Re: [PATCH 03/21] fs/bdev: Add atomic write support info to statx

[John Garry]

On 03/10/2023 03:57, Darrick J. Wong wrote:
> > > > > +#define STATX_ATTR_WRITE_ATOMIC        0x00400000 /* File
> > > > > supports atomic write operations */
> > > > How would this differ from stx_atomic_write_unit_min != 0?
> > Yeah, I suppose that we can just not set this for the case of
> > stx_atomic_write_unit_min == 0.
> Please use the STATX_ATTR_WRITE_ATOMIC flag to indicate that the
> filesystem, file and underlying device support atomic writes when
> the values are non-zero. The whole point of the attribute mask is
> that the caller can check the mask for supported functionality
> without having to read every field in the statx structure to
> determine if the functionality it wants is present.

Sure, but again that would be just checking atomic_write_unit_min_bytes 
or another atomic write block setting as that is the only way to tell 
from the block layer (if atomic writes are supported), so it will be 
something like:

if (request_mask & STATX_WRITE_ATOMIC && 
queue_atomic_write_unit_min_bytes(bdev->bd_queue)) {
    stat->atomic_write_unit_min =
      queue_atomic_write_unit_min_bytes(bdev->bd_queue);
    stat->atomic_write_unit_max =
      queue_atomic_write_unit_max_bytes(bdev->bd_queue);
    stat->attributes |= STATX_ATTR_WRITE_ATOMIC;
    stat->attributes_mask |= STATX_ATTR_WRITE_ATOMIC;
    stat->result_mask |= STATX_WRITE_ATOMIC;
}

Thanks,
John