Add get_sched_policy_name() and use in ps and top

This will make it easier to add additional policies (cgroups) if needed.
Also added comments to the sched_policy APIs.

Change-Id: I33ce1cc4deae10983241f7391294b7a512d2c47c

include/cutils/sched_policy.h

@@ -24,11 +24,28 @@ extern "C" {
 typedef enum {
     SP_BACKGROUND = 0,
     SP_FOREGROUND = 1,
+    SP_CNT,
+    SP_MAX        = SP_CNT - 1,
 } SchedPolicy;
 
+/* Assign thread tid to the cgroup associated with the specified policy.
+ * If the thread is a thread group leader, that is it's gettid() == getpid(),
+ * then the other threads in the same thread group are _not_ affected.
+ * Return value: 0 for success, or -errno for error.
+ */
 extern int set_sched_policy(int tid, SchedPolicy policy);
+
+/* Return the policy associated with the cgroup of thread tid via policy pointer.
+ * Return value: 0 for success, or -1 for error and set errno.
+ */
 extern int get_sched_policy(int tid, SchedPolicy *policy);
 
+/* Return a displayable string corresponding to policy.
+ * Return value: non-NULL NUL-terminated name of unspecified length;
+ * the caller is responsible for displaying the useful part of the string.
+ */
+extern const char *get_sched_policy_name(SchedPolicy policy);
+
 #ifdef __cplusplus
 }
 #endif

libcutils/sched_policy.c

@@ -273,5 +273,17 @@ int set_sched_policy(int tid, SchedPolicy policy)
     return 0;
 }
 
+const char *get_sched_policy_name(SchedPolicy policy)
+{
+    static const char * const strings[SP_CNT] = {
+       [SP_BACKGROUND] = "bg",
+       [SP_FOREGROUND] = "fg",
+    };
+    if ((policy < SP_CNT) && (strings[policy] != NULL))
+        return strings[policy];
+    else
+        return "error";
+}
+
 #endif /* HAVE_PTHREADS */
 #endif /* HAVE_SCHED_H */

toolbox/ps.c

@@ -167,14 +167,8 @@ static int ps_line(int pid, int tid, char *namefilter)
             SchedPolicy p;
             if (get_sched_policy(pid, &p) < 0)
                 printf(" un ");
-            else {
-                if (p == SP_BACKGROUND)
-                    printf(" bg ");
-                else if (p == SP_FOREGROUND)
-                    printf(" fg ");
-                else
-                    printf(" er ");
-            }
+            else
+                printf(" %.2s ", get_sched_policy_name(p));
         }
         printf(" %08x %08x %s %s", wchan, eip, state, cmdline[0] ? cmdline : name);
         if(display_flags&SHOW_TIME)

toolbox/top.c

@@ -48,6 +48,7 @@ struct cpu_info {
 
 #define PROC_NAME_LEN 64
 #define THREAD_NAME_LEN 32
+#define POLICY_NAME_LEN 4
 
 struct proc_info {
     struct proc_info *next;
@@ -67,7 +68,7 @@ struct proc_info {
     long rss;
     int prs;
     int num_threads;
-    char policy[32];
+    char policy[POLICY_NAME_LEN];
 };
 
 struct proc_list {
@@ -381,14 +382,10 @@ static int read_cmdline(char *filename, struct proc_info *proc) {
 static void read_policy(int pid, struct proc_info *proc) {
     SchedPolicy p;
     if (get_sched_policy(pid, &p) < 0)
-        strcpy(proc->policy, "unk");
+        strlcpy(proc->policy, "unk", POLICY_NAME_LEN);
     else {
-        if (p == SP_BACKGROUND)
-            strcpy(proc->policy, "bg");
-        else if (p == SP_FOREGROUND)
-            strcpy(proc->policy, "fg");
-        else
-            strcpy(proc->policy, "er");
+        strlcpy(proc->policy, get_sched_policy_name(p), POLICY_NAME_LEN);
+        proc->policy[2] = '\0';
     }
 }