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Date: Mon, 04 Jun 2007 20:26:53 +0200
From: Oliver Hartkopp <socketcan@...tkopp.net>
To: Urs Thuermann <urs@...ogud.escape.de>,
Patrick McHardy <kaber@...sh.net>
CC: David Miller <davem@...emloft.net>,
Thomas Gleixner <tglx@...utronix.de>,
Oliver Hartkopp <oliver.hartkopp@...kswagen.de>,
netdev@...r.kernel.org
Subject: Re: [patch 5/7] CAN: Add virtual CAN netdevice driver
Oliver Hartkopp wrote:
> I think, it goes into the right direction to use skb->pkt_type. The flag
> should really be somewhere inside the skb as all back references into
> the sk would become sticky in the implementation.
>
> But regarding the use of skb->pkt_type i would suggest to take a closer
> look on the definitions in include/linux/if_packet.h and how the
> pkt_type is to be used inside the kernel. In my opinion we should use ...
>
> * TX-Path:
> PACKET_OTHERHOST: send the CAN frame without loopback
> PACKET_BROADCAST : send the CAN frame with loopback (aka local broadcast)
>
> See an example of this approach in drivers/net/arcnet/rfc1051.c :
> http://www.linux-m32r.org/lxr/http/source/drivers/net/arcnet/rfc1051.c?a=i386#L99
>
> * RX-Path:
> PACKET_HOST : just an incoming CAN frame for this host
>
> Any comments? ACKs?
>
> Best regards,
> Oliver
>
>
>
The updated changes would look like this. Of course it has been tested
and is working fine :-)
Regards,
Oliver
Index: net/can/af_can.c
===================================================================
--- net/can/af_can.c (revision 325)
+++ net/can/af_can.c (working copy)
@@ -257,7 +257,6 @@
*/
int can_send(struct sk_buff *skb, int loop)
{
- struct sock **tx_sk = (struct sock **)skb->cb;
int err;
if (skb->dev->type != ARPHRD_CAN) {
@@ -265,30 +264,43 @@
return -EPERM;
}
+ skb->protocol = htons(ETH_P_CAN);
+
if (loop) {
/* local loopback of sent CAN frames (default) */
- /* indication for the CAN driver: do loopback */
- *tx_sk = skb->sk;
+ /*
+ * This packet is not only sent on the CAN bus but
+ * also broadcasted to local subscribers on this host.
+ */
+ skb->pkt_type = PACKET_BROADCAST;
/*
- * The reference to the originating sock may be also required
+ * The reference to the originating sock may be required
* by the receiving socket to indicate (and ignore) his own
- * sent data. Example: can_raw sockopt CAN_RAW_RECV_OWN_MSGS
+ * sent data. Example: can_raw sockopt CAN_RAW_RECV_OWN_MSGS.
+ * Therefore we have to ensure that skb->sk remains the
+ * reference to the originating sock by restoring skb->sk
+ * after each skb_clone() or skb_orphan() usage.
+ * skb->sk is usually unused and unset in the rx path.
*/
/* interface not capabable to do the loopback itself? */
if (!(skb->dev->flags & IFF_LOOPBACK)) {
+ struct sock *srcsk = skb->sk;
struct sk_buff *newskb = skb_clone(skb, GFP_ATOMIC);
/* perform the local loopback here */
- newskb->protocol = htons(ETH_P_CAN);
newskb->ip_summed = CHECKSUM_UNNECESSARY;
+ newskb->sk = srcsk;
netif_rx(newskb);
}
} else {
- /* indication for the CAN driver: no loopback required */
- *tx_sk = NULL;
+ /*
+ * Indication for the CAN driver: No loopback required!
+ * This packet is only transmitted to the CAN bus.
+ */
+ skb->pkt_type = PACKET_OTHERHOST;
}
if (!(skb->dev->flags & IFF_UP))
@@ -581,10 +593,12 @@
static inline void deliver(struct sk_buff *skb, struct receiver *r)
{
+ struct sock *srcsk = skb->sk;
struct sk_buff *clone = skb_clone(skb, GFP_ATOMIC);
DBG("skbuff %p cloned to %p\n", skb, clone);
if (clone) {
+ clone->sk = srcsk;
r->func(clone, r->data);
r->matches++;
}
Index: net/can/raw.c
===================================================================
--- net/can/raw.c (revision 325)
+++ net/can/raw.c (working copy)
@@ -154,7 +154,7 @@
if (!ro->recv_own_msgs) {
/* check the received tx sock reference */
- if (*(struct sock **)skb->cb == sk) {
+ if (skb->sk == sk) {
DBG("trashed own tx msg\n");
kfree_skb(skb);
return;
Index: drivers/net/can/vcan.c
===================================================================
--- drivers/net/can/vcan.c (revision 325)
+++ drivers/net/can/vcan.c (working copy)
@@ -133,6 +133,7 @@
skb->protocol = htons(ETH_P_CAN);
skb->dev = dev;
skb->ip_summed = CHECKSUM_UNNECESSARY;
+ skb->pkt_type = PACKET_HOST;
DBG("received skbuff on interface %d\n", dev->ifindex);
@@ -149,8 +150,8 @@
stats->tx_packets++;
stats->tx_bytes += skb->len;
- /* tx socket reference pointer: Loopback required if not NULL */
- loop = *(struct sock **)skb->cb != NULL;
+ /* indication for CAN netdevice drivers that loopback is required */
+ loop = (skb->pkt_type == PACKET_BROADCAST);
if (!loopback) {
/* no loopback handling available inside this driver */
@@ -170,6 +171,8 @@
/* perform standard loopback handling for CAN network interfaces */
if (loop) {
+ struct sock *srcsk = skb->sk;
+
if (atomic_read(&skb->users) != 1) {
struct sk_buff *old_skb = skb;
@@ -183,6 +186,8 @@
} else
skb_orphan(skb);
+ skb->sk = srcsk;
+
/* receive with packet counting */
vcan_rx(skb, dev);
} else {
-
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