linux-kernel - Re: UAPI value collision: STATX_ATTR_MOUNT_ROOT vs STATX_ATTR

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Date:   Wed, 25 Nov 2020 20:26:52 +0100
From:   Miklos Szeredi <miklos@...redi.hu>
To:     David Howells <dhowells@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Ira Weiny <ira.weiny@...el.com>, sandeen@...hat.com,
        linux-fsdevel@...r.kernel.org,
        linux-man <linux-man@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: UAPI value collision: STATX_ATTR_MOUNT_ROOT vs STATX_ATTR_DAX

On Wed, Nov 25, 2020 at 5:57 PM David Howells <dhowells@...hat.com> wrote:
>
> Hi Linus, Miklos, Ira,
>
> It seems that two patches that got merged in the 5.8 merge window collided and
> no one noticed until now:
>
> 80340fe3605c0 (Miklos Szeredi     2020-05-14 184) #define STATX_ATTR_MOUNT_ROOT         0x00002000 /* Root of a mount */
> ...
> 712b2698e4c02 (Ira Weiny          2020-04-30 186) #define STATX_ATTR_DAX                        0x00002000 /* [I] File is DAX */
>
> The question is, what do we do about it?  Renumber one or both of the
> constants?

<uapi/linux/stat.h>:
 * Note that the flags marked [I] correspond to generic FS_IOC_FLAGS
 * semantically.  Where possible, the numerical value is picked to correspond
 * also.

<uapi/linux/fs.h>:
#define FS_DAX_FL 0x02000000 /* Inode is DAX */

The DAX one can be the same value as FS_DAX_FL, the placement (after
STATX_ATTR_VERITY, instead of before) seems to confirm this intention.

Not that I care too much, the important thing is to have distinct values.
Thanks,
Miklos