linux-kernel - [PATCH] virtio_net: use correct accessors for scatterlists

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Message-ID: <20090124001053.GA20156@ovro.caltech.edu>
Date:	Fri, 23 Jan 2009 16:10:53 -0800
From:	Ira Snyder <iws@...o.caltech.edu>
To:	linux-kernel@...r.kernel.org, Mark McLoughlin <markmc@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>, netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>
Subject: [PATCH] virtio_net: use correct accessors for scatterlists

Without this fix, virtio_net makes incorrect usage of scatterlists. It sets
the end of the scatterlist chain after the first element, despite the fact
that more entries come after it.

If you try to run dma_map_sg() on one of the scatterlists given to you by
add_buf(), you will get a null pointer oops.

Signed-off-by: Ira W. Snyder <iws@...o.caltech.edu>
---

I found this problem while working on implementing virtio-over-PCI as
suggested by Arnd Bergmann, David Miller, and others.

 drivers/net/virtio_net.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 43f6523..67ea2cf 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -286,7 +286,7 @@ static void try_fill_recv_maxbufs(struct virtnet_info *vi)
 		skb_put(skb, MAX_PACKET_LEN);
 
 		hdr = skb_vnet_hdr(skb);
-		sg_init_one(sg, hdr, sizeof(*hdr));
+		sg_set_buf(sg, hdr, sizeof(*hdr));
 
 		if (vi->big_packets) {
 			for (i = 0; i < MAX_SKB_FRAGS; i++) {
@@ -487,9 +487,9 @@ static int xmit_skb(struct virtnet_info *vi, struct sk_buff *skb)
 
 	/* Encode metadata header at front. */
 	if (vi->mergeable_rx_bufs)
-		sg_init_one(sg, mhdr, sizeof(*mhdr));
+		sg_set_buf(sg, mhdr, sizeof(*mhdr));
 	else
-		sg_init_one(sg, hdr, sizeof(*hdr));
+		sg_set_buf(sg, hdr, sizeof(*hdr));
 
 	num = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
 
-- 
1.5.4.3

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