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

Thanks,
-Eric

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

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