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Re: [Xen-devel] [PATCH 2/2] xen-gntalloc: Userspace grant allocation driver
On 12/08/2010 11:47 AM, Ian Campbell wrote:
> On Fri, 2010-12-03 at 15:38 +0000, Daniel De Graaf wrote:
>> This allows a userspace application to allocate a shared page for
>> implementing inter-domain communication or device drivers. These
>> shared pages can be mapped using the gntdev device or by the kernel
>> in another domain.
> This seems like useful functionality but is it really necessary for it
> to be a separate driver to the existing gntdev driver? The broad high
> level semantics of ioctl+mmap seem pretty similar. It also has some
> similarities with the sort of device we will need in order to properly
> allocate memory which is safe to use as an argument to a hypercall.
> Do you have an example of a user of the driver?
We are using gntalloc with the vchan library that Daniel posted for doing
userspace ring buffers.
Another use of it that we are pursuing is for graphics. Gntalloc would allow
the X server to share one or more virtual framebuffers directly instead of
using the xen-fbfront kernel driver. This would allow multiple X sessions or
screens to be forwarded from the same guest. We are also investigating the
possibility of applications rendering individual windows into their own buffers
and then sharing them to a display server in another domain.
National Security Agency
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