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Re: [bug #46716] Protective MBR partition is not marked as bootable

From: Andrei Borzenkov
Subject: Re: [bug #46716] Protective MBR partition is not marked as bootable
Date: Sat, 19 Dec 2015 19:58:21 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0

19.12.2015 18:53, Thomas Schmitt пишет:
> Hi,
> Alexander E. Patrakov wrote:
>> [resending after the rejection, now I am subscribed to both lists]
> Hm. I got your first reply to Andrei and bug-xorriso after
> i freed it from the bug-xorriso list jail.
> Andrei's was on hold too.
> Hopefully i now exempted both of you from moderator review.
> ... ah yes. My first mail got rejected by bug-grub(-owner)@gnu.org
> I hope bug-xorriso is more friendly to newcomers.
> (I have subscribed to bug-grub now and resend.)
>> So here is an alternative proposal. I was able to fix up the iso by creating
>> a second partition of the same geometry, of type 0, and with bootable flag
>> on.
> I am not sure whether this is generally better from the view
> of EFI.
> Either we shall have MBR partitioning with possibly a 0xef
> partition, or we shall have GPT with only one protective
> partition 0xee in the MBR.
>> 1. The partition with type 0xee should start at sector 1 and be
>> non-bootable, otherwise the GPT is treated as invalid.
>> 2. There should be no overlap between partitions of type != 0.
>> 3. There should be a bootable partition in the MBR.
> I currently try to talk Debian out of nesting partitions,
> even id the big one is type 0x00.
> My proposal is rather to avoid GPT and to use the EFI option to
> partition by a conventional MBR partition table.

a) are we sure every EFI system out there accepts MBR (Apple?)

b) GPT has nice feature of self-identifying block size. This allows grub
rescue CD to access GPT partitions both in HDD mode (with 512B blocks)
and CD mode (with 2K blocks). I am not sure how it important it is
though. GRUB itself does not really need access to underlying ESP; but
there were several requests to support it.

> That would also make possible to have the first partition mountable.
> The price would be (currently):
> - The EFI system partion has to exist twice. Once as file in the
>   ISO to be usable as El Torito boot image. Once after the ISO,
>   so that ISO partition and EFI system partition do not overlap.
> - The EFI system partition would not be covered by the ISO size.
>   Some scripts which checkread after copying might only read
>   that amount of bytes and report mismatch.
> Have a nice day :)
> Thomas
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