The automatic classification engine (cgexec, cgclassify, pam_cgroup)

classify tasks. It is useful for an application to know where it has
been classified. I propose to add a new API
cgroup_get_current_controller_path() that returns the current
classification directory for the specified controller. One can easily
add on and build new API that will return paths of all mounted
controllers, but I want to start with something simple and useful.

I've also added a bunch of test cases for the same purpose.

Test output

# ./pathtest.sh
Test FAIL, get path failed for controller cpuset
Test PASS, controller cpu path /default
Test PASS, controller cpuacct path /default
Test PASS, controller memory path /default
Test FAIL, get path failed for controller memrlimit

I mounted just cpu, cpuacct and memory, thus the path for cpuset and
memrlimit could not be found (as expected).

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


git-svn-id: https://libcg.svn.sourceforge.net/svnroot/libcg/trunk@200 4f4bb910-9a46-0410-90c8-c897d4f1cd53

5 files changed, 149 insertions, 1 deletions

diff --git a/api.c b/api.c
index 60a458c..2cd1a37 100644
--- a/api.c
+++ b/api.c
@@ -1908,3 +1908,89 @@ int cgroup_init_rules_cache()
 
 	return ret;
 }
+
+/**
+ * cgroup_get_current_controller_path
+ * @pid: pid of the current process for which the path is to be determined
+ * @controller: name of the controller for which to determine current path
+ * @current_path: a pointer that is filled with the value of the current
+ * 		path as seen in /proc/<pid>/cgroup
+ */
+int cgroup_get_current_controller_path(pid_t pid, const char *controller,
+					char **current_path)
+{
+	char *path;
+	int ret;
+	FILE *pid_cgroup_fd;
+
+	if (!controller)
+		return ECGOTHER;
+
+	if (!cgroup_initialized) {
+		dbg("libcgroup is not initialized\n");
+		return ECGROUPNOTINITIALIZED;
+	}
+
+	ret = asprintf(&path, "/proc/%d/cgroup", pid);
+	if (ret <= 0) {
+		dbg("cannot allocate memory (/proc/pid/cgroup) ret %d\n", ret);
+		return ret;
+	}
+
+	ret = ECGROUPNOTEXIST;
+	pid_cgroup_fd = fopen(path, "r");
+	if (!pid_cgroup_fd)
+		goto cleanup_path;
+
+	/*
+	 * Why do we grab the cg_mount_table_lock?, the reason is that
+	 * the cgroup of a pid can change via the cgroup_attach_task_pid()
+	 * call. To make sure, we return consitent and safe results,
+	 * we acquire the lock upfront. We can optimize by acquiring
+	 * and releasing the lock in the while loop, but that
+	 * will be more expensive.
+	 */
+	pthread_rwlock_rdlock(&cg_mount_table_lock);
+	while (!feof(pid_cgroup_fd)) {
+		char controllers[FILENAME_MAX];
+		char cgroup_path[FILENAME_MAX];
+		int num;
+		char *savedptr;
+		char *token;
+
+		ret = fscanf(pid_cgroup_fd, "%d:%[^:]:%s\n", &num, controllers,
+				cgroup_path);
+		/*
+		 * Magic numbers like "3" seem to be integrating into
+		 * my daily life, I need some magic to help make them
+		 * disappear :)
+		 */
+		if (ret != 3 || ret == EOF) {
+			dbg("read failed for pid_cgroup_fd ret %d\n", ret);
+			ret = ECGOTHER;
+			goto done;
+		}
+
+		token = strtok_r(controllers, ",", &savedptr);
+		do {
+			if (strncmp(controller, token, strlen(controller) + 1)
+								== 0) {
+				*current_path = strdup(cgroup_path);
+				if (!*current_path) {
+					ret = ECGOTHER;
+					goto done;
+				}
+				ret = 0;
+				goto done;
+			}
+			token = strtok_r(NULL, ",", &savedptr);
+		} while (token);
+	}
+
+done:
+	pthread_rwlock_unlock(&cg_mount_table_lock);
+	fclose(pid_cgroup_fd);
+cleanup_path:
+	free(path);
+	return ret;
+}
diff --git a/libcgroup.h b/libcgroup.h
index c9e9689..97c663d 100644
--- a/libcgroup.h
+++ b/libcgroup.h
@@ -255,6 +255,12 @@ int cgroup_reload_cached_rules(void);
  */
 int cgroup_init_rules_cache(void);
 
+/**
+ * Get the current cgroup path where the task specified by pid_t pid
+ * has been classified
+ */
+int cgroup_get_current_controller_path(pid_t pid, const char *controller,
+					char **current_path);
 
 /* The wrappers for filling libcg structures */
 
diff --git a/tests/Makefile b/tests/Makefile
index 7a38b7a..5c602cb 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -6,7 +6,8 @@ CFLAGS = -g -O2 -Wall -DDEBUG
 
 TARGET= libcgrouptest01 \
 	libcg_ba \
-	setuid
+	setuid \
+	pathtest
 
 all:	$(TARGET)
 
@@ -19,5 +20,8 @@ libcg_ba: libcg_ba.cpp
 setuid: setuid.c
 	$(CC) $(CFLAGS) -o $@ $< $(LDFLAGS) $(LIBS)
 
+pathtest: pathtest.c
+	$(CC) $(CFLAGS) -o $@ $< $(LDFLAGS) $(LIBS)
+
 clean:
 	\rm -f $(TARGET)
diff --git a/tests/pathtest.c b/tests/pathtest.c
new file mode 100644
index 0000000..076c38a
--- /dev/null
+++ b/tests/pathtest.c
@@ -0,0 +1,40 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <string.h>
+#include <libcgroup.h>
+
+int main(int argc, char *argv[])
+{
+	char *path;
+	char *expected_path, *controller;
+	int ret;
+
+	if (argc < 2) {
+		fprintf(stderr, "Usage %s: <controller name> <path>\n",
+			argv[0]);
+		exit(EXIT_FAILURE);
+	}
+
+	controller = argv[1];
+	expected_path = argv[2];
+
+	cgroup_init();
+
+	ret = cgroup_get_current_controller_path(getpid(), controller, &path);
+	if (ret)
+		printf("Test FAIL, get path failed for controller %s\n",
+			controller);
+	else {
+		if (strcmp(path, expected_path))
+			printf("Test FAIL, expected_path %s, got path %s\n",
+				expected_path, path);
+		else
+			printf("Test PASS, controller %s path %s\n",
+				controller, path);
+		free(path);
+	}
+
+	return EXIT_SUCCESS;
+}
diff --git a/tests/pathtest.sh b/tests/pathtest.sh
new file mode 100755
index 0000000..b373389
--- /dev/null
+++ b/tests/pathtest.sh
@@ -0,0 +1,12 @@
+#!/bin/bash
+
+while read name extra
+do
+	echo $name | grep -q '^#'
+	if [ $? -eq 0 ]
+	then
+		continue
+	fi
+	path=`cat /proc/$$/cgroup | cut -d ':' -f 3`
+	./pathtest $name $path
+done < /proc/cgroups