Fix: return error if sendmsg fails on relayd
[lttng-tools.git] / src / bin / lttng-relayd / main.c
index 9e6d4bf9fa594dc2f51e93ee2f918360acf994c8..6d800f50b3c0db40de5997ead9625fee8cf8938c 100644 (file)
@@ -239,8 +239,8 @@ void cleanup(void)
        /* Close thread quit pipes */
        utils_close_pipe(thread_quit_pipe);
 
-       /* Close relay cmd pipes */
-       utils_close_pipe(relay_cmd_pipe);
+       uri_free(control_uri);
+       uri_free(data_uri);
 }
 
 /*
@@ -254,7 +254,7 @@ int notify_thread_pipe(int wpipe)
        do {
                ret = write(wpipe, "!", 1);
        } while (ret < 0 && errno == EINTR);
-       if (ret < 0) {
+       if (ret < 0 || ret != 1) {
                PERROR("write poll pipe");
        }
 
@@ -455,6 +455,13 @@ int close_stream_check(struct relay_stream *stream)
 {
 
        if (stream->close_flag && stream->prev_seq == stream->last_net_seq_num) {
+               /*
+                * We are about to close the stream so set the data pending flag to 1
+                * which will make the end data pending command skip the stream which
+                * is now closed and ready. Note that after proceeding to a file close,
+                * the written file is ready for reading.
+                */
+               stream->data_pending_check_done = 1;
                return 1;
        }
        return 0;
@@ -507,8 +514,6 @@ void *relay_thread_listener(void *data)
        while (1) {
                DBG("Listener accepting connections");
 
-               nb_fd = LTTNG_POLL_GETNB(&events);
-
 restart:
                ret = lttng_poll_wait(&events, -1);
                if (ret < 0) {
@@ -521,6 +526,8 @@ restart:
                        goto error;
                }
 
+               nb_fd = ret;
+
                DBG("Relay new connection received");
                for (i = 0; i < nb_fd; i++) {
                        /* Fetch once the poll data */
@@ -662,7 +669,7 @@ void *relay_thread_dispatcher(void *data)
                                                sizeof(struct relay_command));
                        } while (ret < 0 && errno == EINTR);
                        free(relay_cmd);
-                       if (ret < 0) {
+                       if (ret < 0 || ret != sizeof(struct relay_command)) {
                                PERROR("write cmd pipe");
                                goto error;
                        }
@@ -884,7 +891,6 @@ void relay_delete_session(struct relay_command *cmd, struct lttng_ht *streams_ht
        }
 
        DBG("Relay deleting session %" PRIu64, cmd->session->id);
-       free(cmd->session->sock);
 
        rcu_read_lock();
        cds_lfht_for_each_entry(streams_ht->ht, &iter.iter, node, node) {
@@ -893,7 +899,10 @@ void relay_delete_session(struct relay_command *cmd, struct lttng_ht *streams_ht
                        stream = caa_container_of(node,
                                        struct relay_stream, stream_n);
                        if (stream->session == cmd->session) {
-                               close(stream->fd);
+                               ret = close(stream->fd);
+                               if (ret < 0) {
+                                       PERROR("close stream fd on delete session");
+                               }
                                ret = lttng_ht_del(streams_ht, &iter);
                                assert(!ret);
                                call_rcu(&stream->rcu_node,
@@ -902,6 +911,57 @@ void relay_delete_session(struct relay_command *cmd, struct lttng_ht *streams_ht
                }
        }
        rcu_read_unlock();
+
+       free(cmd->session);
+}
+
+/*
+ * Handle the RELAYD_CREATE_SESSION command.
+ *
+ * On success, send back the session id or else return a negative value.
+ */
+static
+int relay_create_session(struct lttcomm_relayd_hdr *recv_hdr,
+               struct relay_command *cmd)
+{
+       int ret = 0, send_ret;
+       struct relay_session *session;
+       struct lttcomm_relayd_status_session reply;
+
+       assert(recv_hdr);
+       assert(cmd);
+
+       memset(&reply, 0, sizeof(reply));
+
+       session = zmalloc(sizeof(struct relay_session));
+       if (session == NULL) {
+               PERROR("relay session zmalloc");
+               ret = -1;
+               goto error;
+       }
+
+       session->id = ++last_relay_session_id;
+       session->sock = cmd->sock;
+       cmd->session = session;
+
+       reply.session_id = htobe64(session->id);
+
+       DBG("Created session %" PRIu64, session->id);
+
+error:
+       if (ret < 0) {
+               reply.ret_code = htobe32(LTTNG_ERR_FATAL);
+       } else {
+               reply.ret_code = htobe32(LTTNG_OK);
+       }
+
+       send_ret = cmd->sock->ops->sendmsg(cmd->sock, &reply, sizeof(reply), 0);
+       if (send_ret < 0) {
+               ERR("Relayd sending session id");
+               ret = send_ret;
+       }
+
+       return ret;
 }
 
