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/basic/env-file.c

@@ -5,10 +5,12 @@
 #include "alloc-util.h"
 #include "env-file.h"
 #include "env-util.h"
+#include "errno-util.h"
 #include "escape.h"
 #include "fd-util.h"
 #include "fileio.h"
 #include "fs-util.h"
+#include "label.h"
 #include "log.h"
 #include "string-util.h"
 #include "strv.h"
@@ -629,7 +631,7 @@ static void write_env_var(FILE *f, const char *v) {
         fputc_unlocked('\n', f);
 }
 
-int write_env_file(int dir_fd, const char *fname, char **headers, char **l) {
+int write_env_file(int dir_fd, const char *fname, char **headers, char **l, WriteEnvFileFlags flags) {
         _cleanup_fclose_ FILE *f = NULL;
         _cleanup_free_ char *p = NULL;
         int r;
@@ -637,7 +639,18 @@ int write_env_file(int dir_fd, const char *fname, char **headers, char **l) {
         assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
         assert(fname);
 
+        bool call_label_ops_post = false;
+        if (FLAGS_SET(flags, WRITE_ENV_FILE_LABEL)) {
+                r = label_ops_pre(dir_fd, fname, S_IFREG);
+                if (r < 0)
+                        return r;
+
+                call_label_ops_post = true;
+        }
+
         r = fopen_tmpfile_linkable_at(dir_fd, fname, O_WRONLY|O_CLOEXEC, &p, &f);
+        if (call_label_ops_post)
+                RET_GATHER(r, label_ops_post(f ? fileno(f) : dir_fd, f ? NULL : fname, /* created= */ !!f));
         if (r < 0)
                 return r;
 
@@ -672,5 +685,5 @@ int write_vconsole_conf(int dir_fd, const char *fname, char **l) {
                 "# Written by systemd-localed(8) or systemd-firstboot(1), read by systemd-localed",
                 "# and systemd-vconsole-setup(8). Use localectl(1) to update this file.");
 
-        return write_env_file(dir_fd, fname, headers, l);
+        return write_env_file(dir_fd, fname, headers, l, WRITE_ENV_FILE_LABEL);
 }

src/basic/env-file.h

@@ -15,7 +15,11 @@ int load_env_file_pairs_fd(int fd, const char *fname, char ***ret);
 
 int merge_env_file(char ***env, FILE *f, const char *fname);
 
-int write_env_file(int dir_fd, const char *fname, char **headers, char **l);
+typedef enum WriteEnvFileFlags {
+        WRITE_ENV_FILE_LABEL = 1 << 0,
+} WriteEnvFileFlags;
+
+int write_env_file(int dir_fd, const char *fname, char **headers, char **l, WriteEnvFileFlags flags);
 
 int write_vconsole_conf(int dir_fd, const char *fname, char **l);