xref: /openbmc/linux/drivers/md/dm-log-writes.c (revision 3d3337de)
1 /*
2  * Copyright (C) 2014 Facebook. All rights reserved.
3  *
4  * This file is released under the GPL.
5  */
6 
7 #include <linux/device-mapper.h>
8 
9 #include <linux/module.h>
10 #include <linux/init.h>
11 #include <linux/blkdev.h>
12 #include <linux/bio.h>
13 #include <linux/slab.h>
14 #include <linux/kthread.h>
15 #include <linux/freezer.h>
16 
17 #define DM_MSG_PREFIX "log-writes"
18 
19 /*
20  * This target will sequentially log all writes to the target device onto the
21  * log device.  This is helpful for replaying writes to check for fs consistency
22  * at all times.  This target provides a mechanism to mark specific events to
23  * check data at a later time.  So for example you would:
24  *
25  * write data
26  * fsync
27  * dmsetup message /dev/whatever mark mymark
28  * unmount /mnt/test
29  *
30  * Then replay the log up to mymark and check the contents of the replay to
31  * verify it matches what was written.
32  *
33  * We log writes only after they have been flushed, this makes the log describe
34  * close to the order in which the data hits the actual disk, not its cache.  So
35  * for example the following sequence (W means write, C means complete)
36  *
37  * Wa,Wb,Wc,Cc,Ca,FLUSH,FUAd,Cb,CFLUSH,CFUAd
38  *
39  * Would result in the log looking like this:
40  *
41  * c,a,flush,fuad,b,<other writes>,<next flush>
42  *
43  * This is meant to help expose problems where file systems do not properly wait
44  * on data being written before invoking a FLUSH.  FUA bypasses cache so once it
45  * completes it is added to the log as it should be on disk.
46  *
47  * We treat DISCARDs as if they don't bypass cache so that they are logged in
48  * order of completion along with the normal writes.  If we didn't do it this
49  * way we would process all the discards first and then write all the data, when
50  * in fact we want to do the data and the discard in the order that they
51  * completed.
52  */
53 #define LOG_FLUSH_FLAG (1 << 0)
54 #define LOG_FUA_FLAG (1 << 1)
55 #define LOG_DISCARD_FLAG (1 << 2)
56 #define LOG_MARK_FLAG (1 << 3)
57 
58 #define WRITE_LOG_VERSION 1
59 #define WRITE_LOG_MAGIC 0x6a736677736872
60 
61 /*
62  * The disk format for this is braindead simple.
63  *
64  * At byte 0 we have our super, followed by the following sequence for
65  * nr_entries:
66  *
67  * [   1 sector    ][  entry->nr_sectors ]
68  * [log_write_entry][    data written    ]
69  *
70  * The log_write_entry takes up a full sector so we can have arbitrary length
71  * marks and it leaves us room for extra content in the future.
72  */
73 
74 /*
75  * Basic info about the log for userspace.
76  */
77 struct log_write_super {
78 	__le64 magic;
79 	__le64 version;
80 	__le64 nr_entries;
81 	__le32 sectorsize;
82 };
83 
84 /*
85  * sector - the sector we wrote.
86  * nr_sectors - the number of sectors we wrote.
87  * flags - flags for this log entry.
88  * data_len - the size of the data in this log entry, this is for private log
89  * entry stuff, the MARK data provided by userspace for example.
