Optimization: remove unnecessary buffer resizes on partial recvs

Using the dynamic buffer's size to express the current offset
results in unnecessary resized and re-zeroing of areas of the
buffer.

The reception buffer's size is now used to express the total
size of the expected incoming message. The offset can be inferred
from the "bytes_left_to_receive" variable and message size. It
also, arguably, makes the code simpler to follow.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>

diff --git a/src/bin/lttng-sessiond/notification-thread-events.c b/src/bin/lttng-sessiond/notification-thread-events.c
index 0fd97e4e2f1e95172f4c4cb2883d2dd627d18b95..8f250dfdd715f38da9020b746c4cfbb30321f6b0 100644 (file)
--- a/src/bin/lttng-sessiond/notification-thread-events.c
+++ b/src/bin/lttng-sessiond/notification-thread-events.c
@@ -97,6 +97,11 @@ struct notification_client {
        struct cds_lfht_node client_socket_ht_node;
        struct {
                struct {
+                       /*
+                        * During the reception of a message, the reception
+                        * buffers' "size" is set to contain the current
+                        * message's complete payload.
+                        */
                        struct lttng_dynamic_buffer buffer;
                        /* Bytes left to receive for the current message. */
                        size_t bytes_to_receive;
@@ -112,6 +117,7 @@ struct notification_client {
                         * from the client.
                         */
                        bool creds_received;
+                       /* Only used during credentials reception. */
                        lttng_sock_cred creds;
                } inbound;
                struct {
@@ -1153,7 +1159,7 @@ end:
 }
 
 static
-void client_reset_inbound_state(struct notification_client *client)
+int client_reset_inbound_state(struct notification_client *client)
 {
        int ret;
 
@@ -1168,6 +1174,10 @@ void client_reset_inbound_state(struct notification_client *client)
        client->communication.inbound.receive_creds = false;
        LTTNG_SOCK_SET_UID_CRED(&client->communication.inbound.creds, -1);
        LTTNG_SOCK_SET_GID_CRED(&client->communication.inbound.creds, -1);
+       ret = lttng_dynamic_buffer_set_size(
+                       &client->communication.inbound.buffer,
+                       client->communication.inbound.bytes_to_receive);
+       return ret;
 }
 
 int handle_notification_thread_client_connect(
@@ -1187,7 +1197,12 @@ int handle_notification_thread_client_connect(
        CDS_INIT_LIST_HEAD(&client->condition_list);
        lttng_dynamic_buffer_init(&client->communication.inbound.buffer);
        lttng_dynamic_buffer_init(&client->communication.outbound.buffer);
-       client_reset_inbound_state(client);
+       ret = client_reset_inbound_state(client);
+       if (ret) {
+               ERR("[notification-thread] Failed to reset client communication's inbound state");
+               ret = 0;
+               goto error;
+       }
 
        ret = lttcomm_accept_unix_sock(state->notification_channel_socket);
        if (ret < 0) {
@@ -1481,7 +1496,7 @@ int client_dispatch_message(struct notification_client *client,
                        client->communication.inbound.receive_creds = true;
                }
                ret = lttng_dynamic_buffer_set_size(
-                               &client->communication.inbound.buffer, 0);
+                               &client->communication.inbound.buffer, msg->size);
                if (ret) {
                        goto end;
                }
@@ -1548,7 +1563,11 @@ int client_dispatch_message(struct notification_client *client,
                }
 
                /* Set reception state to receive the next message header. */
-               client_reset_inbound_state(client);
+               ret = client_reset_inbound_state(client);
+               if (ret) {
+                       ERR("[notification-thread] Failed to reset client communication's inbound state");
+                       goto end;
+               }
                client->validated = true;
                break;
        }
@@ -1595,7 +1614,11 @@ int client_dispatch_message(struct notification_client *client,
                }
 
                /* Set reception state to receive the next message header. */
-               client_reset_inbound_state(client);
+               ret = client_reset_inbound_state(client);
+               if (ret) {
+                       ERR("[notification-thread] Failed to reset client communication's inbound state");
+                       goto end;
+               }
                break;
        }
        default:
@@ -1609,7 +1632,7 @@ end:
 int handle_notification_thread_client_in(
                struct notification_thread_state *state, int socket)
 {
-       int ret;
+       int ret = 0;
        struct notification_client *client;
        ssize_t recv_ret;
        size_t offset;
@@ -1621,19 +1644,8 @@ int handle_notification_thread_client_in(
                goto end;
        }
 
-       offset = client->communication.inbound.buffer.size;
-       /*
-        * The buffer's size starts out at the size of the command header.
-        * Once the command is determined, the "bytes_to_receive" are bumped
-        * to fit the remainder of the message being received.
-        */
-       ret = lttng_dynamic_buffer_set_size(
-                       &client->communication.inbound.buffer,
-                       client->communication.inbound.bytes_to_receive + offset);
-       if (ret) {
-               goto end;
-       }
-
+       offset = client->communication.inbound.buffer.size -
+                       client->communication.inbound.bytes_to_receive;
        if (client->communication.inbound.receive_creds) {
                recv_ret = lttcomm_recv_creds_unix_sock(socket,
                                client->communication.inbound.buffer.data + offset,
@@ -1653,14 +1665,6 @@ int handle_notification_thread_client_in(
        }
 
        client->communication.inbound.bytes_to_receive -= recv_ret;
-       ret = lttng_dynamic_buffer_set_size(
-                       &client->communication.inbound.buffer,
-                       client->communication.inbound.buffer.size -
-                       client->communication.inbound.bytes_to_receive);
-       if (ret) {
-               goto end;
-       }
-
        if (client->communication.inbound.bytes_to_receive == 0) {
                ret = client_dispatch_message(client, state);
                if (ret) {