ppd-utils: Use simpler write without extra copies

Simplify our writing function by just using pure C open/write calls
since we don't really need to be able to create files.

In fact this made possible to spot a test issue where a file was not
present and in fact in some scenarios we had random valgrind errors in
CI.

Plus, since we just need to write the contents as it is, we can avoid
extra buffers.

src/ppd-utils.c

@@ -10,7 +10,9 @@
 #define G_LOG_DOMAIN "Utils"
 
 #include "ppd-utils.h"
+#include <glib/gstdio.h>
 #include <gio/gio.h>
+#include <fcntl.h>
 #include <stdio.h>
 #include <errno.h>
 
@@ -26,39 +28,42 @@ ppd_utils_get_sysfs_path (const char *filename)
   return g_build_filename (root, filename, NULL);
 }
 
-gboolean ppd_utils_write (const char  *filename,
-                          const char  *value,
-                          GError     **error)
+gboolean
+ppd_utils_write (const char  *filename,
+                 const char  *value,
+                 GError     **error)
 {
-  FILE *sysfsfp;
-  int ret;
+  g_autofd int fd = -1;
+  size_t size;
 
   g_return_val_if_fail (filename, FALSE);
   g_return_val_if_fail (value, FALSE);
 
   g_debug ("Writing '%s' to '%s'", value, filename);
 
-  sysfsfp = fopen (filename, "w");
-  if (sysfsfp == NULL) {
+  fd = g_open (filename, O_WRONLY | O_TRUNC | O_SYNC);
+  if (fd == -1) {
     g_set_error (error, G_IO_ERROR, g_io_error_from_errno (errno),
                  "Could not open '%s' for writing", filename);
     g_debug ("Could not open for writing '%s'", filename);
     return FALSE;
   }
-  setbuf (sysfsfp, NULL);
-  ret = fprintf (sysfsfp, "%s", value);
-  if (ret <= 0) {
-    g_set_error (error, G_IO_ERROR, g_io_error_from_errno (errno),
-                 "Error writing '%s': %s", filename, g_strerror (errno));
-    g_debug ("Error writing '%s': %s", filename, g_strerror (errno));
-    return FALSE;
-  }
-  if (fclose (sysfsfp) != 0) {
-    g_set_error (error, G_IO_ERROR, g_io_error_from_errno (errno),
-                 "Error closing '%s': %s", filename, g_strerror (errno));
-    g_debug ("Error closing '%s': %s", filename, g_strerror (errno));
-    return FALSE;
+
+  size = strlen (value);
+  while (size) {
+    ssize_t written = write (fd, value, size);
+
+    if (written == -1) {
+      g_set_error (error, G_IO_ERROR, g_io_error_from_errno (errno),
+                   "Error writing '%s': %s", filename, g_strerror (errno));
+      g_debug ("Error writing '%s': %s", filename, g_strerror (errno));
+      return FALSE;
+    }
+
+    g_return_val_if_fail (written <= size, FALSE);
+    size -= written;
   }
+
   return TRUE;
 }
 

tests/integration_test.py

@@ -735,6 +735,8 @@ class Tests(dbusmock.DBusTestCase):
             self.testbed.get_root_dir(), "sys/devices/system/cpu/cpufreq/policy0/"
         )
         os.makedirs(dir1)
+        gov_path = os.path.join(dir1, "scaling_governor")
+        self.write_file_contents(gov_path, "performance\n")
         energy_prefs = os.path.join(dir1, "energy_performance_preference")
         self.write_file_contents(energy_prefs, "performance\n")
         pstate_dir = os.path.join(