[CRIU] [PATCH 1/2] cgroups: Add ability to reuse existing cgroup yard directory

[Cyrill Gorcunov]

Currently we always create temporary directory where we restore
cgroups, but this won't work in case if mounting cgroups is forbidden
from inside of a container for some reason (as in OpenVZ kernel).

So one can pass --cgroup-yard option to specify an existing
directory where cgroups are living. By default we assume it
lays in /sys/fs/cgroup.

Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
---
 Documentation/criu.txt |  3 +++
 cgroup.c               | 35 ++++++-----------------------------
 crtools.c              |  6 ++++++
 include/cr_options.h   |  1 +
 4 files changed, 16 insertions(+), 29 deletions(-)

diff --git a/Documentation/criu.txt b/Documentation/criu.txt
index 81783635af89..43958cba4204 100644
--- a/Documentation/criu.txt
+++ b/Documentation/criu.txt
@@ -218,6 +218,9 @@ Restores previously checkpointed processes.
     Change the root cgroup the controller will be installed into. No controller
     means that root is the default for all controllers not specified.
 
+*--cgroup-yard* '<dir>'::
+   Use directory '<dir>' as cgroups yard instead of /sys/fs/cgroup.
+
 *--tcp-established*::
     Restore previously dumped established TCP connections. This implies that
     the network has been locked between *dump* and *restore* phases so other
diff --git a/cgroup.c b/cgroup.c
index b7fef38dd334..6541c628f9e4 100644
--- a/cgroup.c
+++ b/cgroup.c
@@ -935,14 +935,10 @@ int prepare_task_cgroup(struct pstree_item *me)
 
 void fini_cgroup(void)
 {
-	if (!cg_yard)
-		return;
-
-	close_service_fd(CGROUP_YARD);
-	umount2(cg_yard, MNT_DETACH);
-	rmdir(cg_yard);
-	xfree(cg_yard);
-	cg_yard = NULL;
+	if (cg_yard) {
+		close_service_fd(CGROUP_YARD);
+		cg_yard = NULL;
+	}
 }
 
 static int restore_cgroup_prop(const CgroupPropEntry * cg_prop_entry_p,
@@ -1128,27 +1124,8 @@ static int prepare_cgroup_sfd(CgroupEntry *ce)
 
 	pr_info("Preparing cgroups yard\n");
 
-	off = sprintf(paux, ".criu.cgyard.XXXXXX");
-	if (mkdtemp(paux) == NULL) {
-		pr_perror("Can't make temp cgyard dir");
-		return -1;
-	}
-
-	cg_yard = xstrdup(paux);
-	if (!cg_yard) {
-		rmdir(paux);
-		return -1;
-	}
-
-	if (mount("none", cg_yard, "tmpfs", 0, NULL)) {
-		pr_perror("Can't mount tmpfs in cgyard");
-		goto err;
-	}
-
-	if (mount("none", cg_yard, NULL, MS_PRIVATE, NULL)) {
-		pr_perror("Can't make cgyard private");
-		goto err;
-	}
+	cg_yard = opts.cg_yard;
+	off = strlen(opts.cg_yard);
 
 	pr_debug("Opening %s as cg yard\n", cg_yard);
 	i = open(cg_yard, O_DIRECTORY);
diff --git a/crtools.c b/crtools.c
index 6da7afeed067..25a117757bb5 100644
--- a/crtools.c
+++ b/crtools.c
@@ -56,6 +56,7 @@ void init_opts(void)
 	INIT_LIST_HEAD(&opts.inherit_fds);
 	INIT_LIST_HEAD(&opts.new_cgroup_roots);
 
+	opts.cg_yard = "/sys/fs/cgroup";
 	opts.cpu_cap = CPU_CAP_DEFAULT;
 	opts.manage_cgroups = false;
 	opts.ps_socket = -1;
@@ -207,6 +208,7 @@ int main(int argc, char *argv[], char *envp[])
 		{ "enable-fs",			required_argument,	0, 1065 },
 		{ "enable-external-sharing", 	no_argument, 		0, 1066 },
 		{ "enable-external-masters", 	no_argument, 		0, 1067 },
+		{ "cgroup-yard",		required_argument,	0, 1068 },
 		{ },
 	};
 
@@ -434,6 +436,9 @@ int main(int argc, char *argv[], char *envp[])
 		case 1067:
 			opts.enable_external_masters = true;
 			break;
+		case 1068:
+			opts.cg_yard = optarg;
+			break;
 		case 'M':
 			{
 				char *aux;
@@ -674,6 +679,7 @@ usage:
 "                        change the root cgroup the controller will be\n"
 "                        installed into. No controller means that root is the\n"
 "                        default for all controllers not specified.\n"
+"  --cgroup-yard DIR     use DIR as premounted cgroups external yard\n"
 "  --skip-mnt PATH       ignore this mountpoint when dumping the mount namespace.\n"
 "  --enable-fs FSNAMES   a comma separated list of filesystem names or \"all\".\n"
 "                        force criu to (try to) dump/restore these filesystem's\n"
diff --git a/include/cr_options.h b/include/cr_options.h
index 28bed45b0cd8..ecd3825224c6 100644
--- a/include/cr_options.h
+++ b/include/cr_options.h
@@ -60,6 +60,7 @@ struct cr_options {
 	bool			force_irmap;
 	char			**exec_cmd;
 	bool			manage_cgroups;
+	char			*cg_yard;
 	char			*new_global_cg_root;
 	struct list_head	new_cgroup_roots;
 	bool			autodetect_ext_mounts;
-- 
2.4.2