[U-Boot] U-Boot and The Boot Loader Specification

[Alexander Dahl]

Hello Wolfgang,

thanks for your interest in this topic. I think you misunderstood my question, 
I will elaborate on that. You might skip over the technical details and read 
my questions in the end of this mail.

Am Freitag, 19. Oktober 2018, 11:10:48 CEST schrieb Wolfgang Denk:
> > As you might guess, I use ptxdist for building the BSP for an i.MX6 based
> 
> How could I guess this?  It's a pretty exotic proprietary
> environment after all.  All the world is using OE/Yocto these days

Nope, it's not proprietary, it is free software and actively maintained:

https://www.ptxdist.org/

Lots of people are also using buildroot from https://buildroot.org/ and build 
U-Boot with that. So I would not say "all the world", but that's off topic 
here. ;-)

> You still don't explain which exact command you are running that
> produces the output?
> 
> f you are running the default bootcmd secuemnce, it would make a lot
> of sense to run this sequence manually, step by step, so have an
> exact understanding of what is going on.
> 
> It _looks_ to me as if you were running $boot_extlinux in the end,
> but it would be nice to be sure...

Yes, I'm running the default bootcmd sequence, that find's the extlinux.conf 
file on the SD card and in the end boot_extlinux is run, I confirmed that. The 
one and only extlinux.conf file is found, the problem is with parsing.

> > What actually works is using an extlinux.conf similar to the examples in
> > doc/ README.distro, but there are two things to mention:
> > 
> > 1) keywords are used which are not mentioned in the upstream extlinux
> > documentation
> > 2) keywords from the bootloader spec don't work at all
> 
> If you have a look at the code (in "cmd/pxe.c"), the following
> keywords are implemented:
> 
>  864 /*
>  865  * Keywords recognized.
>  866  */
>  867 static const struct token keywords[] = {
>  868         {"menu", T_MENU},
>  869         {"title", T_TITLE},
>  870         {"timeout", T_TIMEOUT},
>  871         {"default", T_DEFAULT},
>  872         {"prompt", T_PROMPT},
>  873         {"label", T_LABEL},
>  874         {"kernel", T_KERNEL},
>  875         {"linux", T_LINUX},
>  876         {"localboot", T_LOCALBOOT},
>  877         {"append", T_APPEND},
>  878         {"initrd", T_INITRD},
>  879         {"include", T_INCLUDE},
>  880         {"devicetree", T_FDT},
>  881         {"fdt", T_FDT},
>  882         {"devicetreedir", T_FDTDIR},
>  883         {"fdtdir", T_FDTDIR},
>  884         {"ontimeout", T_ONTIMEOUT,},
>  885         {"ipappend", T_IPAPPEND,},
>  886         {NULL, T_INVALID}
>  887 };
> 
> This does not fit with your description, as you list:
> > 	Ignoring unknown command: title
> > 	Ignoring unknown command: version
> > 	Ignoring unknown command: options
> > 	Ignoring unknown command: linux
> > 	Ignoring unknown command: devicetree
> 
> OK, "version" and "options" are not implemented, but the other
> keywords are, so you must be doing something else wrong.

That's what I was saying. I suppose the handling of label and title is 
different, so the entry group I had below 'title' was not recognized as group 
of options for one entry, like it was when replacing title with label. I can 
write an actually working extlinux.conf file (as showed in my last mail), but 
that was not the question I had in the first place.

> > Neither does it support multiple files (just /boot/extlinux/extlinux.conf
> > works) nor the keywords specified?
> 
> You can run the sysboot command as often with different data as you
> like, so what o you mean?

The U-Boot documentation in the file 'doc/README.distro' could lead to the 
impression as if U-Boot would support the BootLoaderSpec and even links to it: 
http://www.freedesktop.org/wiki/Specifications/BootLoaderSpec/

That spec says basically, in my own words: "put one conf file for each boot 
menu item in the directory /boot/loader/entries and let it have the following 
format." 

The keywords differ from the ones used by extlinux/U-Boot, in my opinion the 
U-Boot documentation in 'doc/README.distro' however is not very clear about 
that.

Back to my original question:

Is U-Boot supposed to honour that Boot Loader Specification?

If yes: then it does not work as specified. Is anybody working on making U-
Boot comply?

If no: would anybody mind changing the documentation to better reflect what U-
Boot actually does and not mislead people into thinking U-Boot would be 
compliant to that specification (like it was the case for me)? I would send a 
patch if nobody objects.

Greets
Alex