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

[Viktor Mihajlovski]

On 29.06.2017 09:58, Thomas Huth wrote:
> On 28.06.2017 17:02, Viktor Mihajlovski wrote:
>> On 28.06.2017 12:56, Thomas Huth wrote:
>>> On 28.06.2017 10:02, Thomas Huth wrote:
>>>> On 28.06.2017 09:28, Viktor Mihajlovski wrote:
>>>>> 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.
>>>>
>>>> Are you really sure about the popularity of pxelinux? It's just one
>>>> flavor of secondary stage network boot loaders - which also only exist
>>>> on x86 so far, as far as I know.
>>>
>>> And it seems like it also only works with legacy BIOSes, i.e. you can
>>> not use it on EFI-only systems, if I've got that right:
>>>
>>> https://github.com/openSUSE/kiwi/wiki/Setup-PXE-boot-with-EFI-Using-GRUB2
>>>
>>> So I guess the significance of pxelinux will very likely decrease in
>>> the next years...
>>>
>> Maybe, but supposed goners tend to linger more often than not. I.e., the
>> syslinux project offers a EFI bootloader called syslinux.efi equivalent
>> to the pexelinux.0 BIOS loader.
>> Further, the OPAL firmware of newer POWER systems embeds petitboot and
>> thus offers PXELINUX-compatible network boot as well.
> 
> OK, true, ... you're slowly get me convinced that this pxelinux.cfg
> stuff is maybe not such a bad idea after all ... So I guess supporting
> at least the basic commands from the pxelinux config file would be
> appropriate... (the full set of commands is huge, see
> http://www.syslinux.org/wiki/index.php?title=Config )
> 
>> I appreciate the idea of a proper BOOTP implementation though, so maybe
>> a compromise could be to start off with your proposal with the slight
>> modification that the final boot action is controlled by the bootfile
>> content (file magic), similar to what you suggested in order to support
>> both insfile and binary kernel. PXELINUX emulation could be triggered by
>> a specially crafted bootfile then. What do you think?
> 
> Yes, something like this could work:
> 
> 1) Do DHCP to get TFTP server address and boot file name
> 2) Load the boot file from the TFTP server to address 0
> 3) If the boot file name ended with ".ins" or ".INS" (and the content
>    starts with the "* " magic), treat it as an .INS file and load the
>    files that are listed in there accordingly
> 4) If the boot file looks like a kernel, start it directly
> 5) If not successful in 3 or 4, start looking for a pxelinux config
>    file by trying to download the config files as specified in
>    http://www.syslinux.org/wiki/index.php?title=PXELINUX#Configuration
>    and then parse the file and load the kernel + initrd accordingly.
> 
> Quite a bit of work, so I'll continue to ignore 5 for the first
> versions, but I agree now that it can certainly be added later.
That sounds more than fair. Thanks!
> 
>  Thomas
> 


-- 

Mit freundlichen Grüßen/Kind Regards
   Viktor Mihajlovski

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