Using shared memory to send data via nxt_port.

Usage:
    b = nxt_port_mmap_get_buf(task, port, size);
    b->mem.free = nxt_cpymem(b->mem.free, data, size);
    nxt_port_socket_write(task, port, NXT_PORT_MSG_DATA, -1, 0, b);

src/nxt_port_memory.h

@@ -0,0 +1,50 @@
+
+#ifndef _NXT_PORT_MEMORY_H_INCLUDED_
+#define _NXT_PORT_MEMORY_H_INCLUDED_
+
+#define PORT_MMAP_MIN_SIZE (3 * sizeof(uint32_t))
+
+typedef struct nxt_port_mmap_header_s nxt_port_mmap_header_t;
+
+void
+nxt_port_mmap_destroy(nxt_port_mmap_t *port_mmap);
+
+/*
+ * Allocates nxt_but_t structure from port's mem_pool, assigns this buf 'mem'
+ * pointers to first available shared mem bucket(s). 'size' used as a hint to
+ * acquire several successive buckets if possible.
+ *
+ * This function assumes that current thread operates the 'port' exclusively.
+ */
+nxt_buf_t *
+nxt_port_mmap_get_buf(nxt_task_t *task, nxt_port_t *port, size_t size);
+
+nxt_port_mmap_t *
+nxt_port_incoming_port_mmap(nxt_task_t *task, nxt_process_t *process,
+    nxt_fd_t fd);
+
+void
+nxt_port_mmap_write(nxt_task_t *task, nxt_port_t *port,
+    nxt_port_send_msg_t *msg, nxt_sendbuf_coalesce_t *sb);
+
+nxt_inline void
+nxt_port_mmap_completion(nxt_task_t *task, nxt_work_queue_t *wq, nxt_buf_t *b) {
+    nxt_work_queue_add(wq, b->completion_handler, task, b, b->parent);
+}
+
+void
+nxt_port_mmap_read(nxt_task_t *task, nxt_port_t *port,
+    nxt_port_recv_msg_t *msg, size_t size);
+
+enum nxt_port_method_e {
+    NXT_PORT_METHOD_ANY = 0,
+    NXT_PORT_METHOD_PLAIN,
+    NXT_PORT_METHOD_MMAP
+};
+
+typedef enum nxt_port_method_e nxt_port_method_t;
+
+nxt_port_method_t
+nxt_port_mmap_get_method(nxt_task_t *task, nxt_port_t *port, nxt_buf_t *b);
+
+#endif /* _NXT_PORT_MEMORY_H_INCLUDED_ */