size + 4; /* "EOR" */
	header.trigger = trigger;
	ktime_get_real_ts64(&ts);
	header.tv_sec = ts.tv_sec;
	header.tv_usec = ts.tv_nsec / NSEC_PER_USEC;
	strncpy(header.busid, dev_name(&device->cdev->dev),
		DASD_EER_BUSID_SIZE);

	spin_lock_irqsave(&bufferlock, flags);
	list_for_each_entry(eerb, &bufferlist, list) {
		dasd_eer_start_record(eerb, header.total_size);
		dasd_eer_write_buffer(eerb, (char *) &header, sizeof(header));
		for (temp_cqr = cqr; temp_cqr; temp_cqr = temp_cqr->refers) {
			sense = dasd_get_sense(&temp_cqr->irb);
			if (sense)
				dasd_eer_write_buffer(eerb, sense, 32);
		}
		dasd_eer_write_buffer(eerb, "EOR", 4);
	}
	spin_unlock_irqrestore(&bufferlock, flags);
	wake_up_interruptible(&dasd_eer_read_wait_queue);
}

/*
 * This function writes a DASD_EER_STATECHANGE trigger.
 */
static void dasd_eer_write_snss_trigger(struct dasd_device *device,
					struct dasd_ccw_req *cqr,
					int trigger)
{
	int data_size;
	int snss_rc;
	struct timespec64 ts;
	struct dasd_eer_header header;
	unsigned long flags;
	struct eerbuffer *eerb;

	snss_rc = (cqr->status == DASD_CQR_DONE) ? 0 : -EIO;
	if (snss_rc)
		data_size = 0;
	else
		data_size = SNSS_DATA_SIZE;

	header.total_size = sizeof(header) + data_size + 4; /* "EOR" */
	header.trigger = DASD_EER_STATECHANGE;
	ktime_get_real_ts64(&ts);
	header.tv_sec = ts.tv_sec;
	header.tv_usec = ts.tv_nsec / NSEC_PER_USEC;
	strncpy(header.busid, dev_name(&device->cdev->dev),
		DASD_EER_BUSID_SIZE);

	spin_lock_irqsave(&bufferlock, flags);
	list_for_each_entry(eerb, &bufferlist, list) {
		dasd_eer_start_record(eerb, header.total_size);
		dasd_eer_write_buffer(eerb, (char *) &header , sizeof(header));
		if (!snss_rc)
			dasd_eer_write_buffer(eerb, cqr->data, SNSS_DATA_SIZE);
		dasd_eer_write_buffer(eerb, "EOR", 4);
	}
	spin_unlock_irqrestore(&bufferlock, flags);
	wake_up_interruptible(&dasd_eer_read_wait_queue);
}

/*
 * This function is called for all triggers. It calls the appropriate
 * function that writes the actual trigger records.
 */
void dasd_eer_write(struct dasd_device *device, struct dasd_ccw_req *cqr,
		    unsigned int id)
{
	if (!device->eer_cqr)
		return;
	switch (id) {
	case DASD_EER_FATALERROR:
	case DASD_EER_PPRCSUSPEND:
		dasd_eer_write_standard_trigger(device, cqr, id);
		break;
	case DASD_EER_NOPATH:
		dasd_eer_write_standard_trigger(device, NULL, id);
		break;
	case DASD_EER_STATECHANGE:
		dasd_eer_write_snss_trigger(device, cqr, id);
		break;
	default: /* unknown trigger, so we write it without any sense data */
		dasd_eer_write_standard_trigger(device, NULL, id);
		break;
	}
}
EXPORT_SYMBOL(dasd_eer_write);

/*
 * Start a sense subsystem status request.
 * Needs to be called with the device held.
 */
void dasd_eer_snss(struct dasd_device *device)
{
	struct dasd_ccw_req *cqr;

	cqr = device->eer_cqr;
	if (!cqr)	/* Device not eer enabled. */
		return;
	if (test_and_set_bit(DASD_FLAG_EER_IN_USE, &device->flags)) {
		/* Sense subsystem status request in use. */
		set_bit(DASD_FLAG_EER_SNSS, &device->flags);
		return;
	}
	/* cdev is already locked, can't use dasd_add_request_head */
	clear_bit(DASD_FLAG_EER_SNSS, &device->flags);
	cqr->status = DASD_CQR_QUEUED;
	list_add(&cqr->devlist, &device->ccw_queue);
	dasd_schedule_device_bh(device);
}

