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From: Robert Watson <rwatson@FreeBSD.org>
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To: Marcel Moolenaar <xcllnt@mac.com>
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Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org,
	Marcel Moolenaar <marcel@freebsd.org>,
	src-committers@freebsd.org, John Baldwin <jhb@freebsd.org>
Subject: Re: svn commit: r197608 - head/sys/geom/part
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On Tue, 29 Sep 2009, Marcel Moolenaar wrote:

>> Why do you check for zeros at all?  AFAIK, the only real check is for AA55 
>> at the end of the sector (and having an MBR or other Extended MBR partition 
>> entry point at the sector in question).  The '96' thing seems rather 
>> arbitrary in the code, and I think the zero's check is overly restrictive.
>
> Only checking for a signature that 99% of the boot blocks have isn't enough. 
> The msdos file system has that signature and the check for all-zeroes is to 
> prevent false positives there.

And, as I recall, the msdosfs check has been gradually getting weaker over 
time as the constraints it places on things like cylinder counts become 
obsolete.  It's not quite that we'll mount msdosfs on any random pile of 
bytes, but it might be getting there...

Robert