Re: [lwip-users] udp_send: space for IP header is not being allocated?

[Robin Iddon]

I might be barking up the wrong tree here, but when you allocate the 
pbuf for your user data you pass in a flag that says "TRANSPORT" and 
this means that when the pbuf is allocated the  transport header space 
is pre-allocated.  Now, if you're using UDP raw interface, I am not sure 
in what way that is different from the normal udp_send().

Hope this helps,
Robin

David Baird wrote:
> Hi,
>
> I think I found a bug, but wanted to check with people on the mailing
> list before reporting it (since it seems like others are using UDP
> without any problem, I wonder why it is that I am having a problem?).
>
> Space for IP header (IP_HLEN) is not properly allocated when using the
> UDP RAW API.  The problem seems to be constrained to one of these
> functions:
>
> - udp_send (in src/core/udp.c)
> - ip_output_if (in src/core/ipv4/ip.c)
>
> The problem is that no function is assuming the responsibility of
> allocating sufficient memory for the IP header (e.g. by calling
> ``pbuf_alloc`` and ``pbuf_chain``).  Neither ``ip_output_if`` nor
> ``udp_send`` allocate any memory (pbufs) for the IP header.
>
> However, ``udp_send`` does allocate enough memory for the UDP header
> (but not the IP header).  Looking at other code (``raw_send_to`` in
> ``src/core/raw.c``) seems to indicate that space for the IP header
> must be allocated *before* calling ``ip_output_if`` which means that
> ``udp_send`` has a bug (because it does not allocate space for the IP
> header).  In either case, it seems that someone apparently needs to
> allocate a pbuf and call pbuf_chain.
>
> Here are some lines captured when enabling debug output (in
> ``src/include/lwip/debug.h``) and trying to call ``udp_send`` (NOTE:
> this is not captured from the CVS head, but hopefully should follow it
> closely enough)::
>
>    udp_send
>    pbuf_header: old 0x195aa8 new 0x195aa0 (8)
>    udp_send: added header in given pbuf 0x195a88
>    udp_send: sending datagram of length 13
>    udp_send: UDP packet length 13
>    udp_send: UDP checksum 0x0000
>    udp_send: ip_output_if (,,,,IP_PROTO_UDP,)
>    pbuf_header: failed as 0x195a8c < 0x195a98
>    ip_output: not enough room for IP header in pbuf
>
> I am unable to send any UDP packets (even if I try different sizes).
> However, if I rewrite ``udp_send`` to force it to call ``pbuf_alloc``
> and ``pbuf_chain``, then everything works perfect (i.e. I am able to
> send UDP packets).
>
> So, is this a bug?  Or do you think I am missing something important?
>
> -David
>
>
> _______________________________________________
> lwip-users mailing list
> address@hidden
> http://lists.nongnu.org/mailman/listinfo/lwip-users