RE: [lwip-users] TCP_WRITE [Raw]

[Bill Auerbach]

It's a bit wasteful, but could he pre-allocate what tcp_write would do when
copy is enabled, if it passes, free the memory and then call tcp_write.  If
the pre-allocate fails, it would have in tcp_write also.

Is there a way to allocate a pbuf with a mem_malloced payload that the stack
knows to mem_free when it's done?  If so, he could mem_malloc and copy
himself and let the stack free it up.

Bill

>-----Original Message-----
>From: address@hidden
>[mailto:address@hidden On
>Behalf Of Simon Goldschmidt
>Sent: Monday, November 09, 2009 1:35 AM
>To: Chris Strahm; Mailing list for lwIP users
>Subject: Re: [lwip-users] TCP_WRITE [Raw]
>
>
>> In other words, could memory still be required for data copy that is
>not
>> checked by the tcp sndbuf queue space.
>
>Yes. That's because tcp_sndbuf() tests against a counter variable that
>can be configured to any size in lwipopts.h. However, the memory needed
>to enqueue a segment can be configured in lwipopts.h, too. If these
>values don't match, tcp_write() can return ERR_MEM although the sndbuf
>limit isn't reached yet.
>
>> If so, is there a check to test for available mem to copy data?
>
>That's hard: depending on whether you copy data or not, you need a
>PBUF_RAM or PBUF_ROM pbuf. In addition to that, you need one struct
>tcp_seg. These come from the corresponding memp pools, but there is no
>default way (aside from looking at the stats, maybe) to know if
>tcp_write will fail or not.
>
>However, this is just the way lwIP is designed: your application code
>just has to cope with tcp_write failing, that's all :-)
>
>Simon
>--
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