90  */
91 struct log_write_entry {
92 	__le64 sector;
93 	__le64 nr_sectors;
94 	__le64 flags;
95 	__le64 data_len;
96 };
97 
98 struct log_writes_c {
99 	struct dm_dev *dev;
100 	struct dm_dev *logdev;
101 	u64 logged_entries;
102 	u32 sectorsize;
103 	atomic_t io_blocks;
104 	atomic_t pending_blocks;
105 	sector_t next_sector;
106 	sector_t end_sector;
107 	bool logging_enabled;
108 	bool device_supports_discard;
109 	spinlock_t blocks_lock;
110 	struct list_head unflushed_blocks;
111 	struct list_head logging_blocks;
112 	wait_queue_head_t wait;
113 	struct task_struct *log_kthread;
114 };
115 
116 struct pending_block {
117 	int vec_cnt;
118 	u64 flags;
119 	sector_t sector;
120 	sector_t nr_sectors;
121 	char *data;
122 	u32 datalen;
123 	struct list_head list;
124 	struct bio_vec vecs[0];
125 };
126 
127 struct per_bio_data {
128 	struct pending_block *block;
129 };
130 
131 static void put_pending_block(struct log_writes_c *lc)
132 {
133 	if (atomic_dec_and_test(&lc->pending_blocks)) {
134 		smp_mb__after_atomic();
135 		if (waitqueue_active(&lc->wait))
136 			wake_up(&lc->wait);
137 	}
138 }
139 
140 static void put_io_block(struct log_writes_c *lc)
141 {
142 	if (atomic_dec_and_test(&lc->io_blocks)) {
143 		smp_mb__after_atomic();
144 		if (waitqueue_active(&lc->wait))
145 			wake_up(&lc->wait);
146 	}
147 }
148 
149 static void log_end_io(struct bio *bio, int err)
150 {
151 	struct log_writes_c *lc = bio->bi_private;
152 	struct bio_vec *bvec;
153 	int i;
154 
155 	if (err) {
156 		unsigned long flags;
157 
158 		DMERR("Error writing log block, error=%d", err);
159 		spin_lock_irqsave(&lc->blocks_lock, flags);
160 		lc->logging_enabled = false;
161 		spin_unlock_irqrestore(&lc->blocks_lock, flags);
162 	}
163 
164 	bio_for_each_segment_all(bvec, bio, i)
165 		__free_page(bvec->bv_page);
166 
167 	put_io_block(lc);
168 	bio_put(bio);
169 }
170 
171 /*
172  * Meant to be called if there is an error, it will free all the pages
173  * associated with the block.
174  */
175 static void free_pending_block(struct log_writes_c *lc,
176 			       struct pending_block *block)
177 {
178 	int i;
179 
180 	for (i = 0; i < block->vec_cnt; i++) {
181 		if (block->vecs[i].bv_page)
182 			__free_page(block->vecs[i].bv_page);
183 	}
184 	kfree(block->data);
185 	kfree(block);
186 	put_pending_block(lc);
187 }
188 
189 static int write_metadata(struct log_writes_c *lc, void *entry,
190 			  size_t entrylen, void *data, size_t datalen,
191 			  sector_t sector)
192 {
193 	struct bio *bio;
194 	struct page *page;
195 	void *ptr;
196 	size_t ret;
197 
198 	bio = bio_alloc(GFP_KERNEL, 1);
199 	if (!bio) {
200 		DMERR("Couldn't alloc log bio");
201 		goto error;
202 	}
203 	bio->bi_iter.bi_size = 0;
204 	bio->bi_iter.bi_sector = sector;
205 	bio->bi_bdev = lc->logdev->bdev;
206 	bio->bi_end_io = log_end_io;
207 	bio->bi_private = lc;
208 	set_bit(BIO_UPTODATE, &bio->bi_flags);
209 
210 	page = alloc_page(GFP_KERNEL);
211 	if (!page) {
212 		DMERR("Couldn't alloc log page");
213 		bio_put(bio);
214 		goto error;
215 	}
216 
217 	ptr = kmap_atomic(page);
218 	memcpy(ptr, entry, entrylen);
219 	if (datalen)
220 		memcpy(ptr + entrylen, data, datalen);
221 	memset(ptr + entrylen + datalen, 0,
222 	       lc->sectorsize - entrylen - datalen);
223 	kunmap_atomic(ptr);
224 
225 	ret = bio_add_page(bio, page, lc->sectorsize, 0);
226 	if (ret != lc->sectorsize) {
227 		DMERR("Couldn't add page to the log block");
228 		goto error_bio;
229 	}
230 	submit_bio(WRITE, bio);
231 	return 0;
232 error_bio:
233 	bio_put(bio);
234 	__free_page(page);
235 error:
236 	put_io_block(lc);
237 	return -1;
238 }
239 
240 static int log_one_block(struct log_writes_c *lc,
241 			 struct pending_block *block, sector_t sector)
242 {
243 	struct bio *bio;
244 	struct log_write_entry entry;
245 	size_t ret;
246 	int i;
247 
248 	entry.sector = cpu_to_le64(block->sector);
249 	entry.nr_sectors = cpu_to_le64(block->nr_sectors);
250 	entry.flags = cpu_to_le64(block->flags);
251 	entry.data_len = cpu_to_le64(block->datalen);
252 	if (write_metadata(lc, &entry, sizeof(entry), block->data,
253 			   block->datalen, sector)) {
254 		free_pending_block(lc, block);
255 		return -1;
256 	}
257 
258 	if (!block->vec_cnt)
259 		goto out;
260 	sector++;
261 
262 	bio = bio_alloc(GFP_KERNEL, block->vec_cnt);
263 	if (!bio) {
264 		DMERR("Couldn't alloc log bio");
265 		goto error;
266 	}
267 	atomic_inc(&lc->io_blocks);
268 	bio->bi_iter.bi_size = 0;
269 	bio->bi_iter.bi_sector = sector;
270 	bio->bi_bdev = lc->logdev->bdev;
271 	bio->bi_end_io = log_end_io;
272 	bio->bi_private = lc;
273 	set_bit(BIO_UPTODATE, &bio->bi_flags);
274 
275 	for (i = 0; i < block->vec_cnt; i++) {
276 		/*
277 		 * The page offset is always 0 because we allocate a new page
278 		 * for every bvec in the original bio for simplicity sake.
