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Re: Test Proposal for [bug #46716] Protective MBR partition is not marke

From: Andrei Borzenkov
Subject: Re: Test Proposal for [bug #46716] Protective MBR partition is not marked as bootable
Date: Mon, 21 Dec 2015 21:46:16 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0

21.12.2015 10:45, Thomas Schmitt пишет:
> Hi,
> Andrei Borzenkov wrote:
>> MBR is created with 512B sector size but when GRUB is booted
>> from CD-ROM sector size is 2KiB.
> Ain't that a bug ?

What exactly?

> GPT is recognized with 512. El Torito is recognized with its
> weird mix of 512 for size and 2048 for block addresses.
> The reason why APM is recorded with size 2048 is originally
> not CD compatibility but the wish to combine APM and GPT.
> (Else, the first APM entry and the GPT header would collide.)
> Would it be possible that GRUB2 applies the feature of
> self-identifying block size, in order to get MBR partitions
> to the same level of support as GPT ?

I do not see how it can be done.

> (I never found traces of MBR block size other than 512. So one
>  could set 512 as soon as partition type "msdos" is detected.
>  I assume that "msdos" is recognized by the MBR magic number
>  at bytes 510, 511 anyway.)

Yes, that may be an option. Still, using GPT is known to work; and those
implementations I am aware of ignore MBR if partition 0xee is present.
So it still looks like adding dummy bootable partition to MBR is the
least evil. I wonder how Mac will present it.

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