Re: [Qemu-devel] [RFC PATCH 00/14] Implement network booting directly into the s390-ccw BIOS

[Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>]

On 27.06.2017 23:40, Thomas Huth wrote:
[...]
>>> - Is it OK to require loading an .INS file first? Or does anybody
>>>   have a better idea how to load multiple files (kernel, initrd,
>>>   etc. ...)?
>> It would be nice to support PXE-style boot, because the majority of boot
>> servers is set up that way. A straightforward way would be to do a PXE
>> emulation by attempting to download a pxelinux.cfg from the well-known
>> locations, parsing the content (menu) and finally load the kernel,
>> initrd and set the kernel command line as specified there. (I know, but
>> you're already parsing the INS-File).
> 
> Please, don't mix up PXE and pxelinux (since you've used both terms in
> above paragraph). Assuming that you're only talking about pxlinux config
> files... are they that common on s390x already? Using the pxelinux
> config file syntax sounds like we would be completely bound to only
> loading Linux guests to me, since the boot loader has to know where to
> load the initrd and how to patch the kernel so that it can find the initrd.
> Using .INS files sounds more flexible to me instead, since you can also
> specify the addresses here - so you can theoretically also load other
> guest kernels, and that's IMHO the better approach since a firmware
> should stay as generic as possible.
> 
In order to be consumable, the network boot should support the most
common configurations. I would think that most network boot servers are
setup as PXE boot servers using pxelinux configs. It will do no good to
tell system administrators to have a totally different setup for s390
boot clients. If the firmware doesn't support it we will have to fall
back to provide a Linux-based fat netboot image to the pxelinux handling
:-(.
>> Alternatively, one could load a single boot image (consisting of kernel
>> and initrd concatenated, i.e. the bootable ISO format). This could serve
>> as a more potent "stage 2" boot loader.
> 
> Agreed, that's also a common practice when doing network booting. I
> guess the firmware could also support both quite easily, direct single
> boot images, and .INS files. The latter could be detected via the file
> name or with the magic string "* " at the beginning.
> >>> - The code from SLOF uses a different coding style (TABs instead
>>>   of space) ... is it OK to keep that coding style here so we
>>>   can share patches between SLOF and s390-ccw more easil>
>>> - The code only supports TFTP (via UDP) ... I think that is OK for
>>>   most use-cases, but if we ever want to support network booting
>>>   via HTTP or something else that is based on TCP, we would need to
>>>   use something else instead... Should we maybe rather head towards
>>>   grub2, petitboot or something different instead?
>> I don't have an opinion on whether HTTP, FTP, etc is needed, but at some
>> point in time it would definitely be cool to have IPv6 support. Not sure
>> whether SLOF has that included.
> 
> Yes, IPv6 is included in this networking stack.
> 
>  Thomas
> 


-- 

Mit freundlichen Grüßen/Kind Regards
   Viktor Mihajlovski

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