gh-93180: Update documentation of os.copy_file_range

Doc/library/os.rst

@@ -798,18 +798,31 @@ 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
+   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 as binary.
 
    The return value is the amount of bytes copied. This could be less than the
    amount requested.
 
+   .. note::
+
+      This function should not be used for copying a file from special
+      filesystems like procfs and sysfs because of
+      `a known issue <https://lore.kernel.org/linux-fsdevel/20210126135012.1.If45b7cdc3ff707bc1efa17f5366057d60603c45f@changeid/>`_.
+      It will copy nothing and return 0 because file sizes there are not known
+      to the system.
+
    .. 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.