Re: [PATCH 1/2] uapi: fix statx attribute value overlap for DAX & MOUNT_ROOT

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, Dec 01, 2020 at 10:57:11AM -0600, Eric Sandeen wrote:
> STATX_ATTR_MOUNT_ROOT and STATX_ATTR_DAX got merged with the same value,
> so one of them needs fixing. Move STATX_ATTR_DAX.
> 
> While we're in here, clarify the value-matching scheme for some of the
> attributes, and explain why the value for DAX does not match.
> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
>  include/uapi/linux/stat.h | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
> index 82cc58fe9368..9ad19eb9bbbf 100644
> --- a/include/uapi/linux/stat.h
> +++ b/include/uapi/linux/stat.h
> @@ -171,9 +171,10 @@ struct statx {
>   * be of use to ordinary userspace programs such as GUIs or ls rather than
>   * specialised tools.
>   *
> - * Note that the flags marked [I] correspond to generic FS_IOC_FLAGS
> + * Note that the flags marked [I] correspond to the FS_IOC_SETFLAGS flags
>   * semantically.  Where possible, the numerical value is picked to correspond
> - * also.
> + * also. Note that the DAX attribute indicates that the inode is currently
> + * DAX-enabled, not simply that the per-inode flag has been set.

I don't really like using "DAX-enabled" to define "DAX attribute".  How
about cribbing from the statx manpage?

"Note that the DAX attribute indicates that the file is in the CPU
direct access state.  It does not correspond to the per-inode flag that
some filesystems support."

>   */
>  #define STATX_ATTR_COMPRESSED		0x00000004 /* [I] File is compressed by the fs */
>  #define STATX_ATTR_IMMUTABLE		0x00000010 /* [I] File is marked immutable */
> @@ -183,7 +184,7 @@ struct statx {
>  #define STATX_ATTR_AUTOMOUNT		0x00001000 /* Dir: Automount trigger */
>  #define STATX_ATTR_MOUNT_ROOT		0x00002000 /* Root of a mount */
>  #define STATX_ATTR_VERITY		0x00100000 /* [I] Verity protected file */
> -#define STATX_ATTR_DAX			0x00002000 /* [I] File is DAX */
> +#define STATX_ATTR_DAX			0x00400000 /* File is currently DAX-enabled */

Why not use the next bit in the series (0x200000)?  Did someone already
claim it in for-next?

--D

>  
>  
>  #endif /* _UAPI_LINUX_STAT_H */
> -- 
> 2.17.0
>