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

[Tom Rini]

On Mon, Jan 13, 2020 at 12:52:48PM +0200, Andy Shevchenko wrote:
> Hi!
> 
> I recently stumble over FAT partitioning issue. I have a device with
> MMC, one partition of which has been exported as disk via USB Mass
> Storage to the host. When Windows 10 sees that disk it can't handle it
> till I format it there. So far so good. However, the same partition
> can't be used under U-Boot due to Windows flow, i.e. it makes a
> partitioning on top of the actual partition while U-Boot expects that
> we only have one MBR (or partitioning) on the dist. So, the commands
> such fatls, fatload do not recognise any file there.
> 
> In Linux it's easy to use: mount -o loop,offset=65536 /dev/mmcblk0p9 /mnt
> (offset can be different)
> 
> But I would like to use it in U-Boot.
> 
> Any thoughts on this?

I'm not sure.  If you didn't have to use offset+loop to re-expose things
as a new disk and show the partition I'd say we need to support that
case.  But here, hmmm.  We don't have "loopback".  So, I'm not sure.
Can't you just tell Windows to use the whole device as FAT and so
mmcblk0p9 would directly be FAT and work as expected in both Linux and
U-Boot?

-- 
Tom
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