279 		 */
280 		ret = bio_add_page(bio, block->vecs[i].bv_page,
281 				   block->vecs[i].bv_len, 0);
282 		if (ret != block->vecs[i].bv_len) {
283 			atomic_inc(&lc->io_blocks);
284 			submit_bio(WRITE, bio);
285 			bio = bio_alloc(GFP_KERNEL, block->vec_cnt - i);
286 			if (!bio) {
287 				DMERR("Couldn't alloc log bio");
288 				goto error;
289 			}
290 			bio->bi_iter.bi_size = 0;
291 			bio->bi_iter.bi_sector = sector;
292 			bio->bi_bdev = lc->logdev->bdev;
293 			bio->bi_end_io = log_end_io;
294 			bio->bi_private = lc;
295 			set_bit(BIO_UPTODATE, &bio->bi_flags);
296 
297 			ret = bio_add_page(bio, block->vecs[i].bv_page,
298 					   block->vecs[i].bv_len, 0);
299 			if (ret != block->vecs[i].bv_len) {
300 				DMERR("Couldn't add page on new bio?");
301 				bio_put(bio);
302 				goto error;
303 			}
304 		}
305 		sector += block->vecs[i].bv_len >> SECTOR_SHIFT;
306 	}
307 	submit_bio(WRITE, bio);
308 out:
309 	kfree(block->data);
310 	kfree(block);
311 	put_pending_block(lc);
312 	return 0;
313 error:
314 	free_pending_block(lc, block);
315 	put_io_block(lc);
316 	return -1;
317 }
318 
319 static int log_super(struct log_writes_c *lc)
320 {
321 	struct log_write_super super;
322 
323 	super.magic = cpu_to_le64(WRITE_LOG_MAGIC);
324 	super.version = cpu_to_le64(WRITE_LOG_VERSION);
325 	super.nr_entries = cpu_to_le64(lc->logged_entries);
326 	super.sectorsize = cpu_to_le32(lc->sectorsize);
327 
328 	if (write_metadata(lc, &super, sizeof(super), NULL, 0, 0)) {
329 		DMERR("Couldn't write super");
330 		return -1;
331 	}
332 
333 	return 0;
334 }
335 
336 static inline sector_t logdev_last_sector(struct log_writes_c *lc)
337 {
338 	return i_size_read(lc->logdev->bdev->bd_inode) >> SECTOR_SHIFT;
339 }
340 
341 static int log_writes_kthread(void *arg)
342 {
343 	struct log_writes_c *lc = (struct log_writes_c *)arg;
344 	sector_t sector = 0;
345 
346 	while (!kthread_should_stop()) {
347 		bool super = false;
348 		bool logging_enabled;
349 		struct pending_block *block = NULL;
350 		int ret;
351 
352 		spin_lock_irq(&lc->blocks_lock);
353 		if (!list_empty(&lc->logging_blocks)) {
354 			block = list_first_entry(&lc->logging_blocks,
355 						 struct pending_block, list);
356 			list_del_init(&block->list);
357 			if (!lc->logging_enabled)
358 				goto next;
359 
360 			sector = lc->next_sector;
361 			if (block->flags & LOG_DISCARD_FLAG)
362 				lc->next_sector++;
363 			else
364 				lc->next_sector += block->nr_sectors + 1;
365 
366 			/*
367 			 * Apparently the size of the device may not be known
368 			 * right away, so handle this properly.
