On Thu, 24 Jan 2008 23:24:17 +0000 "Daniel P. Berrange" <berrange redhat com> wrote: > On Fri, Jan 25, 2008 at 10:17:05AM +1100, James Morris wrote: > > On Thu, 24 Jan 2008, Daniel P. Berrange wrote: > > > > > > Something to consider perhaps is the use of lguest, which is > > > > currently i386 only, but does boot up nearly instantaneously, > > > > and can be scripted, as its console is the launching shell. > > > > > > > > Is there an efficient technique for mounting a disk image so > > > > that changes made to it are discarded? > > > > > > Sure, just create an LVM writable snapshot of your master image, > > > and boot with that instead, and throw away the snapshot when > > > you're done. > > > > Cool. So if there was a RPM package which contained a barebones > > Fedora image and some management scripts, I don't imagine it would > > be too difficult to do things like build RPMs inside that with e.g. > > different SELinux policies to the host. Any supporting RPMS > > required inside the guest could be installed via a script either > > from host media or over the net, then the final RPM (or whatever is > > being created) could be copied back out to the host before > > discarding the guest instance. > > > > It would not be as fast or simple as chroot, but I suspect it would > > work pretty well, especially if the guest dispenses with all > > non-essential startup. > > Actually you can do some tricks here too. You can boot the guest using > the real disk image. Once it is up & running in desired state you can > save the VM to disk (cf hibernate). Launching it just becomes a case > of taking a snapshot of the disk, and restoring the VM state file. > Much much quicker than normal startup - a matter of seconds - > depending on guest RAM size. As long as you take care to always > restore it against a snapshot of the disk from the same it was saved, > you can repeat this restore process many times over. It is not > entirely straightforward to do these steps in the general case, but > if you want to mandate LVM storage only then it is a tractable problem > > Dan. Yeah, it all sounds pretty exciting, but get back to me when it works on x86_64, ppc, ppc64, ia64, s390, s390x, sparc, sparc64, arm, alpha... -- Jesse Keating Fedora -- All my bits are free, are yours?
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