From 0f9e55b1061457d40a93e39bf88ec59f010fc856 Mon Sep 17 00:00:00 2001
From: Matthew Dillon <dillon@apollo.backplane.com>
Date: Sat, 26 Mar 2011 15:15:34 -0700
Subject: [PATCH] kernel - Change mbuf allocation in tapwrite/tunwrite path to
 blocking

* Tapwrite and tunwrite are called via userland, a blocking mbuf allocation
  is perfectly acceptable here and avoids dropping packets unnecessarily.

* Fixes numerous spurious packet drops when using TAP or TUN, for example
  with openvpn.

* Minor code cleanup in if_tap.c
---
 sys/net/tap/if_tap.c | 12 +++++++-----
 sys/net/tun/if_tun.c |  6 +++---
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/sys/net/tap/if_tap.c b/sys/net/tap/if_tap.c
index 35152eaa2a..fb74f2785a 100644
--- a/sys/net/tap/if_tap.c
+++ b/sys/net/tap/if_tap.c
@@ -890,7 +890,7 @@ tapwrite(struct dev_write_args *ap)
 	struct tap_softc	*tp = dev->si_drv1;
 	struct ifnet		*ifp = &tp->tap_if;
 	struct mbuf		*top = NULL, **mp = NULL, *m = NULL;
-	int			error = 0;
+	int			error;
 	size_t			tlen, mlen;
 
 	TAPDEBUG(ifp, "writing, minor = %#x\n", minor(tp->tap_dev));
@@ -913,20 +913,22 @@ tapwrite(struct dev_write_args *ap)
 	tlen = uio->uio_resid;
 
 	/* get a header mbuf */
-	MGETHDR(m, MB_DONTWAIT, MT_DATA);
+	MGETHDR(m, MB_WAIT, MT_DATA);
 	if (m == NULL)
 		return (ENOBUFS);
 	mlen = MHLEN;
 
-	top = 0;
+	top = NULL;
 	mp = &top;
-	while ((error == 0) && (uio->uio_resid > 0)) {
+	error = 0;
+
+	while (error == 0 && uio->uio_resid > 0) {
 		m->m_len = (int)szmin(mlen, uio->uio_resid);
 		error = uiomove(mtod(m, caddr_t), (size_t)m->m_len, uio);
 		*mp = m;
 		mp = &m->m_next;
 		if (uio->uio_resid > 0) {
-			MGET(m, MB_DONTWAIT, MT_DATA);
+			MGET(m, MB_WAIT, MT_DATA);
 			if (m == NULL) {
 				error = ENOBUFS;
 				break;
diff --git a/sys/net/tun/if_tun.c b/sys/net/tun/if_tun.c
index 54cb34fdff..4be909d078 100644
--- a/sys/net/tun/if_tun.c
+++ b/sys/net/tun/if_tun.c
@@ -602,12 +602,12 @@ tunwrite(struct dev_write_args *ap)
 	tlen = uio->uio_resid;
 
 	/* get a header mbuf */
-	MGETHDR(m, MB_DONTWAIT, MT_DATA);
+	MGETHDR(m, MB_WAIT, MT_DATA);
 	if (m == NULL)
 		return ENOBUFS;
 	mlen = MHLEN;
 
-	top = 0;
+	top = NULL;
 	mp = &top;
 	while (error == 0 && uio->uio_resid > 0) {
 		m->m_len = (int)szmin(mlen, uio->uio_resid);
@@ -615,7 +615,7 @@ tunwrite(struct dev_write_args *ap)
 		*mp = m;
 		mp = &m->m_next;
 		if (uio->uio_resid > 0) {
-			MGET (m, MB_DONTWAIT, MT_DATA);
+			MGET (m, MB_WAIT, MT_DATA);
 			if (m == 0) {
 				error = ENOBUFS;
 				break;
-- 
2.41.0