Here is the v2 of the patch which introduces APIs to read controller

specific stats. Added Makefile.am updates which I had missed in the
previous post.

New APIs to read controller specific statistics.

This patch introduces 3 new APIs which can be used to read controller
statistics iteratively. (Eg. stats from memory.stat etc)

Reading of stats is initiated by cgroup_read_stats_begin() API, which
returns the first stat of the requested controller in addition to returing
a handle that should be used in subsequent reads.

cgroup_read_stats_next() API can be used to read the remaining stats
one by one. This needs the handle returned by cgroup_read_stats_begin().

cgroup_read_stats_end() API will terminate the stats reading iteration
initiated by cgroup_read_stats_begin().

Changelog:

v2
- Update tests/Makefile.am so that it generates appropriate rules
  for tests/read_stats.c in the Makefile. This is in addition to
  the manual updates done to the generated file tests/Makefile.in.

v1
- cgroup_read_stats apis now work with relative cgroup path names instead
  of absolute path names.

v0
- Initial post.

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

2 files changed, 105 insertions, 0 deletions

diff --git a/src/api.c b/src/api.c
index 2d57351..a45802e 100644
--- a/src/api.c
+++ b/src/api.c
@@ -20,6 +20,9 @@
  *
  * Code initiated and designed by Dhaval Giani. All faults are most likely
  * his mistake.
+ *
+ * Bharata B Rao <bharata@linux.vnet.ibm.com> is willing is take blame
+ * for mistakes in APIs for reading statistics.
  */
 
 #include <dirent.h>
@@ -2321,3 +2324,102 @@ int cgroup_walk_tree_begin(char *controller, char *base_path, const int depth,
 	*handle = fts;
 	return ret;
 }
+
+/*
+ * This parses a stat line which is in the form of (name value) pair
+ * separated by a space.
+ */
+int cg_read_stat(FILE *fp, struct cgroup_stat *stat)
+{
+	int ret = 0;
+	char *line = NULL;
+	size_t len = 0;
+	ssize_t read;
+	char *token, *saveptr;
+
+	read = getline(&line, &len, fp);
+	if (read == -1)
+		return ECGEOF;
+
+	token = strtok_r(line, " ", &saveptr);
+	if (!token) {
+		ret = ECGINVAL;
+		goto out_free;
+	}
+	strncpy(stat->name, token, FILENAME_MAX);
+
+	token = strtok_r(NULL, " ", &saveptr);
+	if (!token) {
+		ret = ECGINVAL;
+		goto out_free;
+	}
+	strncpy(stat->value, token, CG_VALUE_MAX);
+
+out_free:
+	free(line);
+	return 0;
+}
+
+int cgroup_read_stats_end(void **handle)
+{
+	FILE *fp;
+
+	if (!cgroup_initialized)
+		return ECGROUPNOTINITIALIZED;
+
+	if (!handle)
+		return ECGINVAL;
+
+	fp = (FILE *)*handle;
+	fclose(fp);
+	return 0;
+}
+
+int cgroup_read_stats_next(void **handle, struct cgroup_stat *stat)
+{
+	int ret = 0;
+	FILE *fp;
+
+	if (!cgroup_initialized)
+		return ECGROUPNOTINITIALIZED;
+
+	if (!handle || !stat)
+		return ECGINVAL;
+
+	fp = (FILE *)*handle;
+	ret = cg_read_stat(fp, stat);
+	*handle = fp;
+	return ret;
+}
+
+/*
+ * TODO: Need to decide a better place to put this function.
+ */
+int cgroup_read_stats_begin(char *controller, char *path, void **handle,
+				struct cgroup_stat *stat)
+{
+	int ret = 0;
+	char stat_file[FILENAME_MAX];
+	FILE *fp;
+
+	if (!cgroup_initialized)
+		return ECGROUPNOTINITIALIZED;
+
+	if (!stat || !handle)
+		return ECGINVAL;
+
+	if (!cg_build_path(path, stat_file, controller))
+		return ECGOTHER;
+
+	sprintf(stat_file, "%s/%s.stat", stat_file, controller);
+
+	fp = fopen(stat_file, "r");
+	if (!fp) {
+		cgroup_dbg("fopen failed\n");
+		return ECGINVAL;
+	}
+
+	ret = cg_read_stat(fp, stat);
+	*handle = fp;
+	return ret;
+}
diff --git a/src/libcgroup.map b/src/libcgroup.map
index 1989f90..dd44fd7 100644
--- a/src/libcgroup.map
+++ b/src/libcgroup.map
@@ -52,5 +52,8 @@ global:
 	cgroup_walk_tree_begin;
 	cgroup_walk_tree_next;
 	cgroup_walk_tree_end;
+	cgroup_read_stats_begin;
+	cgroup_read_stats_next;
+	cgroup_read_stats_end;
 } CGROUP_0.32.1;