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

[Martyn Welch]

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?

Martyn