RETURN VALUE: note that errno is set on error.

Add EINVAL error.
ffix

man3/getpw.3

@@ -67,16 +67,23 @@ struct passwd {
 .SH "RETURN VALUE"
 The
 .BR getpw ()
-function returns 0 on success, or \-1 if an error
-occurs.
+function returns 0 on success; on error, it returns \-1, and
+.I errno
+is set to indicate the error.
 .SH ERRORS
 .TP
+.B EINVAL
+.I buf
+is NULL.
+.TP
 .B ENOENT
 No user corresponding to
 .IR uid .
 .TP
 .B ENOMEM
-Insufficient memory to allocate passwd structure.
+Insufficient memory to allocate
+.I passwd
+structure.
 .SH FILES
 .TP
 .I /etc/passwd