[PATCH v2] zloop: truncate finished zones to zone capacity

From: Xu Rao <[email protected]>

The size of a sequential zone backing file records the amount of data
written and is used to restore the zone state. A backing file whose size
is equal to the zone capacity is restored as a full zone, while a file
larger than the zone capacity is rejected as invalid.

However, zloop_finish_zone() currently truncates the backing file to the
zone size. For devices with a reduced zone capacity, finishing a zone
therefore creates a backing file larger than the zone capacity. After the
device is removed and later re-added, that zone file is rejected instead
of being restored as a full zone.

Truncate finished sequential zones to the zone capacity, matching the
persistent representation accepted by zloop_update_seq_zone() for a full
zone.

Suggested-by: Damien Le Moal <[email protected]>
Fixes: eb0570c7df23 ("block: new zoned loop block device driver")
Cc: [email protected]
Signed-off-by: Xu Rao <[email protected]>
---
Changes in v2:
- Fix zloop_finish_zone() instead of accepting oversized backing files in
  zloop_update_seq_zone(), as suggested by Damien.
- Update documentation to describe the corrected backing file size.

 Documentation/admin-guide/blockdev/zoned_loop.rst | 9 ++++-----
 drivers/block/zloop.c                             | 3 ++-
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/Documentation/admin-guide/blockdev/zoned_loop.rst b/Documentation/admin-guide/blockdev/zoned_loop.rst
index f4f1f3121bf9..95974425ca05 100644
--- a/Documentation/admin-guide/blockdev/zoned_loop.rst
+++ b/Documentation/admin-guide/blockdev/zoned_loop.rst
@@ -30,11 +30,10 @@ indicates the position of the write pointer of the zone.

 When resetting a sequential zone, its backing file size is truncated to zero.
 Conversely, for a zone finish operation, the backing file is truncated to the
-zone size. With this, the maximum capacity of a zloop zoned block device created
-can be larger configured to be larger than the storage space available on the
-backing file system. Of course, for such configuration, writing more data than
-the storage space available on the backing file system will result in write
-errors.
+zone capacity. With this, a zloop zoned block device can be configured with a
+larger capacity than the storage space available on the backing file system. Of
+course, for such configuration, writing more data than the storage space
+available on the backing file system will result in write errors.

 The zoned loop block device driver implements a complete zone transition state
 machine. That is, zones can be empty, implicitly opened, explicitly opened,
diff --git a/drivers/block/zloop.c b/drivers/block/zloop.c
index 55eeb6aac0ea..1333fae05ac5 100644
--- a/drivers/block/zloop.c
+++ b/drivers/block/zloop.c
@@ -478,7 +478,8 @@ static int zloop_finish_zone(struct zloop_device *zlo, unsigned int zone_no)
 	    zone->cond == BLK_ZONE_COND_FULL)
 		goto unlock;

-	if (vfs_truncate(&zone->file->f_path, zlo->zone_size << SECTOR_SHIFT)) {
+	if (vfs_truncate(&zone->file->f_path,
+			 zlo->zone_capacity << SECTOR_SHIFT)) {
 		set_bit(ZLOOP_ZONE_SEQ_ERROR, &zone->flags);
 		ret = -EIO;
 		goto unlock;
--
2.50.1