[U-Boot] [PATCH 1/2] FAT: check for partition 0 not 1 for whole-disk fs

[Stephen Warren <swarren@wwwdotorg.org>]

On 10/05/2012 05:39 PM, Tom Rini wrote:
> On 10/05/12 16:36, Stephen Warren wrote:
>> On 10/05/2012 05:27 PM, Tom Rini wrote:
>>> On 10/05/12 16:17, Stephen Warren wrote:
>>>> From: Stephen Warren <swarren@nvidia.com>
>>> 
>>>> The recent switch to use get_device_and_partition() from 
>>>> do_fat_ls() broke the ability to access a FAT filesystem 
>>>> directly on a whole device; FAT only works within a
>>>> partition on a device.
>>> 
>>>> This change makes e.g. "fatls mmc 0:0" work; explicitly 
>>>> requesting partition ID 0 is something that 
>>>> get_device_and_partition() fully supports. However, 
>>>> fat_register_device() expects partition ID 1 to be used in
>>>> the full-disk case; partition ID 1 was previously implicitly
>>>>  specified when the user didn't actually specify a partition 
>>>> ID. Update fat_register_device() to expect the correct ID.
>>> 
>>>> This change does imply that if a user explicitly executes 
>>>> "fatls mmc 0:1" then this will fail, and may be a change in 
>>>> behaviour.
>>> 
>>> So wait, you can't list device 0, bus 1 after this patch?
> 
>> That's partition 1 not bus 1.
> 
> Er yes, thinko there.
> 
>> In the context of having a raw FAT filesystem on a device with no
>>  partition table, the partition specification "0:1" doesn't work 
>> before or after this patch; I believe (if it worked at all ever 
>> before) it was broken by the previous get_device_and_partition() 
>> rework.
> 
>> If you do have a partition table, then "0:1" works just fine 
>> with/without this patch.
> 
> OK, so the behavior change here, potentially involves 2 partitions 
> without a partition table?  What is the case where fatls mmc 0:1
> would fail now?

The failure case involves zero partitions. The issue is that the
following works just fine:

fdisk /dev/sda
mkfs.dos /dev/sdaN    for any N

but the following fails:

mkfs.dos /dev/sda (i.e. raw on the disk with no partition table)

In the latter case, I /think/ either of the following might have
worked in U-Boot until recently:

(1) fatls mmc 0 /       # Surely this worked
(2) fatls mmc 0:1 /     # I'm not sure if this works

This patch makes (1) above work.

Patch 2 in this series makes the new equivalent of (2) work, namely:

fatls mmc 0:0 /

The second 0 there is "partition 0" which means "the whole disk".
IIRC, I called out that behaviour change in the
get_device_and_partition() series anyway.