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

[AKASHI Takahiro]

On Thu, Jan 16, 2020 at 10:31:49PM +0200, Andy Shevchenko wrote:
> 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

I also misunderstood your assumption above; You are developing
a linux-based USB gadget for Windows (10)?

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

So why do you want to access *that* partition from U-Boot on the board?
I don't think it is a common case.

-Takahiro Akashi

> 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