libcgroup: Add new API to walk tasks

Add a new API to iterate through the tasks file to get
the list of all the tasks in a cgroup.

Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: Bharata B Rao <bharata@linux.vnet.ibm.com>

3 files changed, 93 insertions, 0 deletions

diff --git a/include/libcgroup.h b/include/libcgroup.h
index efa852b..085c17a 100644
--- a/include/libcgroup.h
+++ b/include/libcgroup.h
@@ -274,6 +274,25 @@ int cgroup_read_stats_next(void **handle, struct cgroup_stat *stat);
 
 int cgroup_read_stats_end(void **handle);
 
+/**
+ * Read the tasks file to get the list of tasks in a cgroup
+ * @cgroup: Name of the cgroup
+ * @controller: Name of the cgroup subsystem
+ * @handle: Handle to be used in the iteration
+ * @pid: The pid read from the tasks file. Will be filled in by the API
+ */
+int cgroup_get_task_begin(char *cgroup, char *controller, void **handle,
+								pid_t *pid);
+
+/**
+ * Read the next task value
+ * @handle: The handle used for iterating
+ * @pid: The variable where the value will be stored
+ *
+ * return ECGEOF when the iterator finishes getting the list of tasks.
+ */
+int cgroup_get_task_next(void *handle, pid_t *pid);
+int cgroup_get_task_end(void **handle);
 /* 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 4d5b524..baeb856 100644
--- a/src/api.c
+++ b/src/api.c
@@ -2407,3 +2407,71 @@ int cgroup_read_stats_begin(char *controller, char *path, void **handle,
 	*handle = fp;
 	return ret;
 }
+
+int cgroup_get_task_end(void **handle)
+{
+	if (!cgroup_initialized)
+		return ECGROUPNOTINITIALIZED;
+
+	if (!*handle)
+		return ECGINVAL;
+
+	fclose((FILE *) *handle);
+	*handle = NULL;
+
+	return 0;
+}
+
+int cgroup_get_task_next(void *handle, pid_t *pid)
+{
+	int ret;
+
+	if (!cgroup_initialized)
+		return ECGROUPNOTINITIALIZED;
+
+	if (!handle)
+		return ECGINVAL;
+
+	ret = fscanf((FILE *) handle, "%u", pid);
+
+	if (ret != 1) {
+		if (ret == EOF)
+			return ECGEOF;
+		last_errno = errno;
+		return ECGOTHER;
+	}
+
+	return 0;
+}
+
+int cgroup_get_task_begin(char *cgroup, char *controller, void **handle,
+								pid_t *pid)
+{
+	int ret = 0;
+	char path[FILENAME_MAX];
+	char *fullpath = NULL;
+
+	if (!cgroup_initialized)
+		return ECGROUPNOTINITIALIZED;
+
+	if (!cg_build_path(cgroup, path, controller))
+		return ECGOTHER;
+
+	ret = asprintf(&fullpath, "%s/tasks", path);
+
+	if (ret < 0) {
+		last_errno = errno;
+		return ECGOTHER;
+	}
+
+	*handle = (void *) fopen(fullpath, "r");
+	free(fullpath);
+
+	if (!*handle) {
+		last_errno = errno;
+		return ECGOTHER;
+	}
+	ret = cgroup_get_task_next(*handle, pid);
+
+	return ret;
+}
diff --git a/src/libcgroup.map b/src/libcgroup.map
index dd44fd7..2e2348e 100644
--- a/src/libcgroup.map
+++ b/src/libcgroup.map
@@ -57,3 +57,9 @@ global:
 	cgroup_read_stats_end;
 } CGROUP_0.32.1;
 
+CGROUP_0.34 {
+global:
+	cgroup_get_task_begin;
+	cgroup_get_task_end;
+	cgroup_get_task_next;
+} CGROUP_0.33;