/*
 * Callback function for use with sense subsystem status request.
 */
static void dasd_eer_snss_cb(struct dasd_ccw_req *cqr, void *data)
{
	struct dasd_device *device = cqr->startdev;
	unsigned long flags;

	dasd_eer_write(device, cqr, DASD_EER_STATECHANGE);
	spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
	if (device->eer_cqr == cqr) {
		clear_bit(DASD_FLAG_EER_IN_USE, &device->flags);
		if (test_bit(DASD_FLAG_EER_SNSS, &device->flags))
			/* Another SNSS has been requested in the meantime. */
			dasd_eer_snss(device);
		cqr = NULL;
	}
	spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
	if (cqr)
		/*
		 * Extended error recovery has been switched off while
		 * the SNSS request was running. It could even have
		 * been switched off and on again in which case there
		 * is a new ccw in device->eer_cqr. Free the "old"
		 * snss request now.
		 */
		dasd_kfree_request(cqr, device);
}

/*
 * Enable error reporting on a given device.
 */
int dasd_eer_enable(struct dasd_device *device)
{
	struct dasd_ccw_req *cqr = NULL;
	unsigned long flags;
	struct ccw1 *ccw;
	int rc = 0;

	spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
	if (device->eer_cqr)
		goto out;
	else if (!device->discipline ||
		 strcmp(device->discipline->name, "ECKD"))
		rc = -EMEDIUMTYPE;
	else if (test_bit(DASD_FLAG_OFFLINE, &device->flags))
		rc = -EBUSY;

	if (rc)
		goto out;

	cqr = dasd_kmalloc_request(DASD_ECKD_MAGIC, 1 /* SNSS */,
				   SNSS_DATA_SIZE, device);
	if (IS_ERR(cqr)) {
		rc = -ENOMEM;
		cqr = NULL;
		goto out;
	}

	cqr->startdev = device;
	cqr->retries = 255;
	cqr->expires = 10 * HZ;
	clear_bit(DASD_CQR_FLAGS_USE_ERP, &cqr->flags);
	set_bit(DASD_CQR_ALLOW_SLOCK, &cqr->flags);

	ccw = cqr->cpaddr;
	ccw->cmd_code = DASD_ECKD_CCW_SNSS;
	ccw->count = SNSS_DATA_SIZE;
	ccw->flags = 0;
	ccw->cda = (__u32)(addr_t) cqr->data;

	cqr->buildclk = get_tod_clock();
	cqr->status = DASD_CQR_FILLED;
	cqr->callback = dasd_eer_snss_cb;

	if (!device->eer_cqr) {
		device->eer_cqr = cqr;
		cqr = NULL;
	}

out:
	spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);

	if (cqr)
		dasd_kfree_request(cqr, device);

	return rc;
}

/*
 * Disable error reporting on a given device.
 */
void dasd_eer_disable(struct dasd_device *device)
{
	struct dasd_ccw_req *cqr;
	unsigned long flags;
	int in_use;

	if (!device->eer_cqr)
		return;
	spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
	cqr = device->eer_cqr;
	device->eer_cqr = NULL;
	clear_bit(DASD_FLAG_EER_SNSS, &device->flags);
	in_use = test_and_clear_bit(DASD_FLAG_EER_IN_USE, &device->flags);
	spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
	if (cqr && !in_use)
		dasd_kfree_request(cqr, device);
}

/*
 * SECTION: the device operations
 */

/*
 * On the one side we need a lock to access our internal buffer, on the
 * other side a copy_to_user can sleep. So we need to copy the data we have
 * to transfer in a readbuffer, which is protected by the readbuffer_mutex.
 */
static char readbuffer[PAGE_SIZE];
static DEFINE_MUTEX(readbuffer_mutex);

static int dasd_eer_open(struct inode *inp, struct file *filp)
{
	struct eerbuffer *eerb;
	unsigned long flags;

	eerb = kzalloc(sizeof(struct eerbuffer), GFP_KERNEL);
	if (!eerb)
		return -ENOMEM;
	eerb->buffer_page_count = eer_pages;
	if (eerb->buffer_page_count < 1 ||
	    eerb->buffer_page_count > INT_MAX / PAGE_SIZE) {
		kfree(eerb);
		DBF_EVENT(DBF_WARNING, "can't open device since module "
			"parameter eer_pages is smaller than 1 or"
			" bigger than %d", (int)(INT_MAX / PAGE_SIZE));
		return -EINVAL;
	}
	eerb->buffersize = eerb->buffer_page_count * PAGE_SIZE;
	eerb->buffer = kmalloc(eerb->buffer_page_count * sizeof(char *),
			       GFP_KERNEL);
        if (!eerb->buffer) {
		kfree(eerb);
                return -ENOMEM;
	}
	if (dasd_eer_allocate_buffer_pages(eerb->buffer,
					   eerb->buffer_page_count)) {
		kfree(eerb->buffer);
		kfree(eerb);
		return -ENOMEM;
	}
	filp->private_data = eerb;
	spin_lock_irqsave(&bufferlock, flags);
	list_add(&eerb->list, &bufferlist);
	spin_unlock_irqrestore(&bufferlock, flags);

