[Intel-gfx] [PATCH v3] drm/vgem: Attach sw fences to exported vGEM dma-buf (ioctl)

[Daniel Vetter]

On Thu, Jul 14, 2016 at 02:39:54PM +0100, Chris Wilson wrote:
> On Thu, Jul 14, 2016 at 02:23:04PM +0100, Chris Wilson wrote:
> > The biggest reason I had against going the sw_sync only route was that
> > vgem should provide unprivileged fences and that through the bookkeeping
> > in vgem we can keep them safe, ensure that we don't leak random buffers
> > or fences. (And I need a source of foriegn dma-buf with implicit fence
> > tracking with which I can try and break the driver.)
> 
> And for testing passing around content + fences is more useful than
> passing fences alone.

Yup, agreed. But having fences free-standing isn't a real issue since
their refcounted and the userspace parts (sync_file) will get cleaned up
on process exit latest. Ḯ'm not advocating for any behaviour change at
all, just for hiding these things in debugfs.

Or maybe we could add a special (tainting) module option to vgem.ko which
enables this interface? That would be even less work, can easily be
integrated into igt (just set that knob at runtime, done), and with a
stern enough warning in dmesg + tainting the point should be clear. Of
course that switch would be off by default. Thoughts?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch