[PATCH] Don't return an error if fail to create blkio controller

[Hu Tao <hutao@xxxxxxxxxxxxxx>]

This patch enables cgroup controllers as much as possible by skipping
the creation of blkio controller when running with old kenels that
doesn't support multi-level directory for blkio controller.

Signed-off-by: Hu Tao <hutao@xxxxxxxxxxxxxx>
---
 src/util/cgroup.c |   28 +++++++++++++++++++++++-----
 1 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/src/util/cgroup.c b/src/util/cgroup.c
index c5b8cdd..3fad480 100644
--- a/src/util/cgroup.c
+++ b/src/util/cgroup.c
@@ -527,9 +527,19 @@ static int virCgroupMakeGroup(virCgroupPtr parent, virCgroupPtr group,
         if (access(path, F_OK) != 0) {
             if (!create ||
                 mkdir(path, 0755) < 0) {
-                rc = -errno;
-                VIR_FREE(path);
-                break;
+                /* With a kernel that doesn't support multi-level directory
+                 * for blkio controller, libvirt will fail and disable all
+                 * other controllers even though they are available. So skip
+                 * blkio here if mkdir fails. */
+                if (i == VIR_CGROUP_CONTROLLER_BLKIO) {
+                    rc = 0;
+                    VIR_FREE(path);
+                    continue;
+                } else {
+                    rc = -errno;
+                    VIR_FREE(path);
+                    break;
+                }
             }
             if (group->controllers[VIR_CGROUP_CONTROLLER_CPUSET].mountPoint != NULL &&
                 (i == VIR_CGROUP_CONTROLLER_CPUSET ||
@@ -751,8 +761,16 @@ int virCgroupAddTask(virCgroupPtr group, pid_t pid)
             continue;
 
         rc = virCgroupSetValueU64(group, i, "tasks", (unsigned long long)pid);
-        if (rc != 0)
-            break;
+
+        /* See virCgroupMakeGroup() for the reason why check BLKIO here */
+        if (rc != 0) {
+            if (i != VIR_CGROUP_CONTROLLER_BLKIO)
+                break;
+            else {
+                rc = 0;
+                continue;
+            }
+        }
     }
 
     return rc;
-- 
1.7.3.1

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