[RFC PATCH 0/2] libdrm: Add master <> render node helpers

[Emil Velikov]

On 12/02/15 18:21, David Herrmann wrote:
> Hi
> 
> On Tue, Feb 10, 2015 at 11:37 PM, Emil Velikov <emil.l.velikov at gmail.com> wrote:
>> On 02/02/15 00:14, Emil Velikov wrote:
>>> Hi all,
>>>
>>> As mentioned a couple of days ago at #dri-devel some(most) users of
>>> render nodes tend to rely on strict mapping between the primary and
>>> render node. I.e. something along the lines of
>>>
>>>   fstat(render_fd, &sbuf);
>>>   sprintf(primary_node, "/dev/dri/card%d",
>>>                         ((sbuf.st_rdev & 0x3f) | 0x80));
>>>
>>> Currently the following are (ab)using the above code:
>>>  - xf86-video-nouveau
>>>  - xf86-video-intel
>>>  - libva (vaapi)
>>>
>>> As reminded by David Herrman, this is not the correct solution - thus
>>> I've added a couple of helpers which walk through sysfs of the
>>> respecitive device and return the correct device name.
>>>
>>> I'm not 100% happy with the function names, so suggestions are greatly
>>> appreciated. Any other comments are also welcome :)
>>>
>>> Note: BSD guys - you'll likely need your own version of these functions.
>>>
>> David, Daniel
>>
>> Can you please take a look at these two patches. Would be great if we
>> can minimize the above assumptions before they get too wide spread.
> 
> The patches look ok. I really dislike the direct file-probing, though.
> I'd recommend using libudev or readdir_r() on /dev/dri/, but I'm not
> the one to ask about coding-style for libdrm, so fine with me.
> 
Thanks for having a look. libudev is no used in libdrm so I will stay
away for now. I would prefer to use readdir on /dev/dri/ but AFAICT
there is no way to get the mapping from those alone. Am I missing
something ?

I'm also thinking that changing the prototypes, as below, might be
useful - i.e. return 0 on success, -ENODEV when the corresponding device
lacks render/primary device, and other negative value on error ?

char *drmGetRenderNameFromDeviceFD(int fd);
char *drmGetDeviceNameFromRenderFD(int fd);

int drmGetRenderNameFromDeviceFD(int fd, char **render);
int drmGetDeviceNameFromRenderFD(int fd, char **device);


Cheers,
Emil