[buildd-tools-devel] Bug#639105: Bug#639105: please consider adding support for lvm-snapshot on crypted LV

[Marc Haber]

Hi Roger,

sorry for not getting back to you any sooner.

On Wed, Aug 24, 2011 at 10:32:24AM +0100, Roger Leigh wrote:
> I'll be happy to add this to schroot.  Currently the 05lvm setup
> script is simply doing an lvcreate when creating and lvremove
> when removing a session, respectively.  Could you please provide
> an example of the commands you would need to run to do this for
> an encrypted PV/LV (I guess we should support both; is the PV
> method more transparent)?

Encrypted PV will work with current schroot setup, you can just take a
snapshot from the LV and directly use it.

Encrypted LV is a little bit harder.

I would suggest configuration like:

[sid_build64]
type=crypted-lvm-snapshot
device=/dev/salida/c_sid_build64
mapping-name=sid_build64
script-config=zg2-build/config
description=sid amd64 for building packages
users=mh
source-users=mh
personality=linux
lvm-snapshot-options=-L 4G

You could also auto-generate the mapping-name for the unlocked volume.
That way, things would just work without a new configuration key.
Optionally, you could implement this inside the normal lvm-snapshot
type by trying cryptsetup isLuks <device> which will indicate whether
the device is encrypted or not.

To enable this chroot, you would need:

lvcreate --snapshot <lvm-snapshot-options> --name <mapping-name> <device>
cryptdisks_start <mapping-name>
mount /dev/mapper/<mapping-name> <mountpoint>

This would need the crypttabl line for <device> to be repeated for
<mapping-name>, and the cryptdisks_start call will probably go
interactive, querying the user for the passphrase.

This is horribly untested.

Greetings
Marc

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