Using plain shared memory for configuration pass.

There is no restrictions on configration size and using segmented shared memory
only doubles memory usage because to parse configration on router side,
it needs to be 'plain' e. g. located in single continous memory buffer.

src/nxt_router.c

@@ -906,8 +906,9 @@ nxt_router_new_port_handler(nxt_task_t *task, nxt_port_recv_msg_t *msg)
 void
 nxt_router_conf_data_handler(nxt_task_t *task, nxt_port_recv_msg_t *msg)
 {
+    void                    *p;
+    size_t                  size;
     nxt_int_t               ret;
-    nxt_buf_t               *b;
     nxt_router_temp_conf_t  *tmcf;
 
     tmcf = nxt_router_temp_conf(task);
@@ -915,9 +916,33 @@ nxt_router_conf_data_handler(nxt_task_t *task, nxt_port_recv_msg_t *msg)
         return;
     }
 
-    nxt_debug(task, "nxt_router_conf_data_handler(%O): %*s",
-              nxt_buf_used_size(msg->buf),
-              (size_t) nxt_buf_used_size(msg->buf), msg->buf->mem.pos);
+    if (nxt_slow_path(msg->fd == -1)) {
+        nxt_alert(task, "conf_data_handler: invalid file shm fd");
+        return;
+    }
+
+    if (nxt_buf_mem_used_size(&msg->buf->mem) != sizeof(size_t)) {
+        nxt_alert(task, "conf_data_handler: unexpected buffer size (%d)",
+                  (int) nxt_buf_mem_used_size(&msg->buf->mem));
+
+        nxt_fd_close(msg->fd);
+        msg->fd = -1;
+
+        return;
+    }
+
+    nxt_memcpy(&size, msg->buf->mem.pos, sizeof(size_t));
+
+    p = nxt_mem_mmap(NULL, size, PROT_READ, MAP_SHARED, msg->fd, 0);
+
+    nxt_fd_close(msg->fd);
+    msg->fd = -1;
+
+    if (nxt_slow_path(p == MAP_FAILED)) {
+        return;
+    }
+
+    nxt_debug(task, "conf_data_handler(%uz): %*s", size, size, p);
 
     tmcf->router_conf->router = nxt_router;
     tmcf->stream = msg->port_msg.stream;
@@ -928,20 +953,12 @@ nxt_router_conf_data_handler(nxt_task_t *task, nxt_port_recv_msg_t *msg)
     if (nxt_slow_path(tmcf->port == NULL)) {
         nxt_alert(task, "reply port not found");
 
-        return;
+        goto fail;
     }
 
     nxt_port_use(task, tmcf->port, 1);
 
-    b = nxt_buf_chk_make_plain(tmcf->router_conf->mem_pool,
-                               msg->buf, msg->size);
-    if (nxt_slow_path(b == NULL)) {
-        nxt_router_conf_error(task, tmcf);
-
-        return;
-    }
-
-    ret = nxt_router_conf_create(task, tmcf, b->mem.pos, b->mem.free);
+    ret = nxt_router_conf_create(task, tmcf, p, nxt_pointer_to(p, size));
 
     if (nxt_fast_path(ret == NXT_OK)) {
         nxt_router_conf_apply(task, tmcf, NULL);
@@ -949,6 +966,10 @@ nxt_router_conf_data_handler(nxt_task_t *task, nxt_port_recv_msg_t *msg)
     } else {
         nxt_router_conf_error(task, tmcf);
     }
+
+fail:
+
+    nxt_mem_munmap(p, size);
 }