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SubjectRe: [PATCH 1/2] uapi: fix statx attribute value overlap for DAX & MOUNT_ROOT
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On Dec 1, 2020, at 10:44 AM, Eric Sandeen <sandeen@redhat.com> wrote:
>
> On 12/1/20 11:32 AM, Darrick J. Wong wrote:
>> 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."
>
> Sure. Consistency and specificity is good, I'll change that.
>
>>> */
>>> #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?
>
> Since it didn't match the FS_IOC_SETFLAGS flag, I was trying to pick one that
> seemed unlikely to ever gain a corresponding statx flag, and since 0x00400000 is
> "reserved for ext4" it seemed like a decent choice.
>
> But 0x200000 corresponds to FS_EA_INODE_FL/EXT4_EA_INODE_FL which is ext4-specific
> as well, so sure, I'll change to that.

If you look a few lines up in the context, this is supposed to be using the
same value as the other inode flags:

* Note that the flags marked [I] correspond to generic FS_IOC_FLAGS
* semantically. Where possible, the numerical value is picked to correspond
* also.

#define FS_DAX_FL 0x02000000 /* Inode is DAX */
#define EXT4_DAX_FL 0x02000000 /* Inode is DAX */

(FS_DAX_FL also used by XFS) so this should really be "0x02000000" instead
of some other value.

Cheers, Andreas





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