params: specify path using PARAMS_ROOT (#28257)

* Add PARAMS_ROOT env var

* Change getenv type signature

* Use getenv default_val

common/util.cc

@@ -189,7 +189,7 @@ bool create_directories(const std::string& dir, mode_t mode) {
   return createDirectory(dir, mode);
 }
 
-std::string getenv(const char* key, const char* default_val) {
+std::string getenv(const char* key, std::string default_val) {
   const char* val = ::getenv(key);
   return val ? val : default_val;
 }

common/util.h

@@ -70,7 +70,7 @@ std::string string_format(const std::string& format, Args... args) {
   return std::string(buf.get(), buf.get() + size - 1);
 }
 
-std::string getenv(const char* key, const char* default_val = "");
+std::string getenv(const char* key, std::string default_val = "");
 int getenv(const char* key, int default_val);
 float getenv(const char* key, float default_val);
 

system/hardware/hw.h

@@ -19,7 +19,7 @@ inline std::string log_root() {
   return Hardware::PC() ? util::getenv("HOME") + "/.comma/media/0/realdata" : "/data/media/0/realdata";
 }
 inline std::string params() {
-  return Hardware::PC() ? util::getenv("HOME") + "/.comma/params" : "/data/params";
+  return Hardware::PC() ? util::getenv("PARAMS_ROOT", util::getenv("HOME") + "/.comma/params") : "/data/params";
 }
 inline std::string rsa_file() {
   return Hardware::PC() ? util::getenv("HOME") + "/.comma/persist/comma/id_rsa" : "/persist/comma/id_rsa";