From: Michael S. Tsirkin <mst@redhat.com>
Date: Sat, 9 Oct 2021 14:52:50 +0000 (-0400)
Subject: virtio_net: clarify tailroom logic
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=fc02e8cb0300c0146e1d4668a75663eb225d8182;p=linux.git

virtio_net: clarify tailroom logic

Make tailroom math follow same logic as everything else, subtracing
values in the order in which things are laid out in the buffer.

Tested-by: Corentin Noël <corentin.noel@collabora.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 4ad25a8b0870c..6d8c8745bf242 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -406,12 +406,13 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 	 * add_recvbuf_mergeable() + get_mergeable_buf_len()
 	 */
 	truesize = headroom ? PAGE_SIZE : truesize;
-	tailroom = truesize - len - headroom - (hdr_padded_len - hdr_len);
+	tailroom = truesize - headroom;
 	buf = p - headroom;
 
 	len -= hdr_len;
 	offset += hdr_padded_len;
 	p += hdr_padded_len;
+	tailroom -= hdr_padded_len + len;
 
 	shinfo_size = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));