Re: [ECOS] TCP/IP Stack packet regrouping

[Grant Edwards <grante at visi dot com>]

On Mon, Jul 16, 2001 at 04:35:20PM -0600, Trenton D. Adams wrote:

>>>>> Sending generally will send it all at once, and there's no
>>>>>need for a loop for the outgoing buffer?
>>>
>>>> No, that is not generally true.  For small blocks, it will
>>>> _usually_ be true.  For large blocks of data, you will have to
>>>> check the return value from write() in a loop.  The values of
>>>> "small" and "large" vary from platform to platform.
>>>
>>> Ok, who's actually correct here?  Who's the one that wrote the
>>> TCP/IP stack?  Are they listening?
>
>> I didn't write it, but I'm reading it. :)
>
>> In the eCos/BSD stack, it looks to me that send() is only
>> "atomic" if the PR_ATOMIC flag is set in the protosw struct
>> for the protocol associated with a socket.  That flag isn't
>> set for SOCK_STREAM.  It is set for SOCK_DGRAM and SOCK_RAW.
>> Of course, I could be misreading the code. But that does jibe
>> with what I've always been told regarding checking the return
>> value from a write() on a TCP socket.
>
> I THINK this is the opposite of the Linux version.  The Linux
> TCP version is APPARENTLY atomic. I used to know what this
> means in computer terms, but I can't remember. Can you explain
> the ATOMIC thing to me?

I'm still not 100% sure that the eCos/BSD stack won't try to
loop until all of the data is sent.  I have a really tough time
reading C code that's indented that way.  I'm going to have to
re-indent the eCos sources and study it some more.

-- 
Grant Edwards
grante@visi.com