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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Tue, 19 Jul 2022 09:30:23 +0200
Message-ID: <CAK8P3a17LZNXDW9r3ixfMg_c-vtqqT51MCLEsyF4Loh8VfDw7w@mail.gmail.com>
Subject: Re: [PATCH v3] Add ioctls to get/set the ext4 superblock uuid.
To:     Jeremy Bongio <bongiojp@gmail.com>
Cc:     Ted Tso <tytso@mit.edu>,
        Ext4 Developers List <linux-ext4@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>
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On Tue, Jul 19, 2022 at 8:55 AM Jeremy Bongio <bongiojp@gmail.com> wrote:
>
> This fixes a race between changing the ext4 superblock uuid and operations
> like mounting, resizing, changing features, etc.
>
> Reviewed-by: Theodore Ts'o <tytso@mit.edu>
> Signed-off-by: Jeremy Bongio <bongiojp@gmail.com>
> ---
>
> This pair of ioctls may be implemented in more filesystems in the future,
> namely XFS.
>

> +++ b/fs/ext4/ext4.h
> @@ -724,6 +724,8 @@ enum {
>  #define EXT4_IOC_GETSTATE              _IOW('f', 41, __u32)
>  #define EXT4_IOC_GET_ES_CACHE          _IOWR('f', 42, struct fiemap)
>  #define EXT4_IOC_CHECKPOINT            _IOW('f', 43, __u32)
> +#define EXT4_IOC_GETFSUUID             _IOR('f', 44, struct fsuuid)
> +#define EXT4_IOC_SETFSUUID             _IOW('f', 44, struct fsuuid)

The implementation looks good to me, but maybe it should be defined in
the UAPI headers in a filesystem-independent way? Having it in a private
header means it will not be available to portable user programs, and will
be hidden from tools like strace that parse the uapi headers to find
ioctl definitions.

       Arnd