[libvirt] [PATCH] qemu: Return meaningful error when qemu dies early

[Jiri Denemark]

On Mon, Mar 17, 2014 at 13:21:56 +0100, Jiri Denemark wrote:
> https://bugzilla.redhat.com/show_bug.cgi?id=844378
> 
> When qemu dies early after connecting to its monitor but before we
> actually try to read something from the monitor, we would just fail
> domain start with useless message:
> 
>     "An error occurred, but the cause is unknown"
> 
> This is because the real error gets reported in a monitor EOF handler
> executing within libvirt's event loop.
> 
> The fix is to take any error set in qemuMonitor structure and propagate
> it into the thread-local error when qemuMonitorClose is called and no
> thread-local error is set.
> 
> Signed-off-by: Jiri Denemark <jdenemar at redhat.com>
> ---

Oops, I forgot to send notes:

To reproduce the issue, just apply the following patch and kill
qemu process while libvirtd is sleeping:

diff --git i/src/qemu/qemu_process.c w/src/qemu/qemu_process.c
index 400625a..3b77ecc 100644
--- i/src/qemu/qemu_process.c
+++ w/src/qemu/qemu_process.c
@@ -1415,6 +1415,9 @@ qemuConnectMonitor(virQEMUDriverPtr driver, virDomainObjPtr vm, int logfd)
     if (mon)
         ignore_value(qemuMonitorSetDomainLog(mon, logfd));

+    VIR_DEBUG("Sleeping");
+    sleep(5);
+
     virObjectLock(vm);
     virObjectUnref(vm);
     priv->monStart = 0;