add method AtLocation.as_emptypath for cloning a location

1 files changed, 17 insertions, 0 deletions

diff --git a/linuxnamespaces/atlocation.py b/linuxnamespaces/atlocation.py
index 6aada55..8da5982 100644
--- a/linuxnamespaces/atlocation.py
+++ b/linuxnamespaces/atlocation.py
@@ -9,6 +9,7 @@ code for doing so.
 
 import enum
 import errno
+import fcntl
 import os
 import os.path
 import pathlib
@@ -102,6 +103,22 @@ class AtLocation:
             os.close(self.fd)
             self.fd = AT_FDCWD
 
+    def as_emptypath(self, inheritable: bool = True) -> "AtLocation":
+        """Return a new AtLocation with flag AT_EMPTY_PATH with a new file
+        descriptor. If self already is an empty path, its fd is duplicated. In
+        all cases, the caller is responsible for closing the result object.
+        """
+        if self.flags & AtFlags.AT_EMPTY_PATH:
+            newfd = fcntl.fcntl(
+                self.fd,
+                fcntl.F_DUPFD if inheritable else fcntl.F_DUPFD_CLOEXEC,
+                0,
+            )
+            return AtLocation(newfd, flags=self.flags)
+        return AtLocation(
+            self.open(flags=os.O_PATH | (0 if inheritable else os.O_CLOEXEC))
+        )
+
     def nosymfollow(self) -> "AtLocation":
         """Return a copy with the AT_SYMLINK_NOFOLLOW set."""
         return AtLocation(