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 >
signature.asc
Description: This is a digitally signed message part
