Re: root=PARTUUID for MBR/NT disk signatures?

[Stephen Warren <swarren@wwwdotorg.org>]

On 08/20/2012 12:22 PM, Tejun Heo wrote:
> Hello,
> 
> On Fri, Aug 17, 2012 at 04:10:52PM -0600, Stephen Warren wrote:
>> I was considering extending the kernel command-line option
>> root=PARTUUID= to also support MBR (NT disk signatures). I was thinking
>> of a syntax along the lines of:
>>
>> root=PARTUUID=UUUUUUUU-PP[/PARTNROFF=%d]
>>
>> ... where UUUUUUUU is the hex representation of the NT disk signature,
>> and PP is the hex representation of the partition number. Like GPT,
>> /PARTNROFF could be used too if desired.
>>
>> Related, I was thinking of changing struct partition_meta_info's uuid
>> field to be a string, so that it could simply be strcmp'd against the
>> UUID value on the kernel command-line. That way, the type of the UUID is
>> irrelevant.
>>
>> Does anyone have any objection to that?
> 
> Wouldn't that be able to break setups which work currently?

I don't believe so:

Since the newly supported UUID syntax wouldn't ever match any EFI UUID
(the lengths differ in all cases), I don't believe the new syntax would
affect behavior for any existing usage.

Obviously, part_efi.c would be modified to initialize struct
partition_meta_info's uuid field to the appropriate string
representation of the UUID so that the str(case)cmp would still succeed
for existing command-lines. I ended up coding up that part of the change
late Friday, and the feature was certainly still working OK.