1 files changed, 50 insertions, 0 deletions

diff --git a/tools/power/cpupower/utils/helpers/sysfs.c b/tools/power/cpupower/utils/helpers/sysfs.c
index 55e2466674c6..c6343024a611 100644
--- a/tools/power/cpupower/utils/helpers/sysfs.c
+++ b/tools/power/cpupower/utils/helpers/sysfs.c
@@ -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 */
 
 /*