Re: [libvirt] [Qemu-devel] [PATCH v6 2/2] vl: fix use of --daemonize with --preconfig

On Wed, Jun 13, 2018 at 03:23:09PM +0100, Daniel P. Berrangé wrote: > On Wed, Jun 13, 2018 at 11:17:30AM -0300, Eduardo Habkost wrote: > > On Tue, Jun 12, 2018 at 01:50:33PM +0100, Daniel P. Berrangé wrote: > > > On Tue, Jun 12, 2018 at 02:42:05PM +0200, Igor Mammedov wrote: > > > > We can keep daemonizing flow in QEMU as it's now. > > > > But Eduardo's idea about libvirt created socked + letting QEMU connect to it > > > > has a merit. It should fix current deadlock issue with as monitor > > > > won't be depending on lead exit event. > > > > > > NB, libvirt only ever uses --daemonize when probing capabilities, never > > > when launching QEMU for a real VM. In the latter case, we now use FD > > > passing, so libvirt opens the UNIX domain socket listener, and passes > > > this into QEMU. So libvirt knows it can connect to the listener > > > immediately and will only ever get a failure if QEMU has exited. > > > > So, what I'm really missing here is: do we have a good reason to > > support --daemonize + --preconfig today? > > On the libvirt zero, I don't see a compelling need for it. Good. :) > > The options I see are: > > 1) complete daemonization before preconfig main loop [...] > > 4) Not supporting -preconfig + -daemonize [...] > > I believe the only reasonable options are (1) and (4). > > Agreed. If it was up to me, I would just go with (4) because it's simpler.

But if somebody wants to implement (1), the caveats should be clearly documented. I would prefer to simply document "--daemonize --preconfig" as experimental, with something like: "Note: usage of --daemonize with the --preconfig option is experimental, because it can prevent QEMU from reporting machine initialization errors and prevent some features from working after QEMU is daemonized."