From: Herbert Xu <herbert.xu@redhat.com>
Date: Thu, 4 Jun 2009 21:17:05 +1000
Subject: [tun] use non-linear packets where possible
Message-id: 20090604111705.GB28526@gondor.apana.org.au
O-Subject: [RHEL5.4 PATCH 2/2] tun: Use non-linear packets where possible
Bugzilla: 503309
RH-Acked-by: Thomas Graf <tgraf@redhat.com>
RH-Acked-by: David Miller <davem@redhat.com>

RHEL5 bugzilla 503309

On Thu, Jun 04, 2009 at 09:15:56PM +1000, Herbert Xu wrote:

> This back was incomplete, here's the corrected version.  First we
> need this patch:
>
> net: skb_copy_datagram_from_iovec()

And now,

tun: Use non-linear packets where possible

The tun backport always used linear packets which causes problems
when memory becomes fragmented as we can no longer allocate enough
contiguous pages for linear packets longer than a page.  This patch
backports the current upstream code where we use non-linear packets
to avoid this.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 6e66894..b803dba 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -265,8 +265,9 @@ static inline struct sk_buff *tun_alloc_skb(struct tun_struct *tun,
 	struct sk_buff *skb;
 	int err;
 
-	/* Always linear for now. */
-	linear = len;
+	/* Under a page?  Don't bother with paged skb. */
+	if (prepad + len < PAGE_SIZE || !linear)
+		linear = len;
 
 	skb = sock_alloc_send_pskb(sk, prepad + linear, len - linear, noblock,
 				   &err);
@@ -306,6 +307,10 @@ static __inline__ ssize_t tun_get_user(struct tun_struct *tun,
 		if (memcpy_fromiovec((void *)&gso, iv, sizeof(gso)))
 			return -EFAULT;
 
+		if ((gso.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
+		    gso.csum_start + gso.csum_offset + 2 > gso.hdr_len)
+			gso.hdr_len = gso.csum_start + gso.csum_offset + 2;
+
 		if (gso.hdr_len > len)
 			return -EINVAL;
 	}
@@ -320,9 +325,13 @@ static __inline__ ssize_t tun_get_user(struct tun_struct *tun,
 		return PTR_ERR(skb);
 	}
 
-	if (gso.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
-		unsigned int csum = 0;
+	if (skb_copy_datagram_from_iovec(skb, 0, iv, len)) {
+		tun->stats.rx_dropped++;
+		kfree_skb(skb);
+		return -EFAULT;
+	}
 
+	if (gso.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
 		if (gso.csum_start + gso.csum_offset > len - 2) {
 			if (net_ratelimit())
 				printk(KERN_WARNING
@@ -333,34 +342,12 @@ static __inline__ ssize_t tun_get_user(struct tun_struct *tun,
 			return -EINVAL;
 		}
 
-		if (memcpy_fromiovec(skb->data, iv, gso.csum_start)) {
-			tun->stats.rx_dropped++;
-			kfree_skb(skb);
-			return -EFAULT;
-		}
-
-		if (csum_partial_copy_fromiovecend(skb->data + gso.csum_start,
-						   iv, 0, len - gso.csum_start,
-						   &csum)) {
-			tun->stats.rx_dropped++;
-			kfree_skb(skb);
-			return -EFAULT;
-		}
-
-		*(u16 *)(skb->data + gso.csum_start + gso.csum_offset) =
-			csum_fold(csum);
-
+		skb->ip_summed = CHECKSUM_HW;
+		skb->csum = gso.csum_offset;
+		skb->h.raw = skb->data + gso.csum_start;
+		skb_checksum_help(skb, 0);
+	} else if (tun->flags & TUN_NOCHECKSUM)
 		skb->ip_summed = CHECKSUM_UNNECESSARY;
-	} else {
-		if (memcpy_fromiovec(skb->data, iv, len)) {
-			tun->stats.rx_dropped++;
-			kfree_skb(skb);
-			return -EFAULT;
-		}
-
-		if (tun->flags & TUN_NOCHECKSUM)
-			skb->ip_summed = CHECKSUM_UNNECESSARY;
-	}
 
 	skb->dev = tun->dev;
 	switch (tun->flags & TUN_TYPE_MASK) {