Re: [Xen-users] How to set up trivial shared-memory buffer between VMs (on ARM) ?

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Wed, 2015-10-07 at 20:19 +0000, Chris (Christopher) Brand wrote:
> > > > http://wiki.xenproject.org/wiki/Introduction_to_Xen_3.x, which looks
> > rather out of date so don't trust it too much, suggests:
> > xenstore-write /local/domain/X/device/mydevice/0/state 1 xenstore-write
> > /local/domain/0/backend/mydevice/X/0/frontend-id X xenstore-write
> > /local/domain/0/backend/mydevice/X/0/frontend
> > /local/domain/X/device/mydevice/0 xenstore-write
> > /local/domain/0/backend/mydevice/X/0/state 1
> 
> There's a more complete script at the bottom of that wiki page that does
> seem
> to do the trick. 6 writes and a chmod in total.

Aha, that's _exactly_ the script I was looking for!
> 
> > as a minimal set. Personally I'd do it all with one:
> >     xenstore-write KEY1 VALUE1 KEY2 VALUE2 KEY3 VALUE3 so it all gets
> > done
> > in a single transaction.
> 
> That doesn't seem to be necessary. The frontend probe is triggered by the 
> write
> of frontend state. It then finds the backend and sits waiting for it to come 
> up. Then
> the backend probe is triggered by the write of backend state (which has to be 
> done
> last). Now I just have to debug the actual driver probe itself :-)

Right, setting state last (or at least atomically in the last transaction)
is the important bit.

Ian.

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