loader: Add an environment variable to override driver name choice.

My vc4 simulator has been implemented so far by having an entrypoint
claiming to be i965, which was a bit gross.  The simulator would be a lot
less special if we entered through the vc4 entrypoint like normal, so add
a loader environment variable to allow the i965 fd to probe as vc4.

Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/loader/loader.c b/src/loader/loader.c
index 449ff54d137..4825151ad5e 100644
--- a/src/loader/loader.c
+++ b/src/loader/loader.c
@@ -345,6 +345,17 @@ loader_get_driver_for_fd(int fd)
    int vendor_id, chip_id, i, j;
    char *driver = NULL;
 
+   /* Allow an environment variable to force choosing a different driver
+    * binary.  If that driver binary can't survive on this FD, that's the
+    * user's problem, but this allows vc4 simulator to run on an i965 host,
+    * and may be useful for some touch testing of i915 on an i965 host.
+    */
+   if (geteuid() == getuid()) {
+      driver = getenv("MESA_LOADER_DRIVER_OVERRIDE");
+      if (driver)
+         return strdup(driver);
+   }
+
    if (!loader_get_pci_id_for_fd(fd, &vendor_id, &chip_id)) {
 
 #if HAVE_LIBDRM