[Devel] [patch rh7 2/2] cgroup: Mangle cgroups root from inside of VE view

[Cyrill Gorcunov]

We're bindmounting cgroups for container so if say a container
is having CTID=200 then @cgroups and @mountinfo output will
contain /200 as a root. Which makes Docker to lookup for
appropriate directory inside /sys/fs/cgroup/<controller>
which of course not present because of been bindmounted
from the node (note we can't bindmount into
<controller>/<container> here because it confuses container's
systemd instance and it stuck on boot).

Thus we simply mangle root here so when one is accessing
@cgroups or @mountinfo kernel shows '/' instead of $ctid
which makes both docker and systemd happy.

https://jira.sw.ru/browse/PSBM-33757

Signed-off-by: Cyrill Gorcunov <gorcunov at virtuozzo.com>
CC: Vladimir Davydov <vdavydov at virtuozzo.com>
CC: Konstantin Khorenko <khorenko at virtuozzo.com>
CC: Pavel Emelyanov <xemul at virtuozzo.com>
CC: Andrey Vagin <avagin at virtuozzo.com>
---
 kernel/cgroup.c |   29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

Index: linux-pcs7.git/kernel/cgroup.c
===================================================================
--- linux-pcs7.git.orig/kernel/cgroup.c
+++ linux-pcs7.git/kernel/cgroup.c
@@ -1386,10 +1386,24 @@ static int cgroup_remount(struct super_b
 	return ret;
 }
 
+#ifdef CONFIG_VE
+int cgroup_show_path(struct seq_file *m, struct dentry *dentry)
+{
+	if (!ve_is_super(get_exec_env()))
+		seq_puts(m, "/");
+	else
+		seq_dentry(m, dentry, " \t\n\\");
+	return 0;
+}
+#endif
+
 static const struct super_operations cgroup_ops = {
 	.statfs = simple_statfs,
 	.drop_inode = generic_delete_inode,
 	.show_options = cgroup_show_options,
+#ifdef CONFIG_VE
+	.show_path = cgroup_show_path,
+#endif
 	.remount_fs = cgroup_remount,
 };
 
@@ -1807,6 +1821,21 @@ int cgroup_path(const struct cgroup *cgr
 		return 0;
 	}
 
+#ifdef CONFIG_VE
+	/*
+	 * Containers cgroups are bind-mounted from node
+	 * so they are like '/' from inside, thus we have
+	 * to mangle cgroup path output.
+	 */
+	if (!ve_is_super(get_exec_env())) {
+		if (cgrp->parent && !cgrp->parent->parent) {
+			if (strlcpy(buf, "/", buflen) >= buflen)
+				return -ENAMETOOLONG;
+			return 0;
+		}
+	}
+#endif
+
 	start = buf + buflen - 1;
 	*start = '\0';