Re: GPT detection regression in efi.c from commit 27a7c64

[Matt Porter]

On 09/13/2013 02:07 PM, Davidlohr Bueso wrote:
> On Fri, 2013-09-13 at 13:01 -0400, Matt Porter wrote:
> > On 09/13/2013 12:28 PM, Davidlohr Bueso wrote:
> > > Cc'ing Linus.
> > >
> > > On Fri, 2013-09-13 at 10:50 -0400, Matt Porter wrote:
> > > > The commit, "27a7c64 partitions/efi: account for pmbr size in lba", that
> > > > was just merged in 3.12-rc caused a regression on my system with a GPT
> > > > formatted eMMC device. In 3.11, the GPT partition table was detected
> > > > fine but now a partition table is not detected.
> > > >
> > > > Not being a GPT expert, I did some research and found that the tool used
> > > > to create the PMBR on my system shares characteristics with what is
> > > > mentioned in an explanation of Microsoft created PMBRs [1]. In short,
> > > > the size_in_lba field incorrectly has 0xffffffff even though I have a
> > > > <2TiB drive (16GiB eMMC).
> > >
> > > *sigh*. So Microsoft decided to do its own version of the GPT specs.
> >
> > Don't sound so surprised. :)
> >
> > > Up until now, Linux was incorrectly enforcing pMBR checks: not
> > > recognizing valid labels and vice versa, as with the case you are
> > > mentioning now. The changes that went in the 3.12 merge window attempt
> > > to address those concerns, enforcing the correct checks - which is also
> > > how Linux partitioning tools do it (fdisk, parted).
> >
> > Understood, and we are fixing our own manufacturing tool that was used
> > to prepopulate the eMMC. I definitely prefer to have this correct for my
> > case.
>
> Come to think of it, we do have a long existing workaround: the
> force_gpt option. Setting it will bypass any MBR checking
> (is_pmbr_valid(), specifically).

Yes, that's what I used at first after seeing what the problem was. But 
then I opted to fix my PMBR.

I felt like it was a regression since it required a new option passed on 
the cmdline.

-Matt

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