fat: handle Windows formatted partition (thru USB Mass Storage)

[Andy Shevchenko]

On Thu, Jan 16, 2020 at 9:20 PM Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
> On 1/16/20 11:39 AM, Andy Shevchenko wrote:
> >
> >>> Obviously U-Boot's fat code cannot handle it.
> >>
> >> So precisely, U-Boot cannot handle nested partition( table)s?
> >
> > Seems so. We need to be able to supply the partition number we would
> > like to open, something like
> >    cmd <interface> [<dev>[:<partition>[:<nested partition>]]]
> > otherwise it will require some (error prone) heuristics to understand
> > which one user would like to use.
> >
>
> I have formatted a USB stick Windows 10.

That is *not* the case I'm describing.

Maybe I described it wrong. Let me try again.

Prerequisites:
 - the board with U-Boot and installed Linux OS on eMMC
 - g_multi module in Linux OS that shares *one of the eMMC partitions*
(pay attention here) as a disk to Windows host

Now, when you format that exposed disk (which is actually a partition
on eMMC!) in Windows, you will get nested partitioning.

P.S. I can easily reproduce this on real device with latest U-Boot.
U-Boot has obvious issue with recognizing such disks.

-- 
With Best Regards,
Andy Shevchenko