Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1058 insertions, 0 deletions

diff --git a/drivers/md/dm-log-writes.c b/drivers/md/dm-log-writes.c
new file mode 100644
index 000000000..e3d35c6c9
--- /dev/null
+++ b/drivers/md/dm-log-writes.c
@@ -0,0 +1,1058 @@
+/*
+ * 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/dax.h>
+#include <linux/slab.h>
+#include <linux/kthread.h>
+#include <linux/freezer.h>
+#include <linux/uio.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,b,flush,fuad,<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 LOG_METADATA_FLAG	(1 << 4)
+
+#define WRITE_LOG_VERSION 1ULL
+#define WRITE_LOG_MAGIC 0x6a736677736872ULL
+#define WRITE_LOG_SUPER_SECTOR 0
+
+/*
+ * 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;
+	u32 sectorshift;
+	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 completion super_done;
+};
+
+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[];
+};
+
+struct per_bio_data {
+	struct pending_block *block;
+};
+
+static inline sector_t bio_to_dev_sectors(struct log_writes_c *lc,
+					  sector_t sectors)
+{
+	return sectors >> (lc->sectorshift - SECTOR_SHIFT);
+}
+
+static inline sector_t dev_to_bio_sectors(struct log_writes_c *lc,
+					  sector_t sectors)
+{
+	return sectors << (lc->sectorshift - SECTOR_SHIFT);
+}
+
+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)
+{
+	struct log_writes_c *lc = bio->bi_private;
+
+	if (bio->bi_status) {
+		unsigned long flags;
+
+		DMERR("Error writing log block, error=%d", bio->bi_status);
+		spin_lock_irqsave(&lc->blocks_lock, flags);
+		lc->logging_enabled = false;
+		spin_unlock_irqrestore(&lc->blocks_lock, flags);
+	}
+
+	bio_free_pages(bio);
+	put_io_block(lc);
+	bio_put(bio);
+}
+
+static void log_end_super(struct bio *bio)
+{
+	struct log_writes_c *lc = bio->bi_private;
+
+	complete(&lc->super_done);
+	log_end_io(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_set_dev(bio, lc->logdev->bdev);
+	bio->bi_end_io = (sector == WRITE_LOG_SUPER_SECTOR) ?
+			  log_end_super : log_end_io;
+	bio->bi_private = lc;
+	bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
+
+	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(bio);
+	return 0;
+error_bio:
+	bio_put(bio);
+	__free_page(page);
+error:
+	put_io_block(lc);
+	return -1;
+}
+
+static int write_inline_data(struct log_writes_c *lc, void *entry,
+			     size_t entrylen, void *data, size_t datalen,
+			     sector_t sector)
+{
+	int num_pages, bio_pages, pg_datalen, pg_sectorlen, i;
+	struct page *page;
+	struct bio *bio;
+	size_t ret;
+	void *ptr;
+
+	while (datalen) {
+		num_pages = ALIGN(datalen, PAGE_SIZE) >> PAGE_SHIFT;
+		bio_pages = min(num_pages, BIO_MAX_PAGES);
+
+		atomic_inc(&lc->io_blocks);
+
+		bio = bio_alloc(GFP_KERNEL, bio_pages);
+		if (!bio) {
+			DMERR("Couldn't alloc inline data bio");
+			goto error;
+		}
+
+		bio->bi_iter.bi_size = 0;
+		bio->bi_iter.bi_sector = sector;
+		bio_set_dev(bio, lc->logdev->bdev);
+		bio->bi_end_io = log_end_io;
+		bio->bi_private = lc;
+		bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
+
+		for (i = 0; i < bio_pages; i++) {
+			pg_datalen = min_t(int, datalen, PAGE_SIZE);
+			pg_sectorlen = ALIGN(pg_datalen, lc->sectorsize);
+
+			page = alloc_page(GFP_KERNEL);
+			if (!page) {
+				DMERR("Couldn't alloc inline data page");
+				goto error_bio;
+			}
+
+			ptr = kmap_atomic(page);
+			memcpy(ptr, data, pg_datalen);
+			if (pg_sectorlen > pg_datalen)
+				memset(ptr + pg_datalen, 0, pg_sectorlen - pg_datalen);
+			kunmap_atomic(ptr);
+
+			ret = bio_add_page(bio, page, pg_sectorlen, 0);
