RE: [lwip-devel] ethernetif.c HANDLE error

[Pettinato, Jim]

True... But in all return paths from ip_output or ip_output_if (in tcp_out.c, 
etc.) that I can find (at least in 1.2.0), the return value is ignored. And the 
same is true for UDP.. Though udp_send() passes the error through to the 
caller, no calls from the stack code actually check the return value of 
udp_send(). (I assume applications are free to do so, however.)

-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of Jonathan Larmour
Sent: Wednesday, February 20, 2008 12:05 PM
To: lwip-devel
Subject: Re: [lwip-devel] ethernetif.c HANDLE error

Pettinato, Jim wrote:
> Jonathan, Piero:
> 
> It is my understanding that NO checking is done on the return value of 
> low_level_output()... it looks to me like the return value is passed 
> back up the call chain and then eventually ignored by tcp_output. I 
> think you could return ERR_END_OF_THE_WORLD_IS_AT_HAND without effect.
> ;)
> 
> Am I mistaken perhaps?

There are some situations where that happens, for example if an ARP request 
caused a packet to be queued. But that seems legitimate since by the time you 
know there's an error, you're no longer in the right context.

But in the normal course of things I can see the following calling path for 
normal packets, each stage returning the error of the next:
ip_output -> ip_output_if -> netif->output which is etharp_output -> 
etharp_send_ip -> netif->linkoutput which is low_level_output.

Jifl
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