cutils: Add support for reading a processes scheduler policy
Signed-off-by: San Mehat <san@google.com>
diff --git a/libcutils/sched_policy.c b/libcutils/sched_policy.c
index 7553090..93fcd4a 100644
--- a/libcutils/sched_policy.c
+++ b/libcutils/sched_policy.c
@@ -37,6 +37,8 @@
#define SCHED_BATCH 3
#endif
+static int __sys_supports_schedgroups = -1;
+
static int add_tid_to_cgroup(int tid, const char *grp_name)
{
int fd;
@@ -58,10 +60,8 @@
return 0;
}
-int set_sched_policy(int tid, SchedPolicy policy)
+static inline void initialize()
{
- static int __sys_supports_schedgroups = -1;
-
if (__sys_supports_schedgroups < 0) {
if (!access("/dev/cpuctl/tasks", F_OK)) {
__sys_supports_schedgroups = 1;
@@ -69,6 +69,91 @@
__sys_supports_schedgroups = 0;
}
}
+}
+
+/*
+ * Try to get the scheduler group.
+ *
+ * The data from /proc/<pid>/cgroup looks like:
+ * 2:cpu:/bg_non_interactive
+ *
+ * We return the part after the "/", which will be an empty string for
+ * the default cgroup. If the string is longer than "bufLen", the string
+ * will be truncated.
+ */
+static int getSchedulerGroup(int tid, char* buf, size_t bufLen)
+{
+#ifdef HAVE_ANDROID_OS
+ char pathBuf[32];
+ char readBuf[256];
+ ssize_t count;
+ int fd;
+
+ snprintf(pathBuf, sizeof(pathBuf), "/proc/%d/cgroup", tid);
+ if ((fd = open(pathBuf, O_RDONLY)) < 0) {
+ return -1;
+ }
+
+ count = read(fd, readBuf, sizeof(readBuf));
+ if (count <= 0) {
+ close(fd);
+ errno = ENODATA;
+ return -1;
+ }
+ close(fd);
+
+ readBuf[--count] = '\0'; /* remove the '\n', now count==strlen */
+
+ char* cp = strchr(readBuf, '/');
+ if (cp == NULL) {
+ readBuf[sizeof(readBuf)-1] = '\0';
+ errno = ENODATA;
+ return -1;
+ }
+
+ memcpy(buf, cp+1, count); /* count-1 for cp+1, count+1 for NUL */
+ return 0;
+#else
+ errno = ENOSYS;
+ return -1;
+#endif
+}
+
+int get_sched_policy(int tid, SchedPolicy *policy)
+{
+ initialize();
+
+ if (__sys_supports_schedgroups) {
+ char grpBuf[32];
+ if (getSchedulerGroup(tid, grpBuf, sizeof(grpBuf)) < 0)
+ return -1;
+ if (grpBuf[0] == '\0') {
+ *policy = SP_FOREGROUND;
+ } else if (!strcmp(grpBuf, "bg_non_interactive")) {
+ *policy = SP_BACKGROUND;
+ } else {
+ errno = ERANGE;
+ return -1;
+ }
+ } else {
+ int rc = sched_getscheduler(tid);
+ if (rc < 0)
+ return -1;
+ else if (rc == SCHED_NORMAL)
+ *policy = SP_FOREGROUND;
+ else if (rc == SCHED_BATCH)
+ *policy = SP_BACKGROUND;
+ else {
+ errno = ERANGE;
+ return -1;
+ }
+ }
+ return 0;
+}
+
+int set_sched_policy(int tid, SchedPolicy policy)
+{
+ initialize();
if (__sys_supports_schedgroups) {
const char *grp = NULL;