+			if (ret != pg_sectorlen) {
+				DMERR("Couldn't add page of inline data");
+				__free_page(page);
+				goto error_bio;
+			}
+
+			datalen -= pg_datalen;
+			data	+= pg_datalen;
+		}
+		submit_bio(bio);
+
+		sector += bio_pages * PAGE_SECTORS;
+	}
+	return 0;
+error_bio:
+	bio_free_pages(bio);
+	bio_put(bio);
+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 metadatalen, 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);
+
+	metadatalen = (block->flags & LOG_MARK_FLAG) ? block->datalen : 0;
+	if (write_metadata(lc, &entry, sizeof(entry), block->data,
+			   metadatalen, sector)) {
+		free_pending_block(lc, block);
+		return -1;
+	}
+
+	sector += dev_to_bio_sectors(lc, 1);
+
+	if (block->datalen && metadatalen == 0) {
+		if (write_inline_data(lc, &entry, sizeof(entry), block->data,
+				      block->datalen, sector)) {
+			free_pending_block(lc, block);
+			return -1;
+		}
+		/* we don't support both inline data & bio data */
+		goto out;
+	}
+
+	if (!block->vec_cnt)
+		goto out;
+
+	atomic_inc(&lc->io_blocks);
+	bio = bio_alloc(GFP_KERNEL, min(block->vec_cnt, BIO_MAX_PAGES));
+	if (!bio) {
+		DMERR("Couldn't alloc log bio");
+		goto error;
+	}
+	bio->bi_iter.bi_size = 0;
+	bio->bi_iter.bi_sector = sector;
+	bio_set_dev(bio, lc->logdev->bdev);
+	bio->bi_end_io = log_end_io;
+	bio->bi_private = lc;
+	bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
+
+	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(bio);
+			bio = bio_alloc(GFP_KERNEL, min(block->vec_cnt - i, BIO_MAX_PAGES));
+			if (!bio) {
+				DMERR("Couldn't alloc log bio");
+				goto error;
+			}
+			bio->bi_iter.bi_size = 0;
+			bio->bi_iter.bi_sector = sector;
+			bio_set_dev(bio, lc->logdev->bdev);
+			bio->bi_end_io = log_end_io;
+			bio->bi_private = lc;
+			bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
+
+			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(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,
+			   WRITE_LOG_SUPER_SECTOR)) {
+		DMERR("Couldn't write super");
+		return -1;
+	}
+
+	/*
+	 * Super sector should be writen in-order, otherwise the
+	 * nr_entries could be rewritten incorrectly by an old bio.
+	 */
+	wait_for_completion_io(&lc->super_done);
+
+	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 += dev_to_bio_sectors(lc, block->nr_sectors);
+			lc->next_sector += dev_to_bio_sectors(lc, 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() &&
+			    list_empty(&lc->logging_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;
+	int ret;
+
+	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);
+	init_completion(&lc->super_done);
+	atomic_set(&lc->io_blocks, 0);
+	atomic_set(&lc->pending_blocks, 0);
+
+	devname = dm_shift_arg(&as);
+	ret = dm_get_device(ti, devname, dm_table_get_mode(ti->table), &lc->dev);
+	if (ret) {
+		ti->error = "Device lookup failed";
+		goto bad;
+	}
+
+	logdevname = dm_shift_arg(&as);
+	ret = dm_get_device(ti, logdevname, dm_table_get_mode(ti->table),
+			    &lc->logdev);
+	if (ret) {
+		ti->error = "Log device lookup failed";
+		dm_put_device(ti, lc->dev);
+		goto bad;
+	}
+
+	lc->sectorsize = bdev_logical_block_size(lc->dev->bdev);
+	lc->sectorshift = ilog2(lc->sectorsize);
+	lc->log_kthread = kthread_run(log_writes_kthread, lc, "log-write");
+	if (IS_ERR(lc->log_kthread)) {
+		ret = PTR_ERR(lc->log_kthread);
+		ti->error = "Couldn't alloc kthread";
+		dm_put_device(ti, lc->dev);
+		dm_put_device(ti, lc->logdev);
+		goto bad;
+	}
+
+	/*
+	 * next_sector is in 512b sectors to correspond to what bi_sector expects.
