chown.2: Glibc falls back to chown()/lchown() on kernels that lack fchownat()

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

man2/chown.2

@@ -377,6 +377,21 @@ mount options are supported by ext2, ext3, ext4, and XFS.
 Filesystems that don't support these mount options follow the
 .IR "\-o\ nogrpid"
 rules.
+.SS Glibc notes
+On older kernels where
+.BR fchownat ()
+is unavailable, the glibc wrapper function falls back to the use of
+.BR chown ()
+and
+.BR lchown ().
+When
+.I pathname
+is a relative pathname,
+glibc constructs a pathname based on the symbolic link in
+.IR /proc/self/fd
+that corresponds to the
+.IR dirfd
+argument.
 .SS NFS
 The
 .BR chown ()