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

[Simon Glass]

Hi Tom,

On Thu, 19 Aug 2021 at 07:59, Tom Rini <trini at konsulko.com> wrote:
>
> On Wed, Aug 18, 2021 at 09:45:33PM -0600, Simon Glass wrote:
>
> > 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
>
> My question / concern is this.  Would the next step here be to
> implement the generic UEFI boot path?  Today, I can write Fedora 34 for
> AArch64 to a USB stick, boot U-Boot off of uSD card and the installer
> automatically boots.  I'm sure I could do the same with the BSDs.
> Reading the documentation left me with the impression that every OSV
> would be expected to write something, so that their installer / OS boot.
> But there's already standards for that, which they do, and we should be
> implementing (and do, via the current distro_boot) or making easier to
> enable.  Thanks!

Here you are talking about scanning for a bootflow. It is not actually
OS-specific. If it were, there would be no point to this :-)

If you look in the distro scripts you will see 'scan_dev_for_efi' (and
also scan_dev_for_scrips). At least the first needs to be implemented
a bit like the distro boot is at present. So far I have only
implemented scan_dev_for_extlinux (plus pxe) as it is enough to show
the concept.

Adding EFI it's likely to be about the same amount of code as distro.c
at present, perhaps a little less since we don't have the network
case. It is used by Fedora 34, I believe, so is easy enough for me to
do.  But I wanted to get something out as the concept is visible in
this series.

Regards,
Simon