dm: add log writes target
Introduce a new target that is meant for file system developers to test file
system integrity at particular points in the life of a file system. We capture
all write requests and associated data and log them to a separate device
for later replay. There is a userspace utility to do this replay. The
idea behind this is to give file system developers a tool to verify that
the file system is always consistent.
Signed-off-by: Josef Bacik <jbacik@fb.com>
Reviewed-by: Zach Brown <zab@zabbo.net>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-log-writes.c b/drivers/md/dm-log-writes.c
new file mode 100644
index 0000000..93e0844
--- /dev/null
+++ b/drivers/md/dm-log-writes.c
@@ -0,0 +1,825 @@
+/*
+ * Copyright (C) 2014 Facebook. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#include <linux/device-mapper.h>
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/blkdev.h>
+#include <linux/bio.h>
+#include <linux/slab.h>
+#include <linux/kthread.h>
+#include <linux/freezer.h>
+
+#define DM_MSG_PREFIX "log-writes"
+
+/*
+ * This target will sequentially log all writes to the target device onto the
+ * log device. This is helpful for replaying writes to check for fs consistency
+ * at all times. This target provides a mechanism to mark specific events to
+ * check data at a later time. So for example you would:
+ *
+ * write data
+ * fsync
+ * dmsetup message /dev/whatever mark mymark
+ * unmount /mnt/test
+ *
+ * Then replay the log up to mymark and check the contents of the replay to
+ * verify it matches what was written.
+ *
+ * We log writes only after they have been flushed, this makes the log describe
+ * close to the order in which the data hits the actual disk, not its cache. So
+ * for example the following sequence (W means write, C means complete)
+ *
+ * Wa,Wb,Wc,Cc,Ca,FLUSH,FUAd,Cb,CFLUSH,CFUAd
+ *
+ * Would result in the log looking like this:
+ *
+ * c,a,flush,fuad,b,<other writes>,<next flush>
+ *
+ * This is meant to help expose problems where file systems do not properly wait
+ * on data being written before invoking a FLUSH. FUA bypasses cache so once it
+ * completes it is added to the log as it should be on disk.
+ *
+ * We treat DISCARDs as if they don't bypass cache so that they are logged in
+ * order of completion along with the normal writes. If we didn't do it this
+ * way we would process all the discards first and then write all the data, when
+ * in fact we want to do the data and the discard in the order that they
+ * completed.
+ */
+#define LOG_FLUSH_FLAG (1 << 0)
+#define LOG_FUA_FLAG (1 << 1)
+#define LOG_DISCARD_FLAG (1 << 2)
+#define LOG_MARK_FLAG (1 << 3)
+
+#define WRITE_LOG_VERSION 1
+#define WRITE_LOG_MAGIC 0x6a736677736872
+
+/*
+ * The disk format for this is braindead simple.
+ *
+ * At byte 0 we have our super, followed by the following sequence for
+ * nr_entries:
+ *
+ * [ 1 sector ][ entry->nr_sectors ]
+ * [log_write_entry][ data written ]
+ *
+ * The log_write_entry takes up a full sector so we can have arbitrary length
+ * marks and it leaves us room for extra content in the future.
+ */
+
+/*
+ * Basic info about the log for userspace.
+ */
+struct log_write_super {
+ __le64 magic;
+ __le64 version;
+ __le64 nr_entries;
+ __le32 sectorsize;
+};
+
+/*
+ * sector - the sector we wrote.
+ * nr_sectors - the number of sectors we wrote.
+ * flags - flags for this log entry.
+ * data_len - the size of the data in this log entry, this is for private log
+ * entry stuff, the MARK data provided by userspace for example.
