[U-Boot] [PATCH 2/2] cmd:gpt: randomly generate each partition uuid if undefined

[Tom Rini]

On Mon, Mar 03, 2014 at 04:31:35PM +0100, Przemyslaw Marczak wrote:
> Hello Tom,
> 
> On 03/03/2014 03:13 PM, Tom Rini wrote:
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> >On 03/03/2014 08:45 AM, Przemyslaw Marczak wrote:
> >
> >[snip]
> >>Actually automatically generated uuids was the main purpose of this
> >>patches. Setting each env variable in this place was the most easy way
> >>to make this without a lot of duplicated code.
> >>
> >>Why do you treat it like a side-effect?
> >>If user wants have own generated uuids - then he can manually set env
> >>variables like "uuid_gpt_disk".
> >>This actually is not changed - when uuid env is set then it will be used
> >>like in current version of code.
> >>When user can't generate uuids or just wants to have it automatically
> >>generated then my code do this job.
> >
> >Having been using this code again myself recently, at the high level,
> >this is useful.  Having to copy/paste in N UUIDs gets silly.  But I also
> >wonder..
> >
> >[snip]
> >>The one and only reason for put saveenv() here was that if uuids are
> >>randomly generated or even just are in environment then I can be sure
> >>that next gpt write (e.g. in case of overwrite sector 0 by mistake) is
> >>using the same uuids values.
> >
> >Is this really an important use case to cover?
> 
> It can be important if somebody uses UUIDS to boot kernel. In kernel
> documentation you can find a notice about kernel function
> name_to_dev_t() - so by command line you can pass uuid for root
> partition. And the same is for arg "suspend" in kernel cmd line.

Right.  But that seems to be putting things in the wrong order.  If you
need to restore UUIDs to your partition table, you pass in the optional
and already known UUID.  If you're starting from scratch, by the time
the installer is run U-Boot is long gone.  And tying things back to the
commodity distro stuff, we would be fetching 'root=UUID=...' from some
file generated and controlled on the Linux side of things anyhow.  To be
clear, on the OS side of the equation there's much better ways to find
out that partition1 has a UUID of ... than poking the U-Boot
environment.

> >The way I see things, would it be possible (and not a pain) to make the
> >UUID part of the partition string passed to 'gpt write' optional.  If
> >not passed, generate the UUIDs needed.  What was used would be seen in
> >'part list' and so forth.
> 
> Ok, so I remove saveenv() from my changes and then we will have two cases:
> 
> # gpt write mmc 0 $partitions
> case 1: envorinment uuids are not set; then:
>   proper uuids variables are set automatically (and printed)

I'd go so far as to say we don't need to print the uuids, they're
available via 'part list ...'.  A notice that we're generating UUIDs is
probably not too spammy.

> case 2: environment uuids are set in env (e.g. some user has put his
> own env); then
>   users uuids will be used and new uuids are not generated automatically
> 
> So this will not change current "gpt" usability - just add new
> feature, moreover user will be informed about each uuid generation.
> In case when someone use gpt write by mistake and overwrite uuids by
> randomly generated then he can easily back to his own uuids by
> setting each in environment and run gpt write again.

Right.  We're making the use case of "fresh device, create new table"
easier and we're still allowing "existing device, re-establish old
UUIDs".

-- 
Tom
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