From 61eed15db94ecbe4d2c67e2acb3ff368146a7b4c Mon Sep 17 00:00:00 2001
From: Augustin Cavalier <waddlesplash@gmail.com>
Date: Mon, 27 May 2024 19:45:57 -0400
Subject: [PATCH] kernel/socket: Refactor {get|put}_stack_interface_module and
 keep it loaded.

 * Make the consumer-count int32 atomic, avoiding the need for
   all get/put operations to go through a global lock.

 * Disable the code that unloads the stack interface when there
   are no consumers. Otherwise, we wind up repeatedly loading/
   unloading the stack interface during the boot process (e.g.
   while sockets are being created and destroyed during net_server
   startup.)

   In the future, if we want to really unload it, we can add some
   interaction with low_resource_monitor or something like that.

Reduces register_domain call count during boot from 31 to 7
(it appears the stack was loaded and unloaded 5 times, before
it stayed loaded the 6th.)
---
 src/system/kernel/fs/socket.cpp | 51 ++++++++++++++++++++++-----------
 1 file changed, 34 insertions(+), 17 deletions(-)

diff --git a/src/system/kernel/fs/socket.cpp b/src/system/kernel/fs/socket.cpp
index 890ec35288..1fc0066d6c 100644
--- a/src/system/kernel/fs/socket.cpp
+++ b/src/system/kernel/fs/socket.cpp
@@ -42,26 +42,34 @@
 
 
 static net_stack_interface_module_info* sStackInterface = NULL;
-static vint32 sStackInterfaceInitialized = 0;
-static mutex sLock = MUTEX_INITIALIZER("stack interface");
+static int32 sStackInterfaceConsumers = 0;
+static rw_lock sLock = RW_LOCK_INITIALIZER("stack interface");
 
 
 static net_stack_interface_module_info*
 get_stack_interface_module()
 {
-	MutexLocker _(sLock);
+	atomic_add(&sStackInterfaceConsumers, 1);
 
-	if (sStackInterfaceInitialized++ == 0) {
-		// load module
-		net_stack_interface_module_info* module;
-		// TODO: Add driver settings option to load the userland net stack.
-		status_t error = get_module(NET_STACK_INTERFACE_MODULE_NAME,
-			(module_info**)&module);
-		if (error == B_OK)
-			sStackInterface = module;
-		else
-			sStackInterface = NULL;
-	}
+	ReadLocker readLocker(sLock);
+	if (sStackInterface != NULL)
+		return sStackInterface;
+
+	readLocker.Unlock();
+	WriteLocker writeLocker(sLock);
+	if (sStackInterface != NULL)
+		return sStackInterface;
+
+	// load module
+	net_stack_interface_module_info* module;
+	// TODO: Add driver settings option to load the userland net stack.
+	status_t error = get_module(NET_STACK_INTERFACE_MODULE_NAME,
+		(module_info**)&module);
+	if (error == B_OK)
+		sStackInterface = module;
+
+	if (sStackInterface == NULL)
+		atomic_add(&sStackInterfaceConsumers, -1);
 
 	return sStackInterface;
 }
@@ -70,10 +78,19 @@ get_stack_interface_module()
 static void
 put_stack_interface_module()
 {
-	MutexLocker _(sLock);
+	if (atomic_add(&sStackInterfaceConsumers, -1) != 1)
+		return;
 
-	if (sStackInterfaceInitialized-- == 1)
-		put_module(NET_STACK_INTERFACE_MODULE_NAME);
+#if 0 /* Just leave the stack loaded, for now. */
+	WriteLocker _(sLock);
+	if (atomic_get(&sStackInterfaceConsumers) > 0)
+		return;
+	if (sStackInterface == NULL)
+		return;
+
+	put_module(NET_STACK_INTERFACE_MODULE_NAME);
+	sStackInterface = NULL;
+#endif
 }