369 			 */
370 			if (!lc->end_sector)
371 				lc->end_sector = logdev_last_sector(lc);
372 			if (lc->end_sector &&
373 			    lc->next_sector >= lc->end_sector) {
374 				DMERR("Ran out of space on the logdev");
375 				lc->logging_enabled = false;
376 				goto next;
377 			}
378 			lc->logged_entries++;
379 			atomic_inc(&lc->io_blocks);
380 
381 			super = (block->flags & (LOG_FUA_FLAG | LOG_MARK_FLAG));
382 			if (super)
383 				atomic_inc(&lc->io_blocks);
384 		}
385 next:
386 		logging_enabled = lc->logging_enabled;
387 		spin_unlock_irq(&lc->blocks_lock);
388 		if (block) {
389 			if (logging_enabled) {
390 				ret = log_one_block(lc, block, sector);
391 				if (!ret && super)
392 					ret = log_super(lc);
393 				if (ret) {
394 					spin_lock_irq(&lc->blocks_lock);
395 					lc->logging_enabled = false;
396 					spin_unlock_irq(&lc->blocks_lock);
397 				}
398 			} else
399 				free_pending_block(lc, block);
400 			continue;
401 		}
402 
403 		if (!try_to_freeze()) {
404 			set_current_state(TASK_INTERRUPTIBLE);
405 			if (!kthread_should_stop() &&
406 			    !atomic_read(&lc->pending_blocks))
407 				schedule();
408 			__set_current_state(TASK_RUNNING);
409 		}
410 	}
411 	return 0;
412 }
413 
414 /*
415  * Construct a log-writes mapping:
416  * log-writes <dev_path> <log_dev_path>
417  */
418 static int log_writes_ctr(struct dm_target *ti, unsigned int argc, char **argv)
419 {
420 	struct log_writes_c *lc;
421 	struct dm_arg_set as;
422 	const char *devname, *logdevname;
423 
424 	as.argc = argc;
425 	as.argv = argv;
426 
427 	if (argc < 2) {
428 		ti->error = "Invalid argument count";
429 		return -EINVAL;
430 	}
431 
432 	lc = kzalloc(sizeof(struct log_writes_c), GFP_KERNEL);
433 	if (!lc) {
434 		ti->error = "Cannot allocate context";
435 		return -ENOMEM;
436 	}
437 	spin_lock_init(&lc->blocks_lock);
438 	INIT_LIST_HEAD(&lc->unflushed_blocks);
439 	INIT_LIST_HEAD(&lc->logging_blocks);
440 	init_waitqueue_head(&lc->wait);
441 	lc->sectorsize = 1 << SECTOR_SHIFT;
442 	atomic_set(&lc->io_blocks, 0);
443 	atomic_set(&lc->pending_blocks, 0);
444 
445 	devname = dm_shift_arg(&as);
446 	if (dm_get_device(ti, devname, dm_table_get_mode(ti->table), &lc->dev)) {
447 		ti->error = "Device lookup failed";
448 		goto bad;
449 	}
450 
451 	logdevname = dm_shift_arg(&as);
452 	if (dm_get_device(ti, logdevname, dm_table_get_mode(ti->table), &lc->logdev)) {
453 		ti->error = "Log device lookup failed";
454 		dm_put_device(ti, lc->dev);
455 		goto bad;
456 	}
457 
458 	lc->log_kthread = kthread_run(log_writes_kthread, lc, "log-write");
459 	if (!lc->log_kthread) {
460 		ti->error = "Couldn't alloc kthread";
461 		dm_put_device(ti, lc->dev);
462 		dm_put_device(ti, lc->logdev);
463 		goto bad;
464 	}
465 
466 	/* We put the super at sector 0, start logging at sector 1 */
467 	lc->next_sector = 1;
468 	lc->logging_enabled = true;
469 	lc->end_sector = logdev_last_sector(lc);
470 	lc->device_supports_discard = true;
471 
472 	ti->num_flush_bios = 1;
473 	ti->flush_supported = true;
