linux-kernel - Re: Linux 2.6.39-rc3

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Message-ID: <BANLkTik2eRURBtdWCrYF5g3i90PJTVe9Fw@mail.gmail.com>
Date:	Tue, 19 Apr 2011 01:14:57 +0200
From:	Kay Sievers <kay.sievers@...y.org>
To:	Dave Jones <davej@...hat.com>, Kay Sievers <kay.sievers@...y.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Eric Sandeen <sandeen@...hat.com>
Subject: Re: Linux 2.6.39-rc3

On Tue, Apr 19, 2011 at 01:02, Dave Jones <davej@...hat.com> wrote:
> On Tue, Apr 19, 2011 at 12:57:27AM +0200, Kay Sievers wrote:
>
>  > > uuid:<value> is the option field  as per
>  > > Documentation/filesystem/proc.txt. There was an error in libmount
>  > > parsing which got fixed upstream recently
>  >
>  > 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?
>
> I thought tune2fs on a mounted filesystem was always a
> "you get to keep both pieces if it breaks" situation.

No idea, it works fine that way since forever. :)

$ cat /proc/self/mountinfo | grep sda1
21 1 8:1 / / rw,relatime - ext4 /dev/sda1 rw, ...

$ blkid /dev/sda1
/dev/sda1: LABEL="root" UUID="0e4974cc-6a11-11e0-8d7b-002186a23ce5" TYPE="ext4"

$ tune2fs -U time /dev/sda1
tune2fs 1.41.14 (22-Dec-2010)

$ blkid /dev/sda1
/dev/sda1: LABEL="root" UUID="26be6e7c-6a11-11e0-ad62-002186a23ce5" TYPE="ext4"

I don't think that approach makes any sense without doing a call into
the filesystem, and such calls have no place in mountinfo.

Kay
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