Re: [libvirt] [PATCH 2/3] qemu: support passing pre-opened UNIX socket listen FD

On Wed, Mar 14, 2018 at 05:33:05PM +0000, Daniel P. Berrangé wrote: > There is a race condition when spawning QEMU where libvirt has spawned > QEMU but the monitor socket is not yet open. Libvirt has to repeatedly > try to connect() to QEMU's monitor until eventually it succeeds, or > times out. We use kill() to check if QEMU is still alive so we avoid > waiting a long time if QEMU exited, but having a timeout at all is still > unpleasant. > > With QEMU 2.12 we can pass in a pre-opened FD for UNIX domain or TCP > sockets. If libvirt has called bind() and listen() on this FD, then we > have a guarantee that libvirt can immediately call connect() and > succeed without any race. > > Although we only really care about this for the monitor socket and agent > socket, this patch does FD passing for all UNIX socket based character > devices since there appears to be no downside to it. > > We don't do FD passing for TCP sockets, however, because it is only > possible to pass a single FD, while some hostnames may require listening > on multiple FDs to cover IPv4 and IPv6 concurrently. > > Signed-off-by: Daniel P. Berrangé <berrange(a)redhat.com&gt; > --- > src/qemu/qemu_command.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 56 insertions(+), 2 deletions(-) > > diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c > index fa0aa5d5c3..291aad13cf 100644 > --- a/src/qemu/qemu_command.c > +++ b/src/qemu/qemu_command.c > @@ -5010,8 +5010,62 @@ qemuBuildChrChardevStr(virLogManagerPtr logManager, > break; > > case VIR_DOMAIN_CHR_TYPE_UNIX: > - virBufferAsprintf(&buf, "socket,id=%s,path=", charAlias); > - virQEMUBuildBufferEscapeComma(&buf, dev->data.nix.path); > +#ifndef WIN32 Why the ifdef? Do we even build QEMU driver on WIN32?