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From: rml@hpfcdc.UUCP
Newsgroups: comp.unix.wizards
Subject: Re: Re: Increasing the number of file descriptors
Message-ID: <5980003@hpfcdc.HP.COM>
Date: Wed, 25-Mar-87 20:15:55 EST
Article-I.D.: hpfcdc.5980003
Posted: Wed Mar 25 20:15:55 1987
Date-Received: Sat, 28-Mar-87 11:42:01 EST
References: <138@tijc02.UUCP>
Organization: HP Ft. Collins, Co.
Lines: 27

>                                              If we recompile the kernel with
> NOFILE set to say 40, how would we be affecting the rest of the system? What
> subtle (or not so subtle) problems would we create in doing this?

You need to recompile not only the kernel but various utilities (ps,
debuggers, fuser, possibly others) that include <sys/user.h> or have
other dependencies on NOFILE.  If you want to be able to use stdio with
more than 20 files, you'll need to recompile it.

> Answer:  Ack!
> 
> 	I am not sure about system V but I always store my
> 	file descripters in a single (int).  This means
> 	that my software can handle only 32 file descripters.

Then this code is not portable.  Many implementations allow more than 32
file descriptors.

> As I recall, 4.2 also used 5 bits for the file descriptor in an
> important place, which is why changing the number was a problem.

Actually the 5 bit representation was only for the unimplemented
file-mapping feature.  Select did use a 32-bit int as a file descriptor
mask in 4.2, and this was changed in 4.3.

		Bob Lenk
		{ihnp4, hplabs}!hpfcla!rml