Documentation: block: zloop: clarify capacity alignment

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@kernel.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Xu Rao <raoxu@uniontech.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/4659F8F0C6C328EA+20260804052942.1186727-1-raoxu@uniontech.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 4 insertions, 2 deletions

diff --git a/Documentation/admin-guide/blockdev/zoned_loop.rst b/Documentation/admin-guide/blockdev/zoned_loop.rst
index 95974425ca05..64277494fb36 100644
--- a/Documentation/admin-guide/blockdev/zoned_loop.rst
+++ b/Documentation/admin-guide/blockdev/zoned_loop.rst
@@ -70,8 +70,10 @@ 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