 /*
@@ -918,17 +978,21 @@ int relay_add_stream(struct lttcomm_relayd_hdr *recv_hdr,
        char *path = NULL, *root_path = NULL;
        int ret, send_ret;
 
-       if (!session || session->version_check_done == 0) {
+       if (!session || cmd->version_check_done == 0) {
                ERR("Trying to add a stream before version check");
                ret = -1;
                goto end_no_session;
        }
 
-       /* FIXME : use data_size for something ? */
        ret = cmd->sock->ops->recvmsg(cmd->sock, &stream_info,
-                       sizeof(struct lttcomm_relayd_add_stream), MSG_WAITALL);
+                       sizeof(struct lttcomm_relayd_add_stream), 0);
        if (ret < sizeof(struct lttcomm_relayd_add_stream)) {
-               ERR("Relay didn't receive valid add_stream struct size : %d", ret);
+               if (ret == 0) {
+                       /* Orderly shutdown. Not necessary to print an error. */
+                       DBG("Socket %d did an orderly shutdown", cmd->sock->fd);
+               } else {
+                       ERR("Relay didn't receive valid add_stream struct size : %d", ret);
+               }
                ret = -1;
                goto end_no_session;
        }
@@ -991,6 +1055,7 @@ end:
                        sizeof(struct lttcomm_relayd_status_stream), 0);
        if (send_ret < 0) {
                ERR("Relay sending stream id");
+               ret = send_ret;
        }
        rcu_read_unlock();
 
@@ -1015,16 +1080,21 @@ int relay_close_stream(struct lttcomm_relayd_hdr *recv_hdr,
 
        DBG("Close stream received");
 
-       if (!session || session->version_check_done == 0) {
+       if (!session || cmd->version_check_done == 0) {
                ERR("Trying to close a stream before version check");
                ret = -1;
                goto end_no_session;
        }
 
        ret = cmd->sock->ops->recvmsg(cmd->sock, &stream_info,
-                       sizeof(struct lttcomm_relayd_close_stream), MSG_WAITALL);
+                       sizeof(struct lttcomm_relayd_close_stream), 0);
        if (ret < sizeof(struct lttcomm_relayd_close_stream)) {
-               ERR("Relay didn't receive valid add_stream struct size : %d", ret);
+               if (ret == 0) {
+                       /* Orderly shutdown. Not necessary to print an error. */
+                       DBG("Socket %d did an orderly shutdown", cmd->sock->fd);
+               } else {
+                       ERR("Relay didn't receive valid add_stream struct size : %d", ret);
+               }
                ret = -1;
                goto end_no_session;
        }
@@ -1052,7 +1122,10 @@ int relay_close_stream(struct lttcomm_relayd_hdr *recv_hdr,
        if (close_stream_check(stream)) {
                int delret;
 
-               close(stream->fd);
+               delret = close(stream->fd);
+               if (delret < 0) {
+                       PERROR("close stream");
+               }
                delret = lttng_ht_del(streams_ht, &iter);
                assert(!delret);
                call_rcu(&stream->rcu_node,
@@ -1072,6 +1145,7 @@ end_unlock:
                        sizeof(struct lttcomm_relayd_generic_reply), 0);
        if (send_ret < 0) {
                ERR("Relay sending stream id");
+               ret = send_ret;
        }
 
 end_no_session:
@@ -1172,10 +1246,12 @@ static int write_padding_to_file(int fd, uint32_t size)
        do {
                ret = write(fd, zeros, size);
        } while (ret < 0 && errno == EINTR);
-       if (ret < 0) {
+       if (ret < 0 || ret != size) {
                PERROR("write padding to file");
        }
 
+       free(zeros);
+
 end:
        return ret;
 }
@@ -1209,23 +1285,29 @@ int relay_recv_metadata(struct lttcomm_relayd_hdr *recv_hdr,
 
