cgroup: never try to create files in cgroupfs, only open them for writing

This should have the benefit that cg_set_attribute() returns ENOENT
instead of EACCESS when we use it for non-existing attributes.

1 files changed, 22 insertions, 0 deletions

diff --git a/src/shared/fileio.c b/src/shared/fileio.c
index cbb40c2379..18960abf02 100644
--- a/src/shared/fileio.c
+++ b/src/shared/fileio.c
@@ -58,6 +58,28 @@ int write_string_file(const char *fn, const char *line) {
         return write_string_stream(f, line);
 }
 
+int write_string_file_no_create(const char *fn, const char *line) {
+        _cleanup_fclose_ FILE *f = NULL;
+        int fd;
+
+        assert(fn);
+        assert(line);
+
+        /* We manually build our own version of fopen(..., "we") that
+         * without O_CREAT */
+        fd = open(fn, O_WRONLY|O_CLOEXEC|O_NOCTTY);
+        if (fd < 0)
+                return -errno;
+
+        f = fdopen(fd, "we");
+        if (!f) {
+                safe_close(fd);
+                return -errno;
+        }
+
+        return write_string_stream(f, line);
+}
+
 int write_string_file_atomic(const char *fn, const char *line) {
         _cleanup_fclose_ FILE *f = NULL;
         _cleanup_free_ char *p = NULL;