Subject: Re: Mountng DOS disk causes kernel panic
To: None <port-i386@NetBSD.ORG,>
From: Wolfgang Solfrank <>
List: port-i386
Date: 04/04/1996 22:00:51
> When trying to mount a rather large MessDOS partition under NetBSD,
> I get a kernel panic:
> panic: allocbuf: buffer larger than MAXBSIZE requested

This is a known problem. It results from MAXBSIZE defined in <sys/param.h>
as 16k.

The msdosfs code wants to read full clusters into buffers. Clusters can
have sizes between 512 bytes and 32k.

It was agreed that MAXBSIZE should be increased to MAXPHYS, which happens to
be 64k on all currently supported ports (except 63k on vax). So the problem
would be solved far easier than if the msdosfs code got hacked. Unfortunately,
this hasn't happened yet.

You might get away with redefining MAXBSIZE to 32k in <sys/param.h>
(unfortunately it isn't even protected by #ifndef), but keep in mind that
this will eat quite some amount of virtual memory, which happens to be
scarce on some ports, e.g. the i386.
ws@TooLs.DE     (Wolfgang Solfrank, TooLs GmbH) 	+49-228-985800