env-file: port write_env_file() to label_ops_pre()

Let's make more use of label_ops_pre()/label_ops_post(), and replace
write_env_file_label() by a flag to write_env_file().

This simplifies and normalizes the code.

This also makes one relevant change: it sets the new
WRITE_ENV_FILE_LABEL flag in firstboot.c when we write locale.conf,
where we previously did not (but should have). This should address one
detail of #37857.

src/shared/env-file-label.c

@@ -1,35 +0,0 @@
-/* SPDX-License-Identifier: LGPL-2.1-or-later */
-
-#include <sys/stat.h>
-
-#include "env-file.h"
-#include "env-file-label.h"
-#include "selinux-util.h"
-
-int write_env_file_label(int dir_fd, const char *fname, char **headers, char **l) {
-        int r;
-
-        r = mac_selinux_create_file_prepare(fname, S_IFREG);
-        if (r < 0)
-                return r;
-
-        r = write_env_file(dir_fd, fname, headers, l);
-
-        mac_selinux_create_file_clear();
-
-        return r;
-}
-
-int write_vconsole_conf_label(char **l) {
-        int r;
-
-        r = mac_selinux_create_file_prepare("/etc/vconsole.conf", S_IFREG);
-        if (r < 0)
-                return r;
-
-        r = write_vconsole_conf(AT_FDCWD, "/etc/vconsole.conf", l);
-
-        mac_selinux_create_file_clear();
-
-        return r;
-}

src/shared/env-file-label.h

@@ -1,12 +0,0 @@
-/* SPDX-License-Identifier: LGPL-2.1-or-later */
-#pragma once
-
-#include "forward.h"
-
-/* These functions are split out of fileio.h (and not for example just flags to the functions they wrap) in order to
- * optimize linking: This way, -lselinux is needed only for the callers of these functions that need selinux, but not
- * for all */
-
-int write_env_file_label(int dir_fd, const char *fname, char **headers, char **l);
-
-int write_vconsole_conf_label(char **l);

src/shared/locale-setup.c

@@ -6,7 +6,6 @@
 
 #include "alloc-util.h"
 #include "env-file.h"
-#include "env-file-label.h"
 #include "env-util.h"
 #include "errno-util.h"
 #include "fd-util.h"
@@ -212,7 +211,12 @@ int locale_context_save(LocaleContext *c, char ***ret_set, char ***ret_unset) {
                 return 0;
         }
 
-        r = write_env_file_label(AT_FDCWD, "/etc/locale.conf", NULL, set);
+        r = write_env_file(
+                        AT_FDCWD,
+                        "/etc/locale.conf",
+                        /* headers= */ NULL,
+                        set,
+                        WRITE_ENV_FILE_LABEL);
         if (r < 0)
                 return r;
 

src/shared/meson.build

@@ -68,7 +68,6 @@ shared_sources = files(
         'efi-loader.c',
         'elf-util.c',
         'enable-mempool.c',
-        'env-file-label.c',
         'ethtool-util.c',
         'exec-util.c',
         'exit-status.c',