Re: Re: [PATCH v2 3/3] efi: Capsule update with user helper interface

[Andy Lutomirski <luto@amacapital.net>]

On Tue, Mar 10, 2015 at 8:40 AM, Peter Jones <pjones@redhat.com> wrote:
>
>> >> So, for the sysfs interface, let's not allow loading from /lib. Let's
>> >> not require a userland tool. Let's just do,
>> >>
>> >>   # echo /path/to/my/awesome/capsule.bin > /sys/../capsule
>> >
>> >>
>> >> and be done with it.
>> >>
>> >> Hmmm?
>> >
>> > I assume you're implying a) the capsule header with the guid is embedded
>> > in the .bin there already, and b) one contiguous write(2) with error
>> > reporting coming through something like vars.c's efi_status_to_err()?
>> >
>> > If so, yes, I prefer this API.
>> >
>>
>> Is using a char device really so bad?  I have a "simple_char" that
>> makes this really easy that's pending review.
>
> As long as there's straightforward propagation of the EFI_STATUS return
> from UpdateCapsule() back, sysfs file vs char device makes very little
> difference to me.  Either way it's open(), write(), close().  Using the
> runtime firmware upload interface designed for wifi and scsi devices is
> the part I don't really like.
>

I'm not 100% happy with write(2) (which is all we have in sysfs) for
two reasons:

1. If we write a file name, eww.  That's more complicated, requires
temporary files, has annoying mount namespace issues, etc.

2. If we write the full contents, we need to do it in a single call to
write.  That means that we can't use cat, which mostly defeats the
purpose.  In fact, using cat could be actively harmful.


--Andy