Re: [Qemu-devel] [PATCH 7/8] block: add witness argument to drive-reopen

2012-04-17 Thread Eric Blake
[adding libvir-list for some interesting discussions on potential libvirt design issues] On 04/17/2012 12:47 AM, Paolo Bonzini wrote: > Il 16/04/2012 23:55, Eric Blake ha scritto: >>> Do transient guests have persistent storage for them in /var while they >>> are running? >> >> Yes - that's how li

Re: [Qemu-devel] [PATCH 7/8] block: add witness argument to drive-reopen

2012-04-16 Thread Paolo Bonzini
Il 16/04/2012 23:55, Eric Blake ha scritto: > > Do transient guests have persistent storage for them in /var while they > > are running? > > Yes - that's how libvirt tracks the pid of the qemu process that it > should be re-attaching to on a libvirtd restart, as well as several > other aspects (fo

Re: [Qemu-devel] [PATCH 7/8] block: add witness argument to drive-reopen

2012-04-16 Thread Eric Blake
On 04/16/2012 03:03 AM, Paolo Bonzini wrote: > Il 14/04/2012 00:32, Eric Blake ha scritto: >> But if the world conspires against me, such as libvirt going down, then >> qemu completing the reopen, then the guest VM halting itself so that the >> qemu process goes away, all before libvirt restarts, t

Re: [Qemu-devel] [PATCH 7/8] block: add witness argument to drive-reopen

2012-04-16 Thread Paolo Bonzini
Il 14/04/2012 00:32, Eric Blake ha scritto: > But if the world conspires against me, such as libvirt going down, then > qemu completing the reopen, then the guest VM halting itself so that the > qemu process goes away, all before libvirt restarts, then I'm stuck > figuring out whether qemu finished

Re: [Qemu-devel] [PATCH 7/8] block: add witness argument to drive-reopen

2012-04-13 Thread Eric Blake
On 04/13/2012 10:23 AM, Paolo Bonzini wrote: > Management needs a way for QEMU to confirm that no I/O has been sent to the > target and not to the source. To provide this guarantee we rely on a file > in local persistent storage. QEMU receives a file descriptor via SCM_RIGHTS > and writes a singl