util/path: new clamp mtime function

New utility function to clamp all mtimes of a given path to a
certain timestamp. Clamp here means that any timestamp later
than the specified upper bound will be set to the upper bound.

osbuild/util/path.py

@@ -1,5 +1,36 @@
 """Path handling utility functions"""
+import errno
 import os
+import os.path
+from typing import Optional
+
+from .ctx import suppress_oserror
+
+
+def clamp_mtime(path: str, start: int, to: int):
+    """Clamp all modification times of 'path'
+
+    Set the mtime of 'path' to 'to' if it is greater or equal to 'start'.
+    If 'to' is None, the mtime is set to the current time.
+    """
+
+    times = (to, to)
+
+    def fix_utime(path, dfd: Optional[int] = None):
+        sb = os.stat(path, dir_fd=dfd, follow_symlinks=False)
+        if sb.st_mtime < start:
+            return
+
+        # We might get a permission error when the immutable flag is set;
+        # since there is nothing much we can do, we just ignore it
+        with suppress_oserror(errno.EPERM):
+            os.utime(path, times, dir_fd=dfd, follow_symlinks=False)
+
+    fix_utime(path)
+
+    for _, dirs, files, dfd in os.fwalk(path):
+        for f in dirs + files:
+            fix_utime(f, dfd)
 
 
 def in_tree(path: str, tree: str, must_exist: bool = False) -> bool: