Re: [PATCH] nested partitions

[Bruce Dubbs <bruce.dubbs@gmail.com>]

Robert Millan wrote:
> On Fri, Jan 22, 2010 at 07:03:21PM +0100, Vladimir 'φ-coder/phcoder' Serbinenko wrote:

>> Partition types are easily screwed. Why not just check for the presence
>> of the label?
> 
> I have a feeling I already explained this somewhere.  Doesn't seem to be in
> this thread, maybe on IRC?  Anyway, it won't hurt to ellaborate on it...
> 
> First of all, the whole label type proliferation problem is inherently
> impossible to resolve by technical means.  Labels overlap each other,
> they can coexist without any garantee that the user expects them to be
> there at all or include meaningful data.

There is a fairly long thread at util-linux-ng that discusses this 
problem in the context of very slow and very small devices.  It starts 
approximately at

http://marc.info/?l=util-linux-ng&m=126353611105795&w=2

The ultimate solution was to not search for multiple partition type 
signatures on small devices.

> You *can't* reliably check for any partition label.  

...

> So instead of supporting things like:
> 
>   (hd0,1)
>   (hd0,2)
> 
>   (ambigous; what does this mean in an hybrid MSDOS/GPT ?  What about other
>   hybrid schemes?  GRUB can't tell!)
> 
> ... we could support:
> 
>   (hd0,msdos1)
>   (hd0,gpt1)
>   (hd0,msdos2)
>   (hd0,gpt2)
> 
> whose meaning is pretty clear.  Then the user can nest as much as they like,
> but they will also have to deal with the problem of identifiing the labels.

I like this idea, but wonder if it would be useful to have something 
like (grub drive, partition type, filesystem type) for each partition to 
consider.  For example:

(hd0,gpt1,ext2)

> Minix: (hd0,msdos1,msdos1)
> 
> Solaris: (hd0,msdos2,sun1)
> 
> *BSD: (hd0,msdos3,bsd1)

> With this approach, the burden is no longer in GRUB.  Then I don't care
> how weird disk layouts can become, because GRUB doesn't have to probe
> them.  We can even support things like this if it makes users happy:
> 
>   (hd0,bsd2,msdos1,sun1,apple4,msdos1)

Can you translate that.  I don't understand.

   -- Bruce