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Re: Obtaining the UUID of the system for a PXE boot


From: David Michael
Subject: Re: Obtaining the UUID of the system for a PXE boot
Date: Fri, 19 Jul 2013 12:31:09 -0400

Hi,

On Fri, Jul 19, 2013 at 10:24 AM, Holger Goetz <address@hidden> wrote:
> Yes it's towards the right direction. But it is 32bit only if i understand
> correctly, and it basically is a memory access to fixed/hardcoded  MEMORY
> address (0x80000001). to pick the veondor id and machine info.

It's true that I've mostly been using the module on 32-bit virtual
machines, so it hasn't really been tested elsewhere.  However, I'm not
sure I understand what you mean by the hard-coded memory address.  The
first function grub_smbios_locate_eps searches for the SMBIOS entry
point structure as described in the spec.  The table entries are then
read at the table address found in the EPS, not a hard-coded location.

> I have only 64bit - UEFI here - therefore the approach w/ first searching
> the SMBIOS infoblock in memory is probably required. And then properly walk
> through the info-tables/blocks to get to the UUID entry. It doesn'T need to
> be a fixed info to be retrieved from the SMBIOS memory - maybe a generic
> function to query/search a specific entry and return that to be assigned to
> a variable would be more flexible.

The module's command-line interface does use a (dumb) query/search
method.  You can specify the desired entry's type and/or handle and
the data to retrieve from it.  For example the following command
prints the machine name (i.e. the string at offset 5 in an entry with
type 1).

        smbios -t 1 -s 5

I think you may have found the first patch I sent in that old thread,
which was for different functionality.  The SMBIOS module can be
downloaded from the list archive[1].

Unfortunately it doesn't have any convenient functions to output a
usable UUID.  It shouldn't take much to add one: the variable "entry"
in the "main" function is a pointer to the matched entry, so entry[8]
through entry[23] is the UUID in a call "smbios -t 1 ...".  I've
verified these bytes correspond to dmidecode output on my physical
hardware with the following.

        for i in 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
        do smbios -t 1 -b $i
        done

If the module isn't salvageable on UEFI, maybe I can send out an
updated version whenever I upgrade to such a system.

Thanks.

David

[1] https://lists.gnu.org/archive/html/grub-devel/2013-04/binx8am8MvVSh.bin



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