[Intel-gfx] [PATCH 1/3] drm: Expose a method for creating anonymous struct file around drm_minor

[Daniel Vetter]

On Wed, Nov 6, 2019 at 11:43 AM Chris Wilson <chris at chris-wilson.co.uk> wrote:
>
> Quoting Chris Wilson (2019-11-06 10:26:48)
> > Quoting Daniel Vetter (2019-11-06 10:19:50)
> > > On Wed, Nov 06, 2019 at 10:07:14AM +0000, Chris Wilson wrote:
> > > > Sometimes we need to create a struct file to wrap a drm_device, as it
> > > > the user were to have opened /dev/dri/card0 but to do so anonymously
> > > > (i.e. for internal use). Provide a utility method to create a struct
> > > > file with the drm_device->driver.fops, that wrap the drm_device.
> > > >
> > > > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > >
> > > For proper internal access we already have drm_client_open, so I think
> > > this has limited (but good use) in selftests only. So
> > > EXPORT_SYMBOL_FOR_TESTS_ONLY plus maybe a clearer name for the intended
> > > use like drm_file_mock_open?
> >
> > I found the example in drm_gem_prime_mmap() that was doing the same trick,
> > and the trick of being able to instantiate new struct file and install a
> > fd whenever seems like it will come in handy... Just lacking the third
> > user at the moment to claim generality.
>
> The closest example I found in the spirit of creating a new drm_device
> struct file and installing it is drm_mode_create_lease_ioctl() that uses
> file_clone_open() for this purpose. The argument there would be whether
> cloning the (file->f_path, file->f_flags, file->f_cred) is appropriate
> versus an anonymous inode. I think cloning the credentials seems correct
> for leasing.

Hm ... I think we want the clone for this one here too. Otherwise we
get the wrong inode, and then unmap_mapping_range wont work correctly,
and we cant use this for selftests. That's the only case where I think
we do actually need the file/inode to be functional. For anything else
the drm_client internal api gets away without the file/inode stuff.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch