[parted-devel] [PATCH] GPT -> MBR synchronization

[Alexander Graf]

On Jul 29, 2008, at 7:10 PM, H. Peter Anvin wrote:

> Alexander Graf wrote:
>> While this would work for most Linux systems and other OSs that are  
>> GPT-aware, it fails miserably when you try to bring Windows into  
>> the game.
>> Imagine the following Scenario:
>> I have a Mac. This Mac has 4 partitions on it:
>> 1. EFI driver partition
>> 2. Mac OS X
>> 3. Windows
>> 4. Linux
>> When you did the GPT->MBR sync, Linux was the active partition and  
>> thus the only one being in sync on the MBR. How do you boot Windows?
>> Another problem would be that even if Windows would've been the  
>> active partition at that time and we forget all other points  
>> against that, you wouldn't be able to access the Linux or Mac OS X  
>> partition within Windows, assuming it's not capable of using the  
>> GPT properly (which at least the Windows XP I last used was not).
>> So basically it's not a good idea to sync only the active partition.
>
> Well, if you have more than 4 partitions, you do have to make  
> tradeoffs.
>
> FWIW, I *do* believe at least some types of Windows can understand  
> GPT for the purpose of data partitions, but XP might not be one of  
> them.
>
> I really don't want to see us hard-wire the first four, however;  
> that's worse than anything.  I guess you end up wanting a virtual  
> flag of some sort.

By then you'd be back at Olaf Hering's patch. I don't really like the  
manual attachment of GPT to MBR partitions, because that'd require a  
lot of effort in all the tools actually working with the partition  
table, including consistency throughout them.

If you like Olaf's approach though, feel free to take his old patch,  
help him get it upstream and try to convince everyone to use it :-).  
I'm the last person against that - I only wanted to have something  
that "just works" without the user having to deal with it.

For now it's the only solution that came to my mind that didn't  
require anyone to change existing toolchains or behavior. As soon as  
you use a GPT you'd get the MBR entries "for free". And the "the  
active partition is within the first four partitions" restriction was  
there with MBR already, so I believe it's acceptable for most users -  
at least until we  go all EFI.

Alex