gh-93180: Update documentation of os.copy_file_range

Doc/library/os.rst

@@ -798,18 +798,33 @@ as internal buffering of data.
    Copy *count* bytes from file descriptor *src*, starting from offset
    *offset_src*, to file descriptor *dst*, starting from offset *offset_dst*.
    If *offset_src* is None, then *src* is read from the current position;
-   respectively for *offset_dst*. The files pointed by *src* and *dst*
+   respectively for *offset_dst*.
+
+   In Linux kernel older than 5.3, the files pointed by *src* and *dst*
    must reside in the same filesystem, otherwise an :exc:`OSError` is
    raised with :attr:`~OSError.errno` set to :data:`errno.EXDEV`.
 
    This copy is done without the additional cost of transferring data
    from the kernel to user space and then back into the kernel. Additionally,
-   some filesystems could implement extra optimizations. The copy is done as if
-   both files are opened as binary.
+   some filesystems could implement extra optimizations, such as the use of
+   reflinks (i.e., two or more inodes that share pointers to the same
+   copy-on-write disk blocks; supported file systems include btrfs and XFS)
+   and server-side copy (in the case of NFS).
+
+   The copy is done as if both files are opened in binary mode, meaning that
+   this function will not convert encodings or line endings even if you have
+   opened the files in text mode for that as described in :ref:`tut-files`.
 
    The return value is the amount of bytes copied. This could be less than the
    amount requested.
 
+   .. note::
+
+      :func:`os.copy_file_range` should not be used for copying a range of a
+      pseudo file from a special filesystem like procfs and sysfs. It will
+      always copy no bytes and return 0 as if the file was empty because of a
+      known Linux kernel issue.
+
    .. availability:: Linux kernel >= 4.5 or glibc >= 2.27.
 
    .. versionadded:: 3.8

Misc/NEWS.d/next/Documentation/2022-05-24-21-30-57.gh-issue-93180.V4yMpc.rst

@@ -0,0 +1 @@
+Update documentation of :func:`os.copy_file_range`. Patch by Illia Volochii.