[PATCH v3] Documentation: block: zloop: clarify capacity alignment

[raoxu]

From: Xu Rao <raoxu@xxxxxxxxxxxxx>

zloop divides the requested capacity by the zone size to determine the
number of zones. Since it uses one zone size for all zones, a smaller last
zone is not supported and an unaligned capacity is rounded down.

The capacity_mb description incorrectly states that the capacity is rounded
up. Correct it to document the actual behavior.

Fixes: 9e4f11c1228c ("Documentation: Document the new zoned loop block device driver")
Suggested-by: Damien Le Moal <dlemoal@xxxxxxxxxx>
Reviewed-by: Damien Le Moal <dlemoal@xxxxxxxxxx>
Signed-off-by: Xu Rao <raoxu@xxxxxxxxxxxxx>
---
Changes in v2:
- Replace the code change with a documentation correction.
- State that a smaller last zone is unsupported and that an unaligned
  capacity is rounded down.

Changes in v3:
- Reword the capacity_mb description as suggested by Damien.

 Documentation/admin-guide/blockdev/zoned_loop.rst | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/blockdev/zoned_loop.rst b/Documentation/admin-guide/blockdev/zoned_loop.rst
index f4f1f3121bf9..abaf36f21945 100644
--- a/Documentation/admin-guide/blockdev/zoned_loop.rst
+++ b/Documentation/admin-guide/blockdev/zoned_loop.rst
@@ -71,8 +71,10 @@ follows.
 ===================   =========================================================
 id                    Device number (the X in /dev/zloopX).
                       Default: automatically assigned.
-capacity_mb           Device total capacity in MiB. This is always rounded up
-                      to the nearest higher multiple of the zone size.
+capacity_mb           Device total capacity in MiB. A smaller last zone is not
+                      supported, so a capacity value that is not a multiple of
+                      the zone size is rounded down to the closest multiple of
+                      the zone size.
                       Default: 16384 MiB (16 GiB).
 zone_size_mb          Device zone size in MiB. Default: 256 MiB.
 zone_capacity_mb      Device zone capacity (must always be equal to or lower
--
2.50.1