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

[Damien Le Moal]

On 2026/10/11 7:19, Shashank Mohan Jain wrote:
> 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);

Can you reverse this if to be "if (rep.flags & BLK_ZONE_REP_CACHED) {" and to
call blkdev_report_zones_cached if the condition is true? That would be a lot
more logical.

Also, the condition should probably be:

	if ((rep.flags & BLK_ZONE_REP_CACHED) &&
	    blkdev_has_cached_report_zones(bdev))

to be more efficient and avoid a call to blkdev_report_zones_cached() which will
turn into a regular device report zones.


-- 
Damien Le Moal
Western Digital Research