svn commit: r197608 - head/sys/geom/part

[Marcel Moolenaar]

On Sep 29, 2009, at 10:00 AM, Robert Watson wrote:

>
> 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...

We really need to get to a point where we treat partition types  
seriously and
use it to help avoid false positives. Reducing or eliminating false  
positives
is critical if we ever want to go towards DWIM or auto-mounting. With  
the
partition type taken into consideration, we may be able to eliminate  
ad hoc
checks, like the zero check in g_part_ebr, without creating false  
positives.

-- 
Marcel Moolenaar
xcllnt at mac.com