Re: [lwip-users] Program hangs in ip_frag()

[pekez]

After further examination, I noticed that ip_frag() works fine when 
variable left is set to 1480 initially. However, when it's bigger than 
that value, it get stuck in while (left_to_copy) loop.

When left is initially 1480:
1st iteration through while(left_to_copy): left_to_copy is 1464, p->len 
is 1480, newpbuflen is 1464
2nd iteration: left_to_copy is 16, p->len is 16, newpbuflen is 16

And it gets out of ip_frag function. It works as expected.

When left initially is > 1480 (for example 2964):
1st iteration: left_to_copy is 1464, p->len is 1480, newpbuflen is 1464
2nd iteration: left_to_copy is 1464, p->len is 16, newpbuflen is 16
3rd iteration: left_to_copy is 1448, p->len is 0, newpbuflen is 0
and every next iteration looks as the 3rd one... every next p->len is 0, 
so newpbuf is 0, left_to_copy never gets decremented and it hangs in 
infinite loop :(

Since left is set to p->tot_len - IP_HLEN at the beginning of the 
ip_frag() function, it seems to me as though p->tot_len doesn't 
correspond to the real total len of p??? Is that possible? Can I somehow 
recalculate p->tot_len inside of ip_frag()? Any suggestion on how I 
could handle this condition?

On 3.3.2017 11:45, pekez wrote:
> I am not able to step through files that are part of BSP. Not much 
> help of a debugger. I am using Xilinx SDK. So far I have been 
> printing, and I found out that program get stuck inside of while 
> (left_to_copy) loop in ip_frag(). left_to_copy is 1448 all the time... 
> p->len is 0.
>
> I am confused why ip_frag is called only sometimes. It is called from 
> here:
>
> if (netif->mtu && (p->tot_len > netif->mtu)) {
>     return ip_frag(p, netif, dest);
>   }
>
> netif->mtu is always > 0, so that means the other argument is true as 
> well. I don't get why p->tot_len is sometimes bigger than netif->mtu, 
> since I am always doing the same thing from application. Can you 
> explain this? I have little knowledge on how TCP works under the hood.
>
> When program works fine, it never gets into ip_frag, so that means it 
> get stuck only when this function is called.
>
> On 2.3.2017 19:48, address@hidden wrote:
> > pekez wrote:
> > > I have not real clue what is going on.
> >
> > Me neither.
> >
> > You seem to have a debugger, why don't you try to find out? ;-)
> > (I.e. see where/why it hangs to try to give us more information or 
> > even be able to fix it yourself)
> >
> > Cheers,
> > Simon
> >
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> > https://lists.nongnu.org/mailman/listinfo/lwip-users
>
>
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