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@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
The disk cache mode translates to various frontend and backend
attributes for the qemu block layer. For the frontend device the
'writeback' parameter is used and provided as 'write-cache'. Implement
this so that we can later switch to using -blockdev where we will not
pass the cachemode directly any more.
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Prepare the tests for adding the new parameter. The parameter was
introduced in qemu-2.7.0, so add a forked version of the test case to
see that it is formatted properly.
This test is also an example how the new testing macros should be used.
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
