Re: [PATCH 00/28] Initial implementation of bootmethod/bootflow

[Tom Rini <trini@konsulko.com>]

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On Mon, Aug 23, 2021 at 11:25:42AM -0600, Simon Glass wrote:
> Hi Mark,
> 
> On Mon, 23 Aug 2021 at 05:54, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
> >
> > > From: Simon Glass <sjg@chromium.org>
> > > Date: Wed, 18 Aug 2021 21:45:33 -0600
> > >
> > > Bootmethod and bootflow provide a built-in way for U-Boot to automatically boot
> > > an Operating System without custom scripting and other customisation:
> > >
> > >   - bootmethod - a method to scan a device to find bootflows (owned by U-Boot)
> > >   - bootflow - a description of how to boot (owned by the distro)
> > >
> > > This series provides an initial implementation of these, enable to scan
> > > for bootflows from MMC and Ethernet. The only bootflow supported is
> > > distro boot, i.e. an extlinux.conf file included on a filesystem or
> > > tftp server. It works similiarly to the existing script-based approach,
> > > but is native to U-Boot.
> > >
> > > With this we can boot on a Raspberry Pi 3 with just one command:
> > >
> > >    bootflow scan -lb
> > >
> > > which means to scan, listing (-l) each bootflow and trying to boot each
> > > one (-b). The final patch shows this.
> > >
> > > It is intended that this approach be expanded to support mechanisms other
> > > than distro boot, including EFI-related ones. With a standard way to
> > > identify boot devices, these features become easier. It also should
> > > support U-Boot scripts, for backwards compatibility only.
> > >
> > > The first patch of this series moves boot-related code out of common/ and
> > > into a new boot/ directory. This helps to collect these related files
> > > in one place, as common/ is quite large.
> > >
> > > Like sysboot, this feature makes use of the existing PXE implementation.
> > > Much of this series consists of cleaning up that code and refactoring it
> > > into something closer to a module that can be called, teasing apart its
> > > reliance on the command-line interpreter to access filesystems and the
> > > like. Also it now uses function arguments and its own context struct
> > > internally rather than environment variables, which is very hard to
> > > follow. No core functional change is included in the included PXE patches.
> > >
> > > For documentation, see the 'doc' patch.
> > >
> > > There is quite a long list of future work included in the documentation.
> > > One question is the choice of naming. Since this is a bootloader, should
> > > we just call this a 'method' and a 'flow' ? The 'boot' prefix is already
> > > shared by other commands like bootm, booti, etc.
> > >
> > > The design is described here:
> > >
> > > https://drive.google.com/file/d/1ggW0KJpUOR__vBkj3l61L2dav4ZkNC12/view?usp=sharing
> > >
> > > The series is available at u-boot-dm/bmea-working
> >
> > How does the user control the order in which devices are scanned/booted?
> 
> That is not supported in distroboot at present, at least so far as I
> can see. For Fedora it seems to happen in grub. Do I have that right?

Well, there's "find the next stage", which is boot_targets environment
variable, and then "where that next stage looks for stuff" which is
OS-dependent.  Sometimes the ESP grub.cfg file is just enough to tell
grub to find the full grub.cfg file elsewhere, and sometimes it's a full
grub.cfg file.  I think Mark is talking about the former, and you've
said it's not part of this series, yet, but on the TODO list.

-- 
Tom

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