Make fopen_temporary and fopen_temporary_label unlocked

This is partially a refactoring, but also makes many more places use
unlocked operations implicitly, i.e. all users of fopen_temporary().
AFAICT, the uses are always for short-lived files which are not shared
externally, and are just used within the same context. Locking is not
necessary.

src/basic/cgroup-util.c

@@ -6,7 +6,6 @@
 #include <limits.h>
 #include <signal.h>
 #include <stddef.h>
-#include <stdio_ext.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>

src/basic/env-file.c

@@ -1,7 +1,5 @@
 /* SPDX-License-Identifier: LGPL-2.1+ */
 
-#include <stdio_ext.h>
-
 #include "alloc-util.h"
 #include "env-file.h"
 #include "env-util.h"
@@ -545,7 +543,6 @@ int write_env_file(const char *fname, char **l) {
         if (r < 0)
                 return r;
 
-        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
         (void) fchmod_umask(fileno(f), 0644);
 
         STRV_FOREACH(i, l)

src/basic/fileio.c

@@ -108,7 +108,6 @@ static int write_string_file_atomic(
         if (r < 0)
                 return r;
 
-        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
         (void) fchmod_umask(fileno(f), 0644);
 
         r = write_string_stream_ts(f, line, flags, ts);
@@ -154,11 +153,9 @@ int write_string_file_ts(
                 assert(!ts);
 
         if (flags & WRITE_STRING_FILE_CREATE) {
-                f = fopen(fn, "we");
-                if (!f) {
-                        r = -errno;
+                r = fopen_unlocked(fn, "we", &f);
+                if (r < 0)
                         goto fail;
-                }
         } else {
                 int fd;
 
@@ -176,9 +173,9 @@ int write_string_file_ts(
                         safe_close(fd);
                         goto fail;
                 }
-        }
 
-        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+                (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+        }
 
         if (flags & WRITE_STRING_FILE_DISABLE_BUFFER)
                 setvbuf(f, NULL, _IONBF, 0);

src/basic/mountpoint-util.c

@@ -2,7 +2,6 @@
 
 #include <errno.h>
 #include <fcntl.h>
-#include <stdio_ext.h>
 #include <sys/mount.h>
 
 #include "alloc-util.h"

src/basic/process-util.c

@@ -8,7 +8,6 @@
 #include <signal.h>
 #include <stdbool.h>
 #include <stdio.h>
-#include <stdio_ext.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/mman.h>

src/basic/tmpfile-util.c

@@ -1,5 +1,7 @@
 /* SPDX-License-Identifier: LGPL-2.1+ */
 
+#include <stdio.h>
+#include <stdio_ext.h>
 #include <sys/mman.h>
 
 #include "alloc-util.h"
@@ -37,6 +39,9 @@ int fopen_temporary(const char *path, FILE **_f, char **_temp_path) {
                 return -errno;
         }
 
+        /* This assumes that returned FILE object is short-lived and used within the same single-threaded
+         * context and never shared externally, hence locking is not necessary. */
+
         f = fdopen(fd, "w");
         if (!f) {
                 unlink_noerrno(t);
@@ -45,6 +50,8 @@ int fopen_temporary(const char *path, FILE **_f, char **_temp_path) {
                 return -errno;
         }
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         *_f = f;
         *_temp_path = t;