Re: [PATCH v3.18-rc3] drm: msm: Allow exported dma-bufs to be mapped

Rob Clark
2014-11-11T16:26:24Z

On Tue, Nov 11, 2014 at 9:28 AM, Daniel Thompson
<daniel.thompson@linaro.org> wrote:
> On 10/11/14 17:36, Rob Clark wrote:
>> On Mon, Nov 10, 2014 at 12:16 PM, Daniel Thompson
>> <daniel.thompson@linaro.org> wrote:
>>> diff --git a/drivers/gpu/drm/msm/msm_gem_prime.c b/drivers/gpu/drm/msm/msm_gem_prime.c
>>> index ad772fe36115..4e4fa5828d5d 100644
>>> --- a/drivers/gpu/drm/msm/msm_gem_prime.c
>>> +++ b/drivers/gpu/drm/msm/msm_gem_prime.c
>>> @@ -20,6 +20,14 @@
>>>
>>> #include <linux/dma-buf.h>
>>>
>>> +struct dma_buf *msm_gem_prime_export(struct drm_device *dev,
>>> + struct drm_gem_object *obj, int flags)
>>> +{
>>> + /* we want to be able to write in mmapped buffer */
>>> + flags |= O_RDWR;
>>> + return drm_gem_prime_export(dev, obj, flags);
>>> +}
>>> +
>>
>> seems like this probably should be done more centrally.. and in fact,
>> might be better to have something like this in
>> drm_prime_handle_to_fd_ioctl:
>>
>> /* check flags are valid */
>> - if (args->flags & ~DRM_CLOEXEC)
>> + if (args->flags & ~(DRM_CLOEXEC | O_RDWR))
>> return -EINVAL;
>>
>> so exporter can specify whether to allow mmap or not.
>
> That makes sense I'll try this.
>
> Do we need to wrap O_RDWR in the same way we wrap O_CLOEXEC? (I don't
> really understand why DRM_CLOEXEC exists; even the patch description
> from when the symbol was introduced names it O_CLOEXEC).

I *think* wrapping it w/ DRM_CLOEXEC was mostly just for purposes of
making it clear which flags are appropriate.. probably best to do the
same w/ a DRM_RDWR I guess

BR,
-R

> Also the "flags |= O_RDWR" approach is copied from the sti driver. I'll
> share a patch to remove it but that will definitely needs Benjamin's ack
> because it will stop some userspaces working correctly (however I
> suspect that Benjamin may be the only person currently with such a
> userspace and that he can be persuaded not to call it a regression).
>
>
> Daniel.