On 2/5/2012 1:40 PM, Tyrel Newton wrote:
I have a system with two netifs and I'm trying to forward packets
between the two interfaces. One netif is my Ethernet interface while
the other is a custom wireless interface. The problem is that the
forwarded pbuf is getting corrupted somehow before I can send it back
out. At first I thought the forwarded pbuf was getting free'd
prematurely, but an additional pbuf_ref does not fix the problem. I
know the pbuf enters my second netif correctly, but before I can get
it sent out, its either being free'd or modified somehow again. At the
moment its working, but its because I'm copying the forwarded pbuf
before sending it back out.
I have gone over the code numerous times and traced the pbuf from the
rx of my ethernet interface, through the etharp code, through ip
forward, and into my second netif driver and I can't figure out where
the problem is. I'm currently running the latest code in the git repo
(as of yesterday).
Does anybody have any clues as to where to look for the problem? My
guess is that its somewhere in the etharp code, but I can't find it.
Copying the entire pbuf is not exactly a good solution, though it
definitely works.
In case anybody else runs into a similar problem, the reason for the
corruption was in my own netif drivers and is related to the placement
of the pbuf->payload within the contiguous memory of the pbuf/payload
combo and differing link layer header sizes between my Ethernet netif
driver and my other "custom" netif driver.
The part that caught me up for so long is that the placement of the
payload in Rx and Tx packets is inherently different. That is, its
common to pack the Rx packet at the very beginning of the payload memory
region while Tx packets are offset by an amount that is easily adjusted
by the PBUF_LINK_HLEN configuration parameter.
The best solution I can think of to this problem is to pack my Rx
Ethernet packets at a payload offset of "PBUF_LINK_HLEN -
SIZEOF_ETH_HDR". This would still allow me to set the "maximum link
layer header size" by simply adjusting the PBUF_LINK_HLEN parameter,
which is what I've been doing to date.
Has anybody else ran into a similar problem or have further insight into
different solutions?
Tyrel
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