474 	ti->num_discard_bios = 1;
475 	ti->discards_supported = true;
476 	ti->per_bio_data_size = sizeof(struct per_bio_data);
477 	ti->private = lc;
478 	return 0;
479 
480 bad:
481 	kfree(lc);
482 	return -EINVAL;
483 }
484 
485 static int log_mark(struct log_writes_c *lc, char *data)
486 {
487 	struct pending_block *block;
488 	size_t maxsize = lc->sectorsize - sizeof(struct log_write_entry);
489 
490 	block = kzalloc(sizeof(struct pending_block), GFP_KERNEL);
491 	if (!block) {
492 		DMERR("Error allocating pending block");
493 		return -ENOMEM;
494 	}
495 
496 	block->data = kstrndup(data, maxsize, GFP_KERNEL);
497 	if (!block->data) {
498 		DMERR("Error copying mark data");
499 		kfree(block);
500 		return -ENOMEM;
501 	}
502 	atomic_inc(&lc->pending_blocks);
503 	block->datalen = strlen(block->data);
504 	block->flags |= LOG_MARK_FLAG;
505 	spin_lock_irq(&lc->blocks_lock);
506 	list_add_tail(&block->list, &lc->logging_blocks);
507 	spin_unlock_irq(&lc->blocks_lock);
508 	wake_up_process(lc->log_kthread);
509 	return 0;
510 }
511 
512 static void log_writes_dtr(struct dm_target *ti)
513 {
514 	struct log_writes_c *lc = ti->private;
515 
516 	spin_lock_irq(&lc->blocks_lock);
517 	list_splice_init(&lc->unflushed_blocks, &lc->logging_blocks);
518 	spin_unlock_irq(&lc->blocks_lock);
519 
520 	/*
521 	 * This is just nice to have since it'll update the super to include the
522 	 * unflushed blocks, if it fails we don't really care.
523 	 */
524 	log_mark(lc, "dm-log-writes-end");
525 	wake_up_process(lc->log_kthread);
526 	wait_event(lc->wait, !atomic_read(&lc->io_blocks) &&
527 		   !atomic_read(&lc->pending_blocks));
528 	kthread_stop(lc->log_kthread);
529 
530 	WARN_ON(!list_empty(&lc->logging_blocks));
531 	WARN_ON(!list_empty(&lc->unflushed_blocks));
532 	dm_put_device(ti, lc->dev);
533 	dm_put_device(ti, lc->logdev);
534 	kfree(lc);
535 }
536 
537 static void normal_map_bio(struct dm_target *ti, struct bio *bio)
538 {
539 	struct log_writes_c *lc = ti->private;
540 
541 	bio->bi_bdev = lc->dev->bdev;
542 }
543 
544 static int log_writes_map(struct dm_target *ti, struct bio *bio)
545 {
546 	struct log_writes_c *lc = ti->private;
547 	struct per_bio_data *pb = dm_per_bio_data(bio, sizeof(struct per_bio_data));
548 	struct pending_block *block;
549 	struct bvec_iter iter;
550 	struct bio_vec bv;
551 	size_t alloc_size;
552 	int i = 0;
553 	bool flush_bio = (bio->bi_rw & REQ_FLUSH);
554 	bool fua_bio = (bio->bi_rw & REQ_FUA);
555 	bool discard_bio = (bio->bi_rw & REQ_DISCARD);
556 
557 	pb->block = NULL;
558 
559 	/* Don't bother doing anything if logging has been disabled */
560 	if (!lc->logging_enabled)
561 		goto map_bio;
562 
563 	/*
564 	 * Map reads as normal.
565 	 */
566 	if (bio_data_dir(bio) == READ)
567 		goto map_bio;
568 
569 	/* No sectors and not a flush?  Don't care */
570 	if (!bio_sectors(bio) && !flush_bio)
571 		goto map_bio;
572 
573 	/*
574 	 * Discards will have bi_size set but there's no actual data, so just
575 	 * allocate the size of the pending block.
