[RFC PATCH v4 07/11] fs: statx add write zeroes unmap attribute

[Darrick J. Wong]

On Mon, May 05, 2025 at 03:22:08PM +0200, Christoph Hellwig wrote:
> On Mon, Apr 21, 2025 at 10:15:05AM +0800, Zhang Yi wrote:
> > From: Zhang Yi <yi.zhang at huawei.com>
> > 
> > Add a new attribute flag to statx to determine whether a bdev or a file
> > supports the unmap write zeroes command.
> > 
> > Signed-off-by: Zhang Yi <yi.zhang at huawei.com>
> > ---
> >  block/bdev.c              | 4 ++++
> >  fs/ext4/inode.c           | 9 ++++++---
> >  include/uapi/linux/stat.h | 1 +
> >  3 files changed, 11 insertions(+), 3 deletions(-)
> > 
> > diff --git a/block/bdev.c b/block/bdev.c
> > index 4844d1e27b6f..29b0e5feb138 100644
> > --- a/block/bdev.c
> > +++ b/block/bdev.c
> > @@ -1304,6 +1304,10 @@ void bdev_statx(struct path *path, struct kstat *stat,
> >  			queue_atomic_write_unit_max_bytes(bd_queue));
> >  	}
> >  
> > +	if (bdev_write_zeroes_unmap(bdev))
> > +		stat->attributes |= STATX_ATTR_WRITE_ZEROES_UNMAP;
> > +	stat->attributes_mask |= STATX_ATTR_WRITE_ZEROES_UNMAP;
> 
> Hmm, shouldn't this always be set by stat?  But I might just be
> really confused what attributes_mask is, and might in fact have
> misapplied it in past patches of my own..

attributes_mask contains attribute flags known to the filesystem,
whereas attributes contains flags actually set on the file.
"known_attributes" would have been a better name, but that's water under
the bridge. :P

> Also shouldn't the patches to report the flag go into the bdev/ext4
> patches that actually implement the feature for the respective files
> to keep bisectability?

/I/ think so...

--D