Re: [PATCH] Add GRUB_DISABLE_UUID.

[Javier Martinez Canillas]

On 9/20/19 5:03 PM, Didier Spaier wrote:
> On 20/09/2019 15:23, Javier Martinez Canillas wrote:
>> On 9/20/19 2:42 PM, Daniel Kiper wrote:
>>> On Thu, Sep 19, 2019 at 02:20:06PM +0200, Javier Martinez Canillas wrote:
>>>> Hello Daniel,
>>>>
>>>> On 9/18/19 2:39 PM, Daniel Kiper wrote:
>>>>> Adding Nicholas...
>>>>>
>>>>> On Tue, Sep 17, 2019 at 05:48:45PM +0200, Javier Martinez Canillas wrote:
>>>>>> From: Peter Jones <address@hidden>
>>>>>>
>>>>>> This will cause "search --fs-uuid --set=root ..." not to be generated by
>>>>>> grub2-mkconfig, and instead simply attempt to use the grub device name
>>>>>> as it understands it.
>>>>>>
>>>>>> Signed-off-by: Peter Jones <address@hidden>
>>>>>> Signed-off-by: Javier Martinez Canillas <address@hidden>
>>>>>
>>>>> We have this functionality in GRUB upstream. Please take a look at
>>>>> commit 51be3372e (templates: Update grub script template files).
>>>>> Could you pick it up in RH/Fedora?
>>>>>
>>>>
>>>> That commit does something different if I'm reading it correctly. It's 
>>>> about
>>>> allowing to set the root kernel command line parameter to a PARTUUID 
>>>> instead
>>>> of a UUID or a device name, by using the grub-probe --target=partuuid 
>>>> option.
>>>>
>>>> But Peter's patch is about setting the root param to a device name instead
>>>> of a UUID.
>>>>
>>>> And also about not adding search commands in the grub.cfg to set the $root
>>>> and $boot grub environment variables by searching using a UUID.
>>>>
>>>> Now digging more I found that there's already a GRUB_DISABLE_LINUX_UUID 
>>>> option
>>>
>>> There are two variables: GRUB_DISABLE_LINUX_UUID and 
>>> GRUB_DISABLE_LINUX_PARTUUID.
>>>
>>
>> Yes. I didn't mention the GRUB_DISABLE_LINUX_PARTUUID variable because the 
>> search
>> command only has support to search using the UUID and not the PARTUUID.
> 
> It has support to search using the PARTUUID in case of a GPT, cf. commit
> f2b9083f859c7dbf44a7a8e96ee0cf202f9a4187
>

I see. I missed that commit since is newer than grub-2.04 which is what we
are using as the base for our package now.

But that commit adds PARTUUID support to the probe command, not the search
command. We can later add a GRUB_DISABLE_PARTUUID variable to disable the
search using a PARTUUID, once the search command gets a --part-uuid option
and a command using that option is added to grub.cfg to search the devices.

> As an aside, it would be very useful to extend this support to dos
> partition tables. I believe that all partition tools create a disk
> identifier when creating a dos partition table (at least fdisk, cfdisk
> and parted do) so if I am not mislead-ed all dos partitions should have
> a partuuid in the form DisklabelPartitionnumber.
>
> This would allow e.g. to find the root Linux partitions from a rescue
> media, even if the kernel has no associated initrd.
>

Agreed.

Best regards,
-- 
Javier Martinez Canillas
Software Engineer - Desktop Hardware Enablement
Red Hat