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From: Kay Sievers <kay.sievers@vrfy.org>
Date: Tue, 19 Apr 2011 11:55:50 +0200
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Subject: Re: Linux 2.6.39-rc3
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Dave Jones <davej@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Eric Sandeen <sandeen@redhat.com>
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On Tue, Apr 19, 2011 at 10:23, Aneesh Kumar K.V
<aneesh.kumar@linux.vnet.ibm.com> wrote:
> On Tue, 19 Apr 2011 00:57:27 +0200, Kay Sievers <kay.sievers@vrfy.org> wrote:

>> Just a simple question about this approach in general? A filesystem
>> UUID can be changed on disk at any time (tune2fs -U ...).
>>
>> Your code looks like you copy the bytes to the in-kernel superblock
>> structure without noticing any later changes on disk? How is that
>> supposed to work?
>
> Isn't that true even for the fsid returned by statfs ?.  IIUC tune2fs
> won't change even the ext4_super_block.s_uuid .

What matter is that it's common practice today, to change labels
on-disks of mounted filesystems.

There should probably be getter/setter (like generic ioctls, or
whatever fits) for uuid/label of a mounted filesystem. That call would
also update this new superblock info. Guess that's needed before the
kernel can export such stuff in mountinfo.

So tools at least have a chance to do it right here, and the current
on-disk edit can rightfully be deprecated. Exporting possible
out-of-sync data, without the chance to update it without a "reboot"
really doesn't sound convincing.

Kay