[PATCH 1/4] boot: pxe_utils: Add fallback support

[Tom Rini]

On Thu, Oct 03, 2024 at 10:00:33AM +0100, Martyn Welch wrote:
> On Wed, 2024-10-02 at 13:16 -0600, Tom Rini wrote:
> > On Wed, Oct 02, 2024 at 02:26:30PM +0100, Martyn Welch wrote:
> > > When configured correctly, we can detect when boot fails after the
> > > boot
> > > process has been handed over to the kernel through the use of U-
> > > Boot's
> > > bootcount support. In some instances, such as when we are
> > > performing
> > > atomic updates via a system such as OSTree, it is desirable to
> > > provide a
> > > fallback option so that we can return to a previous (hopefully
> > > working)
> > > state.
> > > 
> > > Add a "fallback" option to the supported extlinux configuration
> > > options
> > > that points to a label like "default" so that we can utilise this
> > > in
> > > later commits.
> > > 
> > > Signed-off-by: Martyn Welch <martyn.welch at collabora.com>
> > 
> > Is "fallback" part of the nominal extlinux specification?
> > 
> 
> When looking at options to implement this functionality, I did spend
> some time looking for an extlinux specification. The best I could find
> was:
> 
> https://wiki.syslinux.org/wiki/index.php
> 
> Putting aside the difference in syntax from that used by the syslinux
> project, of the 22 keywords currently supported by U-Boot, only 13 of
> them are mentioned there (surprisingly the syslinux documentation
> doesn't include "title" as an option).
> 
> I'd come to the conclusion that U-Boot already provides a greatly
> extended version of the syntax, made suitable for booting in a wider
> variety of instances than catered for by the syslinux project.
> 
> Though I admit, I could have missed another better source to
> documentation. Is that the one you're thinking of or is there a better
> one?

I was thinking of https://systemd.io/BOOT_LOADER_SPECIFICATION/ which is
now https://uapi-group.org/specifications/specs/boot_loader_specification/
and only has 11 keywords. So, yeah, I guess this is another place where
we'll keep doing what's needed to make things more useful and see what
happens down the road. I'm fine with what's being added in this series.
Thanks!

-- 
Tom
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