[3.13] gh-81520: Document unexpected `os.path.ismount` behaviour with btrfs subvolume...

gh-81520: Document unexpected `os.path.ismount` behaviour with btrfs subvolumes (GH-136058)
(cherry picked from commit 591abcc01fcf1c65c7fdfaca7274f5d3f9f022da)

Co-authored-by: Oskar Roesler <o.roesler@oscloud.info>

diff --git a/Doc/library/os.path.rst b/Doc/library/os.path.rst
index 8713581d1c05edaf836021dec392302ca56dba09..35cfb96ba09564a6fb76696bb0758a5328c9b153 100644 (file)
--- a/Doc/library/os.path.rst
+++ b/Doc/library/os.path.rst
@@ -298,9 +298,10 @@ the :mod:`glob` module.)
    device than *path*, or whether :file:`{path}/..` and *path* point to the same
    i-node on the same device --- this should detect mount points for all Unix
    and POSIX variants.  It is not able to reliably detect bind mounts on the
-   same filesystem.  On Windows, a drive letter root and a share UNC are
-   always mount points, and for any other path ``GetVolumePathName`` is called
-   to see if it is different from the input path.
+   same filesystem. On Linux systems, it will always return ``True`` for btrfs
+   subvolumes, even if they aren't mount points. On Windows, a drive letter root
+   and a share UNC are always mount points, and for any other path
+   ``GetVolumePathName`` is called to see if it is different from the input path.
 
    .. versionchanged:: 3.4
       Added support for detecting non-root mount points on Windows.