+ */
+struct log_write_entry {
+ __le64 sector;
+ __le64 nr_sectors;
+ __le64 flags;
+ __le64 data_len;
+};
+
+struct log_writes_c {
+ struct dm_dev *dev;
+ struct dm_dev *logdev;
+ u64 logged_entries;
+ u32 sectorsize;
+ atomic_t io_blocks;
+ atomic_t pending_blocks;
+ sector_t next_sector;
+ sector_t end_sector;
+ bool logging_enabled;
+ bool device_supports_discard;
+ spinlock_t blocks_lock;
+ struct list_head unflushed_blocks;
+ struct list_head logging_blocks;
+ wait_queue_head_t wait;
+ struct task_struct *log_kthread;
+};
+
+struct pending_block {
+ int vec_cnt;
+ u64 flags;
+ sector_t sector;
+ sector_t nr_sectors;
+ char *data;
+ u32 datalen;
+ struct list_head list;
+ struct bio_vec vecs[0];
+};
+
+struct per_bio_data {
+ struct pending_block *block;
+};
+
+static void put_pending_block(struct log_writes_c *lc)
+{
+ if (atomic_dec_and_test(&lc->pending_blocks)) {
+ smp_mb__after_atomic();
+ if (waitqueue_active(&lc->wait))
+ wake_up(&lc->wait);
+ }
+}
+
+static void put_io_block(struct log_writes_c *lc)
+{
+ if (atomic_dec_and_test(&lc->io_blocks)) {
+ smp_mb__after_atomic();
+ if (waitqueue_active(&lc->wait))
+ wake_up(&lc->wait);
+ }
+}
+
+static void log_end_io(struct bio *bio, int err)
+{
+ struct log_writes_c *lc = bio->bi_private;
+ struct bio_vec *bvec;
+ int i;
+
+ if (err) {
+ unsigned long flags;
+
+ DMERR("Error writing log block, error=%d", err);
+ spin_lock_irqsave(&lc->blocks_lock, flags);
+ lc->logging_enabled = false;
+ spin_unlock_irqrestore(&lc->blocks_lock, flags);
+ }
+
+ bio_for_each_segment_all(bvec, bio, i)
+ __free_page(bvec->bv_page);
+
+ put_io_block(lc);
+ bio_put(bio);
+}
+
+/*
+ * Meant to be called if there is an error, it will free all the pages
+ * associated with the block.
+ */
+static void free_pending_block(struct log_writes_c *lc,
+ struct pending_block *block)
+{
+ int i;
+
+ for (i = 0; i < block->vec_cnt; i++) {
+ if (block->vecs[i].bv_page)
+ __free_page(block->vecs[i].bv_page);
+ }
+ kfree(block->data);
+ kfree(block);
+ put_pending_block(lc);
+}
+
+static int write_metadata(struct log_writes_c *lc, void *entry,
+ size_t entrylen, void *data, size_t datalen,
+ sector_t sector)
+{
+ struct bio *bio;
+ struct page *page;
+ void *ptr;
+ size_t ret;
+
+ bio = bio_alloc(GFP_KERNEL, 1);
+ if (!bio) {
+ DMERR("Couldn't alloc log bio");
+ goto error;
+ }
+ bio->bi_iter.bi_size = 0;
+ bio->bi_iter.bi_sector = sector;
+ bio->bi_bdev = lc->logdev->bdev;
+ bio->bi_end_io = log_end_io;
+ bio->bi_private = lc;
+ set_bit(BIO_UPTODATE, &bio->bi_flags);
+
+ page = alloc_page(GFP_KERNEL);
+ if (!page) {
+ DMERR("Couldn't alloc log page");
+ bio_put(bio);
+ goto error;
+ }
+
+ ptr = kmap_atomic(page);
+ memcpy(ptr, entry, entrylen);
+ if (datalen)
+ memcpy(ptr + entrylen, data, datalen);
+ memset(ptr + entrylen + datalen, 0,
+ lc->sectorsize - entrylen - datalen);
+ kunmap_atomic(ptr);
+
+ ret = bio_add_page(bio, page, lc->sectorsize, 0);
+ if (ret != lc->sectorsize) {
+ DMERR("Couldn't add page to the log block");
+ goto error_bio;
+ }
+ submit_bio(WRITE, bio);
+ return 0;
+error_bio:
+ bio_put(bio);
+ __free_page(page);
+error:
+ put_io_block(lc);
+ return -1;
+}
+
+static int log_one_block(struct log_writes_c *lc,
