Re: [edk2-devel] [PATCH edk2-platforms 1/4] Ext4Pkg: Use depex for unicode collation protocols

["Pedro Falcato" <pedro.falcato@gmail.com>]

On Fri, Feb 17, 2023 at 3:38 PM Marvin Häuser <mhaeuser@posteo.de> wrote:
>
>
> > On 17. Feb 2023, at 16:17, Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > So the FAT driver will happily load, but then fail in an obscure
> > manner when being started on a controller handle, in a way that is
> > indistinguishable (afict) from a partition that has not FAT file
> > system in the first place.
> >
> > So it doesn't look fine to me at all, tbh. If the collation protocols
> > are required, we should check for them in supported(), and make a lot
> > of noise in a DEBUG build if the failure condition is an unexpected
> > one, i.e., some additional protocol we dependent on (even though we
> > pretend to be a UEFI driver)  does not exist.

Hi Ard, Marvin,

First of all, thank you for raising this issue and sending a patch. I
had been quietly following the thread while trying to get my ideas
straight.

>
> Right, I meant the approach to rely on the UEFI Driver Binding handling to defer locating UC, not the exact implementation. Sounds good.
>
> @Pedro What do you think?
>

I think deferring the Unicode collation init to Start()/Supported() is
a good idea. I believe there's good value in keeping Ext4Dxe a
UEFI_DRIVER.
I was trying to come up with reasons why this would not work (in a
general UEFI-spec sense, not only in Tiano, but for instance if you
would ever want to plug this into i.e u-boot's EFI implementation).
As far as I can tell, there doesn't seem to be any? At least from a PI
PoV things should only get Start()'d in BDS right? And since other
PI-unaware implementations don't know what DXE or DXE_DRIVERs are,
it's not like that would fix those use cases.

> >
> > Alternatively, we might defer installation of the driver binding
> > protocol implementation to a callback on the collation protocol
> > installation, but that seems like more work for the same result.
>
> Agreed.

+1

-- 
Pedro