link.2: Glibc falls back to link() on kernels that lack linkat()

Unless 'flags' contains AT_SYMLINK_FOLLOW.

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

man2/link.2

@@ -382,6 +382,26 @@ is dereferenced if it is a symbolic link.
 For precise control over the treatment of symbolic links when
 creating a link, use
 .BR linkat (2).
+.SS Glibc notes
+On older kernels where
+.BR linkat ()
+is unavailable, the glibc wrapper function falls back to the use of
+.BR link (),
+unless the
+.B AT_SYMLINK_FOLLOW
+is specified.
+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, the return code may be wrong in case the NFS server
 performs the link creation and dies before it can say so.