Re: [Xen-devel] Driver domains and hotplug scripts, redux

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2012-01-17 at 10:00 +0000, Roger Pau Monnà wrote:
> 2012/1/17 Ian Campbell <Ian.Campbell@xxxxxxxxxx>:
> > On Tue, 2012-01-17 at 09:40 +0000, Roger Pau Monnà wrote:
> >> 2012/1/17 Ian Campbell <Ian.Campbell@xxxxxxxxxx>:
> >> > However xend should not be transition to this new scheme but should
> >> > continue to use its existing scripts in the current manner.
> >> >
> >> > There was a conversation last year[0] about how a toolstack could
> >> > opt-in/out of the use of the hotplug scripts. We decided that toolstacks
> >> > should have to opt into the use of these scripts, by touching a stamp
> >> > file.
> >> >
> >> > Although this wasn't implemented yet (unless I missed it) I guess the
> >> > same scheme would apply to this work if that sort of thing turns out to
> >> > be necessary.
> >>
> >> Sorry for replying so many times, this is a big maybe, and possibly
> >> it's too drastic, but after this changes xl and xend will not be
> >> compatible anymore, so why don't we disable xend by default, and only
> >> build xl?
> >
> > I don't think they are compatible now, are they? I've certainly seen odd
> > behaviour when using xl with xend (accidentally) running, usually xend
> > reaps the domain I've just started...
> >
> > I'm all for disabling the build of xend by default but I had assumed
> > that others would think 4.2 was rather an aggressive timeline for that.
> >
> >> When the new configure script is in, it will be trivial to select if
> >> you want xl or xend, and only install one of those. Adding the option
> >> --enable-xend should disable xl and only build and install xend
> >> (printing a very big warning that xend is deprecated).
> >
> > I don't think --enable-xend should ever disable xl (or vice versa). Many
> > folks (e.g. distros) will want to build both, perhaps to package them in
> > two different binary packages, but certainly to offer their users the
> > choice, at least for the time being.
> 
> My main concern with this is that xend and xl will start to use
> different udev rules (well, xend will continue to use the existing
> ones, while xl will only use a subset of those). So we have to decide
> which udev rules file to install, because we can't have both installed
> at the same time.

Sure we can. Perhaps they need to have an "if $TOOLSTACK" check (e.g. if
[ -f /var/run/xend.hotplug ]) added to the top, that is all.

> Another option is to install xl udev rules by default, and make xend
> move it's own rules in the init script.

I don't think initscripts should be messing with udev rules.

Perhaps the opt-in needs to be more fine grained e.g. opt-in to vif but
not block scripts or whatever distinction you think is necessary instead
of jut a global opt in, it's just a different naming convention for the
stamp file. This avoids reconfiguration and the need to install subsets
of the scripts etc.

>  Since xl doesn't use a daemon,
> xl should always check if xend is running before doing anything and
> fail if xend is found.

I think that is a separate question/issue to the one of hotplug scripts.

Ian.

> 
> >>
> >> > Ian.
> >> >
> >> > [0] http://lists.xen.org/archives/html/xen-devel/2011-06/msg00952.html
> >> >
> >
> >



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