[PATCH] zloop: round capacity up to a zone-size multiple

From: Xu Rao <[email protected]>

zloop_ctl_add() derives the number of zones by shifting the requested
capacity by ilog2(zone_size). Since zone_size is validated as a power of
two, this is equivalent to integer division and discards any remainder.
However, Documentation/admin-guide/blockdev/zoned_loop.rst specifies that
capacity_mb is always rounded up to the nearest higher multiple of the
zone size.

Only configurations whose requested capacity is not aligned to the zone
size are affected. Aligned configurations, including the defaults of
16384 MiB capacity and 256 MiB zones, keep the same geometry. An affected
device is also internally consistent and remains usable, but it is
smaller than requested. For example, capacity_mb=130 with
zone_size_mb=64 currently creates two zones and exposes 128 MiB instead
of the documented three zones and 192 MiB. Since this does not cause an
error or an I/O failure, and normal test configurations generally use an
integral number of zones, the discrepancy can remain unnoticed.

Calculate the number of zones with DIV_ROUND_UP_SECTOR_T() so a partial
final zone request is represented by one additional full zone. This
matches the documented control interface while preserving the existing
sector_t handling on both 32-bit and 64-bit architectures.

Fixes: eb0570c7df23 ("block: new zoned loop block device driver")
Cc: [email protected]
Signed-off-by: Xu Rao <[email protected]>
---
 drivers/block/zloop.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/zloop.c b/drivers/block/zloop.c
index b69d798f203c..e29d82ff52ae 100644
--- a/drivers/block/zloop.c
+++ b/drivers/block/zloop.c
@@ -1187,7 +1187,7 @@ static int zloop_ctl_add(struct zloop_options *opts)

 	__module_get(THIS_MODULE);

-	nr_zones = opts->capacity >> ilog2(opts->zone_size);
+	nr_zones = DIV_ROUND_UP_SECTOR_T(opts->capacity, opts->zone_size);
 	if (opts->nr_conv_zones >= nr_zones) {
 		pr_err("Invalid number of conventional zones %u\n",
 		       opts->nr_conv_zones);
--
2.50.1