Re: [Xen-devel] [PATCH 20 of 29 RFC] libxl: introduce libxl hotplug public API functions

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-02-09 at 16:00 +0000, Stefano Stabellini wrote:
> On Thu, 9 Feb 2012, Ian Campbell wrote:
> > On Thu, 2012-02-09 at 15:32 +0000, Stefano Stabellini wrote:
> > > On Thu, 9 Feb 2012, Ian Jackson wrote:
> > > > Stefano Stabellini writes ("Re: [Xen-devel] [PATCH 20 of 29 RFC] libxl: 
> > > > introduce libxl hotplug public API functions"):
> > > > > - we can reuse the "state" based mechanism to establish a connection:
> > > > > again not a great protocol, but very well known and understood.
> > > > 
> > > > I don't think we have, in general, a good understanding of these
> > > > "state" based protocols ...
> > > 
> > > What?! We have netback, netfront, blkback, blkfront, pciback, pcifront,
> > > kbdfront, fbfront, xenconsole, and these are only the ones in Linux!!
> > 
> > And no one I know is able to describe, accurately, exactly what the
> > state diagram for even one of those actually looks like or indeed should
> > look like. It became quite evident in these threads about hotplug script
> > handling etc that no one really knows for sure what (is supposed to)
> > happens when.
> 
> I thought that most of the thread was about the interface with the block
> scripts, that is an entirely different matter and completely obscure.
> If I am mistaken, please point me at the right email.

We are talking about reusing the existing xenbus state machine schema
for a new purpose. Ian J pointed out that these are not generally well
understood, you replied that it was and cited some examples. I pointed
out why these were not examples of why this stuff was well understood at
all, in fact quite the opposite.

> > Justin just posted a good description for blkif.h which included a state
> > machine description. We need the same for pciif.h, netif.h etc etc.
>  
> The state machine is the same for block and network.

No, it's not. This is exactly what IanJ and I are talking about.

Ian.


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