Re: [PATCH 0/2] Userspace grant communication

[Daniel De Graaf <dgdegra@tycho.nsa.gov>]

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.

- 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
>>
>