libcgroup: Introduce an API to get the mount point of a specific subsystem

Introduce an API which will query the mount table and return the mount point
of a specific subsystem. This is needed in the case when the user knows which
subsystem he wants the details of, which would make the use of the get_controller*
APIs cumbersome.

Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>

4 files changed, 40 insertions, 1 deletions

diff --git a/include/libcgroup.h b/include/libcgroup.h
index ce0d8a5..9bc74d6 100644
--- a/include/libcgroup.h
+++ b/include/libcgroup.h
@@ -324,6 +324,15 @@ int cgroup_get_controller_begin(void **handle, struct cgroup_mount_point *info);
  */
 int cgroup_get_controller_next(void **handle, struct cgroup_mount_point *info);
 int cgroup_get_controller_end(void **handle);
+
+/*
+ * Reads the mount to table to give the mount point of a controller
+ * @controller: Name of the controller
+ * @mount_point: The string where the mount point is stored. Please note,
+ * the caller must free mount_point.
+ */
+int cgroup_get_subsys_mount_point(char *controller, char **mount_point);
+
 /* The wrappers for filling libcg structures */
 
 struct cgroup *cgroup_new_cgroup(const char *name);
diff --git a/src/api.c b/src/api.c
index 76ba833..03d7520 100644
--- a/src/api.c
+++ b/src/api.c
@@ -2668,3 +2668,31 @@ int cgroup_get_uid_gid_from_procfs(pid_t pid, uid_t *euid, gid_t *egid)
 	return 0;
 }
 
+int cgroup_get_subsys_mount_point(char *controller, char **mount_point)
+{
+	int i;
+	int ret = ECGROUPNOTEXIST;
+
+	if (!cgroup_initialized)
+		return ECGROUPNOTINITIALIZED;
+
+	pthread_rwlock_rdlock(&cg_mount_table_lock);
+	for (i = 0; cg_mount_table[i].name[0] != '\0'; i++) {
+		if (strncmp(cg_mount_table[i].name, controller, FILENAME_MAX))
+			continue;
+
+		*mount_point = strdup(cg_mount_table[i].path);
+
+		if (!*mount_point) {
+			last_errno = errno;
+			ret = ECGOTHER;
+			goto out_exit;
+		}
+
+		ret = 0;
+		break;
+	}
+out_exit:
+	pthread_rwlock_unlock(&cg_mount_table_lock);
+	return ret;
+}
diff --git a/src/libcgroup.map b/src/libcgroup.map
index 5b088d4..5359892 100644
--- a/src/libcgroup.map
+++ b/src/libcgroup.map
@@ -69,4 +69,5 @@ global:
 	cgroup_unload_cgroups;
 	cgroup_get_controller;
 	cgroup_get_uid_gid_from_procfs;
+	cgroup_get_subsys_mount_point;
 } CGROUP_0.33;
diff --git a/tests/Makefile.am b/tests/Makefile.am
index e8401f2..b10f356 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -2,7 +2,7 @@ INCLUDES = -I$(top_srcdir)/include
 LDADD = $(top_srcdir)/src/.libs/libcgroup.la
 
 # compile the tests, but do not install them
-noinst_PROGRAMS = libcgrouptest01 libcg_ba setuid pathtest walk_test read_stats walk_task get_controller
+noinst_PROGRAMS = libcgrouptest01 libcg_ba setuid pathtest walk_test read_stats walk_task get_controller get_mount_point
 
 libcgrouptest01_SOURCES=libcgrouptest01.c test_functions.c libcgrouptest.h
 libcg_ba_SOURCES=libcg_ba.cpp
@@ -12,6 +12,7 @@ walk_test_SOURCES=walk_test.c
 read_stats_SOURCES=read_stats.c
 walk_task_SOURCES=walk_task.c
 get_controller_SOURCES=get_controller.c
+get_mount_point_SOURCES=get_mount_point.c
 
 EXTRA_DIST = pathtest.sh runlibcgrouptest.sh