On Friday, July 02, 2010, Chris Mason wrote:
> On Wed, Jun 30, 2010 at 09:26:11AM -0500, C Anthony Risinger wrote:
[...]
> > what about this: would it be possible to have TWO subvolumes by
> > "default"? the regular one (current directory, "."):
> >
> > mount -o subvol=. <btrfs_dev> /mnt
> >
> > would behave as it does now. BUT... there would then be a special,
> > permanent (like "." is right now) subvol, say "parent directory"
> > (".."):
> >
> > mount -o subvol=.. <btrfs_dev> /mnt
> >
> > TWO dots would mount the parent of ".", where i could then swap out
> > the real default (".").
> >
> > would that work?
>
> We do provide a set-default ioctl that can be used to change the default
> for the next mount. This is pretty close to what you want, let me
> think about ways to make it easier to use.
>
> -chris
Hello Chris,
to me it seems that the Anthony request make sense. And it not so difficult to
have. We have all the pieces, we need only a "policy" regarding the subvolume
use and a bit of glue
It should be sufficent to "replace" the standard mkfs.btrfs command with the
following commands sequence
# mkfs.btrfs <device>
# mount <device> /mnt/<tmp>
# btrfs subvol create /mnt/<tmp>/__root__
# btrfs subvol set-default __root__ /mnt/<tmp>/
# umount <device>
So if an user don't want to care about a subvolume, he simply mount a btrfs
filesystem without any option. This user will work inside the __root__
subvolume, where he can create snapshot, subvolume...
Instead if an user want to play with different root in different subvolumes,
he have to mount the ".", where he can manage the root-subvolume(s) (renaming,
moving, snapshotting/branching ... ).
The key is to think the "." subvolume only to handling the subvolumes and not
to storing files. If you don't want to use it, you can simply ignore it,
because the default is to mount the __root__ subvolume.
Goffredo
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