+ struct pending_block *block, sector_t sector)
+{
+ struct bio *bio;
+ struct log_write_entry entry;
+ size_t ret;
+ int i;
+
+ entry.sector = cpu_to_le64(block->sector);
+ entry.nr_sectors = cpu_to_le64(block->nr_sectors);
+ entry.flags = cpu_to_le64(block->flags);
+ entry.data_len = cpu_to_le64(block->datalen);
+ if (write_metadata(lc, &entry, sizeof(entry), block->data,
+ block->datalen, sector)) {
+ free_pending_block(lc, block);
+ return -1;
+ }
+
+ if (!block->vec_cnt)
+ goto out;
+ sector++;
+
+ bio = bio_alloc(GFP_KERNEL, block->vec_cnt);
+ if (!bio) {
+ DMERR("Couldn't alloc log bio");
+ goto error;
+ }
+ atomic_inc(&lc->io_blocks);
+ bio->bi_iter.bi_size = 0;
+ bio->bi_iter.bi_sector = sector;
+ bio->bi_bdev = lc->logdev->bdev;
+ bio->bi_end_io = log_end_io;
+ bio->bi_private = lc;
+ set_bit(BIO_UPTODATE, &bio->bi_flags);
+
+ for (i = 0; i < block->vec_cnt; i++) {
+ /*
+ * The page offset is always 0 because we allocate a new page
+ * for every bvec in the original bio for simplicity sake.
+ */
+ ret = bio_add_page(bio, block->vecs[i].bv_page,
+ block->vecs[i].bv_len, 0);
+ if (ret != block->vecs[i].bv_len) {
+ atomic_inc(&lc->io_blocks);
+ submit_bio(WRITE, bio);
+ bio = bio_alloc(GFP_KERNEL, block->vec_cnt - i);
+ if (!bio) {
+ DMERR("Couldn't alloc log bio");
+ goto error;
+ }
+ bio->bi_iter.bi_size = 0;
+ bio->bi_iter.bi_sector = sector;
+ bio->bi_bdev = lc->logdev->bdev;
+ bio->bi_end_io = log_end_io;
+ bio->bi_private = lc;
+ set_bit(BIO_UPTODATE, &bio->bi_flags);
+
+ ret = bio_add_page(bio, block->vecs[i].bv_page,
+ block->vecs[i].bv_len, 0);
+ if (ret != block->vecs[i].bv_len) {
+ DMERR("Couldn't add page on new bio?");
+ bio_put(bio);
+ goto error;
+ }
+ }
+ sector += block->vecs[i].bv_len >> SECTOR_SHIFT;
+ }
+ submit_bio(WRITE, bio);
+out:
+ kfree(block->data);
+ kfree(block);
+ put_pending_block(lc);
+ return 0;
+error:
+ free_pending_block(lc, block);
+ put_io_block(lc);
+ return -1;
+}
+
+static int log_super(struct log_writes_c *lc)
+{
+ struct log_write_super super;
+
+ super.magic = cpu_to_le64(WRITE_LOG_MAGIC);
+ super.version = cpu_to_le64(WRITE_LOG_VERSION);
+ super.nr_entries = cpu_to_le64(lc->logged_entries);
+ super.sectorsize = cpu_to_le32(lc->sectorsize);
+
+ if (write_metadata(lc, &super, sizeof(super), NULL, 0, 0)) {
+ DMERR("Couldn't write super");
+ return -1;
+ }
+
+ return 0;
+}
+
+static inline sector_t logdev_last_sector(struct log_writes_c *lc)
+{
+ return i_size_read(lc->logdev->bdev->bd_inode) >> SECTOR_SHIFT;
+}
+
+static int log_writes_kthread(void *arg)
+{
+ struct log_writes_c *lc = (struct log_writes_c *)arg;
+ sector_t sector = 0;
+
+ while (!kthread_should_stop()) {
+ bool super = false;
+ bool logging_enabled;
+ struct pending_block *block = NULL;
+ int ret;
+
+ spin_lock_irq(&lc->blocks_lock);
+ if (!list_empty(&lc->logging_blocks)) {
+ block = list_first_entry(&lc->logging_blocks,
+ struct pending_block, list);
+ list_del_init(&block->list);
+ if (!lc->logging_enabled)
+ goto next;
+
+ sector = lc->next_sector;
+ if (block->flags & LOG_DISCARD_FLAG)
+ lc->next_sector++;
+ else
+ lc->next_sector += block->nr_sectors + 1;
+
+ /*
+ * Apparently the size of the device may not be known
+ * right away, so handle this properly.
