Re: [PATCH V2] uapi: fix statx attribute value overlap for DAX & MOUNT_ROOT

[Ira Weiny <ira.weiny@intel.com>]

On Tue, Dec 01, 2020 at 05:21:40PM -0600, Eric Sandeen wrote:
> [*] Note: This needs to be merged as soon as possible as it's introducing an incompatible UAPI change...
> 
> 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.
> 
> Fixes: 80340fe3605c ("statx: add mount_root")
> Fixes: 712b2698e4c0 ("fs/stat: Define DAX statx attribute")
> Reported-by: David Howells <dhowells@redhat.com>
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> Reviewed-by: David Howells <dhowells@redhat.com>

Reviewed-by: Ira Weiny <ira.weiny@intel.com>

> ---
> V2: Change flag value per Darrick Wong
>     Tweak comment per Darrick Wong
>     Add Fixes: tags & reported-by & RVB per dhowells
> 
>  include/uapi/linux/stat.h | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
> index 82cc58fe9368..1500a0f58041 100644
> --- a/include/uapi/linux/stat.h
> +++ b/include/uapi/linux/stat.h
> @@ -171,9 +171,12 @@ 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 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 +186,7 @@ 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			0x00200000 /* File is currently in DAX state */
>  
>  
>  #endif /* _UAPI_LINUX_STAT_H */
> -- 
> 2.17.0
>