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>

6 files changed, 226 insertions, 4 deletions

diff --git a/include/libcgroup.h b/include/libcgroup.h
index 750e36e..efa852b 100644
--- a/include/libcgroup.h
+++ b/include/libcgroup.h
@@ -129,6 +129,11 @@ struct cgroup_file_info {
  */
 #define CG_HIER_MAX  CG_CONTROLLER_MAX
 
+struct cgroup_stat {
+	char name[FILENAME_MAX];
+	char value[CG_VALUE_MAX];
+};
+
 /* Functions and structures that can be used by the application*/
 struct cgroup;
 struct cgroup_controller;
@@ -250,6 +255,25 @@ int cgroup_walk_tree_next(const int depth, void **handle,
 				struct cgroup_file_info *info, int base_level);
 int cgroup_walk_tree_end(void **handle);
 
+/**
+ * Read the statistics values for the specified controller
+ * @controller: Name of the controller for which stats are requested.
+ * @path: cgroup path.
+ * @handle: Handle to be used during iteration.
+ * @stat: Stats values will be filled and returned here.
+ */
+int cgroup_read_stats_begin(char *controller, char *path, void **handle,
+				struct cgroup_stat *stat);
+
+/**
+ * Read the next stat value.
+ * @handle: Handle to be used during iteration.
+ * @stat: Stats values will be filled and returned here.
+ */
+int cgroup_read_stats_next(void **handle, struct cgroup_stat *stat);
+
+int cgroup_read_stats_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 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;
 
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 3927621..5999389 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -2,13 +2,14 @@ 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
+noinst_PROGRAMS = libcgrouptest01 libcg_ba setuid pathtest walk_test read_stats
 
 libcgrouptest01_SOURCES=libcgrouptest01.c test_functions.c libcgrouptest.h
 libcg_ba_SOURCES=libcg_ba.cpp
 setuid_SOURCES=setuid.c
 pathtest_SOURCES=pathtest.c
 walk_test_SOURCES=walk_test.c
+read_stats_SOURCES=read_stats.c
 
 EXTRA_DIST = pathtest.sh runlibcgrouptest.sh
 
diff --git a/tests/Makefile.in b/tests/Makefile.in
index dae7a12..704e96f 100644
--- a/tests/Makefile.in
+++ b/tests/Makefile.in
@@ -33,7 +33,8 @@ POST_UNINSTALL = :
 build_triplet = @build@
 host_triplet = @host@
 noinst_PROGRAMS = libcgrouptest01$(EXEEXT) libcg_ba$(EXEEXT) \
-	setuid$(EXEEXT) pathtest$(EXEEXT) walk_test$(EXEEXT)
+	setuid$(EXEEXT) pathtest$(EXEEXT) walk_test$(EXEEXT) \
+	read_stats$(EXEEXT)
 subdir = tests
 DIST_COMMON = $(srcdir)/Makefile.am $(srcdir)/Makefile.in
 ACLOCAL_M4 = $(top_srcdir)/aclocal.m4
@@ -65,6 +66,10 @@ am_walk_test_OBJECTS = walk_test.$(OBJEXT)
 walk_test_OBJECTS = $(am_walk_test_OBJECTS)
 walk_test_LDADD = $(LDADD)
 walk_test_DEPENDENCIES = $(top_srcdir)/src/.libs/libcgroup.la
+am_read_stats_OBJECTS = read_stats.$(OBJEXT)
+read_stats_OBJECTS = $(am_read_stats_OBJECTS)
+read_stats_LDADD = $(LDADD)
+read_stats_DEPENDENCIES = $(top_srcdir)/src/.libs/libcgroup.la
 DEFAULT_INCLUDES = -I.@am__isrc@ -I$(top_builddir)
 depcomp = $(SHELL) $(top_srcdir)/depcomp
 am__depfiles_maybe = depfiles
@@ -87,9 +92,11 @@ CXXLINK = $(LIBTOOL) --tag=CXX $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) \
 	--mode=link $(CXXLD) $(AM_CXXFLAGS) $(CXXFLAGS) $(AM_LDFLAGS) \
 	$(LDFLAGS) -o $@
 SOURCES = $(libcg_ba_SOURCES) $(libcgrouptest01_SOURCES) \
-	$(pathtest_SOURCES) $(setuid_SOURCES) $(walk_test_SOURCES)
+	$(pathtest_SOURCES) $(setuid_SOURCES) $(walk_test_SOURCES) \
+	$(read_stats_SOURCES)
 DIST_SOURCES = $(libcg_ba_SOURCES) $(libcgrouptest01_SOURCES) \
-	$(pathtest_SOURCES) $(setuid_SOURCES) $(walk_test_SOURCES)
+	$(pathtest_SOURCES) $(setuid_SOURCES) $(walk_test_SOURCES) \
+	$(read_test_SOURCES)
 ETAGS = etags
 CTAGS = ctags
 DISTFILES = $(DIST_COMMON) $(DIST_SOURCES) $(TEXINFOS) $(EXTRA_DIST)
@@ -214,6 +221,7 @@ libcg_ba_SOURCES = libcg_ba.cpp
 setuid_SOURCES = setuid.c
 pathtest_SOURCES = pathtest.c
 walk_test_SOURCES = walk_test.c
+read_stats_SOURCES = read_stats.c
 EXTRA_DIST = pathtest.sh runlibcgrouptest.sh
 TESTS = runlibcgrouptest.sh
 all: all-am
@@ -271,6 +279,9 @@ setuid$(EXEEXT): $(setuid_OBJECTS) $(setuid_DEPENDENCIES)
 walk_test$(EXEEXT): $(walk_test_OBJECTS) $(walk_test_DEPENDENCIES) 
 	@rm -f walk_test$(EXEEXT)
 	$(LINK) $(walk_test_OBJECTS) $(walk_test_LDADD) $(LIBS)
+read_stats$(EXEEXT): $(read_stats_OBJECTS) $(read_stats_DEPENDENCIES)
+	@rm -f read_stats$(EXEEXT)
+	$(LINK) $(read_stats_OBJECTS) $(read_stats_LDADD) $(LIBS)
 
