[U-Boot] [PATCH 1/3] config: introduce a generic $bootcmd

Stephen Warren
2014-08-11T16:53:30Z

On 08/10/2014 10:53 AM, Jeroen Hofstee wrote:
> Hello Stephan,
>
> On 10-08-14 05:11, Stephen Warren wrote:
>> The entire point of this series is to prevent distros from having to
>> install bootloader-specific boot configuration files.
>
> I fail to see why this is something to pursue. Since the distro knows
> the boot path, why should u-boot be polling all possible options?

This patch series allows U-Boot to find the OS and boot it. U-Boot is
searching for some kind of boot configuration file.

This part of the process is the same as the BIOS searching all known
possible boot devices for a partition marked bootable, and with a valid
MBR. Or, it's the same as UEFI searching all possible boot devices for
whatever config file or boot binary is mandated by UEFI.

U-Boot performs this searching before having any knowledge of the OS;
there's no way for the OS to parameterize this search path, just like
OSs don't configure a PC BIOS to search a specific HDD/floppy/CDROM for
the MBR to boot.

Once U-Boot locates extlinux.conf or boot.scr, that file encodes what
files (kernel, DTB, initrd) to load to boot the OS, what kernel
command-line to use, etc. This configuration file or script is written
by the OS, and is where knowledge such as root filesystem identity may
be encoded.