loader: Use drirc device_id parameter in complement to DRI_PRIME

DRI_PRIME is not very handy, because you have to launch the executable
with it set, which is not always easy to do.
By using drirc, the user specifies the target executable
and the device to use. After that the program will be launched everytime
on the target device.

For example if .drirc contains:

<driconf>
    <device driver="loader">
        <application name="Glmark2" executable="glmark2">
            <option name="device_id" value="pci-0000_01_00_0" />
        </application>
    </device>
</driconf>

Then glmark2 will use if possible the render-node of
ID_PATH_TAG pci-0000_01_00_0.

v2: Fix compilation issue
v3: Add "-lm" and rebase.

Signed-off-by: Axel Davy <axel.davy@ens.fr>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/loader/loader.c

@@ -74,6 +74,10 @@
 #include <unistd.h>
 #include <stdlib.h>
 #include <errno.h>
+#ifdef USE_DRICONF
+#include "xmlconfig.h"
+#include "xmlpool.h"
+#endif
 #endif
 #ifdef HAVE_SYSFS
 #include <sys/stat.h>
@@ -323,9 +327,22 @@ drm_open_device(const char *device_name)
    return fd;
 }
 
+#ifdef USE_DRICONF
+const char __driConfigOptionsLoader[] =
+DRI_CONF_BEGIN
+    DRI_CONF_SECTION_INITIALIZATION
+        DRI_CONF_DEVICE_ID_PATH_TAG()
+    DRI_CONF_SECTION_END
+DRI_CONF_END;
+#endif
+
 int loader_get_user_preferred_fd(int default_fd, int *different_device)
 {
    struct udev *udev;
+#ifdef USE_DRICONF
+   driOptionCache defaultInitOptions;
+   driOptionCache userInitOptions;
+#endif
    const char *dri_prime = getenv("DRI_PRIME");
    char *prime = NULL;
    int is_different_device = 0, fd = default_fd;
@@ -337,6 +354,16 @@ int loader_get_user_preferred_fd(int default_fd, int *different_device)
 
    if (dri_prime)
       prime = strdup(dri_prime);
+#ifdef USE_DRICONF
+   else {
+      driParseOptionInfo(&defaultInitOptions, __driConfigOptionsLoader);
+      driParseConfigFiles(&userInitOptions, &defaultInitOptions, 0, "loader");
+      if (driCheckOption(&userInitOptions, "device_id", DRI_STRING))
+         prime = strdup(driQueryOptionstr(&userInitOptions, "device_id"));
+      driDestroyOptionCache(&userInitOptions);
+      driDestroyOptionInfo(&defaultInitOptions);
+   }
+#endif
 
    if (prime == NULL) {
       *different_device = 0;