From 937060a8433525dc6ed7857ffd2b661719a5683c Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Mon, 28 Mar 2011 13:21:26 +0000
Subject: [PATCH] Handle zero length in copyout_unmap().

Submitted by:	John Wehle <john feith com>
MFC after:	2 weeks
---
 sys/kern/subr_uio.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/sys/kern/subr_uio.c b/sys/kern/subr_uio.c
index 8304aeaf2d80..d8fa68f37e0b 100644
--- a/sys/kern/subr_uio.c
+++ b/sys/kern/subr_uio.c
@@ -498,6 +498,9 @@ copyout_unmap(struct thread *td, vm_offset_t addr, size_t sz)
 	vm_map_t map;
 	vm_size_t size;
     
+	if (sz == 0)
+		return (0);
+
 	map = &td->td_proc->p_vmspace->vm_map;
 	size = (vm_size_t) round_page(sz);