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Date:      Thu, 15 Jan 2009 11:35:21 -0800
From:      Marcel Moolenaar <xcllnt@mac.com>
To:        Dimitry Andric <dimitry@andric.com>
Cc:        Randy Bush <randy@psg.com>, Luiz Otavio O Souza <lists.br@gmail.com>, George Neville-Neil <gnn@neville-neil.com>, Ben Kaduk <minimarmot@gmail.com>, current@freebsd.org
Subject:   Re: GEOM and moving to CURRENT from 7.1
Message-ID:  <BC6ACB2A-CBC5-428B-8749-999B48B2D1C8@mac.com>
In-Reply-To: <496F8D8A.1060508@andric.com>
References:  <FC3D3CF7-091B-4ECF-BE38-6C7751C20994@neville-neil.com> <alpine.BSF.2.00.0901112002080.3696@ibyngvyr.purzvxnyf.bet> <496D0364.2060505@psg.com> <47d0403c0901131335h46e7b151p3768de9a3e2c2027@mail.gmail.com> <EC370904A7B74B93887C79E120CA2835@adnote989> <085BEE07-BAE5-4A45-A14D-9587987FAA5C@mac.com> <496F44FA.1070004@andric.com> <48C1C477-B7BE-43B0-AC57-9DEB7BF9AA88@mac.com> <496F7347.4060007@andric.com> <A8E47805-888E-4282-8623-72A65B593D47@mac.com> <496F8D8A.1060508@andric.com>

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On Jan 15, 2009, at 11:24 AM, Dimitry Andric wrote:

> On 2009-01-15 19:05, Marcel Moolenaar wrote:
>>> Hmm, strangely enough I have multiple systems which really do use  
>>> ad0s1
>>> while installed DD using sysinstall, and have been using that  
>>> since years...
>> This is a problem with sysinstall. It looks like DD is broken.
>> MBR partitions are always created.
>
> Indeed, and the MBR itself is filled with /boot/boot1, plus a  
> partition
> table.  It is possible this was done to appease some PC BIOSes,  
> because
> some of those refuse to boot, if there is no "valid" MBR with an  
> active
> partition...

You need a boot sector for the BIOS to jump into, but
it doesn't have to be a MBR with slices. That's why
a DD has something that looks an awful lot like a MBR
in the first sector. It could very well be boot sector
of an FAT* file system.
>
>> GEOM_PART correctly uses the
>> BSD disklabel that's in the 2nd sector, but GEOM_MBR claims the
>> MBR being unaware that the disk is DD.
>
> But how can this be, if I don't have GEOM_MBR in my kernel config?   
> (I'm
> using GENERIC, in fact.)

sys/i386/config DEFAULTS is included implicitly. It
used to have GEOM_BSD and GEOM_MBR.

>> libdisk is broken in that it should
>> not create MBR slices for DD configurations to begin with...
>
> As stated above, this might be on purpose; enough braindead BIOSes out
> there... :)

Creating ambiguous, conflicting and/or overlapping partition
information to work around broken BIOSes to support DD, is
not a solution *if* it was on purpose. You want it to fail
so that the user partitions the disk in the normal way.

Put differently: if there are enough braindead BIOSes out
there that won't support DD, then DD should be de-supported
by FreeBSD.

-- 
Marcel Moolenaar
xcllnt@mac.com






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