+ */
+ if (!lc->end_sector)
+ lc->end_sector = logdev_last_sector(lc);
+ if (lc->end_sector &&
+ lc->next_sector >= lc->end_sector) {
+ DMERR("Ran out of space on the logdev");
+ lc->logging_enabled = false;
+ goto next;
+ }
+ lc->logged_entries++;
+ atomic_inc(&lc->io_blocks);
+
+ super = (block->flags & (LOG_FUA_FLAG | LOG_MARK_FLAG));
+ if (super)
+ atomic_inc(&lc->io_blocks);
+ }
+next:
+ logging_enabled = lc->logging_enabled;
+ spin_unlock_irq(&lc->blocks_lock);
+ if (block) {
+ if (logging_enabled) {
+ ret = log_one_block(lc, block, sector);
+ if (!ret && super)
+ ret = log_super(lc);
+ if (ret) {
+ spin_lock_irq(&lc->blocks_lock);
+ lc->logging_enabled = false;
+ spin_unlock_irq(&lc->blocks_lock);
+ }
+ } else
+ free_pending_block(lc, block);
+ continue;
+ }
+
+ if (!try_to_freeze()) {
+ set_current_state(TASK_INTERRUPTIBLE);
+ if (!kthread_should_stop() &&
+ !atomic_read(&lc->pending_blocks))
+ schedule();
+ __set_current_state(TASK_RUNNING);
+ }
+ }
+ return 0;
+}
+
+/*
+ * Construct a log-writes mapping:
+ * log-writes <dev_path> <log_dev_path>
+ */
+static int log_writes_ctr(struct dm_target *ti, unsigned int argc, char **argv)
+{
+ struct log_writes_c *lc;
+ struct dm_arg_set as;
+ const char *devname, *logdevname;
+
+ as.argc = argc;
+ as.argv = argv;
+
+ if (argc < 2) {
+ ti->error = "Invalid argument count";
+ return -EINVAL;
+ }
+
+ lc = kzalloc(sizeof(struct log_writes_c), GFP_KERNEL);
+ if (!lc) {
+ ti->error = "Cannot allocate context";
+ return -ENOMEM;
+ }
+ spin_lock_init(&lc->blocks_lock);
+ INIT_LIST_HEAD(&lc->unflushed_blocks);
+ INIT_LIST_HEAD(&lc->logging_blocks);
+ init_waitqueue_head(&lc->wait);
+ lc->sectorsize = 1 << SECTOR_SHIFT;
+ atomic_set(&lc->io_blocks, 0);
+ atomic_set(&lc->pending_blocks, 0);
+
+ devname = dm_shift_arg(&as);
+ if (dm_get_device(ti, devname, dm_table_get_mode(ti->table), &lc->dev)) {
+ ti->error = "Device lookup failed";
+ goto bad;
+ }
+
+ logdevname = dm_shift_arg(&as);
+ if (dm_get_device(ti, logdevname, dm_table_get_mode(ti->table), &lc->logdev)) {
+ ti->error = "Log device lookup failed";
+ dm_put_device(ti, lc->dev);
+ goto bad;
+ }
+
+ lc->log_kthread = kthread_run(log_writes_kthread, lc, "log-write");
+ if (!lc->log_kthread) {
+ ti->error = "Couldn't alloc kthread";
+ dm_put_device(ti, lc->dev);
+ dm_put_device(ti, lc->logdev);
+ goto bad;
+ }
+
+ /* We put the super at sector 0, start logging at sector 1 */
+ lc->next_sector = 1;
+ lc->logging_enabled = true;
+ lc->end_sector = logdev_last_sector(lc);
+ lc->device_supports_discard = true;
+
+ ti->num_flush_bios = 1;
+ ti->flush_supported = true;
+ ti->num_discard_bios = 1;
+ ti->discards_supported = true;
