[PATCH] Fix qemu-nbd cleanup crashes

[Cédric Bosdonnat <cbosdonnat@xxxxxxxx>]

The virLXCControllerAppendNBDPids function didn't properly initialize
pids and npids. In case of failure it was crashing when freeing those.

The nbd device pid file doesn't appear immediately after starting
qemu-nbd: adding a small loop to wait for it.
---
 src/lxc/lxc_controller.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/lxc/lxc_controller.c b/src/lxc/lxc_controller.c
index 828b8a8..78d3eee 100644
--- a/src/lxc/lxc_controller.c
+++ b/src/lxc/lxc_controller.c
@@ -533,16 +533,31 @@ static int virLXCControllerAppendNBDPids(virLXCControllerPtr ctrl,
                                          const char *dev)
 {
     char *pidpath = NULL;
-    pid_t *pids;
-    size_t npids;
+    pid_t *pids = NULL;
+    size_t npids = 0;
     size_t i;
     int ret = -1;
+    size_t loops = 0;
     pid_t pid;
 
     if (!STRPREFIX(dev, "/dev/") ||
         virAsprintf(&pidpath, "/sys/devices/virtual/block/%s/pid", dev + 5) < 0)
         goto cleanup;
 
+    /* Wait for the pid file to appear */
+    while (!virFileExists(pidpath)) {
+        /* wait for 100ms before checking again, but don't do it for ever */
+        if (errno == ENOENT && loop < 10) {
+            usleep(100 * 1000);
+            loop++;
+        } else {
+            virReportSystemError(errno,
+                                 _("Cannot check NBD device %s pid"),
+                                 dev + 5);
+            goto cleanup;
+        }
+    }
+
     if (virPidFileReadPath(pidpath, &pid) < 0)
         goto cleanup;
 
-- 
2.1.4

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