 mostlyclean-compile:
 	-rm -f *.$(OBJEXT)
@@ -284,6 +295,7 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/setuid.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/test_functions.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/walk_test.Po@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/read_stats.Po@am__quote@
 
 .c.o:
 @am__fastdepCC_TRUE@	$(COMPILE) -MT $@ -MD -MP -MF $(DEPDIR)/$*.Tpo -c -o $@ $<
diff --git a/tests/read_stats.c b/tests/read_stats.c
new file mode 100644
index 0000000..6e61b97
--- /dev/null
+++ b/tests/read_stats.c
@@ -0,0 +1,80 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <string.h>
+#include <libcgroup.h>
+
+int read_stats(char *path, char *controller)
+{
+	int ret;
+	void *handle;
+	struct cgroup_stat stat;
+
+	ret = cgroup_read_stats_begin(controller, path,  &handle, &stat);
+
+	if (ret != 0) {
+		fprintf(stderr, "stats read failed\n");
+		return -1;
+	}
+
+	printf("Stats for %s:\n", path);
+	printf("%s: %s", stat.name, stat.value);
+
+	while ((ret = cgroup_read_stats_next(&handle, &stat)) !=
+			ECGEOF) {
+		printf("%s: %s", stat.name, stat.value);
+	}
+
+	cgroup_read_stats_end(&handle);
+	printf("\n");
+	return 0;
+}
+
+int main(int argc, char *argv[])
+{
+	int ret;
+	char *controller;
+	void *handle;
+	struct cgroup_file_info info;
+	int lvl;
+	char cgroup_path[FILENAME_MAX];
+	int root_len;
+
+	if (argc < 2) {
+		fprintf(stderr, "Usage %s: <controller name>\n",
+			argv[0]);
+		exit(EXIT_FAILURE);
+	}
+
+	controller = argv[1];
+
+	cgroup_init();
+
+	ret = cgroup_walk_tree_begin(controller, "/", 0, &handle, &info, &lvl);
+
+	if (ret != 0) {
+		fprintf(stderr, "Walk failed\n");
+		exit(EXIT_FAILURE);
+	}
+
+	root_len = strlen(info.full_path) - 1;
+	strncpy(cgroup_path, info.path, FILENAME_MAX);
+	ret = read_stats(cgroup_path, controller);
+	if (ret < 0)
+		exit(EXIT_FAILURE);
+
+	while ((ret = cgroup_walk_tree_next(0, &handle, &info, lvl)) !=
+			ECGEOF) {
+		if (info.type != CGROUP_FILE_TYPE_DIR)
+			continue;
+		strncpy(cgroup_path, info.full_path + root_len, FILENAME_MAX);
+		strcat(cgroup_path, "/");
+		ret = read_stats(cgroup_path, controller);
+		if (ret < 0)
+			exit(EXIT_FAILURE);
+	}
+	cgroup_walk_tree_end(&handle);
+
+	return EXIT_SUCCESS;
+}