+ ti->per_bio_data_size = sizeof(struct per_bio_data);
+ ti->private = lc;
+ return 0;
+
+bad:
+ kfree(lc);
+ return -EINVAL;
+}
+
+static int log_mark(struct log_writes_c *lc, char *data)
+{
+ struct pending_block *block;
+ size_t maxsize = lc->sectorsize - sizeof(struct log_write_entry);
+
+ block = kzalloc(sizeof(struct pending_block), GFP_KERNEL);
+ if (!block) {
+ DMERR("Error allocating pending block");
+ return -ENOMEM;
+ }
+
+ block->data = kstrndup(data, maxsize, GFP_KERNEL);
+ if (!block->data) {
+ DMERR("Error copying mark data");
+ kfree(block);
+ return -ENOMEM;
+ }
+ atomic_inc(&lc->pending_blocks);
+ block->datalen = strlen(block->data);
+ block->flags |= LOG_MARK_FLAG;
+ spin_lock_irq(&lc->blocks_lock);
+ list_add_tail(&block->list, &lc->logging_blocks);
+ spin_unlock_irq(&lc->blocks_lock);
+ wake_up_process(lc->log_kthread);
+ return 0;
+}
+
+static void log_writes_dtr(struct dm_target *ti)
+{
+ struct log_writes_c *lc = ti->private;
+
+ spin_lock_irq(&lc->blocks_lock);
+ list_splice_init(&lc->unflushed_blocks, &lc->logging_blocks);
+ spin_unlock_irq(&lc->blocks_lock);
+
+ /*
+ * This is just nice to have since it'll update the super to include the
+ * unflushed blocks, if it fails we don't really care.
+ */
+ log_mark(lc, "dm-log-writes-end");
+ wake_up_process(lc->log_kthread);
+ wait_event(lc->wait, !atomic_read(&lc->io_blocks) &&
+ !atomic_read(&lc->pending_blocks));
+ kthread_stop(lc->log_kthread);
+
+ WARN_ON(!list_empty(&lc->logging_blocks));
+ WARN_ON(!list_empty(&lc->unflushed_blocks));
+ dm_put_device(ti, lc->dev);
+ dm_put_device(ti, lc->logdev);
+ kfree(lc);
+}
+
+static void normal_map_bio(struct dm_target *ti, struct bio *bio)
+{
+ struct log_writes_c *lc = ti->private;
+
+ bio->bi_bdev = lc->dev->bdev;
+}
+
+static int log_writes_map(struct dm_target *ti, struct bio *bio)
+{
+ struct log_writes_c *lc = ti->private;
+ struct per_bio_data *pb = dm_per_bio_data(bio, sizeof(struct per_bio_data));
+ struct pending_block *block;
+ struct bvec_iter iter;
+ struct bio_vec bv;
+ size_t alloc_size;
+ int i = 0;
+ bool flush_bio = (bio->bi_rw & REQ_FLUSH);
+ bool fua_bio = (bio->bi_rw & REQ_FUA);
+ bool discard_bio = (bio->bi_rw & REQ_DISCARD);
+
+ pb->block = NULL;
+
+ /* Don't bother doing anything if logging has been disabled */
+ if (!lc->logging_enabled)
+ goto map_bio;
+
+ /*
+ * Map reads as normal.
+ */
+ if (bio_data_dir(bio) == READ)
+ goto map_bio;
+
+ /* No sectors and not a flush? Don't care */
+ if (!bio_sectors(bio) && !flush_bio)
+ goto map_bio;
+
+ /*
+ * Discards will have bi_size set but there's no actual data, so just
+ * allocate the size of the pending block.
