[Mesa-dev] [PATCH] egl/dri2: implement platform_null.

[Haixia Shi]

Hi Emil

On Thu, Jan 22, 2015 at 1:36 PM, Emil Velikov <emil.l.velikov at gmail.com> wrote:
> Hi Haixia Shi,
>
> On 22/01/15 17:35, Haixia Shi wrote:
>> Try the render node first and use it if available. Otherwise fall back to
>> normal nodes.
>>
> What is the use-case for such a platform - I assume it's worth
> mentioning in the commit message ?
>
> No other platform picks the device at random as seen below. Why did you
> choose such an approach ? It seems like one can easily shoot themselves
> by using it.

CC Stephane. The goal here is just to pick the first available node
for off-screen rendering only.

>
> ...
>> diff --git a/src/egl/drivers/dri2/platform_null.c b/src/egl/drivers/dri2/platform_null.c
>> new file mode 100644
>> index 0000000..4f0b18f
>> --- /dev/null
>> +++ b/src/egl/drivers/dri2/platform_null.c
> ...
>> +static const char* node_path_fmt_card = "/dev/dri/card%d";
> You can reuse the DRM_DIR_NAME + DRM_DEV_NAME macros (from xf86drm.h)
> for this.
>
>> +static const char* node_path_fmt_render = "/dev/dri/renderD%d";
> There is no macro for the renderD%d, although you can still use
> DRM_DIR_NAME for the path.

Will update this part shortly.

>
>> +
>> +EGLBoolean
>> +dri2_initialize_null(_EGLDriver *drv, _EGLDisplay *disp)
>> +{
>> +   struct dri2_egl_display *dri2_dpy;
>> +   const char* err;
>> +   int i, render_node;
>> +   int driver_loaded = 0;
>> +
>> +   loader_set_logger(_eglLog);
>> +
>> +   dri2_dpy = calloc(1, sizeof *dri2_dpy);
>> +   if (!dri2_dpy)
>> +      return _eglError(EGL_BAD_ALLOC, "eglInitialize");
>> +
>> +   disp->DriverData = (void *) dri2_dpy;
>> +
>> +   for (render_node = 1; render_node >= 0; --render_node) {
>> +      const char* node_path_fmt =
>> +            render_node ? node_path_fmt_render : node_path_fmt_card;
>> +      const int base = render_node ? 128 : 0;
>> +      for (i = 0; i < 16; ++i) {
> What was the reason behind choosing 16 here ?

It's an arbitrary number. How about choosing 64 here as it is the
limit chosen by drm_stub.c: drm_minor_get_id()?

>
>> +         char *card_path;
>> +         if (asprintf(&card_path, node_path_fmt, base + i) < 0)
>> +            continue;
>> +
>> +         dri2_dpy->fd = open(card_path, O_RDWR);
> If you open a normal node (card%d) I believe that you'll need an
> authenticate hook in dri2_egl_display_vtbl. Does things work without it
> on your system/platform ?

You're correct; normal node would require the legacy auth hook, and it
would only work without auth if the process is run as root, which is
why we're trying render nodes first.

>
> Cheers
> Emil
>