Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!haven!ncifcrf!nlm-mcs!adm!smoke!gwyn
From: gwyn@smoke.BRL.MIL (Doug Gwyn)
Newsgroups: comp.unix.wizards
Subject: Re: Write calls which do partial writes
Keywords: write select poll SIGIO connect
Message-ID: <10198@smoke.BRL.MIL>
Date: 3 May 89 11:19:34 GMT
References: <103@matrix.UUCP>
Reply-To: gwyn@brl.arpa (Doug Gwyn)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 19

In article <103@matrix.UUCP> neeraj@matrix.UUCP (neeraj sangal) writes:
>        n = write(fd, buf, len);
>    1. Can n be less than len if fd is NOT set to non-blocking?

Certainly; if only some but not all bytes were transferred,
for example due to the system call being interrupted by a signal,
then the best thing for write() to report is the number of bytes
successfully transferred.  (I forget whether IEEE 1003.1 ended up
permitting this or not; it was hotly debated.)  Robust stdio
implementations have to loop on the write() call until all bytes
are transferred or an error occurs.

>Will the underlying protocol complete select the moment a single
>byte can be transferred...?

Obviously it should.

The details depend on the exact implementation and are complicated
by things like the guaranteed pipe atomic write size, etc.