netdev - [PATCH] Re: PACKET_TX_RING: packet size is too long

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Message-ID: <20091009220546.GB7618@boogie.lpds.sztaki.hu>
Date:	Sat, 10 Oct 2009 00:05:46 +0200
From:	Gabor Gombas <gombasg@...aki.hu>
To:	netdev@...r.kernel.org
Cc:	johann.baudy@...-log.net
Subject: [PATCH] Re: PACKET_TX_RING: packet size is too long

Hi,

Digging list archives I suspect the current value of size_max is the
remnant of the zero-copy mode that was not merged. So I propose the
following patch that IMHO makes the value of size_max consistent with
how the frame is actually handled in tpacket_fill_skb().

If the zero-copy mode is ever to be resurrected, then the user should
explicitely request it, and either the length of the extra padding
should be the same for 32-bit and 64-bit kernels or there must be a way
to query the value at run time.

Gabor

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index f9f7177..745a016 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -985,10 +985,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 		goto out_put;
 
 	size_max = po->tx_ring.frame_size
-		- sizeof(struct skb_shared_info)
-		- po->tp_hdrlen
-		- LL_ALLOCATED_SPACE(dev)
-		- sizeof(struct sockaddr_ll);
+		- (po->tp_hdrlen - sizeof(struct sockaddr_ll));
 
 	if (size_max > dev->mtu + reserve)
 		size_max = dev->mtu + reserve;

-- 
     ---------------------------------------------------------
     MTA SZTAKI Computer and Automation Research Institute
                Hungarian Academy of Sciences
     ---------------------------------------------------------
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