[buildd-tools-devel] Bug#710073: Bug#710073: sbuild: add copy-on-write support

[Roger Leigh]

On Tue, May 28, 2013 at 11:29:31AM +0800, Paul Wise wrote:
> I would like to switch from pbuilder/cowbuilder to schroot/sbuild but
> the lack of easy copy-on-write support in sbuild is blocking this. It
> would be nice if sbuild supported that. It would be nice if sbuild
> supported both of these mechanisms for copy-on-write:
> 
>       * overlayfs: this is planned to be merged into Linux 3.10
>       * cowdancer: this is what cowbuilder uses
> 
> I would really like to see pbuilder/sbuild unified and this is one step
> towards that long-term goal.

I looked at cowdancer in the past, and IIRC it was too fragile to
implement safely--it requires the use of LD_PRELOAD and this can
break things, and it also breaks a number of sbuild use cases
including non-native arch building using binfmt and qemu.  It
makes assumptions about the chroot environment which may not
always be true.

Note that schroot already supports a number of copy-on-write solutions
including:
 - aufs
 - unionfs
 - btrfs snapshots
 - lvm snapshots
And I'll be happy to add overlayfs support once it's available.  If
you have an existing chroot, making it use aufs/unionfs is just a 1-2
line addition to your configuration.  I would suspect that we can
make it use overlayfs using the same infrastructure--it'll just need
teaching about the new filesystem type.

I can revisit the cowdancer support when I have a bit more time;
if things have changed or my understanding is wrong I'm happy to
be corrected.


Regards,
Roger

-- 
  .''`.  Roger Leigh
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