commit 2e336b1da1ed66e943089c812f7697f5de450936
author John Reck <jreck@google.com> Fri Aug 26 13:43:19 2016 -0700
committer John Reck <jreck@google.com> Fri Aug 26 14:05:03 2016 -0700
tree 8f4a4e15a7e102299a65a12d9b24bdd139a4b3e5
parent 091b631915c68c801bbded01ac8bb3a7af18436e

Fix access check

Fixes a bug where USE_CPUSET used access(F_OK)
as a sign that it should try writing to the cpuset
path. It needs to instead use access(W_OK) to
ensure that it has write access as that's what
it would try to open() with.

And stop trying to repeatedly open a file that
doesn't exist.

Change-Id: Ib391ee6f08345051c48a986a732eda30143cb614

libcutils/sched_policy.c

diff --git a/libcutils/sched_policy.c b/libcutils/sched_policy.c
index 32e6c25..ad5671b 100644
--- a/libcutils/sched_policy.c
+++ b/libcutils/sched_policy.c
@@ -52,6 +52,7 @@
 static pthread_once_t the_once = PTHREAD_ONCE_INIT;
 
 static int __sys_supports_schedgroups = -1;
+static int __sys_supports_timerslack = -1;
 
 // File descriptors open to /dev/cpuctl/../tasks, setup by initialize, or -1 on error.
 static int bg_cgroup_fd = -1;
@@ -104,7 +105,7 @@
 
 static void __initialize(void) {
     char* filename;
-    if (!access("/dev/cpuctl/tasks", F_OK)) {
+    if (!access("/dev/cpuctl/tasks", W_OK)) {
         __sys_supports_schedgroups = 1;
 
         filename = "/dev/cpuctl/tasks";
@@ -123,7 +124,7 @@
     }
 
 #ifdef USE_CPUSETS
-    if (!access("/dev/cpuset/tasks", F_OK)) {
+    if (!access("/dev/cpuset/tasks", W_OK)) {
 
         filename = "/dev/cpuset/foreground/tasks";
         fg_cpuset_fd = open(filename, O_WRONLY | O_CLOEXEC);
@@ -142,6 +143,10 @@
 #endif
     }
 #endif
+
+    char buf[64];
+    snprintf(buf, sizeof(buf), "/proc/%d/timerslack_ns", getpid());
+    __sys_supports_timerslack = !access(buf, W_OK);
 }
 
 /*
@@ -417,8 +422,10 @@
                            &param);
     }
 
-    set_timerslack_ns(tid, policy == SP_BACKGROUND ?
+    if (__sys_supports_timerslack) {
+        set_timerslack_ns(tid, policy == SP_BACKGROUND ?
                                TIMER_SLACK_BG : TIMER_SLACK_FG);
+    }
 
     return 0;
 }