Syslinux - Jun 2015 - chainloading syslinux from an EFI partition to an ext4

On 6 June 2015 at 14:03, Didier Spaier via Syslinux <syslinux at
zytor.com> wrote:
>
>
> On 06/06/2015 12:19, Stoppa, Igor via Syslinux wrote:
>
>> So I'd like to not put all the kernels/initrds in it, because when
I
>> update one of the OSes, I would also have to update the corresponding
>> kernel in the EFI partition.
>
>
> IIRC this is not possible (yet?) as kernels and initrd should lie in the
ESP
> alongside the EFI image(s) and the config file. But I am not sure, so if I
> am wrong please someone correct me.
>From what I understood, that's what you want to do if you want the EFI
syslinux
to boot your kernel, yes.
But.
What I'm trying to do is to have the EFI bootloader to chainload an
ext4 partition
where I have installed extlinux. The kernels and initrd lie alongside
the extlinux bootloader.

In a more schematic way:

1) the EFI BIOS loads the EFI syslinux
2) the EFI syslinux chainloads the extlinux that is on a separate partition
3) the extlinux loads the kernel & initrd that are colocated in the
same directory

point 2 is failing

I hope this is more clear than my previous, long, post :-)

-- 
igor

On 06/06/2015 13:14, Stoppa, Igor wrote:
> On 6 June 2015 at 14:03, Didier Spaier via Syslinux <syslinux at
zytor.com> wrote:
>>
>>
>> On 06/06/2015 12:19, Stoppa, Igor via Syslinux wrote:
>>
>>> So I'd like to not put all the kernels/initrds in it, because
when I
>>> update one of the OSes, I would also have to update the
corresponding
>>> kernel in the EFI partition.
>>
>>
>> IIRC this is not possible (yet?) as kernels and initrd should lie in
the ESP
>> alongside the EFI image(s) and the config file. But I am not sure, so
if I
>> am wrong please someone correct me.
>
>
>>From what I understood, that's what you want to do if you want the
EFI syslinux
> to boot your kernel, yes.
> But.
> What I'm trying to do is to have the EFI bootloader to chainload an
> ext4 partition
> where I have installed extlinux. The kernels and initrd lie alongside
> the extlinux bootloader.
>
> In a more schematic way:
>
> 1) the EFI BIOS loads the EFI syslinux
> 2) the EFI syslinux chainloads the extlinux that is on a separate partition
> 3) the extlinux loads the kernel & initrd that are colocated in the
> same directory
>
> point 2 is failing

I have no experience in chainloading but am rather pessimistic as I see 
this warning in http://www.syslinux.org/wiki/index.php/Doc/chain#file

"It is often convenient to load a file directly and transfer control to 
it, instead of the sector from the disk. Note that the <file> must 
reside on the SYSLINUX's partition."

Maybe you could get the expected result fiddling with the seg and sect 
options of chain, but I really don't know.

Didier

On 6 June 2015 at 14:47, Didier Spaier <didier at slint.fr> wrote:
> "It is often convenient to load a file directly and transfer control
to it,
> instead of the sector from the disk. Note that the <file> must reside
on the
> SYSLINUX's partition."

Yes, I have seen that too, but it says "convenient", which in theory
leaves
open also the less convenient options :-)

In practice for me, doing what the recommendation describes, is not a viable
option, because I want to avoid having the kernel(s) in the same partition as
the EFI bootloader.
> Maybe you could get the expected result fiddling with the seg and sect
> options of chain, but I really don't know.
Yes, that might be the last resort, if everything else fails, but I
had other hopes.
>From the googling I did before initiating this thread, it seems that people
have successfully chainloaded both Windows and linux, but on different disks.

I need to do it from the same disk because I'm prototyping a system
(on the USB stick) that later on will live on the only internal storage device.



-- 
igor

> 1) the EFI BIOS loads the EFI syslinux
> 2) the EFI syslinux chainloads the extlinux that is on a separate partition
> 3) the extlinux loads the kernel & initrd that are colocated in the
> same directory
> 
> point 2 is failing
> 
> I hope this is more clear than my previous, long, post :-)
> 
> -- 
> igor
 
FWIW, the most current (or "up-to-date") documentation about chain.c32
at this time is located at:
 http://www.syslinux.org/wiki/index.php/Chain.c32 

Note that, in the official wiki of The Syslinux Project, the wiki pages 
containing "... /Doc/ ..." are mainly copies of documents already 
included in some official release, which are usually outdated.


As per the intended setup, it is not possible. There are several 
reasons for such impossibility.

*Independently of this particular case*, if someone wants to improve 
chain.c32 (or any other part of Syslinux), patches are welcome.

Regards,
Ady.
 
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On 6 June 2015 at 17:22, Ady via Syslinux <syslinux at zytor.com> wrote:
> FWIW, the most current (or "up-to-date") documentation about
chain.c32
> at this time is located at:
>  http://www.syslinux.org/wiki/index.php/Chain.c32
Yes, I had a look at that, but frankly the archlinux pages were
more newbie-friendly, so my research is 50% based on what I found
there and for the rest syslinux.org and the internet at large.
> Note that, in the official wiki of The Syslinux Project, the wiki pages
> containing "... /Doc/ ..." are mainly copies of documents already
> included in some official release, which are usually outdated.
>
>
> As per the intended setup, it is not possible. There are several
> reasons for such impossibility.
Could you elaborate a bit more? What are the impediments?
> *Independently of this particular case*, if someone wants to improve
> chain.c32 (or any other part of Syslinux), patches are welcome.
I have no experience with bootloaders, but I could give it a shot,
if I had some confidence that it's a task I can tackle within the
time I have been given to find a solution.

Unfortunately my set of choices is fairly limited, so syslinux
still seems a possible solution, if the effort to modify it is
compatible with my skills and time frame.

In that sense, a hint of what to do would also be very appreciated.

Ex: would it be more reasonable to improve support for chainloading
or to add support for loading a kernel from another partition?

-- 
igor