Re: default subvolume abilities/restrictions

[C Anthony Risinger <anthony@extof.me>]

On Sun, Jun 13, 2010 at 12:47 PM, C Anthony Risinger <anthony@extof.me>=
 wrote:
> On Sat, Jun 12, 2010 at 8:06 PM, C Anthony Risinger <anthony@extof.me=
> wrote:
>> On Sat, Jun 12, 2010 at 7:22 PM, David Brown <btrfs@davidb.org> wrot=
e:
>>> On Sat, Jun 12, 2010 at 06:06:23PM -0500, C Anthony Risinger wrote:
>>>
>>>>> # btrfs subvolume create new_root
>>>>> # mv . new_root/old_root
>>>
>>>> can i at least get confirmation that the above is possible?
>>>
>>> I've had no problem with
>>>
>>> =A0# btrfs subvolume snapshot . new_root
>>> =A0# mkdir old_root
>>> =A0# mv * old_root
>>> =A0# rm -rf old_root
>>>
>>> Make sure the 'mv' fails fo move new_root, and I'd look at the
>>> new_root before removing everything.
>>>
>>> David
>>
>> heh, yeah i as i was writing the last email i realized that all i
>> really wanted was to:
>>
>> # mv * new_root
>>
>> for some reason i was convinced that i must snapshot the old_root (.=
)
>> to new_root... and then remove the erroneous stuff from old_root (.)=
=2E
>> thus a way to "parent" the default subvol (old_root/.) seemed a bett=
er
>> solution...
>>
>> but alas, a snapshot isn't necessary. =A0i can create an empty subvo=
l
>> "new_root", and then "mv * new_root".
>>
>> i don't know how that escaped me :-), sorry for all the noise.
>> however, there probably is a legitimate use case for wanting to
>> replace the default subvolume, but this isn't it.
>>
>> C Anthony
>
> ok i take it all back, i DO need this...
>
> i rewrote my initramfs hook to do the following operations:
>
> # btrfs subvolume create /new_root
> # mv /* /new_root
>
> instead of what i had:
>
> # btrfs subvolume snapshot / /new_root
>
> and it resulted in scarily COPYING my entire system... several gigs
> worth... to the newly created subvolume, which took forever, and
> grinded on my HD for awhile. =A0i don't know how long because i went =
to
> bed.
>
> this is why i need a way to "parent" the default subvolume.
>
> a snapshot is nice and quick, but it leaves / full of erroneous
> folders (dev/etc/usr/lib), an entire system, that will no longer be
> used. =A0this space will in time become dead wasted space unless my
> users manually "rm -rf" themselves.
>
> so... any input on this? =A0how can i effectively, and efficiently, m=
ove
> a users installation into a dedicated subvolume, when they have
> already installed into the default subvolume?
>
> i think the best way is what i originally suggested; make an empty
> subvolume the new top-level subvol, and place the old top-level subvo=
l
> INTO it with a new name.
>
> thoughts?

can i get a little feedback on this problem?  i choke slightly when
telling users the only way to clean their old / is by rm -rf'ing
everything....

i need the ability to "move" the default subvolume into a new, empty
subvolume.  the empty subvolume then becomes the new default.

the end result is moving the users installation into a dedicated
subvolume, cleanly and efficiently, so the system can do other things
with the "subroot" structure.

the way i am doing it now is snapshotting the users / to /__active...
however, the side effect is an entire system worth of files that will
in time become dead space.

moving the users install via "mv" into an empty subvol does not work.
everything is actually copied =3D slow,slow,slow.

ideas???  how can i "parent" the default subvol with an empty subvol?
this seems a legitimate operation.

thanks,
C Anthony
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