	return nonseekable_open(inp,filp);
}

static int dasd_eer_close(struct inode *inp, struct file *filp)
{
	struct eerbuffer *eerb;
	unsigned long flags;

	eerb = (struct eerbuffer *) filp->private_data;
	spin_lock_irqsave(&bufferlock, flags);
	list_del(&eerb->list);
	spin_unlock_irqrestore(&bufferlock, flags);
	dasd_eer_free_buffer_pages(eerb->buffer, eerb->buffer_page_count);
	kfree(eerb->buffer);
	kfree(eerb);

	return 0;
}

static ssize_t dasd_eer_read(struct file *filp, char __user *buf,
			     size_t count, loff_t *ppos)
{
	int tc,rc;
	int tailcount,effective_count;
        unsigned long flags;
	struct eerbuffer *eerb;

	eerb = (struct eerbuffer *) filp->private_data;
	if (mutex_lock_interruptible(&readbuffer_mutex))
		return -ERESTARTSYS;

	spin_lock_irqsave(&bufferlock, flags);

	if (eerb->residual < 0) { /* the remainder of this record */
		                  /* has been deleted             */
		eerb->residual = 0;
		spin_unlock_irqrestore(&bufferlock, flags);
		mutex_unlock(&readbuffer_mutex);
		return -EIO;
	} else if (eerb->residual > 0) {
		/* OK we still have a second half of a record to deliver */
		effective_count = min(eerb->residual, (int) count);
		eerb->residual -= effective_count;
	} else {
		tc = 0;
		while (!tc) {
			tc = dasd_eer_read_buffer(eerb, (char *) &tailcount,
						  sizeof(tailcount));
			if (!tc) {
				/* no data available */
				spin_unlock_irqrestore(&bufferlock, flags);
				mutex_unlock(&readbuffer_mutex);
				if (filp->f_flags & O_NONBLOCK)
					return -EAGAIN;
				rc = wait_event_interruptible(
					dasd_eer_read_wait_queue,
					eerb->head != eerb->tail);
				if (rc)
					return rc;
				if (mutex_lock_interruptible(&readbuffer_mutex))
					return -ERESTARTSYS;
				spin_lock_irqsave(&bufferlock, flags);
			}
		}
		WARN_ON(tc != sizeof(tailcount));
		effective_count = min(tailcount,(int)count);
		eerb->residual = tailcount - effective_count;
	}

	tc = dasd_eer_read_buffer(eerb, readbuffer, effective_count);
	WARN_ON(tc != effective_count);

	spin_unlock_irqrestore(&bufferlock, flags);

	if (copy_to_user(buf, readbuffer, effective_count)) {
		mutex_unlock(&readbuffer_mutex);
		return -EFAULT;
	}

	mutex_unlock(&readbuffer_mutex);
	return effective_count;
}

static __poll_t dasd_eer_poll(struct file *filp, poll_table *ptable)
{
	__poll_t mask;
	unsigned long flags;
	struct eerbuffer *eerb;

	eerb = (struct eerbuffer *) filp->private_data;
	poll_wait(filp, &dasd_eer_read_wait_queue, ptable);
	spin_lock_irqsave(&bufferlock, flags);
	if (eerb->head != eerb->tail)
		mask = POLLIN | POLLRDNORM ;
	else
		mask = 0;
	spin_unlock_irqrestore(&bufferlock, flags);
	return mask;
}

static const struct file_operations dasd_eer_fops = {
	.open		= &dasd_eer_open,
	.release	= &dasd_eer_close,
	.read		= &dasd_eer_read,
	.poll		= &dasd_eer_poll,
	.owner		= THIS_MODULE,
	.llseek		= noop_llseek,
};

static struct miscdevice *dasd_eer_dev = NULL;

int __init dasd_eer_init(void)
{
	int rc;

	dasd_eer_dev = kzalloc(sizeof(*dasd_eer_dev), GFP_KERNEL);
	if (!dasd_eer_dev)
		return -ENOMEM;

	dasd_eer_dev->minor = MISC_DYNAMIC_MINOR;
	dasd_eer_dev->name  = "dasd_eer";
	dasd_eer_dev->fops  = &dasd_eer_fops;

	rc = misc_register(dasd_eer_dev);
	if (rc) {
		kfree(dasd_eer_dev);
		dasd_eer_dev = NULL;
		DBF_EVENT(DBF_ERR, "%s", "dasd_eer_init could not "
		       "register misc device");
		return rc;
	}

	return 0;
}

void dasd_eer_exit(void)
{
	if (dasd_eer_dev) {
		misc_deregister(dasd_eer_dev);
		kfree(dasd_eer_dev);
		dasd_eer_dev = NULL;
	}
}