EFI Variables
John Baldwin
jhb at freebsd.org
Wed Nov 25 02:27:05 UTC 2015
On Wednesday, October 28, 2015 01:38:28 PM Rui Paulo wrote:
> On Wed, 2015-10-28 at 07:27 +0100, Ganael Laplanche wrote:
> > On Tuesday, October 27, 2015 07:24:23 PM Emmanuel Vadot wrote:
> >
> > Hi Emmanuel,
> >
> > > I'm currently hacking around the loader.efi
> >
> > Great :)
> >
> > > I've also added the list and get command to the not working
> > > "nvram"
> > > command.
> >
> > I had myself posted a PR to fix that command as well as add a verbose
> > switch
> > and the ability to specify a variable name, see :
> >
> > https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=202614
> >
> > > For the "set" subcommand I think that the best way to handle it
> > > is :
> > > "nvram set myvar data" -> This will set the variable myvar to
> > > data with
> > > the freebsd guid (if there is any)
> > >
> > > and
> > >
> > > "nvram set myvar guid data" -> This will force the guid to <guid>
> >
> > It can be useful to set variables containing *strings*, but will
> > hardly handle
> > binary stuff :/
> >
> > I am not sure whether it should be the loader's job to set
> > variables... I can
> > think of changing the boot order, but it may be difficult to get it
> > right by
> > hand and would probably require an upper-level tool, such as
> > efibootmgr on
> > Linux.
> >
> > > I'll look tomorrow how to access efivars once the kernel is
> > > booted so
> > > we can set some from some userland tool (especially the boot
> > > related
> > > one).
> >
> > Yes, this is interesting as the current kernel (amd64) does not
> > provide access
> > to EFI variables at all.
> >
> > 10.x/ia64 provided access to EFI variables through libefi(3) and
> > io(4). It
> > should be possible to import that code to other archs too, but you'll
> > have to
> > save the entry point to the Runtime Services Tables and maybe set a
> > Virtual
> > Address Map too (not sure about that point).
> >
>
> It would be nice to set some EFI variables in the loader, but you can't
> expect to handle binary data from the loader. Like you said, we need a
> special tool to change EFI variables on a system already running
> FreeBSD.
I belive Warner has been working on adding more support for EFI runtime
services to FreeBSD multiuser which might permit this.
--
John Baldwin
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