+ */
+ if (discard_bio)
+ alloc_size = sizeof(struct pending_block);
+ else
+ alloc_size = sizeof(struct pending_block) + sizeof(struct bio_vec) * bio_segments(bio);
+
+ block = kzalloc(alloc_size, GFP_NOIO);
+ if (!block) {
+ DMERR("Error allocating pending block");
+ spin_lock_irq(&lc->blocks_lock);
+ lc->logging_enabled = false;
+ spin_unlock_irq(&lc->blocks_lock);
+ return -ENOMEM;
+ }
+ INIT_LIST_HEAD(&block->list);
+ pb->block = block;
+ atomic_inc(&lc->pending_blocks);
+
+ if (flush_bio)
+ block->flags |= LOG_FLUSH_FLAG;
+ if (fua_bio)
+ block->flags |= LOG_FUA_FLAG;
+ if (discard_bio)
+ block->flags |= LOG_DISCARD_FLAG;
+
+ block->sector = bio->bi_iter.bi_sector;
+ block->nr_sectors = bio_sectors(bio);
+
+ /* We don't need the data, just submit */
+ if (discard_bio) {
+ WARN_ON(flush_bio || fua_bio);
+ if (lc->device_supports_discard)
+ goto map_bio;
+ bio_endio(bio, 0);
+ return DM_MAPIO_SUBMITTED;
+ }
+
+ /* Flush bio, splice the unflushed blocks onto this list and submit */
+ if (flush_bio && !bio_sectors(bio)) {
+ spin_lock_irq(&lc->blocks_lock);
+ list_splice_init(&lc->unflushed_blocks, &block->list);
+ spin_unlock_irq(&lc->blocks_lock);
+ goto map_bio;
+ }
+
+ /*
+ * We will write this bio somewhere else way later so we need to copy
+ * the actual contents into new pages so we know the data will always be
+ * there.
+ *
+ * We do this because this could be a bio from O_DIRECT in which case we
+ * can't just hold onto the page until some later point, we have to
+ * manually copy the contents.
+ */
+ bio_for_each_segment(bv, bio, iter) {
+ struct page *page;
+ void *src, *dst;
+
+ page = alloc_page(GFP_NOIO);
+ if (!page) {
+ DMERR("Error allocing page");
+ free_pending_block(lc, block);
+ spin_lock_irq(&lc->blocks_lock);
+ lc->logging_enabled = false;
+ spin_unlock_irq(&lc->blocks_lock);
+ return -ENOMEM;
+ }
+
+ src = kmap_atomic(bv.bv_page);
+ dst = kmap_atomic(page);
+ memcpy(dst, src + bv.bv_offset, bv.bv_len);
+ kunmap_atomic(dst);
+ kunmap_atomic(src);
+ block->vecs[i].bv_page = page;
+ block->vecs[i].bv_len = bv.bv_len;
+ block->vec_cnt++;
+ i++;
+ }
+
+ /* Had a flush with data in it, weird */
+ if (flush_bio) {
+ spin_lock_irq(&lc->blocks_lock);
+ list_splice_init(&lc->unflushed_blocks, &block->list);
+ spin_unlock_irq(&lc->blocks_lock);
+ }
+map_bio:
+ normal_map_bio(ti, bio);
+ return DM_MAPIO_REMAPPED;
+}
+
+static int normal_end_io(struct dm_target *ti, struct bio *bio, int error)
+{
+ struct log_writes_c *lc = ti->private;
+ struct per_bio_data *pb = dm_per_bio_data(bio, sizeof(struct per_bio_data));
+
+ if (bio_data_dir(bio) == WRITE && pb->block) {
+ struct pending_block *block = pb->block;
+ unsigned long flags;
+
+ spin_lock_irqsave(&lc->blocks_lock, flags);
+ if (block->flags & LOG_FLUSH_FLAG) {
+ list_splice_tail_init(&block->list, &lc->logging_blocks);
+ list_add_tail(&block->list, &lc->logging_blocks);
+ wake_up_process(lc->log_kthread);
+ } else if (block->flags & LOG_FUA_FLAG) {
+ list_add_tail(&block->list, &lc->logging_blocks);
+ wake_up_process(lc->log_kthread);
+ } else
+ list_add_tail(&block->list, &lc->unflushed_blocks);
+ spin_unlock_irqrestore(&lc->blocks_lock, flags);
+ }
+
+ return error;
+}
+
+/*
+ * INFO format: <logged entries> <highest allocated sector>
+ */
+static void log_writes_status(struct dm_target *ti, status_type_t type,
+ unsigned status_flags, char *result,
+ unsigned maxlen)
+{
+ unsigned sz = 0;
+ struct log_writes_c *lc = ti->private;
+
+ switch (type) {
+ case STATUSTYPE_INFO:
+ DMEMIT("%llu %llu", lc->logged_entries,
+ (unsigned long long)lc->next_sector - 1);
+ if (!lc->logging_enabled)
+ DMEMIT(" logging_disabled");
+ break;
+
+ case STATUSTYPE_TABLE:
+ DMEMIT("%s %s", lc->dev->name, lc->logdev->name);
+ break;
+ }
+}
+
+static int log_writes_ioctl(struct dm_target *ti, unsigned int cmd,
+ unsigned long arg)
+{
+ struct log_writes_c *lc = ti->private;
+ struct dm_dev *dev = lc->dev;
+ int r = 0;
+
+ /*
+ * Only pass ioctls through if the device sizes match exactly.
