netdev - RE: Question about SOCK

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6DCFFE60CD@AcuExch.aculab.com>
Date:   Fri, 5 May 2017 11:21:02 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Steven Whitehouse' <swhiteho@...hat.com>,
        Sowmini Varadhan <sowmini.varadhan@...cle.com>
CC:     Sam Kumar <samkumar99@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: Question about SOCK_SEQPACKET

From: Steven Whitehouse
> Sent: 05 May 2017 11:34
...
> Just before the part that you've quoted, the description for
> SOCK_SEQPACKET says:
> "The SOCK_SEQPACKET socket type is similar to the SOCK_STREAM type, and
> is also connection-oriented. The only difference between these types is
> that record boundaries are maintained using the SOCK_SEQPACKET type. A
> record can be sent using one or more output operations and received
> using one or more input operations, but a single operation never
> transfers parts of more than one record."

Right SOCK_SEQPACKET is for protocols like ISO transport.
There is no limit on the length of a 'record'.
I've written file transfer programs that put the entire file
data into a single 'record'. The receiver disconnected on
receipt of the 'end of record'.

The socket man pages could easily be wrong - they are very IP-centric.
Remember ISO transport use declined when Unix became more popular
back in the mid 1980s. Unix sockets have never really been used for
it - the address information needed just doesn't match that IP
(especially IPv4).

	David