Now that we have the ability log filesystem writes using a flat buffer, add
support for DAX. Unfortunately we can't easily track data that has been
written via mmap() now that the dax_flush() abstraction was removed by this
commit:
commit c3ca015fab6d ("dax: remove the pmem_dax_ops->flush abstraction")
Otherwise we could just treat each flush as a big write, and store the data
that is being synced to media. It may be worthwhile to add the dax_flush()
entry point back, just as a notifier so we can do this logging.
The motivation for this support is the need for an xfstest that can test
the new MAP_SYNC DAX flag. By logging the filesystem activity with
dm-log-writes we can show that the MAP_SYNC page faults are writing out
their metadata as they happen, instead of requiring an explicit
msync/fsync.
Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
---
Here's a link to Jan's latest MAP_SYNC set, which can be used for the
fstest:
https://www.spinics.net/lists/linux-xfs/msg11852.html
MAP_SYNC is not needed for basic DAX+dm-log-writes functionality.
---
drivers/md/dm-log-writes.c | 90 +++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 89 insertions(+), 1 deletion(-)
diff --git a/drivers/md/dm-log-writes.c b/drivers/md/dm-log-writes.c
index c65f9d1..6a8d352 100644
--- a/drivers/md/dm-log-writes.c
+++ b/drivers/md/dm-log-writes.c
@@ -10,9 +10,11 @@
#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"
@@ -609,6 +611,50 @@ static int log_mark(struct log_writes_c *lc, char *data)
return 0;
}
+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 void log_writes_dtr(struct dm_target *ti)
{
struct log_writes_c *lc = ti->private;
@@ -874,9 +920,49 @@ static void log_writes_io_hints(struct dm_target *ti, struct queue_limits *limit
limits->io_min = limits->physical_block_size;
}
+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;
+ struct block_device *bdev = lc->dev->bdev;
+ struct dax_device *dax_dev = lc->dev->dax_dev;
+ sector_t sector = pgoff * PAGE_SECTORS;
+ int ret;
+
+ ret = bdev_dax_pgoff(bdev, sector, nr_pages * PAGE_SIZE, &pgoff);
+ if (ret)
+ return ret;
+ return dax_direct_access(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;
+ struct block_device *bdev = lc->dev->bdev;
+ struct dax_device *dax_dev = lc->dev->dax_dev;
+ sector_t sector = pgoff * PAGE_SECTORS;
+ int err;
+
+ if (bdev_dax_pgoff(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(dax_dev, pgoff, addr, bytes, i);
+}
+
static struct target_type log_writes_target = {
.name = "log-writes",
- .version = {1, 0, 0},
+ .version = {1, 0, 1},
.module = THIS_MODULE,
.ctr = log_writes_ctr,
.dtr = log_writes_dtr,
@@ -887,6 +973,8 @@ static struct target_type log_writes_target = {
.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,
};
static int __init dm_log_writes_init(void)
--
2.9.5
