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

[Frank Binns <frank.binns@imgtec.com>]

Hi Emil,

On 13/02/15 09:18, Emil Velikov wrote:
> On 12/02/15 18:21, David Herrmann wrote:
>> Hi
>>
>> On Tue, Feb 10, 2015 at 11:37 PM, Emil Velikov <emil.l.velikov@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 ?
Can you you not just use use readdir on /dev/dri and stat on each
entry's d_name comparing the result to an fstat on the fd? Once you find
a match you just
strdup the d_name.

>
> 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);
I personally prefer this as it fits in better with what we already have.

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