cpupower: Better detect offlined CPUs
[linux-2.6.git] / tools / power / cpupower / utils / helpers / sysfs.c
index 55e2466..c634302 100644 (file)
@@ -56,6 +56,56 @@ static unsigned int sysfs_write_file(const char *path,
        return (unsigned int) numwrite;
 }
 
+/*
+ * Detect whether a CPU is online
+ *
+ * Returns:
+ *     1 -> if CPU is online
+ *     0 -> if CPU is offline
+ *     negative errno values in error case
+ */
+int sysfs_is_cpu_online(unsigned int cpu)
+{
+       char path[SYSFS_PATH_MAX];
+       int fd;
+       ssize_t numread;
+       unsigned long long value;
+       char linebuf[MAX_LINE_LEN];
+       char *endp;
+       struct stat statbuf;
+
+       snprintf(path, sizeof(path), PATH_TO_CPU "cpu%u", cpu);
+
+       if (stat(path, &statbuf) != 0)
+               return 0;
+
+       /*
+        * kernel without CONFIG_HOTPLUG_CPU
+        * -> cpuX directory exists, but not cpuX/online file
+        */
+       snprintf(path, sizeof(path), PATH_TO_CPU "cpu%u/online", cpu);
+       if (stat(path, &statbuf) != 0)
+               return 1;
+
+       fd = open(path, O_RDONLY);
+       if (fd == -1)
+               return -errno;
+
+       numread = read(fd, linebuf, MAX_LINE_LEN - 1);
+       if (numread < 1) {
+               close(fd);
+               return -EIO;
+       }
+       linebuf[numread] = '\0';
+       close(fd);
+
+       value = strtoull(linebuf, &endp, 0);
+       if (value > 1 || value < 0)
+               return -EINVAL;
+
+       return value;
+}
+
 /* CPUidle idlestate specific /sys/devices/system/cpu/cpuX/cpuidle/ access */
 
 /*