[U-Boot] [PATCH v3 8/8] cmd: env: add "-e" option for handling UEFI variables

Alexander Graf
2018-12-23T01:56:40Z

On 19.12.18 13:23, Heinrich Schuchardt wrote:
> On 12/19/18 2:49 AM, AKASHI Takahiro wrote:
>> Heinrich,
>>
>> On Tue, Dec 18, 2018 at 07:07:02AM +0100, Heinrich Schuchardt wrote:
>>> On 12/18/18 6:05 AM, AKASHI Takahiro wrote:
>>>> "env [print|set] -e" allows for handling uefi variables without
>>>> knowing details about mapping to corresponding u-boot variables.
>>>>
>>>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
>>>
>>> Hello Takahiro,
>>>
>>> in several patch series you are implementing multiple interactive
>>> commands that concern
>>>
>>> - handling of EFI variables
>>> - executing EFI binaries
>>> - managing boot sequence
>>>
>>> I very much appreciate your effort to provide an independent UEFI shell
>>> implementation. What I am worried about is that your current patches
>>> make it part of the monolithic U-Boot binary.
>>
>> First of all, in v3, CONFIG_CMD_EFISHELL was introduced after Alex's
>> comment on v2. So you can disable efishell command if you don't want it.
>>
>> Are you still worried?
>>
>>> This design has multiple drawbacks:
>>>
>>> The memory size available for U-Boot is very limited for many devices.
>>> We already had to disable EFI_LOADER for some boards due to this
>>> limitations. Hence we want to keep everything out of the U-Boot binary
>>> that does not serve the primary goal of loading and executing the next
>>> binary.
>>
>> I don't know your point here. If EFI_LOADER is disabled, efishell
>> will never be compiled in.
>>
>>> The UEFI forum has published a UEFI Shell specification which is very
>>> extensive. We still have a lot of deficiencies in U-Boot's UEFI API
>>> implementation. By merging in parts of an UEFI shell implementation our
>>> project looses focus.
>>
>> What is "our project?" What is "focus?"
>> I'm just asking as I want to share that information with you.
>>
>>> There is an EDK2 implementation of said
>>> specification. If we fix the remaining bugs of the EFI API
>>> implementation in U-Boot we could simply run the EDK2 shell which
>>> provides all that is needed for interactive work.
>>>
>>> With you monolithic approach your UEFI shell implementation can neither
>>> be used with other UEFI API implementations than U-Boot nor can it be
>>> tested against other API implementations.
>>
>> Let me explain my stance.
>> My efishell is basically something like a pursuit as well as
>> a debug/test tool which was and is still quite useful for me.
>> Without it, I would have completed (most of) my efi-related work so far.
>> So I believe that it will also be useful for other people who may want
>> to get involved and play with u-boot's efi environment.
>
> On SD-Cards U-Boot is installed between the MBR and the first partition.
> On other devices it is put into a very small ROM. Both ways the maximum
> size is rather limited.
>
> U-Boot provides all that is needed to load and execute an EFI binary. So
> you can put your efishell as file into the EFI partition like you would
> install the EDK2 shell.
>
> The only hardshift this approach brings is that you have to implement
> your own printf because UEFI does not offer formatted output. But this
> can be copied from lib/efi_selftest/efi_selftest_console.c.
>
> The same decision I took for booting from iSCSI. I did not try to put an
> iSCSI driver into U-Boot instead I use iPXE as an executable that is
> loaded from the EFI partition.
>
>>
>> I have never intended to fully implement a shell which is to be compliant
>> with UEFI specification while I'm trying to mimick some command
>> interfaces for convenience. UEFI shell, as you know, provides plenty
>> of "protocols" on which some UEFI applications, including UEFI SCT,
>> reply. I will never implement it with my efishell.
>>
>> I hope that my efishell is a quick and easy way of learning more about
>> u-boot's uefi environment. I will be even happier if more people
>> get involved there.
>>
>>> Due to these considerations I suggest that you build your UEFI shell
>>> implementation as a separate UEFI binary (like helloworld.efi). You may
>>> offer an embedding of the binary (like the bootefi hello command) into
>>> the finally linked U-Boot binary via a configuration variable. Please,
>>> put the shell implementation into a separate directory. You may want to
>>> designate yourself as maintainer (in file MAINTAINERS).
>>
>> Yeah, your suggestion is reasonable and I have thought of it before.
>> There are, however, several reasons that I haven't done so; particularly,
>> efishell is implemented not only with boottime services but also
>> other helper functions, say, from device path utilities. Exporting them
>> as libraries is possible but I don't think that it would be so valuable.
>>
>> Even if efishell is a separate application, it will not contribute to
>> reduce the total footprint if it is embedded along with u-boot binary.
>
> That is why CONFIG_CMD_BOOTEFI_HELLO - which embeds helloworld.efi into
> the U-Boot binary - is default no. Same I would do for efishell.efi.

One big drawback with a separate binary is the missing command line
integration. It becomes quite awkward to execute efi debug commands
then, since you'll have to run them through a special bootefi subcommand.

If you really want to have a "uefi shell", I think the sanest option is
to just provide a built-in copy of the edk2 uefi shell, similar to the
hello world binary. The big benefit of this patch set however, is not
that we get a shell - it's that we get quick and tiny debug
introspectability into efi_loader data structures.

I think the biggest problem here really is the name of the code. Why
don't we just call it "debugefi"? It would be default N except for debug
targets (just like bootefi_hello).

That way when someone wants to just quickly introspect internal data
structures, they can. I also hope that if the name contains debug,
nobody will expect command line compatibility going forward, so we have
much more freedom to change internals (which is my biggest concern).

So in my opinion, if you fix the 2 other comments from Heinrich and
rename everything from "efishell" to "debugefi" (so it aligns with
bootefi), we should be good.

Alex