Use a varargs style prototype in the manual page, with accompanying

explanation in the text.

lib/libc/sys/ioctl.2

@@ -40,7 +40,7 @@
 .Sh SYNOPSIS
 .Fd #include <sys/ioctl.h>
 .Ft int
-.Fn ioctl "int d" "unsigned long request" "char *argp"
+.Fn ioctl "int d" "unsigned long request" "..."
 .Sh DESCRIPTION
 The
 .Fn ioctl
@@ -54,6 +54,19 @@ The argument
 .Fa d
 must be an open file descriptor.
 .Pp
+The third argument to
+.Nm
+is traditionally named
+.Ar "char *argp" .
+Most uses of 
+.Nm
+in
+.Fx 3.0
+however, require the third argument to be a 
+.Ar caddr_t
+or an
+.Ar int .
+.Pp
 An  ioctl
 .Fa request
 has encoded in it whether the argument is an