        if (data_buffer_size < data_size) {
                /* In case the realloc fails, we can free the memory */
-               char *tmp_data_ptr = data_buffer;
-               data_buffer = realloc(data_buffer, data_size);
-               if (!data_buffer) {
+               char *tmp_data_ptr;
+
+               tmp_data_ptr = realloc(data_buffer, data_size);
+               if (!tmp_data_ptr) {
                        ERR("Allocating data buffer");
-                       free(tmp_data_ptr);
+                       free(data_buffer);
                        ret = -1;
                        goto end;
                }
+               data_buffer = tmp_data_ptr;
                data_buffer_size = data_size;
        }
        memset(data_buffer, 0, data_size);
        DBG2("Relay receiving metadata, waiting for %" PRIu64 " bytes", data_size);
-       ret = cmd->sock->ops->recvmsg(cmd->sock, data_buffer, data_size,
-                       MSG_WAITALL);
+       ret = cmd->sock->ops->recvmsg(cmd->sock, data_buffer, data_size, 0);
        if (ret < 0 || ret != data_size) {
+               if (ret == 0) {
+                       /* Orderly shutdown. Not necessary to print an error. */
+                       DBG("Socket %d did an orderly shutdown", cmd->sock->fd);
+               } else {
+                       ERR("Relay didn't receive the whole metadata");
+               }
                ret = -1;
-               ERR("Relay didn't receive the whole metadata");
                goto end;
        }
        metadata_struct = (struct lttcomm_relayd_metadata_payload *) data_buffer;
@@ -1242,7 +1324,7 @@ int relay_recv_metadata(struct lttcomm_relayd_hdr *recv_hdr,
                ret = write(metadata_stream->fd, metadata_struct->payload,
                                payload_size);
        } while (ret < 0 && errno == EINTR);
-       if (ret < payload_size) {
+       if (ret < 0 || ret != payload_size) {
                ERR("Relay error writing metadata on file");
                ret = -1;
                goto end_unlock;
@@ -1270,25 +1352,33 @@ int relay_send_version(struct lttcomm_relayd_hdr *recv_hdr,
                struct relay_command *cmd)
 {
        int ret;
-       struct lttcomm_relayd_version reply;
-       struct relay_session *session;
+       struct lttcomm_relayd_version reply, msg;
 
-       if (cmd->session == NULL) {
-               session = zmalloc(sizeof(struct relay_session));
-               if (session == NULL) {
-                       PERROR("relay session zmalloc");
-                       ret = -1;
-                       goto end;
+       assert(cmd);
+
+       cmd->version_check_done = 1;
+
+       /* Get version from the other side. */
+       ret = cmd->sock->ops->recvmsg(cmd->sock, &msg, sizeof(msg), 0);
+       if (ret < 0 || ret != sizeof(msg)) {
+               if (ret == 0) {
+                       /* Orderly shutdown. Not necessary to print an error. */
+                       DBG("Socket %d did an orderly shutdown", cmd->sock->fd);
+               } else {
+                       ERR("Relay failed to receive the version values.");
                }
-               session->id = ++last_relay_session_id;
-               DBG("Created session %" PRIu64, session->id);
-               cmd->session = session;
-       } else {
-               session = cmd->session;
+               ret = -1;
+               goto end;
        }
-       session->version_check_done = 1;
 
-       ret = sscanf(VERSION, "%u.%u", &reply.major, &reply.minor);
+       /*
+        * For now, we just ignore the received version but after 2.1 stable
+        * release, a check must be done to see if we either adapt to the other
+        * side version (which MUST be lower than us) or keep the latest data
+        * structure considering that the other side will adapt.
+        */
+
+       ret = sscanf(VERSION, "%10u.%10u", &reply.major, &reply.minor);
        if (ret < 2) {
                ERR("Error in scanning version");
                ret = -1;
@@ -1309,14 +1399,14 @@ end:
 }
 
 /*
- * Check for data availability for a given stream id from the session daemon.
+ * Check for data pending for a given stream id from the session daemon.
  */
 static
-int relay_data_available(struct lttcomm_relayd_hdr *recv_hdr,
+int relay_data_pending(struct lttcomm_relayd_hdr *recv_hdr,
                struct relay_command *cmd, struct lttng_ht *streams_ht)
 {
        struct relay_session *session = cmd->session;
-       struct lttcomm_relayd_data_available msg;
+       struct lttcomm_relayd_data_pending msg;
        struct lttcomm_relayd_generic_reply reply;
        struct relay_stream *stream;
        int ret;
@@ -1324,17 +1414,23 @@ int relay_data_available(struct lttcomm_relayd_hdr *recv_hdr,
        struct lttng_ht_iter iter;
        uint64_t last_net_seq_num, stream_id;
 
-       DBG("Data available command received");
+       DBG("Data pending command received");
 
-       if (!session || session->version_check_done == 0) {
+       if (!session || cmd->version_check_done == 0) {
                ERR("Trying to check for data before version check");
                ret = -1;
                goto end_no_session;
        }
 
