On 05/17/2018 09:40 AM, 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@xxxxxxxxxx> > --- > src/qemu/qemu_command.c | 64 ++++++++++++++++++- > src/qemu/qemu_command.h | 4 ++ > .../disk-drive-write-cache.x86_64-latest.args | 3 +- > ...irtio-scsi-reservations.x86_64-latest.args | 3 +- > tests/qemuxml2argvmock.c | 16 +++++ > 5 files changed, 84 insertions(+), 6 deletions(-) > Using a mocked socket number seems to be a reasonable mechanism to achieve the goal. There's certainly other tests that used mocked paths or results to get a standard result/answer. Reviewed-by: John Ferlan <jferlan@xxxxxxxxxx> John -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
