i965: Only enable __DRI2_ROBUSTNESS if kernel support is available

This is a squash of the following two cherry-picked patches:

    i965: Only enable __DRI2_ROBUSTNESS if kernel support is available

    Rather than always advertising the extension but failing to create a
    context with reset notifiction, just don't advertise it.  I don't know
    why it didn't occur to me to do it this way in the first place.

    NOTE: Kristian requested that I provide a follow-up for master that
    dynamically generates the list of DRI extensions instead of selected
    between two hardcoded lists.

    Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
    Suggested-by: Kristian Høgsberg <krh@bitplanet.net>
    Reviewed-by: Matt Turner <mattst88@gmail.com>
    Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
    Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
    Cc: "10.0" <mesa-stable@lists.freedesktop.org>
    (cherry picked from commit 9b1c68638d)

and

    i965: Properly reject __DRI_CTX_FLAG_ROBUST_BUFFER_ACCESS when __DRI2_ROBUSTNESS is not enabled

    Only allow __DRI_CTX_FLAG_ROBUST_BUFFER_ACCESS in brwCreateContext if
    intelInitScreen2 also enabled __DRI2_ROBUSTNESS (thereby enabling
    GLX_ARB_create_context).

    This fixes a regression in the piglit test
    "glx/GLX_ARB_create_context/invalid flag"

    v2: Remove commented debug code.  Noticed by Jordan.

    Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
    Reported-by: Paul Berry <stereotype441@gmail.com>
    Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
    Reviewed-by: Matt Turner <mattst88@gmail.com>
    Cc: "10.0" <mesa-stable@lists.freedesktop.org>
    (cherry picked from commit 53a65e547c)

src/mesa/drivers/dri/i965/brw_context.c

@@ -589,9 +589,16 @@ brwCreateContext(gl_api api,
    struct dd_function_table functions;
    struct gl_config visual;
 
-   if (flags & ~(__DRI_CTX_FLAG_DEBUG
-                 | __DRI_CTX_FLAG_FORWARD_COMPATIBLE
-                 | __DRI_CTX_FLAG_ROBUST_BUFFER_ACCESS)) {
+   /* Only allow the __DRI_CTX_FLAG_ROBUST_BUFFER_ACCESS flag if the kernel
+    * provides us with context reset notifications.
+    */
+   uint32_t allowed_flags = __DRI_CTX_FLAG_DEBUG
+      | __DRI_CTX_FLAG_FORWARD_COMPATIBLE;
+
+   if (screen->has_context_reset_notification)
+      allowed_flags |= __DRI_CTX_FLAG_ROBUST_BUFFER_ACCESS;
+
+   if (flags & ~allowed_flags) {
       *dri_ctx_error = __DRI_CTX_ERROR_UNKNOWN_FLAG;
       return false;
    }
@@ -713,21 +720,6 @@ brwCreateContext(gl_api api,
       }
    }
 
-   /* Notification of GPU resets requires hardware contexts and a kernel new
-    * enough to support DRM_IOCTL_I915_GET_RESET_STATS.
-    */
-   if (notify_reset &&
-       (brw->hw_ctx == NULL
-        || drm_intel_get_reset_stats(brw->hw_ctx, &brw->reset_count, NULL,
-                                     NULL))) {
-      /* This is the wrong error code, but the correct error code (one that
-       * will cause EGL to generate EGL_BAD_MATCH) doesn't seem to exist.
-       */
-      *dri_ctx_error = __DRI_CTX_ERROR_UNKNOWN_ATTRIBUTE;
-      intelDestroyContext(driContextPriv);
-      return false;
-   }
-
    brw_init_surface_formats(brw);
 
    if (brw->is_g4x || brw->gen >= 5) {

src/mesa/drivers/dri/i965/intel_screen.c

@@ -894,6 +894,15 @@ static const struct __DRIrobustnessExtensionRec dri2Robustness = {
 };
 
 static const __DRIextension *intelScreenExtensions[] = {
+    &intelTexBufferExtension.base,
+    &intelFlushExtension.base,
+    &intelImageExtension.base,
+    &intelRendererQueryExtension.base,
+    &dri2ConfigQueryExtension.base,
+    NULL
+};
+
+static const __DRIextension *intelRobustScreenExtensions[] = {
     &intelTexBufferExtension.base,
     &intelFlushExtension.base,
     &intelImageExtension.base,
@@ -1302,7 +1311,22 @@ __DRIconfig **intelInitScreen2(__DRIscreen *psp)
 
    set_max_gl_versions(intelScreen);
 
-   psp->extensions = intelScreenExtensions;
+   /* Notification of GPU resets requires hardware contexts and a kernel new
+    * enough to support DRM_IOCTL_I915_GET_RESET_STATS.  If the ioctl is
+    * supported, calling it with a context of 0 will either generate EPERM or
+    * no error.  If the ioctl is not supported, it always generate EINVAL.
+    * Use this to determine whether to advertise the __DRI2_ROBUSTNESS
+    * extension to the loader.
+    */
+   struct drm_i915_reset_stats stats;
+   memset(&stats, 0, sizeof(stats));
+
+   const int ret = drmIoctl(psp->fd, DRM_IOCTL_I915_GET_RESET_STATS, &stats);
+
+   intelScreen->has_context_reset_notification = (ret != -1 || errno != EINVAL);
+
+   psp->extensions = !intelScreen->has_context_reset_notification
+      ? intelScreenExtensions : intelRobustScreenExtensions;
 
    return (const __DRIconfig**) intel_screen_make_configs(psp);
 }

src/mesa/drivers/dri/i965/intel_screen.h

@@ -50,6 +50,11 @@ struct intel_screen
 
    bool hw_has_swizzling;
 
+   /**
+    * Does the kernel support context reset notifications?
+    */
+   bool has_context_reset_notification;
+
    dri_bufmgr *bufmgr;
 
    /**