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Re: Fwd: [Xen-devel] Inter-domain shared memory facility in Xen?

  • To: "Derek Murray" <Derek.Murray@xxxxxxxxxxxx>
  • From: "David Stone" <unclestoner@xxxxxxxxx>
  • Date: Thu, 1 Nov 2007 11:31:16 -0400
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, takebe_akio@xxxxxxxxxxxxxx
  • Delivery-date: Thu, 01 Nov 2007 08:31:57 -0700
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Thanks guys, I'm clear now.

On Nov 1, 2007 10:16 AM, Derek Murray <Derek.Murray@xxxxxxxxxxxx> wrote:
> David Stone wrote:
> > Thanks for your help on this.  So based on your responses I just want
> > to confirm my understanding is correct...is it true that:
> >
> > 1. It is currently possible to establish shared memory between Dom0
> > and DomU, but
> > 2. It is currently not possible to establish shared memory between two
> > DomUs in an released Xen versions, nor the current xen-unstable branch
> > nor any other branch on http://xenbits.xensource.org.  There are
> > projects that address this that you mentioned though.
> It *is* possible to establish shared memory between two DomUs, using the
> grant table mechanism. At present, it is only possible to grant access
> to memory from a VM kernel, but it is possible to map that granted
> memory into either the kernel (using the kernel wrappers to the
> necessary hypercalls) or user-space (using gntdev, the user-space
> granted memory driver).
> Up to and including the current stable release (3.1.1), it is only
> possible for domains that have I/O memory permissions (typically only
> Dom0) to map granted pages. Therefore, it is necessary to give some
> dummy permissions to any domain that you want to allow to map grants.
> However, the issue that led to this restriction has been fixed in the
> current version of xen-unstable.
> As I understand it, the other projects that were mentioned provide a
> socket-like communication mechanism for Xen, with the advantage that
> they do not (necessarily) use the networking stack. I presume that you
> are looking for something simpler, such as creating a shared data
> structure between two or more domains. In that case, the mechanisms that
>  exist in Xen today and that I have described above are sufficient for
> your needs.
> Regards,
> Derek Murray.

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