Re: [Xen-devel] [PATCH,RFC]: Introduce libxl_domain_create()

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Tue, 2010-12-21 at 14:07 +0000, Ian Jackson wrote:
> Ian Campbell writes ("Re: [Xen-devel] [PATCH,RFC]: Introduce 
> libxl_domain_create()"):
> > On Tue, 2010-12-21 at 11:33 +0000, Ian Jackson wrote:
> > > Yes.  The primary console for an HVM guest is not a PV console, but
> > > the guest's emulated serial port provided by qemu.  So to connect to
> > > it you need qemu running.
> > 
> > Why is that?
> > 
> > In the PV case the xenconsole client is quite happy to sit and wait (on
> > a xenstore watch) for the console entries to be created in xenstore. Why
> > can the qemu case not do the same?
> 
> TBH I think this is a bug in the xenconsole client, because it means
> that the xenconsole client has an arbitrary timeout when it ought to
> be started at the point when we know that the console is there.
> 
> But I think you are right and this isn't the reason why it's done like
> that at the moment.
> 
> I vaguely remember some complication with the bootloader.  Perhaps the
> problem was that we can't start the console client until the
> bootloader has finished using our controlling terminal ?

The opposite -- the bootloader interacts with the user via xenconsole.

> It seems to me that the right approach is
>  (a) the domain creation function should call back to the application
>      to say "your domain's console is ready now and you can connect to
>      it if you like"
>  (b) the bootloader's console should be plumbed explicitly rather
>      than simply relying on inheriting a suitable terminal from the
>      library's caller.
> 
> Without (b), doing xapi or libvirt on top of libxl is going to be
> impossible.

(b) is already done and has been since Tim first plumbed the bootloader
stuff through.

> TBH some of the console plumbing is pretty horrid and needs a
> redesign.  For example, why can't you connect to the same domain more
> than once ?  (Ans: because xenconsoled uses ptys for talking to
> xenconsole!!)  Why can't you automatically log the guest's serial
> console ?  (Ans: because that's done with completely separate code in
> qemu which doesn't know how to do more than speak to a particular
> tty.)



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