Re: Pairing drm_prime_handle_from_fd with close

[Thomas Hellstrom <thellstrom@vmware.com>]

On 11/08/2013 06:19 PM, Daniel Vetter wrote:
> On Fri, Nov 8, 2013 at 11:02 AM, Thomas Hellstrom <thellstrom@vmware.com> wrote:
>> It seems like prime_handle_from_fd needs to be paired with a GEM_CLOSE ioctl
>> instead of a new generic HANDLE_CLOSE ioctl.
>>
>> This oversight is not really a big problem but there are two solutions:
>> 1) Create a new ioctl called HANDLE_CLOSE or something similar.
>> 2) Use the GEM_CLOSE ioctl, but add a driver callback for drivers that are
>> not GEM-aware.
>>
>> It seems like GEM_CLOSE has already spread into user-space clients, so
>> unless someone tell me otherwise, I'll be using
>> 2) for the vmwgfx prime implementation.
> Oops, I didn't really realize when fixing the prime lifetime stuff
> that vmwgfx doesn't use gem handles for it's buffers. What about
> 3) Move drm_gem_remove_prime_handles to drm_prime.c, expose it to
> modules and use that in the vmwgfx handle close ioctl?
> Imo GEM_CLOSE shouldn't ever be called by generic code in userspace,
> so if that's already broken it should be fixed in userspace not
> papered over in the kernel by partially faking gem on vmwgfx. I just
> fear that if we start doing that we need to virtualize more of the few
> gem bits, which renders the point of gem being optional moot.
> -Daniel
Hi!

I'm afraid I don't quite follow you here..
The problem is not in the kernel, with vmwgfx we don't even need to 
populate the drm prime list structures.

The problem is for user-space clients that have a prime fd, and call 
drm_prime_handle_from_fd. Since this function is
pretty generic, they need a generic way to close that handle. I don't 
really have any preferences, except
IMHO user space shouldn't need to guess what's the type of the 
underlying kernel object of that handle..

(This is for generic user-space using prime for buffer sharing between 
processes, not primarily for sharing buffers between devices).

Thanks,
Thomas