576 	 */
577 	if (discard_bio)
578 		alloc_size = sizeof(struct pending_block);
579 	else
580 		alloc_size = sizeof(struct pending_block) + sizeof(struct bio_vec) * bio_segments(bio);
581 
582 	block = kzalloc(alloc_size, GFP_NOIO);
583 	if (!block) {
584 		DMERR("Error allocating pending block");
585 		spin_lock_irq(&lc->blocks_lock);
586 		lc->logging_enabled = false;
587 		spin_unlock_irq(&lc->blocks_lock);
588 		return -ENOMEM;
589 	}
590 	INIT_LIST_HEAD(&block->list);
591 	pb->block = block;
592 	atomic_inc(&lc->pending_blocks);
593 
594 	if (flush_bio)
595 		block->flags |= LOG_FLUSH_FLAG;
596 	if (fua_bio)
597 		block->flags |= LOG_FUA_FLAG;
598 	if (discard_bio)
599 		block->flags |= LOG_DISCARD_FLAG;
600 
601 	block->sector = bio->bi_iter.bi_sector;
602 	block->nr_sectors = bio_sectors(bio);
603 
604 	/* We don't need the data, just submit */
605 	if (discard_bio) {
606 		WARN_ON(flush_bio || fua_bio);
607 		if (lc->device_supports_discard)
608 			goto map_bio;
609 		bio_endio(bio, 0);
610 		return DM_MAPIO_SUBMITTED;
611 	}
612 
613 	/* Flush bio, splice the unflushed blocks onto this list and submit */
614 	if (flush_bio && !bio_sectors(bio)) {
615 		spin_lock_irq(&lc->blocks_lock);
616 		list_splice_init(&lc->unflushed_blocks, &block->list);
617 		spin_unlock_irq(&lc->blocks_lock);
618 		goto map_bio;
619 	}
620 
621 	/*
622 	 * We will write this bio somewhere else way later so we need to copy
623 	 * the actual contents into new pages so we know the data will always be
624 	 * there.
625 	 *
626 	 * We do this because this could be a bio from O_DIRECT in which case we
627 	 * can't just hold onto the page until some later point, we have to
628 	 * manually copy the contents.
629 	 */
630 	bio_for_each_segment(bv, bio, iter) {
631 		struct page *page;
632 		void *src, *dst;
633 
634 		page = alloc_page(GFP_NOIO);
635 		if (!page) {
636 			DMERR("Error allocing page");
637 			free_pending_block(lc, block);
638 			spin_lock_irq(&lc->blocks_lock);
639 			lc->logging_enabled = false;
640 			spin_unlock_irq(&lc->blocks_lock);
641 			return -ENOMEM;
642 		}
643 
644 		src = kmap_atomic(bv.bv_page);
645 		dst = kmap_atomic(page);
646 		memcpy(dst, src + bv.bv_offset, bv.bv_len);
647 		kunmap_atomic(dst);
648 		kunmap_atomic(src);
649 		block->vecs[i].bv_page = page;
650 		block->vecs[i].bv_len = bv.bv_len;
651 		block->vec_cnt++;
652 		i++;
653 	}
654 
655 	/* Had a flush with data in it, weird */
656 	if (flush_bio) {
657 		spin_lock_irq(&lc->blocks_lock);
658 		list_splice_init(&lc->unflushed_blocks, &block->list);
659 		spin_unlock_irq(&lc->blocks_lock);
660 	}
661 map_bio:
662 	normal_map_bio(ti, bio);
663 	return DM_MAPIO_REMAPPED;
664 }
665 
666 static int normal_end_io(struct dm_target *ti, struct bio *bio, int error)
667 {
668 	struct log_writes_c *lc = ti->private;
669 	struct per_bio_data *pb = dm_per_bio_data(bio, sizeof(struct per_bio_data));
670 
671 	if (bio_data_dir(bio) == WRITE && pb->block) {
672 		struct pending_block *block = pb->block;
673 		unsigned long flags;
674 
675 		spin_lock_irqsave(&lc->blocks_lock, flags);
676 		if (block->flags & LOG_FLUSH_FLAG) {
677 			list_splice_tail_init(&block->list, &lc->logging_blocks);
678 			list_add_tail(&block->list, &lc->logging_blocks);
679 			wake_up_process(lc->log_kthread);
680 		} else if (block->flags & LOG_FUA_FLAG) {
681 			list_add_tail(&block->list, &lc->logging_blocks);
682 			wake_up_process(lc->log_kthread);
683 		} else
684 			list_add_tail(&block->list, &lc->unflushed_blocks);
685 		spin_unlock_irqrestore(&lc->blocks_lock, flags);
686 	}
687 
688 	return error;
689 }
690 
691 /*
692  * INFO format: <logged entries> <highest allocated sector>
693  */
694 static void log_writes_status(struct dm_target *ti, status_type_t type,
695 			      unsigned status_flags, char *result,
696 			      unsigned maxlen)
697 {
698 	unsigned sz = 0;
699 	struct log_writes_c *lc = ti->private;
700 
701 	switch (type) {
702 	case STATUSTYPE_INFO:
703 		DMEMIT("%llu %llu", lc->logged_entries,
704 		       (unsigned long long)lc->next_sector - 1);
705 		if (!lc->logging_enabled)
706 			DMEMIT(" logging_disabled");
707 		break;
708 
709 	case STATUSTYPE_TABLE:
710 		DMEMIT("%s %s", lc->dev->name, lc->logdev->name);
711 		break;
712 	}
713 }
714 
715 static int log_writes_ioctl(struct dm_target *ti, unsigned int cmd,
716 			    unsigned long arg)
717 {
718 	struct log_writes_c *lc = ti->private;
719 	struct dm_dev *dev = lc->dev;
720 	int r = 0;
721 
722 	/*
723 	 * Only pass ioctls through if the device sizes match exactly.
