repart: respect SOURCE_DATE_EPOCH on mkdir_p_root

This let's systemd-repart respect the `SOURCE_DATE_EPOCH` environment
variable when creating directories in the local tree through `CopyFiles`
or `MakeDirectories`.

To do this, we pass a timestamp `ts` to `mkdir_p_root`, which it will
use to fix up `mtime` and `atime` of the directory it creates as
well as the `mtime` of the directory it creates the other directory *in*,
as the `mtime` of the latter is modified when creating a directory in it.

For the same reason, it also needs to fixup the `mtime` of the upper
directory when copying a file into it through `CopyFiles`.

If `SOURCE_DATE_EPOCH`, times are left as is. (`UTIME_OMIT`)

src/basic/mkdir.h

@@ -4,6 +4,8 @@
 #include <fcntl.h>
 #include <sys/types.h>
 
+#include "time-util.h"
+
 typedef enum MkdirFlags {
         MKDIR_FOLLOW_SYMLINK  = 1 << 0,
         MKDIR_IGNORE_EXISTING = 1 << 1,  /* Quietly accept a preexisting directory (or file) */
@@ -23,7 +25,10 @@ static inline int mkdir_parents(const char *path, mode_t mode) {
 int mkdir_parents_safe(const char *prefix, const char *path, mode_t mode, uid_t uid, gid_t gid, MkdirFlags flags);
 int mkdir_p(const char *path, mode_t mode);
 int mkdir_p_safe(const char *prefix, const char *path, mode_t mode, uid_t uid, gid_t gid, MkdirFlags flags);
-int mkdir_p_root(const char *root, const char *p, uid_t uid, gid_t gid, mode_t m, char **subvolumes);
+int mkdir_p_root_full(const char *root, const char *p, uid_t uid, gid_t gid, mode_t m, usec_t ts, char **subvolumes);
+static inline int mkdir_p_root(const char *root, const char *p, uid_t uid, gid_t gid, mode_t m) {
+        return mkdir_p_root_full(root, p, uid, gid, m, USEC_INFINITY, NULL);
+}
 
 /* The following are used to implement the mkdir_xyz_label() calls, don't use otherwise. */
 typedef int (*mkdirat_func_t)(int dir_fd, const char *pathname, mode_t mode);