lxc: don't try to hide parent cgroups inside container

On the host when we start a container, it will be
placed in a cgroup path of

   /machine.slice/machine-lxc\x2ddemo.scope

under /sys/fs/cgroup/*

Inside the containers' namespace we need to setup
/sys/fs/cgroup mounts, and currently will bind
mount /machine.slice/machine-lxc\x2ddemo.scope on
the host to appear as / in the container.

While this may sound nice, it confuses applications
dealing with cgroups, because /proc/$PID/cgroup
now does not match the directory in /sys/fs/cgroup

This particularly causes problems for systems and
will make it create repeated path components in
the cgroup for apps run in the container eg

  /machine.slice/machine-lxc\x2ddemo.scope/machine.slice/machine-lxc\x2ddemo.scope/user.slice/user-0.slice/session-61.scope

This also causes any systemd service that uses
sd-notify to fail to start, because when systemd
receives the notification it won't be able to
identify the corresponding unit it came from.
In particular this break rabbitmq-server startup

Future kernels will provide proper cgroup namespacing
which will handle this problem, but until that time
we should not try to play games with hiding parent
cgroups.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/libvirt_private.syms

@@ -1196,6 +1196,7 @@ virCgroupAllowDevice;
 virCgroupAllowDeviceMajor;
 virCgroupAllowDevicePath;
 virCgroupAvailable;
+virCgroupBindMount;
 virCgroupControllerAvailable;
 virCgroupControllerTypeFromString;
 virCgroupControllerTypeToString;
@@ -1233,7 +1234,6 @@ virCgroupGetMemSwapUsage;
 virCgroupGetPercpuStats;
 virCgroupHasController;
 virCgroupHasEmptyTasks;
-virCgroupIsolateMount;
 virCgroupKill;
 virCgroupKillPainfully;
 virCgroupKillRecursive;

src/lxc/lxc_container.c

@@ -1827,7 +1827,7 @@ static int lxcContainerSetupPivotRoot(virDomainDefPtr vmDef,
 
     /* Now we can re-mount the cgroups controllers in the
      * same configuration as before */
-    if (virCgroupIsolateMount(cgroup, "/.oldroot/", sec_mount_options) < 0)
+    if (virCgroupBindMount(cgroup, "/.oldroot/", sec_mount_options) < 0)
         goto cleanup;
 
     /* Mounts /dev */

src/util/vircgroup.c

@@ -3917,7 +3917,7 @@ virCgroupGetFreezerState(virCgroupPtr group, char **state)
 
 
 int
-virCgroupIsolateMount(virCgroupPtr group, const char *oldroot,
+virCgroupBindMount(virCgroupPtr group, const char *oldroot,
                    const char *mountopts)
 {
     int ret = -1;
@@ -3954,10 +3954,9 @@ virCgroupIsolateMount(virCgroupPtr group, const char *oldroot,
 
         if (!virFileExists(group->controllers[i].mountPoint)) {
             char *src;
-            if (virAsprintf(&src, "%s%s%s",
+            if (virAsprintf(&src, "%s%s",
                             oldroot,
-                            group->controllers[i].mountPoint,
-                            group->controllers[i].placement) < 0)
+                            group->controllers[i].mountPoint) < 0)
                 goto cleanup;
 
             VIR_DEBUG("Create mount point '%s'",

src/util/vircgroup.h

@@ -286,7 +286,7 @@ int virCgroupKill(virCgroupPtr group, int signum);
 int virCgroupKillRecursive(virCgroupPtr group, int signum);
 int virCgroupKillPainfully(virCgroupPtr group);
 
-int virCgroupIsolateMount(virCgroupPtr group,
+int virCgroupBindMount(virCgroupPtr group,
                        const char *oldroot,
                        const char *mountopts);