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firewire net: Ignore spd and max_payload advertised by ARP.

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Stefan Richter <stefanr@s5r6.in-berlin.de> says:
| As far as I can tell, it would be best to ignore max_rec and sspd from ARP
| and NDP but keep using the respective information from firewire-core
| instead (handed over by fwnet_probe()).
|
| Why?  As I noted earlier, RFC 2734:1999 and RFC 3146:2001 were apparently
| written with a too simplistic notion of IEEE 1394 bus topology, resulting
| in max_rec and sspd in ARP-1394 and NDP-1394 to be useless, IMO.
|
| Consider a bus like this:
|
|     A ---- B ==== C
|
| A, B, C are all IP-over-1394 capable nodes.  ---- is an S400 cable hop,
| and ==== is an S800 cable hop.
|
| In case of unicasts or multicasts in which node A is involved as
| transmitter or receiver, as well as in case of broadcasts, the speeds
| S100, S200, S400 work and speed S400 is optimal.
|
| In case of anything else, IOW in case of unicasts or multicasts in which
| only nodes B and C are involved, the speeds S100, S200, S400, S800 work
| and speed S800 is optimal.
|
| Clearly, node A should indicate sspd = S400 in its ARP or NDP packets.
| But which sspd should nodes B and C set there?  Maybe they set S400, which
| would work but would waste half of the available bandwidth in the second
| case.  Or maybe they set S800, which is OK in the second case but would
| prohibit any communication with node A if blindly taken for correct.
|
| On the other hand, firewire-core *always* gives us the correct and optimum
| peer-to-peer speed and asynchronous packet payload, no matter how simple
| or complex the bus topology is and no matter in which temporal order nodes
| join the bus and are discovered.

CC: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
YOSHIFUJI Hideaki / 吉藤英明 2013-03-25 08:26:08 +00:00 committed by David S. Miller
parent 382c4b4090
commit 61a7839a19
1 changed files with 0 additions and 16 deletions
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16
drivers/firewire/net.c
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@ -552,8 +552,6 @@ static int fwnet_finish_incoming_packet(struct net_device *net,
unsigned char *arp_ptr;
u64 fifo_addr;
u64 peer_guid;
unsigned sspd;
u16 max_payload;
struct fwnet_peer *peer;
unsigned long flags;
@ -564,24 +562,10 @@ static int fwnet_finish_incoming_packet(struct net_device *net,
fifo_addr = (u64)get_unaligned_be16(&arp1394->fifo_hi) << 32
| get_unaligned_be32(&arp1394->fifo_lo);
sspd = arp1394->sspd;
/* Sanity check. OS X 10.3 PPC reportedly sends 131. */
if (sspd > SCODE_3200) {
dev_notice(&net->dev, "sspd %x out of range\n", sspd);
sspd = SCODE_3200;
}
max_payload = fwnet_max_payload(arp1394->max_rec, sspd);
spin_lock_irqsave(&dev->lock, flags);
peer = fwnet_peer_find_by_guid(dev, peer_guid);
if (peer) {
peer->fifo = fifo_addr;
if (peer->speed > sspd)
peer->speed = sspd;
if (peer->max_payload > max_payload)
peer->max_payload = max_payload;
peer->ip = arp1394->sip;
}
spin_unlock_irqrestore(&dev->lock, flags);