+	 * The super starts at sector 0, and the next_sector is the next logical
+	 * one based on the sectorsize of the device.
+	 */
+	lc->next_sector = lc->sectorsize >> SECTOR_SHIFT;
+	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_io_data_size = sizeof(struct per_bio_data);
+	ti->private = lc;
+	return 0;
+
+bad:
+	kfree(lc);
+	return ret;
+}
+
+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 - 1, 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_set_dev(bio, 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_opf & REQ_PREFLUSH);
+	bool fua_bio = (bio->bi_opf & REQ_FUA);
+	bool discard_bio = (bio_op(bio) == REQ_OP_DISCARD);
+	bool meta_bio = (bio->bi_opf & REQ_META);
+
+	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 = struct_size(block, vecs, 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 DM_MAPIO_KILL;
+	}
+	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;
+	if (meta_bio)
+		block->flags |= LOG_METADATA_FLAG;
+
+	block->sector = bio_to_dev_sectors(lc, bio->bi_iter.bi_sector);
+	block->nr_sectors = bio_to_dev_sectors(lc, 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);
+		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 DM_MAPIO_KILL;
+		}
+
+		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,
+		blk_status_t *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 DM_ENDIO_DONE;
+}
+
+/*
+ * 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_prepare_ioctl(struct dm_target *ti,
+				    struct block_device **bdev)
+{
+	struct log_writes_c *lc = ti->private;
+	struct dm_dev *dev = lc->dev;
+
+	*bdev = dev->bdev;
+	/*
+	 * Only pass ioctls through if the device sizes match exactly.
+	 */
+	if (ti->len != i_size_read(dev->bdev->bd_inode) >> SECTOR_SHIFT)
+		return 1;
+	return 0;
+}
+
+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,
+			      char *result, unsigned maxlen)
+{
+	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 = lc->sectorsize;
+		limits->max_discard_sectors = (UINT_MAX >> SECTOR_SHIFT);
+	}
+	limits->logical_block_size = bdev_logical_block_size(lc->dev->bdev);
+	limits->physical_block_size = bdev_physical_block_size(lc->dev->bdev);
+	limits->io_min = limits->physical_block_size;
+}
+
+#if IS_ENABLED(CONFIG_DAX_DRIVER)
+static int log_dax(struct log_writes_c *lc, sector_t sector, size_t bytes,
+		   struct iov_iter *i)
+{
+	struct pending_block *block;
+
+	if (!bytes)
+		return 0;
+
+	block = kzalloc(sizeof(struct pending_block), GFP_KERNEL);
+	if (!block) {
+		DMERR("Error allocating dax pending block");
+		return -ENOMEM;
+	}
+
+	block->data = kzalloc(bytes, GFP_KERNEL);
+	if (!block->data) {
+		DMERR("Error allocating dax data space");
+		kfree(block);
+		return -ENOMEM;
+	}
+
+	/* write data provided via the iterator */
+	if (!copy_from_iter(block->data, bytes, i)) {
+		DMERR("Error copying dax data");
+		kfree(block->data);
+		kfree(block);
+		return -EIO;
+	}
+
+	/* rewind the iterator so that the block driver can use it */
+	iov_iter_revert(i, bytes);
+
