basic: add make_mount_point_inode helper

Creates a file or a directory depending on the source path, useful
for creating mount points.

src/basic/mountpoint-util.c

@@ -8,14 +8,17 @@
 #include "fd-util.h"
 #include "fileio.h"
 #include "fs-util.h"
+#include "label.h"
 #include "missing_stat.h"
 #include "missing_syscall.h"
+#include "mkdir.h"
 #include "mountpoint-util.h"
 #include "parse-util.h"
 #include "path-util.h"
 #include "stat-util.h"
 #include "stdio-util.h"
 #include "strv.h"
+#include "user-util.h"
 
 /* This is the original MAX_HANDLE_SZ definition from the kernel, when the API was introduced. We use that in place of
  * any more currently defined value to future-proof things: if the size is increased in the API headers, and our code
@@ -509,3 +512,25 @@ int mount_propagation_flags_from_string(const char *name, unsigned long *ret) {
                 return -EINVAL;
         return 0;
 }
+
+int make_mount_point_inode_from_stat(const struct stat *st, const char *dest, mode_t mode) {
+        assert(st);
+        assert(dest);
+
+        if (S_ISDIR(st->st_mode))
+                return mkdir_label(dest, mode);
+        else
+                return mknod(dest, S_IFREG|(mode & ~0111), 0);
+}
+
+int make_mount_point_inode_from_path(const char *source, const char *dest, mode_t mode) {
+        struct stat st;
+
+        assert(source);
+        assert(dest);
+
+        if (stat(source, &st) < 0)
+                return -errno;
+
+        return make_mount_point_inode_from_stat(&st, dest, mode);
+}

src/basic/mountpoint-util.h

@@ -23,3 +23,7 @@ int dev_is_devtmpfs(void);
 
 const char *mount_propagation_flags_to_string(unsigned long flags);
 int mount_propagation_flags_from_string(const char *name, unsigned long *ret);
+
+/* Creates a mount point (not parents) based on the source path or stat - ie, a file or a directory */
+int make_mount_point_inode_from_stat(const struct stat *st, const char *dest, mode_t mode);
+int make_mount_point_inode_from_path(const char *source, const char *dest, mode_t mode);