[libvirt] [PATCH 1/2] vircgroupv2: Fix VM startup when legacy cgroups are defined
On Fedora 31, starting a 'mock' build alters /proc/$pid/cgroup,
probably due to usage of systemd-nspawn.
Before:
$ cat /proc/self/cgroup
0::/user.slice/user-1000.slice/...
After:
$ cat /proc/self/cgroup
1:name=systemd:/
0::/user.slice/user-1000.slice/...
The cgroupv2 code mishandles that first line in the second case, which
causes VM startup to fail with: Unable to read from
'/sys/fs/cgroup/machine/cgroup.controllers': No such file or directory
The kernel docs[1] say that the cgroupv2 path will always start with
'0::', which in the code here controllers="". Only set the v2 placement
path when we see that cgroup file entry.
[1] https://www.kernel.org/doc/html/v5.3/admin-guide/cgroup-v2.html#processes
https://bugzilla.redhat.com/show_bug.cgi?id=1751120
Signed-off-by: Cole Robinson <crobinso(a)redhat.com>
---
src/util/vircgroupv2.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/src/util/vircgroupv2.c b/src/util/vircgroupv2.c
index 0663c67190..0cb20e4896 100644
--- a/src/util/vircgroupv2.c
+++ b/src/util/vircgroupv2.c
@@ -194,12 +194,16 @@ virCgroupV2DetectMounts(virCgroupPtr group,
static int
virCgroupV2DetectPlacement(virCgroupPtr group,
const char *path,
- const char *controllers ATTRIBUTE_UNUSED,
+ const char *controllers,
const char *selfpath)
{
if (group->unified.placement)
return 0;
+ /* controllers="" indicates the cgroupv2 controller path */
+ if (STRNEQ_NULLABLE(controllers, ""))
+ return 0;
+
/*
* selfpath == "/" + path="" -> "/"
* selfpath == "/libvirt.service" + path == "" ->
"/libvirt.service"
--
2.23.0