[PATCH 1/2] block: only use the cached zone report if BLK_ZONE_REP_CACHED is set

[Shashank Mohan Jain]

BLKREPORTZONEV2 takes the flags field of struct blk_zone_report as an
input. With BLK_ZONE_REP_CACHED the report is built from the zone
information cached by the block layer. Without it, BLKREPORTZONEV2 is
documented to behave like BLKREPORTZONE and to get the report from the
device: this is what the changelog of the commit that added the ioctl
and the comments in include/uapi/linux/blkzoned.h say.

blkdev_report_zones_ioctl() only uses the flag to validate the input
and calls blkdev_report_zones_cached() for every BLKREPORTZONEV2
request. A caller that passes flags == 0 gets the cached report, in
which implicitly open, explicitly open and closed zones all have the
condition BLK_ZONE_COND_ACTIVE, and an explicitly opened empty zone is
reported as empty.

Example with a zoned null_blk device (10 MiB, 4 MiB zones) after
BLKOPENZONE on zone 0, and a write of 8 sectors to zone 1 followed by
BLKCLOSEZONE:

  BLKREPORTZONE:             zone 0 cond 0x3 (EXP_OPEN)
                             zone 1 cond 0x4 (CLOSED)
  BLKREPORTZONEV2, flags 0:  zone 0 cond 0x1 (EMPTY)
                             zone 1 cond 0xff (ACTIVE)

The uapi header marks BLKREPORTZONE as deprecated in favour of
BLKREPORTZONEV2. A program that follows this and does not ask for
cached information can no longer tell open zones from closed ones, and
is handed BLK_ZONE_COND_ACTIVE, which is only defined for the cached
report.

Call blkdev_report_zones_cached() only if BLK_ZONE_REP_CACHED is set,
and blkdev_report_zones() otherwise.

Tested with zoned null_blk devices in qemu: a program that compares
the reports of BLKREPORTZONE and BLKREPORTZONEV2 with flags 0 after
the sequence above finds the differences before this change and none
with it. The report with BLK_ZONE_REP_CACHED is unchanged.

Fixes: b30ffcdc0c15 ("block: introduce BLKREPORTZONESV2 ioctl")
Cc: stable@xxxxxxxxxxxxxxx
Assisted-by: LLM
Signed-off-by: Shashank Mohan Jain <jain.sm@xxxxxxxxx>
---
Prepared with Claude Code (Anthropic), model Claude Opus 5.5
(claude-opus-5-5).

 block/blk-zoned.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index 475aa16bc4..9555eae91a 100644
--- a/block/blk-zoned.c
+++ b/block/blk-zoned.c
@@ -400,6 +400,13 @@ int blkdev_report_zones_ioctl(struct block_device *bdev, unsigned int cmd,
 	case BLKREPORTZONEV2:
 		if (rep.flags & ~BLK_ZONE_REPV2_INPUT_FLAGS)
 			return -EINVAL;
+		if (!(rep.flags & BLK_ZONE_REP_CACHED)) {
+			ret = blkdev_report_zones(bdev, rep.sector,
+						  rep.nr_zones,
+						  blkdev_copy_zone_to_user,
+						  &args);
+			break;
+		}
 		ret = blkdev_report_zones_cached(bdev, rep.sector, rep.nr_zones,
 					 blkdev_copy_zone_to_user, &args);
 		break;
-- 
2.43.0