[PATCH 1/2] drm/vgem: Do not allocate backing shmemfs file for an import dmabuf object

[Chris Wilson]

Quoting lepton (2020-07-07 18:05:21)
> On Tue, Jul 7, 2020 at 9:00 AM Chris Wilson <chris at chris-wilson.co.uk> wrote:
> >
> > If we assign obj->filp, we believe that the create vgem bo is native and
> > allow direct operations like mmap() assuming it behaves as backed by a
> > shmemfs inode. When imported from a dmabuf, the obj->pages are
> > not always meaningful and the shmemfs backing store misleading.
> >
> > Note, that regular mmap access to a vgem bo is via the dumb buffer API,
> > and that rejects attempts to mmap an imported dmabuf,
> What do you mean by "regular mmap access" here?  It looks like vgem is
> using vgem_gem_dumb_map as .dumb_map_offset callback then it doesn't call
> drm_gem_dumb_map_offset

As I too found out, and so had to correct my story telling.

By regular mmap() access I mean mmap on the vgem bo [via the dumb buffer
API] as opposed to mmap() via an exported dma-buf fd. I had to look at
igt to see how it was being used.
-Chris