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Date: Wed, 17 Dec 1997 09:30:02 -0800 (PST)
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From: Bruce Evans <bde@zeta.org.au>
Subject: Re: bin/5306: gethostbyname() returns herror "Unknown host" on well known hosts
Reply-To: Bruce Evans <bde@zeta.org.au>
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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