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

John Garry
2023-10-03T07:24:18Z

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