amazon/xen... any way at all to pass a message/signal/semaphoere/morse-code to the boot loader?

[Julian Elischer]

On 12/4/17 2:09 pm, Toomas Soome wrote:
>> On 12. apr 2017, at 9:04, Julian Elischer <julian at freebsd.org> wrote:
>>
>> On 12/4/17 12:34 pm, Colin Percival wrote:
>>> [CCing freebsd-cloud, which is the right place for discussions of FreeBSD/EC2]
>>>
>>> On 04/11/17 21:03, Julian Elischer wrote:
>>>> In Amazon ec2 they have no console access (though I heard rumors that it was
>>>> available I have not seen any sign of it) so I'd like to put a "recovery
>>>> partition" into an AMI.
>>>> The trick is how to convince it to boot to that instead of the regular action.
>>> Can you get what you want via gptboot's support for selecting the partition
>>> to boot via "bootonce" and "bootme" flags?
>> not if you can't get onto to the machine.
>> When I talk about a recovery partition I mean it in the same way that apple means it..
>> "system won't boot? press the power button and hold down the 'option' key.
>> it will give you the option to boot to a recovery mode"
>> (* actually I can't remember the keys but you get the idea..)
>>
>> in our case we would like to be able to recover a customer's AMI by giving a simple set of instructions over the phone.
>> We can assume they know how to get into the amazon menus, but we would like to not have to assume much more.
>>
>>>> The ideal thing would be if there was  way to 'influence' one of the smbios
>>>> values in some way, and have the boot code see it, but I'm open to any
>>>> suggestions.
>>>> I really need only 1 bit of information to get through.
>>>>
>>>> Possibilties include "changing the VM to have only 2G of ram" (we'd never do
>>>> that in a real machine).
>>>> or maybe temporarily removing all the disks other than the root drive? Almost
>>>> anything I could do to signal the boot code to behave differently.
>>> I don't think adding/removing disks will be useful, since the extra disks will
>>> be Xen blkfront devices; AFAIK the boot loader doesn't know anything about
>>> these.  (The boot device is also a blkfront device but gets ATA emulation for
>>> the benefit of boot loaders.)
>>>
>>> Maybe you can repurpose some of the logic used for booting over NFS?  I've
>>> never heard of people booting over NFS when the initial bootstrap comes from
>>> disk rather than PXE, but I assume it's possible...?
>> Oh I've done it, in the past but you still have the same issue..
>> how do you signal the boot code to do this?
>>
>> (does an AMI have a bios capable of doing network operations?) I was thinking
>> about whether we could add a really simple xn driver into the bootcode to allow
>> us to have an console of sorts (accessible from an adjacent machine only??)
>>
>>
>>
>
> basically you want what zfsbootcfg does but in reverse — with fallback to recovery…
yes,
that is also a possibility  N failed boots in a row..

>
> rgds,
> toomas
>
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