net: sockets: socketpair: Allow statically allocated socketpairs

When the target board does not have heap by default, allows
statically reserving the space for required socketpairs.

Signed-off-by: Seppo Takalo <[email protected]>

Author: SeppoTakalo

subsys/net/lib/sockets/Kconfig

@@ -246,18 +246,38 @@ config NET_SOCKETS_CAN_RECEIVERS
 config NET_SOCKETPAIR
 	bool "Support for socketpair"
 	select PIPES
-	depends on HEAP_MEM_POOL_SIZE != 0
 	help
 	  Communicate over a pair of connected, unnamed UNIX domain sockets.
 
+if NET_SOCKETPAIR
+
 config NET_SOCKETPAIR_BUFFER_SIZE
 	int "Size of the intermediate buffer, in bytes"
 	default 64
 	range 1 4096
-	depends on NET_SOCKETPAIR
 	help
 	  Buffer size for socketpair(2)
 
+choice
+	prompt "Memory management for socketpair"
+	default NET_SOCKETPAIR_HEAP if HEAP_MEM_POOL_SIZE != 0
+
+config NET_SOCKETPAIR_STATIC
+	bool "Pre-allocate memory statically"
+
+config NET_SOCKETPAIR_HEAP
+	bool "Use heap for allocating socketpairs"
+	depends on HEAP_MEM_POOL_SIZE != 0
+
+endchoice
+
+if NET_SOCKETPAIR_STATIC
+config NET_SOCKETPAIR_MAX
+	int "How many socketpairs to pre-allocate"
+	default 1
+endif
+endif
+
 config NET_SOCKETS_NET_MGMT
 	bool "Network management socket support [EXPERIMENTAL]"
 	depends on NET_MGMT_EVENT

subsys/net/lib/sockets/socketpair.c

@@ -56,6 +56,11 @@ __net_socket struct spair {
 	uint8_t buf[CONFIG_NET_SOCKETPAIR_BUFFER_SIZE];
 };
 
+#ifdef CONFIG_NET_SOCKETPAIR_STATIC
+K_MEM_SLAB_DEFINE_STATIC(spair_slab, sizeof(struct spair), CONFIG_NET_SOCKETPAIR_MAX * 2,
+			 __alignof__(struct spair));
+#endif /* CONFIG_NET_SOCKETPAIR_STATIC */
+
 /* forward declaration */
 static const struct socket_op_vtable spair_fd_op_vtable;
 
@@ -188,7 +193,9 @@ static void spair_delete(struct spair *spair)
 
 	/* ensure no private information is released to the memory pool */
 	memset(spair, 0, sizeof(*spair));
-#ifdef CONFIG_USERSPACE
+#ifdef CONFIG_NET_SOCKETPAIR_STATIC
+	k_mem_slab_free(&spair_slab, (void **) &spair);
+#elif CONFIG_USERSPACE
 	k_object_free(spair);
 #else
 	k_free(spair);
@@ -213,7 +220,14 @@ static struct spair *spair_new(void)
 	struct spair *spair;
 	int res;
 
-#ifdef CONFIG_USERSPACE
+#ifdef CONFIG_NET_SOCKETPAIR_STATIC
+
+	res = k_mem_slab_alloc(&spair_slab, (void **) &spair, K_NO_WAIT);
+	if (res != 0) {
+		spair = NULL;
+	}
+
+#elif CONFIG_USERSPACE
 	struct z_object *zo = z_dynamic_object_create(sizeof(*spair));
 
 	if (zo == NULL) {