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Date: Tue, 17 Oct 1995 19:29:19 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199510170929.TAA03697@godzilla.zeta.org.au>
To: bakul@netcom.com, terry@lambert.org
Subject: Re: getdtablesize() broken?
Cc: current@freefall.freebsd.org, hackers@freefall.freebsd.org
Sender: owner-hackers@FreeBSD.org
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>(BTW, If you don't change the limit, you will discover an off by
>one bug: the default limit is 64 but you can only open 63 fds)

I get 64.  Perhaps you have a shell bug.

>So I can do everything with fd > 255 except select().  This
>happens because of this line in /sys/kern/sys_generic.c:select()

>	if (uap->nd > FD_SETSIZE)

>It should be replaced with

>	if (uap->nd > p->fd->fd_nfiles)

>It is this hardwired use of FD_SETSIZE *in* the kernel I am
>bitching about.

This would just give random errors or clobber the kernel stack.
The limit is built in to the fd_set type.  The FD_SETSIZE check
just makes sure that all the bits fit in the kernel fd_set
variables.  The kernel needs to use dynamically allocated
arrays to hold more bits, and different methods to access the
bits...

Bruce