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From: mike@BRL.ARPA (Mike Muuss)
Newsgroups: net.unix-wizards
Subject: Re:  readv(), writev()
Message-ID: <4251@brl-smoke.ARPA>
Date: Tue, 30-Sep-86 00:57:25 EDT
Article-I.D.: brl-smok.4251
Posted: Tue Sep 30 00:57:25 1986
Date-Received: Sat, 4-Oct-86 10:33:36 EDT
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Exactly right.  readv() and writev() allow one to, say, transmit
a packet (header+data) from two separate buffers as one unit,
without needing either (a) extra system calls, or (b) a bcopy().

Small efficiency nit, you say.  True, EXCEPT for the fact that
the 4.2 TCP sets the TCP_PUSH bit at the end of each sys-write.
This can have extreme effects on network performance.

Note that readv() and writev() have a maximum vector length
of 16 items in 4.2 BSD.  You will find this limit strictly enforced
by the kernel, and perplexing to the unwary.
	-Mike