Re: [Xen-devel] [PATCH 0/2] Userspace grant communication / XenClient (XCI) inter-domain communication

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Fri, Dec 03, 2010 at 01:27:54PM -0500, Daniel De Graaf wrote:
> On 12/03/2010 11:30 AM, Pasi Kärkkäinen wrote:
> > On Fri, Dec 03, 2010 at 10:36:17AM -0500, Daniel De Graaf wrote:
> >> For fast communication between userspace applications in different domains,
> >> it is useful to be able to set up a shared memory page. This can be used to
> >> implement device driver frontends and backends completely in userspace, or
> >> as a faster alternative to network communication. The current gntdev is
> >> limited to PV domains, and does not allow grants to be created. The 
> >> following
> >> patches change gntdev to remapping existing pages, allowing the same code
> >> to be used in PV and HVM, and add a gntalloc driver to allow mappings to be
> >> created by userspace. These changes also make the mappings more 
> >> application-
> >> friendly: the mmap() calls can be made multiple times, persist across 
> >> fork(),
> >> and allow the device to be closed without invalidating the mapped areas. 
> >> This
> >> matches the behavior of mmap() on a normal file.
> >>
> > 
> > Btw are you aware of the new fast inter-domain communication method in 
> > XenClient ?
> > 
> > -- Pasi
> > 
> 
> No, I have not looked at that; is there a whitepaper or some information on 
> it?
> If not, a pointer to the relevant source would be of interest.
> 

Unfortunately I can't remember the name of the feature.. 
hopefully someone from Citrix working with XCI can help out.

-- Pasi


> - Daniel
> 
> > 
> >> API changes from the existing /dev/xen/gntdev:
> >>
> >> The unused "pad" field in ioctl_gntdev_map_grant_ref is now used for flags
> >> on the mapping (currently used to specify if the mapping should be 
> >> writable).
> >> This provides sufficient information to perform the mapping when the ioctl 
> >> is
> >> called. To retain compatibility with current userspace, a new ioctl number 
> >> is
> >> used for this functionality and the legacy error on first mapping is 
> >> retained
> >> when the old ioctl is used.
> >>
> >> IOCTL_GNTDEV_SET_MAX_GRANTS is not exposed in the Xen userspace libraries,
> >> and is not very useful: it cannot be used to raise the limit of grants per
> >> file descriptor, and is trivial to bypass by opening the device multiple
> >> times. This version uses a global limit specified as a module parameter
> >> (modifiable at runtime via sysfs).
> >>
> >> -- 
> >> Daniel De Graaf
> >> National Security Agency
> >>
> > 

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