[U-Boot] [PATCH] gpt: add part-uuid and part-num subcommands

[Lukasz Majewski <l.majewski@majess.pl>]

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Hi Andrey,

> Hi Lukasz,
> 
> On Tue, Nov 14, 2017 at 1:45 AM, Lukasz Majewski
> <l.majewski@majess.pl> wrote:
> > Hi Andrey,
> >  
> >> Hi Lukasz,
> >>
> >> On Thu, Nov 9, 2017 at 2:28 PM, Lukasz Majewski
> >> <l.majewski@majess.pl> wrote:  
> >> > On Thu, 9 Nov 2017 07:34:44 -0800
> >> > Andrey Yurovsky <yurovsky@gmail.com> wrote:
> >> >  
> >> >> On Thu, Nov 9, 2017 at 1:55 AM, Lukasz Majewski
> >> >> <l.majewski@majess.pl> wrote:  
> >> >> > Hi Andrey,
> >> >> >  
> >> >> >> Hi Otavio,
> >> >> >>
> >> >> >> On Wed, Nov 8, 2017 at 2:47 AM, Otavio Salvador
> >> >> >> <otavio.salvador@ossystems.com.br> wrote:  
> >> >> >> > On Tue, Nov 7, 2017 at 10:43 PM, your name
> >> >> >> > <yurovsky@gmail.com> wrote:  
> >> >> >> >> From: Andrey Yurovsky <yurovsky@gmail.com>
> >> >> >> >>
> >> >> >> >> It is useful to be able to retrieve a partition UUID or
> >> >> >> >> number given the partition label, for instance some
> >> >> >> >> systems use the partition label to indicate the purpose
> >> >> >> >> of the partition (such as "rootfs0" being the 0th root
> >> >> >> >> file system in an A/B image scheme).
> >> >> >> >>
> >> >> >> >> Add "gpt part-uuid" to retrieve the partition UUID for a
> >> >> >> >> given label and "gpt part-num" to retrieve the partition
> >> >> >> >> number for a given label along with some documentation.
> >> >> >> >>
> >> >> >> >> Signed-off-by: Andrey Yurovsky <yurovsky@gmail.com>  
> >> >> >> >
> >> >> >> > Why not use the 'part' cmd? it provides it.  
> >> >> >>
> >> >> >> Sorry, I missed the part cmd, it doesn't seem to be
> >> >> >> documented in doc/ and it's unclear what <dev> means there.  
> >> >> >
> >> >> > If I may ask - Andrey, if you are now on this "topic" - would
> >> >> > you dare to add some ./doc entry for 'part' command?  
> >> >>
> >> >> Yes, I will do that.  
> >> >
> >> > Thanks :-)  
> >>
> >> On further investigation I am not sure that it's possible to extend
> >> the part command to retrieve UUIDs by label because of the design
> >> of the partition type drivers. Here is how I understand it to work:
> >> 1. the "part" command uses part_get_info() and in turn gets a
> >> partition driver and can call print() there (which is how EFI/GPT
> >> disks are printed with "part list"). The right information
> >> (including label) is printed but it's not tied to the caller in
> >> any way.  
> >
> > Maybe you can set some env variable with proper data?
> >
> > For example, please refer to ./cmd/part.c do_part_start() function.
> >
> > Example call from envs (include/configs/display5.h):
> >         "part start mmc ${mmcdev} ${kernel_part} lba_start; " \
> >  
> 
> Again that assumes the partition is referred to by number, I need it
> to be by label, and the part/disk interface does not seem to have any
> way to utilize labels. Unfortunately it looks like my original
> approach with the gpt command is the only way to implement this with
> the current design (at least from what I see here). Please let me know
> if I've missed something. Thanks!

Please correct me if I'm wrong - you need the starting LBA of the
partition named e.g. "FOO" in gpt ?

Conceptually it would be correct to have:

part start <interface> <dev> <NAME - e.g.'FOO'> <env to set>
gpt start <interface> <dev> <NAME- e.g. 'FOO'> <env to set>

If your code is really _small_ and can be used only with GPT, then lets
go for the second option.

-- 
Best regards,

Łukasz Majewski
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