[libvirt PATCH 2/2] Revert "cgroup/LXC: Do not condition availability of v2 by controllers"

[Pavel Hrdina]

This reverts commit a0f37232b9c4296ca16955cc625f75eb848ace39.

This fix of the issue is incorrect and breaks usage of other controllers
in hybrid mode that systemd creates, specifically usage of devices and
cpuacct controllers as they are now assumed to be part of the cgroup v2
topology which is not true.

We need to find different solution to the issue.

Signed-off-by: Pavel Hrdina <phrdina at redhat.com>
---
 src/util/vircgroup.c   |  6 ++----
 src/util/vircgroupv2.c | 12 ++++++++++++
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/src/util/vircgroup.c b/src/util/vircgroup.c
index 49ebd37ded..a6a409af3d 100644
--- a/src/util/vircgroup.c
+++ b/src/util/vircgroup.c
@@ -2921,12 +2921,10 @@ int
 virCgroupBindMount(virCgroup *group, const char *oldroot,
                    const char *mountopts)
 {
-    ssize_t i;
+    size_t i;
     virCgroup *parent = virCgroupGetNested(group);
 
-    /* In hybrid environments, V2 may be mounted over V1.
-     * Mount the backends in reverse order. */
-    for (i = VIR_CGROUP_BACKEND_TYPE_LAST - 1; i >= 0; i--) {
+    for (i = 0; i < VIR_CGROUP_BACKEND_TYPE_LAST; i++) {
         if (parent->backends[i] &&
             parent->backends[i]->bindMount(parent, oldroot, mountopts) < 0) {
             return -1;
diff --git a/src/util/vircgroupv2.c b/src/util/vircgroupv2.c
index 0e0c61d466..4c110940cf 100644
--- a/src/util/vircgroupv2.c
+++ b/src/util/vircgroupv2.c
@@ -75,10 +75,22 @@ virCgroupV2Available(void)
         if (STRNEQ(entry.mnt_type, "cgroup2"))
             continue;
 
+        /* Systemd uses cgroup v2 for process tracking but no controller is
+         * available. We should consider this configuration as cgroup v2 is
+         * not available. */
+        contFile = g_strdup_printf("%s/cgroup.controllers", entry.mnt_dir);
+
+        if (virFileReadAll(contFile, 1024 * 1024, &contStr) < 0)
+            goto cleanup;
+
+        if (STREQ(contStr, ""))
+            continue;
+
         ret = true;
         break;
     }
 
+ cleanup:
     VIR_FORCE_FCLOSE(mounts);
     return ret;
 }
-- 
2.37.3