Date: Wed, 17 Dec 1997 09:30:02 -0800 (PST) From: Bruce Evans <bde@zeta.org.au> To: freebsd-bugs Subject: Re: bin/5306: gethostbyname() returns herror "Unknown host" on well known hosts Message-ID: <199712171730.JAA26387@hub.freebsd.org>
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The following reply was made to PR bin/5306; it has been noted by GNATS.
From: Bruce Evans <bde@zeta.org.au>
To: bde@zeta.org.au, chris@netmonger.net, freebsd-gnats-submit@freebsd.org,
robert@superior.net
Cc: Subject: Re: bin/5306: gethostbyname() returns herror "Unknown host" on well known hosts
Date: Thu, 18 Dec 1997 04:23:38 +1100
>I don't know whether the gethostbyname() problem Robert is having is
>related to PR 3622, but I think there is a problem with the default
>login.conf.
>
>I had to lower openfiles settings to 256 because having it larger
>breaks select(). It's been a while, so I'm a bit fuzzy on the details,
>but I do remember that it was causing rxvt to fail.. a quick perusal
>of the rxvt source indicates that it does:
It breaks buggy applications.
>I believe that it ends up obtaining the 1024 that was defined in login.conf,
>but the FD_SETSIZE in sys/types.h is defined as 256. IIRC, select() bombs
>out when nfds is > 256.
Naive use of the FD_* macros doesn't work if nfds > FD_SETSIZE. The
application should know about this and either not supports fd's >=
FD_SETSIZE, or handle them somehow. The documented way is to #define
FD_SETSIZE before including <sys/types.h>. The networking libraries
use a more flexible way.
>I suppose I should test this rather than just make the claim. Try this:
>
>#include <stdio.h>
>#include <unistd.h>
>#include <sys/types.h>
>#include <sys/time.h>
>#include <sys/select.h>
>
>void testselect(int num)
>{
> fd_set fds;
> struct timeval tv = {0, 0};
>
> printf("testing select(%d,...)\n", num);
> FD_ZERO(&fds);
> if (select(num, &fds, &fds, &fds, &tv) < 0) {
> perror("select()");
> }
If nfds > FD_SETSIZE, in FreeBSD-2.2.0 and later versions, select()
will probably succeed and scribble on the stack beyond the end of
fds. In earlier versions, it rejects the request if nfds > 256.
FD_SETSIZE happens to be 256 in 2.2.5 and 1024 in -current. Programs
should not depend on this (but many probably do :-().
Bruce
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