Re: [PATCH 0/2] Support plain encryption mode.

[Glenn Washburn]

On Wed, 02 Feb 2022 15:00:10 +0000
Maxim Fomin <maxim@fomin.one> wrote:

> ------- Original Message -------
> > >
> > > Plainmount can work with '(hdX,gptY)' syntax in config or shell 
> > > (actually, this
> > >
> > > is the base syntax) and thus it is not limited to GPT paritions, what is 
> > > limited
> > >
> > > is the ability to use UUID - currently only on GPT. If partition scheme 
> > > does not
> > >
> > > have UUID then UUID as a convenience feature cannot be supported - 
> > > inconvenient,
> > >
> > > but technically fair. I will take a look at MBR UUID and see whether they 
> > > can be
> > >
> > > supported. Possible situations (under current implementaion) are follows:
> > >
> > > a) GPT disk, multi-disk environment, disks map unpredictably: can name 
> > > partitions
> > >
> > > by GPT UUID in config file/shell, no problem, ability to name by UUID has 
> > > value
> >
> > I agree that searching by partition UUID is useful and desirable.
> >
> > However, I don't think this is the right approach. GRUB should have
> >
> > generic searching by partition UUID. There is already a patch for
> >
> > this[1]. Perhaps you can test/review this patch to help it gain more
> >
> > visibility and advocate for it being accepted.
> >
> > Glenn
> >
> > [1] https://lists.gnu.org/archive/html/grub-devel/2021-04/msg00055.html
> >
> 
> Such function (or several functions) should be added into grub 'library', so 
> it can be
> used to search disk by PART UUID in different places. The patch you refer to 
> seems to
> add this functionality only to 'search' grub command via 'void 
> grub_search_partuuid'
> function. Can it be reused on other places? It seems in oder to use it, grub 
> code must
> call 'search' command and receive the result from grub environment variable 
> which is
> not convinient for other grub code interested in this feature. I think the 
> proper way
> to do it is to write some library function which can be used by search, probe 
> (btw I
> borrowed some details from it - so there is code duplication in search/probe),
> plainmount commands and other commands in grub.

I agree that reducing code duplication would be a good idea.
Essentially the grub 'library' you're wanting exists as the kernel code
that is always loaded. Would you like to find a good place to put the
common partition uuid matching code and send a patch?

As far as plainmount is concerned, I wasn't envisioning that it use
that code directly and it shouldn't. I was imagining something like
this snippet of GRUB script:

  search --partuuid --set KEYFILEDISK -u $PARTUUID
  plainmount -k ($KEYFILEDISK)/path/to/keyfile <other options>

Glenn