rename.2: Glibc falls back to rename() when the kernel doesn't have renameat()

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/rename.2

@@ -411,6 +411,24 @@ POSIX.1-2008.
 
 .BR renameat2 ()
 is Linux-specific.
+.SH NOTES
+.SS Glibc notes
+On older kernels where
+.BR renameat ()
+is unavailable, the glibc wrapper function falls back to the use of
+.BR rename ().
+When
+.I oldpath
+and
+.I newpath
+are relative pathnames,
+glibc constructs pathnames based on the symbolic links in
+.IR /proc/self/fd
+that correspond to the
+.I olddirfd
+and
+.IR newdirfd
+arguments.
 .SH BUGS
 On NFS filesystems, you can not assume that if the operation
 failed, the file was not renamed.