From: James Shubin <purpleidea@redhat.com>
To: kreijack@inwind.it
Cc: Eric Sandeen <sandeen@redhat.com>,
linux-btrfs <linux-btrfs@vger.kernel.org>,
jshubin@redhat.com
Subject: Re: [PATCH] mkfs.btrfs: allow UUID specification at mkfs time
Date: Wed, 14 May 2014 10:47:29 -0400 [thread overview]
Message-ID: <1400078849.15603.177.camel@rh> (raw)
In-Reply-To: <5373803E.9000406@libero.it>
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On Wed, 2014-05-14 at 16:39 +0200, Goffredo Baroncelli wrote:
> Hi Eric,
>
> On 05/14/2014 03:18 AM, Eric Sandeen wrote:
> > Allow the specification of the filesystem UUID at mkfs time.
>
> I suggest to add some warning when this options is used, because the behavior could be very different than the one expected.
>
> I suspect that BTRFS tracks the filesystem by UUID and not by devices. When two filesystems have the same UUID at the same time, it may mount the wrong one.
>
> $ #
> $ # Make two *different* filesystems with the *same* UUID
> $ #
> $ UUID=e285c9bd-ea97-40b3-ad7d-8713dcfd5eea
> $ sudo ./mkfs.btrfs -f -U $UUID /dev/vdg
> $ sudo ./mkfs.btrfs -f -U $UUID /dev/vdh
>
> $ #
> $ # from the beginning "btrfs fi show" reports wrong information
> $ #
> $ sudo btrfs fi show
> Label: none uuid: e285c9bd-ea97-40b3-ad7d-8713dcfd5eea
> Total devices 1 FS bytes used 96.00KB
> devid 1 size 50.00GB used 4.00MB path /dev/vdh
> devid 1 size 50.00GB used 2.04GB path /dev/vdg
>
> $ #
> $ # mount the first one, create a new file then un-mount it
> $ #
> $ sudo mount /dev/vdg /mnt/btrfs1
> $ sudo touch /mnt/btrfs1/dev-vdg
> $ sudo umount /dev/vdg
>
> $ #
> $ # mount the second one, it should be empty
> $ # instead btrfs mount the first one
> $ #
> $ sudo mount /dev/vdh /mnt/btrfs2
> $ ls -l /mnt/btrfs2
> total 0
> -rw-r--r-- 1 root root 0 May 14 16:12 dev-vdg
>
>
> I am not against this option; I am suggesting to add a explicit warning to the user about the risk of doing that, both on the man pages and into the program.
> The warning should say that this option is only for testing. Better ask for a confirmation (even with an undocumented switch like '--I-know-that-I-am-doing-something-really-dangerous').
I don't think is necessary since xfs and ext4 both have these options
too... There probably *should* be a conflict, because typically this
will cause an entry to show up in
/dev/disks/by-uuid/$UUID
I'm sure this same bug exists if two "randomly generated UUID's" get
created too. I think a warning in the man page would be enough.
>
> For the record, BTRFS seems unable to mount at the same time two different filesystems with the same UUID:
>
> $ #
> $ # try to mount two fs with the same UUID, but BTRFS doesn't allow it
> $ #
> $ sudo mount /dev/vdh /mnt/btrfs2
> $ sudo mount /dev/vdg /mnt/btrfs1
> ERROR: mount failed : 16 - Device or resource busy
>
>
> BR
> G.Baroncelli
>
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next prev parent reply other threads:[~2014-05-14 14:47 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-14 1:18 [PATCH] mkfs.btrfs: allow UUID specification at mkfs time Eric Sandeen
2014-05-14 7:31 ` Wang Shilong
2014-05-14 12:25 ` Brendan Hide
2014-05-14 13:34 ` Duncan
2014-05-14 14:42 ` James Shubin
2014-05-14 13:28 ` Eric Sandeen
2014-05-14 13:34 ` David Pottage
2014-05-14 14:39 ` Goffredo Baroncelli
2014-05-14 14:41 ` Eric Sandeen
2014-05-14 15:14 ` Goffredo Baroncelli
2014-05-14 15:27 ` David Sterba
2014-05-14 14:47 ` James Shubin [this message]
2014-05-14 15:35 ` [PATCH V2] " Eric Sandeen
2014-05-14 16:01 ` David Sterba
2014-05-14 16:09 ` Eric Sandeen
2014-05-14 16:52 ` Goffredo Baroncelli
2014-05-14 17:39 ` PATCH V3] " Eric Sandeen
2014-05-14 22:04 ` Goffredo Baroncelli
2014-05-14 22:07 ` Eric Sandeen
2014-05-15 17:39 ` David Sterba
2014-05-15 17:53 ` Eric Sandeen
2014-05-16 17:24 ` David Sterba
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