Date: Wed, 15 Jun 2011 16:10:12 GMT From: Marcel Moolenaar <marcel@xcllnt.net> To: freebsd-geom@FreeBSD.org Subject: Re: kern/157819: [geom] gpart(8): drop serial from MBR Message-ID: <201106151610.p5FGAC8E009874@freefall.freebsd.org>
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The following reply was made to PR kern/157819; it has been noted by GNATS.
From: Marcel Moolenaar <marcel@xcllnt.net>
To: "Andrey V. Elsukov" <ae@FreeBSD.org>
Cc: bug-followup@FreeBSD.org, eirnym@gmail.com,
Marcel Moolenaar <marcel@FreeBSD.org>
Subject: Re: kern/157819: [geom] gpart(8): drop serial from MBR
Date: Wed, 15 Jun 2011 08:43:02 -0700
On Jun 15, 2011, at 2:21 AM, Andrey V. Elsukov wrote:
> Hi,
>
> Yes, you are right. `gpart bootcode` does not keep disk signature.
> It just overwrites the whole sector and fills partition table area.
>
> I see three ways how this can be fixed:
> 1. Do not change anything :)
> 2. Always keep disk signature for each boot code.
> 3. Introduce new option for `gpart bootcode` command, i.e:
> # gpart bootcode -b /boot/boot0 -o some,boot,options ada0
I would advise against adding options. That never scales and
in this case is even the wrong thing to do.
The fundamental question we need to answer is this:
Is the serial number a well-defined field in the MBR that is
independent and unrelated to the bootcode, or not?
If those are entirely independent, then writing the bootcode
should not have the side effect of clobbering the serial
number and the MBR scheme should "merge" contents.
If they are related then what we do is right and no change
is to be made.
Since the MBR is one of those legacy structures that have
grown warts over time, I can see that different definitions
would tell us different things. Let's take the definition
that is most applicable in today's world.
My off the cuff response would be this:
If we instructions in our bootcode that occupies the space
of the serial number, then we cannot change anything, other-
wise we should probably preserve the serial number.
HTH,
--
Marcel Moolenaar
marcel@xcllnt.net
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