tmpfile-util: turn last parameter of link_tmpfile() into a proper flags

This changes a boolean param into a proper bitflag field.

Given this only defines a single flag for now this doesn't look like
much of an improvement. But we'll add another flag shortly, where it
starts to make more sense.

src/basic/tmpfile-util.c

@@ -349,7 +349,7 @@ static int link_fd(int fd, int newdirfd, const char *newpath) {
         return RET_NERRNO(linkat(fd, "", newdirfd, newpath, AT_EMPTY_PATH));
 }
 
-int link_tmpfile_at(int fd, int dir_fd, const char *path, const char *target, bool replace) {
+int link_tmpfile_at(int fd, int dir_fd, const char *path, const char *target, LinkTmpfileFlags flags) {
         _cleanup_free_ char *tmp = NULL;
         int r;
 
@@ -362,14 +362,14 @@ int link_tmpfile_at(int fd, int dir_fd, const char *path, const char *target, bo
          * is not supported on the directory, and renameat2() is used instead. */
 
         if (path) {
-                if (replace)
+                if (FLAGS_SET(flags, LINK_TMPFILE_REPLACE))
                         return RET_NERRNO(renameat(dir_fd, path, dir_fd, target));
 
                 return rename_noreplace(dir_fd, path, dir_fd, target);
         }
 
         r = link_fd(fd, dir_fd, target);
-        if (r != -EEXIST || !replace)
+        if (r != -EEXIST || !FLAGS_SET(flags, LINK_TMPFILE_REPLACE))
                 return r;
 
         /* So the target already exists and we were asked to replace it. That sucks a bit, since the kernel's
@@ -394,7 +394,7 @@ int link_tmpfile_at(int fd, int dir_fd, const char *path, const char *target, bo
         return 0;
 }
 
-int flink_tmpfile(FILE *f, const char *path, const char *target, bool replace) {
+int flink_tmpfile(FILE *f, const char *path, const char *target, LinkTmpfileFlags flags) {
         int fd, r;
 
         assert(f);
@@ -408,7 +408,7 @@ int flink_tmpfile(FILE *f, const char *path, const char *target, bool replace) {
         if (r < 0)
                 return r;
 
-        return link_tmpfile(fd, path, target, replace);
+        return link_tmpfile(fd, path, target, flags);
 }
 
 int mkdtemp_malloc(const char *template, char **ret) {

src/basic/tmpfile-util.h

@@ -29,11 +29,16 @@ static inline int open_tmpfile_linkable(const char *target, int flags, char **re
 }
 int fopen_tmpfile_linkable(const char *target, int flags, char **ret_path, FILE **ret_file);
 
-int link_tmpfile_at(int fd, int dir_fd, const char *path, const char *target, bool replace);
-static inline int link_tmpfile(int fd, const char *path, const char *target, bool replace) {
-        return link_tmpfile_at(fd, AT_FDCWD, path, target, replace);
+
+typedef enum LinkTmpfileFlags {
+        LINK_TMPFILE_REPLACE = 1 << 0,
+} LinkTmpfileFlags;
+
+int link_tmpfile_at(int fd, int dir_fd, const char *path, const char *target, LinkTmpfileFlags flags);
+static inline int link_tmpfile(int fd, const char *path, const char *target, LinkTmpfileFlags flags) {
+        return link_tmpfile_at(fd, AT_FDCWD, path, target, flags);
 }
-int flink_tmpfile(FILE *f, const char *path, const char *target, bool replace);
+int flink_tmpfile(FILE *f, const char *path, const char *target, LinkTmpfileFlags flags);
 
 int mkdtemp_malloc(const char *template, char **ret);
 int mkdtemp_open(const char *template, int flags, char **ret);