Re: [PATCH RFC 1/2] block: add BLK_FEAT_ATOMIC_WRITE_MULTI

[Arthur Simchaev]

On Tue, Sep 29, 2026 at 01:17:11PM +0200, Daniel Gomez wrote:
[...]
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index d003a9d2d1f6c..92efd4ff67f26 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -360,6 +360,9 @@ typedef unsigned int __bitwise blk_features_t;
>  #define BLK_FEAT_RAID_PARTIAL_STRIPES_EXPENSIVE \
>  	((__force blk_features_t)(1u << 15))
>  
> +/* device writes each atomic write boundary window of a command atomically */
> +#define BLK_FEAT_ATOMIC_WRITE_MULTI	((__force blk_features_t)(1u << 16))

With this flag set, a request with REQ_ATOMIC may now carry several independent
atomic writes rather than one. Code that looks at REQ_ATOMIC on a request (e.g.
blk_insert_cloned_request(), or a future SCSI WRITE ATOMIC user) needs to know
that. Could the comment here (or Documentation/block/) spell out what REQ_ATOMIC
means on a merged request, and what a driver must guarantee before setting the
flag?

It might also be useful to expose the feature in sysfs next to the other
atomic_write_* attributes, so users can tell whether merging across boundaries
is active on a device.

Regards,
Arthur