From 4749fec10d414dc45b7bbf04bddd2620528d5f5a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?C=C3=A9dric=20Bosdonnat?= <cbosdonnat@suse.com>
Date: Wed, 15 Jul 2015 10:13:21 +0200
Subject: [PATCH] lxc: wait for nbd device to be up to get its PIDs

The nbd device pid file doesn't appear immediately after starting
qemu-nbd: adding a small loop to wait for it before getting it's
processes PIDs.
---
 src/lxc/lxc_controller.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/lxc/lxc_controller.c b/src/lxc/lxc_controller.c
index c73bb4f580..110a55662b 100644
--- a/src/lxc/lxc_controller.c
+++ b/src/lxc/lxc_controller.c
@@ -537,12 +537,27 @@ static int virLXCControllerAppendNBDPids(virLXCControllerPtr ctrl,
     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 && loops < 10) {
+            usleep(100 * 1000);
+            loops++;
+        } else {
+            virReportSystemError(errno,
+                                 _("Cannot check NBD device %s pid"),
+                                 dev + 5);
+            goto cleanup;
+        }
+    }
+
     if (virPidFileReadPath(pidpath, &pid) < 0)
         goto cleanup;