Re: [Xen-devel] Booting NetBSD in pygrub

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2013-09-13 at 18:00 +0000, M. Boerschig wrote:
> 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.

Probably generic 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 J (cc-d) knows all about POSIX semantics i.e. when POLLHUP can and
should be received etc, I think I might leave this one to him ;-)

> 
> 
> > 
> > Ian.
> > 
> > 
> 



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