724 	 */
725 	if (ti->len != i_size_read(dev->bdev->bd_inode) >> SECTOR_SHIFT)
726 		r = scsi_verify_blk_ioctl(NULL, cmd);
727 
728 	return r ? : __blkdev_driver_ioctl(dev->bdev, dev->mode, cmd, arg);
729 }
730 
731 static int log_writes_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
732 			    struct bio_vec *biovec, int max_size)
733 {
734 	struct log_writes_c *lc = ti->private;
735 	struct request_queue *q = bdev_get_queue(lc->dev->bdev);
736 
737 	if (!q->merge_bvec_fn)
738 		return max_size;
739 
740 	bvm->bi_bdev = lc->dev->bdev;
741 	bvm->bi_sector = dm_target_offset(ti, bvm->bi_sector);
742 
743 	return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
744 }
745 
746 static int log_writes_iterate_devices(struct dm_target *ti,
747 				      iterate_devices_callout_fn fn,
748 				      void *data)
749 {
750 	struct log_writes_c *lc = ti->private;
751 
752 	return fn(ti, lc->dev, 0, ti->len, data);
753 }
754 
755 /*
756  * Messages supported:
757  *   mark <mark data> - specify the marked data.
758  */
759 static int log_writes_message(struct dm_target *ti, unsigned argc, char **argv)
760 {
761 	int r = -EINVAL;
762 	struct log_writes_c *lc = ti->private;
763 
764 	if (argc != 2) {
765 		DMWARN("Invalid log-writes message arguments, expect 2 arguments, got %d", argc);
766 		return r;
767 	}
768 
769 	if (!strcasecmp(argv[0], "mark"))
770 		r = log_mark(lc, argv[1]);
771 	else
772 		DMWARN("Unrecognised log writes target message received: %s", argv[0]);
773 
774 	return r;
775 }
776 
777 static void log_writes_io_hints(struct dm_target *ti, struct queue_limits *limits)
778 {
779 	struct log_writes_c *lc = ti->private;
780 	struct request_queue *q = bdev_get_queue(lc->dev->bdev);
781 
782 	if (!q || !blk_queue_discard(q)) {
783 		lc->device_supports_discard = false;
784 		limits->discard_granularity = 1 << SECTOR_SHIFT;
785 		limits->max_discard_sectors = (UINT_MAX >> SECTOR_SHIFT);
786 	}
787 }
788 
789 static struct target_type log_writes_target = {
790 	.name   = "log-writes",
791 	.version = {1, 0, 0},
792 	.module = THIS_MODULE,
793 	.ctr    = log_writes_ctr,
794 	.dtr    = log_writes_dtr,
795 	.map    = log_writes_map,
796 	.end_io = normal_end_io,
797 	.status = log_writes_status,
798 	.ioctl	= log_writes_ioctl,
799 	.merge	= log_writes_merge,
800 	.message = log_writes_message,
801 	.iterate_devices = log_writes_iterate_devices,
802 	.io_hints = log_writes_io_hints,
803 };
804 
805 static int __init dm_log_writes_init(void)
806 {
807 	int r = dm_register_target(&log_writes_target);
808 
809 	if (r < 0)
810 		DMERR("register failed %d", r);
811 
812 	return r;
813 }
814 
815 static void __exit dm_log_writes_exit(void)
816 {
817 	dm_unregister_target(&log_writes_target);
818 }
819 
820 module_init(dm_log_writes_init);
821 module_exit(dm_log_writes_exit);
822 
823 MODULE_DESCRIPTION(DM_NAME " log writes target");
824 MODULE_AUTHOR("Josef Bacik <jbacik@fb.com>");
825 MODULE_LICENSE("GPL");
826