[libvirt] [PATCH] do not send monitor command after monitor met error

[Wen Congyang]

If the monitor met a error, and we will call qemuProcessHandleMonitorEOF().
But we may try to send monitor command after qemuProcessHandleMonitorEOF()
returned. Then libvirtd will be blocked in qemuMonitorSend().

Steps to reproduce this bug:
1. use gdb to attach libvirtd, and set a breakpoint in the function
   qemuConnectMonitor()
2. start a vm
3. let the libvirtd to run until qemuMonitorOpen() returns.
4. kill the qemu process
5. continue running libvirtd

Signed-off-by: Wen Congyang <wency at cn.fujitsu.com>

---
 src/qemu/qemu_monitor.c |   13 +++++++++++++
 1 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
index 800f744..eed83f4 100644
--- a/src/qemu/qemu_monitor.c
+++ b/src/qemu/qemu_monitor.c
@@ -572,6 +572,13 @@ qemuMonitorIO(int watch, int fd, int events, void *opaque) {
                 mon->msg->lastErrno = EIO;
                 virCondSignal(&mon->notify);
             }
+            /* If qemu quited unexpectedly, and we may try to send monitor
+             * command later. But we have no chance to wake up it. So set
+             * mon->lastErrno to EIO, and check it before sending monitor
+             * command.
+             */
+            if (!mon->lastErrno)
+                mon->lastErrno = EIO;
             quit = 1;
         } else if (events) {
             VIR_ERROR(_("unhandled fd event %d for monitor fd %d"),
@@ -725,6 +732,12 @@ int qemuMonitorSend(qemuMonitorPtr mon,
 {
     int ret = -1;
 
+    /* Check whether qemu quited unexpectedly */
+    if (mon->lastErrno) {
+        msg->lastErrno = mon->lastErrno;
+        return -1;
+    }
+
     mon->msg = msg;
     qemuMonitorUpdateWatch(mon);
 
-- 
1.7.1