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Re: Several GNU projects wondering about the reason for mformat partitio
From: |
Mihai Moldovan |
Subject: |
Re: Several GNU projects wondering about the reason for mformat partition table |
Date: |
Tue, 21 May 2019 00:09:43 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 |
* On 5/20/19 6:52 PM, Thomas Schmitt wrote:
> in the course of a problem search between GRUB, Guix, and xorriso we found
> the trigger of a problem with some old Macbook EFI firmware in a gesture
> of mformat.
> Line 1375 of
>
> http://svn.savannah.gnu.org/viewvc/mtools/trunk/mformat.c?revision=506&view=markup
> has
>
> /* install fake partition table pointing to itself */
>
> Now we are wondering for which use case there is this MBR partition table
> entry starting with LBA 0 and claiming the whole device.
>
> The SVN at savannah shows that this gesture was introduced with revision 4
> in may 2002 by "aknaff". My hope is that this was you and that you can tell
> grub-devel (Cc'ed) more about the motivation.
No authoritative answer from me, but if this is coupling GPT + MBR, creating a
MBR partition table from LBA 0 to the end of (reachable) device space (which is
not necessarily the actual device space/end for limiting factors such as disk
sector size [mis-]usage and the like) is a pretty common thing to do and called
"protective MBR". The rationale being to "trick" tools that are only MBR-aware
into thinking that the device is NOT unpartitioned and hence not erroring out or
offering to "correct the situation".
Mihai
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