+	block->datalen = bytes;
+	block->sector = bio_to_dev_sectors(lc, sector);
+	block->nr_sectors = ALIGN(bytes, lc->sectorsize) >> lc->sectorshift;
+
+	atomic_inc(&lc->pending_blocks);
+	spin_lock_irq(&lc->blocks_lock);
+	list_add_tail(&block->list, &lc->unflushed_blocks);
+	spin_unlock_irq(&lc->blocks_lock);
+	wake_up_process(lc->log_kthread);
+
+	return 0;
+}
+
+static long log_writes_dax_direct_access(struct dm_target *ti, pgoff_t pgoff,
+					 long nr_pages, void **kaddr, pfn_t *pfn)
+{
+	struct log_writes_c *lc = ti->private;
+	sector_t sector = pgoff * PAGE_SECTORS;
+	int ret;
+
+	ret = bdev_dax_pgoff(lc->dev->bdev, sector, nr_pages * PAGE_SIZE, &pgoff);
+	if (ret)
+		return ret;
+	return dax_direct_access(lc->dev->dax_dev, pgoff, nr_pages, kaddr, pfn);
+}
+
+static size_t log_writes_dax_copy_from_iter(struct dm_target *ti,
+					    pgoff_t pgoff, void *addr, size_t bytes,
+					    struct iov_iter *i)
+{
+	struct log_writes_c *lc = ti->private;
+	sector_t sector = pgoff * PAGE_SECTORS;
+	int err;
+
+	if (bdev_dax_pgoff(lc->dev->bdev, sector, ALIGN(bytes, PAGE_SIZE), &pgoff))
+		return 0;
+
+	/* Don't bother doing anything if logging has been disabled */
+	if (!lc->logging_enabled)
+		goto dax_copy;
+
+	err = log_dax(lc, sector, bytes, i);
+	if (err) {
+		DMWARN("Error %d logging DAX write", err);
+		return 0;
+	}
+dax_copy:
+	return dax_copy_from_iter(lc->dev->dax_dev, pgoff, addr, bytes, i);
+}
+
+static size_t log_writes_dax_copy_to_iter(struct dm_target *ti,
+					  pgoff_t pgoff, void *addr, size_t bytes,
+					  struct iov_iter *i)
+{
+	struct log_writes_c *lc = ti->private;
+	sector_t sector = pgoff * PAGE_SECTORS;
+
+	if (bdev_dax_pgoff(lc->dev->bdev, sector, ALIGN(bytes, PAGE_SIZE), &pgoff))
+		return 0;
+	return dax_copy_to_iter(lc->dev->dax_dev, pgoff, addr, bytes, i);
+}
+
+static int log_writes_dax_zero_page_range(struct dm_target *ti, pgoff_t pgoff,
+					  size_t nr_pages)
+{
+	int ret;
+	struct log_writes_c *lc = ti->private;
+	sector_t sector = pgoff * PAGE_SECTORS;
+
+	ret = bdev_dax_pgoff(lc->dev->bdev, sector, nr_pages << PAGE_SHIFT,
+			     &pgoff);
+	if (ret)
+		return ret;
+	return dax_zero_page_range(lc->dev->dax_dev, pgoff,
+				   nr_pages << PAGE_SHIFT);
+}
+
+#else
+#define log_writes_dax_direct_access NULL
+#define log_writes_dax_copy_from_iter NULL
+#define log_writes_dax_copy_to_iter NULL
+#define log_writes_dax_zero_page_range NULL
+#endif
+
+static struct target_type log_writes_target = {
+	.name   = "log-writes",
+	.version = {1, 1, 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,
+	.prepare_ioctl = log_writes_prepare_ioctl,
+	.message = log_writes_message,
+	.iterate_devices = log_writes_iterate_devices,
+	.io_hints = log_writes_io_hints,
+	.direct_access = log_writes_dax_direct_access,
+	.dax_copy_from_iter = log_writes_dax_copy_from_iter,
+	.dax_copy_to_iter = log_writes_dax_copy_to_iter,
+	.dax_zero_page_range = log_writes_dax_zero_page_range,
+};
+
+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");