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Date: Fri, 29 Nov 1996 00:20:01 -0800 (PST)
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From: "John S. Dyson" <toor@dyson.iquest.net>
Subject: Re: kern/2121: MAXBSIZE in param.h causes kernel panic if MSDOSFS LKM loaded
Reply-To: "John S. Dyson" <toor@dyson.iquest.net>
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The following reply was made to PR kern/2121; it has been noted by GNATS.

From: "John S. Dyson" <toor@dyson.iquest.net>
To: jehamby@lightside.com
Cc: FreeBSD-gnats-submit@freebsd.org
Subject: Re: kern/2121: MAXBSIZE in param.h causes kernel panic if MSDOSFS LKM loaded
Date: Fri, 29 Nov 1996 03:19:44 -0500 (EST)

 > 
 > sys/param.h was recently changed to define MAXBSIZE as 32768 if MSDOSFS is
 > defined, or 16384 otherwise.  If MSDOSFS is not compiled into the kernel,
 > but instead loaded as an LKM (as I have done), then the kernel immediately
 > panics with: "panic: getblk: size(32768) > MAXBSIZE(16384)" when the LKM
 > is loaded.
 > 
 Good, it caught a possible system corruption.
 
 > 
 > Because we have no idea if the user is going to load the msdos LKM, the
 > only sensible patch is to always define MAXBSIZE as 32768, and I
 > recommend that this be done immediately.
 >
 Might be a bad idea because it takes lots of kernel virtual space
 on bigger machines. 
 
 >
 >  Perhaps a comment could be
 > added to param.h for expert users, stating that they can decrease this
 > manually, but at their own risk, and only if they NEVER plan to use the DOS
 > filesystem, even as an LKM.
 > 
 Or perhaps panic the system when we run out of KVA space on a critical
 server system? :-).
 
 The problem is still being reviewed and visited, and consider your
 input as registered.  The biggest problem that I have is that the
 "fix" of increasing MAXBSIZE to 32K isn't good enough, and we will
 have to increase it again to 64K...  That is more evil for larger
 machines (which are going to become more and more common.)
 
 John