Date: Thu, 6 Jun 2002 06:51:27 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Alexander Leidinger <Alexander@Leidinger.net> Cc: Todd.Miller@courtesan.com, <drosih@rpi.edu>, <audit@FreeBSD.ORG> Subject: Re: [PATCH] making dump EINTR resistant Message-ID: <20020606064418.N8685-100000@gamplex.bde.org> In-Reply-To: <200206050838.g558c0PP000854@Magelan.Leidinger.net>
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On Wed, 5 Jun 2002, Alexander Leidinger wrote:
> On 5 Jun, Bruce Evans wrote:
>
> >> It would probably be better to just make the code in question to
> >> just use sigaction() if you are concerned about portability. That
> >> way you get consistent handling of syscall restarts.
> >
> > I agree, but not that SA_RESTART wasn't portable until tomorrow (sic),
> > since it is in POSIX.1-2001 but not in older POSIXes (.1-1996 at least).
>
> Stevens uses this as a portable example for a signal() with restartable
> syscalls:
>
> ---snip---
> #include <signal.h>
>
> typedef void Sigfunc(int);
>
> Sigfunc *
> signal(int signo, Sigfunc *func)
> {
> struct sigaction act, oact;
>
> act.sa_handler = func;
> sigemptyset(&act.sa_mask);
> act.sa_flags = 0;
> if (signo == SIGALRM) {
> #ifdef SA_INTERRUPT
> act.sa_flags |= SA_INTERRUPT; /* SunOS */
> #endif
> } else {
> #ifdef SA_RESTART
> act.sa_flags |= SA_RESTART; /* SVR4, 4.3+BSD */
> #endif
> }
> if (sigaction(signo, &act, &oact) < 0)
> return(SIG_ERR);
> return (oact.sa_handler);
> }
It's not very portable since it doesn't give restartable syscalls on
systems that don't have SA_INTERRUPT or SA_RESTART. The rest of the
application would have to deal with this possibilty, and once it does
that it can just slightly more easily deal with non-restartable syscalls
in all cases.
> He doesn't want restartable syscalls for SIGALRM to allow to set a time
> out for I/O operations.
This is probably necessary for programs that need i/o's to time out or
be terminated by a keyboard signal, but it requires the whole program
to be concerned about i/o's failing with EINTR -- it is only a small
simplification for only one type of signal to not restart syscalls,
since that signal may occur.
Bruce
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