Date: Sat, 24 Jan 1998 12:08:19 +1030 From: Mike Smith <mike@smith.net.au> To: daniel_sobral@voga.com.br Cc: mike@smith.net.au, hackers@FreeBSD.ORG Subject: Re: uiomove() Message-ID: <199801240138.MAA00419@word.smith.net.au> In-Reply-To: Your message of "Fri, 23 Jan 1998 16:19:36 -0300." <83256595.006A05B5.00@papagaio.voga.com.br>
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>
> > There are a few other things I left out, particularly the correct
> > handling of returns from tsleep() when PCATCH is specified.
>
> Yup... I forgot to bother you about that... Currently, I'm not PCATCHing
> and what the hell, but I intend to be more politically correct. I just have
> not figured exactly what I'm supposed to do at ERESTART.
OK. Here's a more "politically correct" read() routine. You should be
able to mirror this into a write() fairly easily.
foo_read()
{
int s, result, hmany, got;
struct foo_softc *sc = ...
got = 0;
while (uio->uio_resid > 0) {
s = splfoo();
while (!result && (sc->ready == 0)) {
if (flags & F_NONBLOCK)
result = EWOUDLBLOCK;
else
result = tsleep(&sc->ready, PRIFOO | PCATCH,
"fooread", 0);
if (result = ERESTART)
if (got == 0)
result = 0;
else
result = EINTR;
}
splx(s);
if (result)
return(result);
hmany = min(sc->ready, uio->uio_resid);
result = uiomove(sc->buf, hmany, uio);
if (result)
return(result);
s = splfoo();
if (hmany < sc->ready)
bcopy(sc->buf + hmany, sc->buf, sc->ready - hmany);
sc->ready -= hmany;
splx(s);
got += hmany;
}
return(0);
}
This implements the policy "If a signal is received we will return a
short read count, except where that count would be zero" (because
returning EOF tends to upset some people 8).
You might want to always convert ERESTART to EINTR (always error on
interrupt), but that becomes more complex as you may already have
consumed data from the read buffer, which may throw your caller out of
sync.
Another approach is to ignore ERESTART, ie. never return a short count.
That's also quite legitimate with the above code, ie.
if (result == ERESTART)
result = 0;
--
\\ Sometimes you're ahead, \\ Mike Smith
\\ sometimes you're behind. \\ mike@smith.net.au
\\ The race is long, and in the \\ msmith@freebsd.org
\\ end it's only with yourself. \\
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