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Subject: kern/2121: MAXBSIZE in param.h causes kernel panic if MSDOSFS LKM loaded
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>Number:         2121
>Category:       kern
>Synopsis:       MAXBSIZE in param.h causes kernel panic if MSDOSFS LKM loaded
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Fri Nov 29 00:00:04 PST 1996
>Last-Modified:
>Originator:     Jake Hamby
>Organization:
Jet Propulsion Laboratory
>Release:        FreeBSD 3.0-CURRENT i386
>Environment:

3.0-CURRENT cvsupped on 96/11/28 without MSDOSFS defined in the kernel
config, but with the msdos LKM loaded at boot.

>Description:

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.

>How-To-Repeat:

Build a kernel without MSDOSFS.  Boot with it, then attempt to mount an
MSDOS filesystem or manually load the msdos LKM.

>Fix:
	
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.  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.
>Audit-Trail:
>Unformatted: