On Fri, Apr 20, 2018 at 10:18:18 -0400, John Ferlan wrote: > > > On 04/18/2018 01:30 PM, 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. > > > > Reviewed-by: John Ferlan <jferlan@xxxxxxxxxx> > > Signed-off-by: Daniel P. Berrangé <berrange@xxxxxxxxxx> > > --- > > src/qemu/qemu_command.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++-- > > 1 file changed, 52 insertions(+), 2 deletions(-) > > > > This one is now affected by Peter's recent xml2argv adjustment for: > > tests/qemuxml2argvdata/disk-drive-write-cache.x86_64-latest.args > > which now fails w/ : > > 253) QEMU XML-2-ARGV disk-drive-write-cache.x86_64-latest > ... libvirt: QEMU Driver error : Unable to bind to UNIX socket path > '/tmp/lib/domain--1-QEMUGuest1/monitor.sock': No such file or directory > FAILED I'm kind of glad I've added this test :) > because the qemuProcessCreatePretendCmd doesn't allow this code to > distinguish that it shouldn't attempt a bind/listen <sigh> > > I "think" this may require moving the socket setup code into > qemuProcessLaunch or somehow passing a flag into BuildCommandLine to > tell it not to do anything "real". Yeah. The command line generator should be inert to the host, so this needs to be moved to the preparation steps.
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