[CRIU] Handling Named Cgroup Hierarchies

[Saied Kazemi]

The restore code in CRIU 1.3rc2 for cgroups does not seem to correctly
handle named hierarchies.  A named hierarchy can be created by "mount -t
cgroup -o none,name=<name> <source> <target>".  One such named cgroup is
systemd.  Below is a snippet of the cgroup image file after CRIU dump
showing the entry for systemd.

# criu show -f img/cgroup.img
...
:{
name: "name=systemd"
path: "/user/1000.user/4.session"
 }
...

The function prepare_cgroup_sfd() creates a directory called "name=systemd"
and mounts it.

I applied the following patch as a quick workaround but I think the issue
needs further study.

diff --git a/cgroup.c b/cgroup.c
index 2d9ebad..d2185fb 100644
--- a/cgroup.c
+++ b/cgroup.c
@@ -258,7 +258,10 @@ static int move_in_cgroup(CgSetEntry *se)
                int fd, err;
                ControllerEntry *ce = se->ctls[i];

-               sprintf(aux, "%s/%s/tasks", ce->name, ce->path);
+               if (strstartswith(ce->name, "name="))
+                       sprintf(aux, "%s/%s/tasks", ce->name + 5, ce->path);
+               else
+                       sprintf(aux, "%s/%s/tasks", ce->name, ce->path);
                pr_debug("  `-> %s\n", aux);
                err = fd = openat(cg, aux, O_WRONLY);
                if (fd >= 0) {
@@ -366,11 +369,12 @@ static int prepare_cgroup_sfd(CgSetEntry *root_set)
                ControllerEntry *ce = root_set->ctls[i];
                char *opt = ce->name;

-               sprintf(paux + off, "/%s", ce->name);
                if (strstartswith(ce->name, "name=")) {
+                       sprintf(paux + off, "/%s", ce->name + 5);
                        sprintf(aux, "none,%s", ce->name);
                        opt = aux;
                }
+                       sprintf(paux + off, "/%s", ce->name);

                if (mkdir(paux, 0700)) {
                        pr_perror("Can't make cgyard subdir");

What do you think?

--Saied
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