On Wed, Apr 18, 2018 at 11:55:26AM +0100, Roger Pau Monné wrote: > On Wed, Apr 18, 2018 at 01:39:35PM +0300, Oleksandr Andrushchenko wrote: > > On 04/18/2018 01:18 PM, Paul Durrant wrote: > > > > -----Original Message----- > > > > From: Xen-devel [mailto:[email protected]] On > > > > Behalf > > > > Of Roger Pau Monné > > > > Sent: 18 April 2018 11:11 > > > > To: Oleksandr Andrushchenko <[email protected]> > > > > Cc: [email protected]; Artem Mygaiev <[email protected]>; > > > > Dongwon Kim <[email protected]>; [email protected]; > > > > [email protected]; [email protected]; dri- > > > > [email protected]; Potrola, MateuszX > > > > <[email protected]>; [email protected]; > > > > [email protected]; [email protected]; Matt Roper > > > > <[email protected]> > > > > Subject: Re: [Xen-devel] [PATCH 0/1] drm/xen-zcopy: Add Xen zero-copy > > > > helper DRM driver > > > > > > > > On Wed, Apr 18, 2018 at 11:01:12AM +0300, Oleksandr Andrushchenko > > > > wrote: > > > > > On 04/18/2018 10:35 AM, Roger Pau Monné wrote: > > > > After speaking with Oleksandr on IRC, I think the main usage of the > > > > gntdev extension is to: > > > > > > > > 1. Create a dma-buf from a set of grant references. > > > > 2. Share dma-buf and get a list of grant references. > > > > > > > > I think this set of operations could be broken into: > > > > > > > > 1.1 Map grant references into user-space using the gntdev. > > > > 1.2 Create a dma-buf out of a set of user-space virtual addresses. > > > > > > > > 2.1 Map a dma-buf into user-space. > > > > 2.2 Get grefs out of the user-space addresses where the dma-buf is > > > > mapped. > > > > > > > > So it seems like what's actually missing is a way to: > > > > > > > > - Create a dma-buf from a list of user-space virtual addresses. > > > > - Allow to map a dma-buf into user-space, so it can then be used with > > > > the gntdev. > > > > > > > > I think this is generic enough that it could be implemented by a > > > > device not tied to Xen. AFAICT the hyper_dma guys also wanted > > > > something similar to this. > > Ok, so just to summarize, xen-zcopy/hyper-dmabuf as they are now, > > are no go from your POV? > > My opinion is that there seems to be a more generic way to implement > this, and thus I would prefer that one. > > > Instead, we have to make all that fancy stuff > > with VAs <-> device-X and have that device-X driver live out of drivers/xen > > as it is not a Xen specific driver? > > That would be my preference if feasible, simply because it can be > reused by other use-cases that need to create dma-bufs in user-space. > > In any case I just knew about dma-bufs this morning, there might be > things that I'm missing.
See my other reply, I really don't want a generic userspace memory -> dma-buf thing, it doesn't work. Having a xen-specific grant references <-> dma-buf conversion thing (and I'm honestly still not sure whether the dma-buf -> grant renferences is a good idea) seems much more reasonable to me. Imo simplest way forward would be to start out with a grant refs -> dma-buf ioctl, and see how far that gets us. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
