[PATCH v2] cpupower: Implement powercap enabled setters

["Mateusz Jaśkiewicz" <jaskiewiczteo@gmail.com>]

powercap_set_enabled() and powercap_zone_set_enabled() are part of the
public libcpupower API, but both currently return success without
updating sysfs.

Write the requested value to the matching enabled attribute so callers
can actually enable or disable the powercap control type or zone, and
report write failures back to the caller.

---
Changes in v2:
- Check current enabled value before writing.
- Use fd < 0 style for open() failures.
- Print sysfs open/write failures with perror().
- Drop the sizeof(path) typecast.

Signed-off-by: Mateusz Jaśkiewicz <jaskiewiczteo@gmail.com>
---
 tools/power/cpupower/lib/powercap.c | 58 +++++++++++++++++++++++------
 1 file changed, 47 insertions(+), 11 deletions(-)

diff --git a/tools/power/cpupower/lib/powercap.c b/tools/power/cpupower/lib/powercap.c
index 94a0c69e5..80af65287 100644
--- a/tools/power/cpupower/lib/powercap.c
+++ b/tools/power/cpupower/lib/powercap.c
@@ -21,7 +21,7 @@ static unsigned int sysfs_read_file(const char *path, char *buf, size_t buflen)
 	ssize_t numread;
 
 	fd = open(path, O_RDONLY);
-	if (fd == -1)
+	if (fd < 0)
 		return 0;
 
 	numread = read(fd, buf, buflen - 1);
@@ -36,7 +36,7 @@ static unsigned int sysfs_read_file(const char *path, char *buf, size_t buflen)
 	return (unsigned int) numread;
 }
 
-static int sysfs_get_enabled(char *path, int *mode)
+static int sysfs_get_enabled(const char *path, int *mode)
 {
 	int fd;
 	char yes_no;
@@ -45,7 +45,7 @@ static int sysfs_get_enabled(char *path, int *mode)
 	*mode = 0;
 
 	fd = open(path, O_RDONLY);
-	if (fd == -1) {
+	if (fd < 0) {
 		ret = -1;
 		goto out;
 	}
@@ -70,6 +70,36 @@ static int sysfs_get_enabled(char *path, int *mode)
 	return ret;
 }
 
+static int sysfs_set_enabled(const char *path, int mode)
+{
+	char yes_no;
+	int fd;
+	int current_mode;
+	ssize_t ret;
+
+	if (mode != 0 && mode != 1)
+		return -1;
+
+	if (sysfs_get_enabled(path, &current_mode) == 0 &&
+	    current_mode == mode)
+		return 0;
+
+	yes_no = mode ? '1' : '0';
+	fd = open(path, O_WRONLY);
+	if (fd < 0) {
+		perror(path);
+		return -1;
+	}
+	ret = write(fd, &yes_no, 1);
+	if (ret != 1) {
+		if (ret < 0)
+			perror(path);
+		close(fd);
+		return -1;
+	}
+	return close(fd);
+}
+
 int powercap_get_enabled(int *mode)
 {
 	char path[SYSFS_PATH_MAX] = PATH_TO_POWERCAP "/intel-rapl/enabled";
@@ -77,17 +107,13 @@ int powercap_get_enabled(int *mode)
 	return sysfs_get_enabled(path, mode);
 }
 
-/*
- * TODO: implement function. Returns dummy 0 for now.
- */
 int powercap_set_enabled(int mode)
 {
-	return 0;
+	return sysfs_set_enabled(PATH_TO_RAPL "/enabled", mode);
 }
-
 /*
  * Hardcoded, because rapl is the only powercap implementation
-- * this needs to get more generic if more powercap implementations
+ * this needs to get more generic if more powercap implementations
  * should show up
  */
 int powercap_get_driver(char *driver, int buflen)
@@ -180,8 +206,18 @@ int powercap_zone_get_enabled(struct powercap_zone *zone, int *mode)
 
 int powercap_zone_set_enabled(struct powercap_zone *zone, int mode)
 {
-	/* To be done if needed */
-	return 0;
+	char path[SYSFS_PATH_MAX];
+	int ret;
+
+	if (!zone)
+		return -1;
+
+	ret = snprintf(path, sizeof(path), "%s/%s/enabled",
+		       PATH_TO_POWERCAP, zone->sys_name);
+	if (ret < 0 || ret >= sizeof(path))
+		return -1;
+
+	return sysfs_set_enabled(path, mode);
 }
 
 
-- 
2.54.0