On 03/21/2013 08:56 AM, Stefan Hajnoczi wrote: > On Thu, Mar 21, 2013 at 02:42:23PM +0100, Paolo Bonzini wrote: >> Il 21/03/2013 14:38, Stefan Hajnoczi ha scritto: >>> There already is a guest RAM cloning mechanism: fork the QEMU process. >>> Then you have a copy-on-write guest RAM. >>> >>> In a little more detail: >>> >>> 1. save non-RAM device state >>> 2. quiesce QEMU to a state that is safe for forking >>> 3. create an EventNotifier for live savevm completion signal >>> 4. fork and pass completion EventNotifier to child >>> 5. parent continues running VM >>> 6. child performs vmsave of copy-on-write guest RAM >>> 7. child signals completion EventNotifier and terminates >>> 8. parent raises live savevm completion QMP event >> >> Forking a threaded program is not so easy, but it could be done if the >> child is very simple and only uses syscalls to communicate back with the >> parent: > > On Linux you should be able to use clone(2) to spawn a thread with > copy-on-write memory. Too bad it's not portable because it gets around > the messy fork issues.
And introduces its own messy issues - once you clone() using different flags than what fork() does, you have invalidated the use of a LOT of libc interfaces in that child; in particular, any use of pthread is liable to break. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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