[PATCH net-next] firewire: net: really fix maximum possible MTU

From: Stefan Richter
Date: Sat Oct 29 2016 - 16:17:28 EST


The maximum unicast datagram size /without/ link fragmentation is
4096 - 4 = 4092 (max IEEE 1394 async payload size at >= S800 bus speed,
minus unfragmented encapssulation header). Max broadcast datagram size
without fragmentation is 8 bytes less than that (due to GASP header).

The maximum datagram size /with/ link fragmentation is 0xfff = 4095
for unicast and broadcast. This is because the RFC 2734 fragment
encapsulation header field for datagram size is only 12 bits wide.

Fixes: 5d48f00d836a('firewire: net: fix maximum possible MTU')
Signed-off-by: Stefan Richter <stefanr@xxxxxxxxxxxxxxxxx>
---
drivers/firewire/net.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/firewire/net.c b/drivers/firewire/net.c
index 03715e7d9d92..363fc5ec1a4e 100644
--- a/drivers/firewire/net.c
+++ b/drivers/firewire/net.c
@@ -1465,7 +1465,7 @@ static int fwnet_probe(struct fw_unit *unit,

net->mtu = 1500U;
net->min_mtu = ETH_MIN_MTU;
- net->max_mtu = ETH_MAX_MTU;
+ net->max_mtu = 0xfff;

/* Set our hardware address while we're at it */
ha = (union fwnet_hwaddr *)net->dev_addr;
--
Stefan Richter
-======----- =-=- ===-=
http://arcgraph.de/sr/