Re: [PATCH 01/10] block: introduce BLK_FEAT_WRITE_ZEROES_UNMAP to queue limits features

[Darrick J. Wong]

On Thu, Jun 12, 2025 at 07:20:45PM +0800, Zhang Yi wrote:
> On 2025/6/12 12:47, Christoph Hellwig wrote:
> > On Wed, Jun 11, 2025 at 03:31:21PM +0800, Zhang Yi wrote:
> >>>> +/* supports unmap write zeroes command */
> >>>> +#define BLK_FEAT_WRITE_ZEROES_UNMAP	((__force blk_features_t)(1u << 17))
> >>>
> >>>
> >>> Should this be exposed through sysfs as a read-only value?
> >>
> >> Uh, are you suggesting adding another sysfs interface to expose
> >> this feature?
> > 
> > That was the idea.  Or do we have another way to report this capability?
> > 
> 
> Exposing this feature looks useful, but I think adding a new interface
> might be somewhat redundant, and it's also difficult to name the new
> interface. What about extend this interface to include 3 types? When
> read, it exposes the following:
> 
>  - none     : the device doesn't support BLK_FEAT_WRITE_ZEROES_UNMAP.
>  - enabled  : the device supports BLK_FEAT_WRITE_ZEROES_UNMAP, but the
>               BLK_FLAG_WRITE_ZEROES_UNMAP_DISABLED is not set.
>  - disabled : the device supports BLK_FEAT_WRITE_ZEROES_UNMAP, and the
>               BLK_FLAG_WRITE_ZEROES_UNMAP_DISABLED is set.
> 
> Users can write '0' and '1' to disable and enable this operation if it
> is not 'none', thoughts?

Perhaps it should reuse the enumeration pattern elsewhere in sysfs?
For example,

# cat /sys/block/sda/queue/scheduler
none [mq-deadline]
# echo none > /sys/block/sda/queue/scheduler
# cat /sys/block/sda/queue/scheduler
[none] mq-deadline

(Annoying that this seems to be opencoded wherever it appears...)

--D

> Best regards,
> Yi.
> 
>