Re: [Xen-devel] [PATCH 2/2] xen-gntalloc: Userspace grant allocation driver

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 12/08/2010 01:15 PM, Daniel De Graaf wrote:
> On 12/08/2010 11:47 AM, Ian Campbell wrote:
>> Do you have an example of a user of the driver?
> 
> I do have an communication library (vchan, based on code from Qubes); I am
> currently modifying it to allow the use of more than one page for the ring
> to reduce context switches when passing large amounts of data (this cost is
> increased due to both ends being in userspace, rather than kernel space). If
> that isn't ready soon, I will just post the version of vchan using this
> device and the modified gntdev API.
> 


Actually, I'll just post the vchan code that I have now. It's a simple wrapper
around Xen's idea of a ring buffer implemented in userspace. The gntdev use is
currently abstracted using xc library calls, which doesn't match how gntalloc
is used; changing to direct use of gntdev will be better especially since the
calling xc_gnttab_open with a NULL argument is not a documented use of the API.

The gntdev and gntalloc devices are useful for more than just stream
communication; they can be used as building blocks for implementing the
majority of Xen devices as userspace drivers.

-- 
Daniel De Graaf
National Security Agency

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