util/u_process: add MESA_PROCESS_NAME override to util_get_process_name()

Allow processes to set a custom process name before loading drivers.

Especially useful for virtualized workloads hidden behind a
generically-named host renderer process (e.g. Venus render_server) to
retain game-specific driconf option matching.

Signed-off-by: Ryan Neph <ryanneph@google.com>
Reviewed-by: Emma Anholt <emma@anholt.net>
Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20779>

docs/envvars.rst

@@ -86,6 +86,12 @@ Core Mesa environment variables
       print error and performance messages to stderr (or
       ``MESA_LOG_FILE``).
 
+.. envvar:: MESA_PROCESS_NAME
+
+   if set, overrides the process name string used internally for various
+   purposes (e.g. for driconf option matching, logging, artifact storage,
+   etc.).
+
 .. envvar:: MESA_LOG_FILE
 
    specifies a file name for logging all errors, warnings, etc., rather

src/util/u_process.c

@@ -206,10 +206,11 @@ free_program_name(void)
 static void
 util_get_process_name_callback(void)
 {
-   program_name = __getProgramName();
-   if (program_name) {
+   const char *override_name = os_get_option("MESA_PROCESS_NAME");
+   program_name = override_name ? strdup(override_name) : __getProgramName();
+
+   if (program_name)
       atexit(free_program_name);
-   }
 }
 
 const char *