Re: Booting NetBSD in pygrub

["M. Boerschig" <code+mlist@boerschig.net>]

On 09/10/13 08:56, Ian Campbell wrote:
> On Mon, 2013-09-09 at 19:52 +0200, M. Boerschig wrote:
>> On 09/09/13 14:35, Ian Campbell wrote:
>>> On Sat, 2013-09-07 at 11:56 +0000, M. Boerschig wrote:
>>> I think this implies a Linux dom0?
>>
>> Yes, of course. I didn't even get a recent xen (> 4.2) to compile on my 
>> NetBSD machine.
>>
>>>
>>> I imagine this is equally broken with a Linux domU, because it doesn't
>>> seem likely to be guest specific, given that it is mostly before the
>>> guest runs...
>>>
>>
>> An Ubuntu domU works on this same machine, so I think this problem is 
>> limited to my use case (or a similar one, like solaris)
> 
> In this case do you get the interactive menu? I wonder if passing
> bootloader_args = ["--entry=0"] would reproduce the same error you are
> seeing by skipping the menu and making it behave like sniff_solaris?
> 

This triggers exactly the same error as with booting a netbsd domU.
I tested this also on a Ubuntu 13.04 dom0 with an unmodified stable-4.3
(4.3.1-pre) on a different machine (with another 13.04 domU), just to
make sure it's nothing I broke.
So either this problem is specific to debian(-derived) systems or a
generic problem with libxl.


>>> This stuff ha been a bit fragile in the past, I wouldn't be too
>>> surprised if it had regressed, especially since it isn't especially
>>> amenable to automated testing.
>>>
>>> What is supposed to happen is that pygrub gets launched attached to a
>>> pty, and that ptr gets written to xenstore such that the xenconsole
>>> client connects to it and presents the pygrub output to the user as if
>>> it were the guest console, xl acts as a pump copying data back and forth
>>> between the console pty and pygrubs pty (since both console and pygrub
>>> expect to be a slave). Much of this code is in libxl_bootloader.c.
>>>
>>> Once pygrub exits this pty disappears and the console client should
>>> reattach to the real guest console pty, which is provided by
>>> xenconsoled.
>>>
>>> It sounds like that first connection is not going to the right place or
>>> is otherwise broken.
>>>
>>> Are you seeing the pygrub menu? DO you expect to? Perhaps the automatic
>>> exit of the first session is not working?
>>
>> No, and I didn't expect a menu to appear.
>> I assumed a menu is only displayed if the run_grub()-method succeeds in 
>> finding a valid GRUB menu.lst/config on the disk.
>> I used the sniff_solaris() code as a guideline: if I understand the code 
>> correctly it just returns a configuration dictionary without displaying 
>> anything.
> 
> OK.
> 
>>> The last relevant looking commit to libxl_bootloader.c was
>>> 7253e0fd1aeb3ae7d4714bcc1d86b846b3331995 which looks like the sort of
>>> thing which might accidentally introduce such behaviour.
>>
>> Thanks for the pointer, I'll investigate if pygrub's exit is properly 
>> handled later this week.
> 
> Great, please let us know how you get on!

I did have less time than anticipated to familiarize with libxl, as I'm
quite busy studying for an exam ...
However, I did some debugging and the
libxl_aoutils.c:datacopier_pollhup_handled() never received a POLLHUP
event, although execution goes through
libxl_bootloader.c:bootloader_finished().
Maybe someone more knowledgable about libxl might want a look at this.


> 
> Ian.
> 
>