In the iso-to-disk script, one can add an overlay file. However, I don't see that it is being used at all--livesys does not reference it at all. It looks like the XO team passes a kernel parameter, but I haven't seen the code to actually use it. My assumption is that the overlay file would be the backend storage for an LVM snapshot. Has anyone actually used an overlay file? Any ideas on the implementation?

On Wed, 2009-01-21 at 14:00 -0500, Jeremy Katz wrote: > On Wednesday, January 21 2009, Forrest Taylor said: > > In the iso-to-disk script, one can add an overlay file. However, I > > don't see that it is being used at all--livesys does not reference it at > > all. It looks like the XO team passes a kernel parameter, but I haven't > > seen the code to actually use it. > > > > My assumption is that the overlay file would be the backend storage for > > an LVM snapshot. Has anyone actually used an overlay file? Any ideas > > on the implementation? > > The overlay gets set up in the initramfs, so see mkliveinitrd in the > mkinitrd package. Basically what happens is that instead of creating a > file that's backed by RAM to use as our dm-snapshot device, we set up > dm-snapshot to write to the file on the USB stick instead. Thanks, Jeremy, that makes sense now. It looks like mayflower was the script that did this in RHEL5, so I'll see if I can backport it.

Is there any way to see how much of the overlay is being used from within the live image?