+ */
+ if (ti->len != i_size_read(dev->bdev->bd_inode) >> SECTOR_SHIFT)
+ r = scsi_verify_blk_ioctl(NULL, cmd);
+
+ return r ? : __blkdev_driver_ioctl(dev->bdev, dev->mode, cmd, arg);
+}
+
+static int log_writes_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
+ struct bio_vec *biovec, int max_size)
+{
+ struct log_writes_c *lc = ti->private;
+ struct request_queue *q = bdev_get_queue(lc->dev->bdev);
+
+ if (!q->merge_bvec_fn)
+ return max_size;
+
+ bvm->bi_bdev = lc->dev->bdev;
+ bvm->bi_sector = dm_target_offset(ti, bvm->bi_sector);
+
+ return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
+}
+
+static int log_writes_iterate_devices(struct dm_target *ti,
+ iterate_devices_callout_fn fn,
+ void *data)
+{
+ struct log_writes_c *lc = ti->private;
+
+ return fn(ti, lc->dev, 0, ti->len, data);
+}
+
+/*
+ * Messages supported:
+ * mark <mark data> - specify the marked data.
+ */
+static int log_writes_message(struct dm_target *ti, unsigned argc, char **argv)
+{
+ int r = -EINVAL;
+ struct log_writes_c *lc = ti->private;
+
+ if (argc != 2) {
+ DMWARN("Invalid log-writes message arguments, expect 2 arguments, got %d", argc);
+ return r;
+ }
+
+ if (!strcasecmp(argv[0], "mark"))
+ r = log_mark(lc, argv[1]);
+ else
+ DMWARN("Unrecognised log writes target message received: %s", argv[0]);
+
+ return r;
+}
+
+static void log_writes_io_hints(struct dm_target *ti, struct queue_limits *limits)
+{
+ struct log_writes_c *lc = ti->private;
+ struct request_queue *q = bdev_get_queue(lc->dev->bdev);
+
+ if (!q || !blk_queue_discard(q)) {
+ lc->device_supports_discard = false;
+ limits->discard_granularity = 1 << SECTOR_SHIFT;
+ limits->max_discard_sectors = (UINT_MAX >> SECTOR_SHIFT);
+ }
+}
+
+static struct target_type log_writes_target = {
+ .name = "log-writes",
+ .version = {1, 0, 0},
+ .module = THIS_MODULE,
+ .ctr = log_writes_ctr,
+ .dtr = log_writes_dtr,
+ .map = log_writes_map,
+ .end_io = normal_end_io,
+ .status = log_writes_status,
+ .ioctl = log_writes_ioctl,
+ .merge = log_writes_merge,
+ .message = log_writes_message,
+ .iterate_devices = log_writes_iterate_devices,
+ .io_hints = log_writes_io_hints,
+};
+
+static int __init dm_log_writes_init(void)
+{
+ int r = dm_register_target(&log_writes_target);
+
+ if (r < 0)
+ DMERR("register failed %d", r);
+
+ return r;
+}
+
+static void __exit dm_log_writes_exit(void)
+{
+ dm_unregister_target(&log_writes_target);
+}
+
+module_init(dm_log_writes_init);
+module_exit(dm_log_writes_exit);
+
+MODULE_DESCRIPTION(DM_NAME " log writes target");
+MODULE_AUTHOR("Josef Bacik <jbacik@fb.com>");
+MODULE_LICENSE("GPL");