-       ret = cmd->sock->ops->recvmsg(cmd->sock, &msg, sizeof(msg), MSG_WAITALL);
+       ret = cmd->sock->ops->recvmsg(cmd->sock, &msg, sizeof(msg), 0);
        if (ret < sizeof(msg)) {
-               ERR("Relay didn't receive valid data_available struct size : %d", ret);
+               if (ret == 0) {
+                       /* Orderly shutdown. Not necessary to print an error. */
+                       DBG("Socket %d did an orderly shutdown", cmd->sock->fd);
+               } else {
+                       ERR("Relay didn't receive valid data_pending struct size : %d",
+                                       ret);
+               }
                ret = -1;
                goto end_no_session;
        }
@@ -1354,26 +1450,29 @@ int relay_data_available(struct lttcomm_relayd_hdr *recv_hdr,
        stream = caa_container_of(node, struct relay_stream, stream_n);
        assert(stream);
 
-       DBG("Data available for stream id %" PRIu64 " prev_seq %" PRIu64
+       DBG("Data pending for stream id %" PRIu64 " prev_seq %" PRIu64
                        " and last_seq %" PRIu64, stream_id, stream->prev_seq,
                        last_net_seq_num);
 
        /* Avoid wrapping issue */
-       if (((int64_t) (stream->prev_seq - last_net_seq_num)) <= 0) {
-               /* Data has in fact been written and is available */
-               ret = 1;
-       } else {
-               /* Data still being streamed. */
+       if (((int64_t) (stream->prev_seq - last_net_seq_num)) >= 0) {
+               /* Data has in fact been written and is NOT pending */
                ret = 0;
+       } else {
+               /* Data still being streamed thus pending */
+               ret = 1;
        }
 
+       /* Pending check is now done. */
+       stream->data_pending_check_done = 1;
+
 end_unlock:
        rcu_read_unlock();
 
        reply.ret_code = htobe32(ret);
        ret = cmd->sock->ops->sendmsg(cmd->sock, &reply, sizeof(reply), 0);
        if (ret < 0) {
-               ERR("Relay data available ret code failed");
+               ERR("Relay data pending ret code failed");
        }
 
 end_no_session:
@@ -1389,19 +1488,201 @@ end_no_session:
  */
 static
 int relay_quiescent_control(struct lttcomm_relayd_hdr *recv_hdr,
-               struct relay_command *cmd)
+               struct relay_command *cmd, struct lttng_ht *streams_ht)
 {
        int ret;
+       uint64_t stream_id;
+       struct relay_stream *stream;
+       struct lttng_ht_iter iter;
+       struct lttcomm_relayd_quiescent_control msg;
        struct lttcomm_relayd_generic_reply reply;
 
        DBG("Checking quiescent state on control socket");
 
+       if (!cmd->session || cmd->version_check_done == 0) {
+               ERR("Trying to check for data before version check");
+               ret = -1;
+               goto end_no_session;
+       }
+
+       ret = cmd->sock->ops->recvmsg(cmd->sock, &msg, sizeof(msg), 0);
+       if (ret < sizeof(msg)) {
+               if (ret == 0) {
+                       /* Orderly shutdown. Not necessary to print an error. */
+                       DBG("Socket %d did an orderly shutdown", cmd->sock->fd);
+               } else {
+                       ERR("Relay didn't receive valid begin data_pending struct size: %d",
+                                       ret);
+               }
+               ret = -1;
+               goto end_no_session;
+       }
+
+       stream_id = be64toh(msg.stream_id);
+
+       rcu_read_lock();
+       cds_lfht_for_each_entry(streams_ht->ht, &iter.iter, stream, stream_n.node) {
+               if (stream->stream_handle == stream_id) {
+                       stream->data_pending_check_done = 1;
+                       DBG("Relay quiescent control pending flag set to %" PRIu64,
+                                       stream_id);
+                       break;
+               }
+       }
+       rcu_read_unlock();
+
+       reply.ret_code = htobe32(LTTNG_OK);
+       ret = cmd->sock->ops->sendmsg(cmd->sock, &reply, sizeof(reply), 0);
+       if (ret < 0) {
+               ERR("Relay data quiescent control ret code failed");
+       }
+
+end_no_session:
+       return ret;
+}
+
+/*
+ * Initialize a data pending command. This means that a client is about to ask
+ * for data pending for each stream he/she holds. Simply iterate over all
+ * streams of a session and set the data_pending_check_done flag.
+ *
+ * This command returns to the client a LTTNG_OK code.
+ */
+static
+int relay_begin_data_pending(struct lttcomm_relayd_hdr *recv_hdr,
+               struct relay_command *cmd, struct lttng_ht *streams_ht)
+{
+       int ret;
+       struct lttng_ht_iter iter;
+       struct lttcomm_relayd_begin_data_pending msg;
+       struct lttcomm_relayd_generic_reply reply;
+       struct relay_stream *stream;
+       uint64_t session_id;
+
+       assert(recv_hdr);
+       assert(cmd);
+       assert(streams_ht);
+
+       DBG("Init streams for data pending");
+
+       if (!cmd->session || cmd->version_check_done == 0) {
+               ERR("Trying to check for data before version check");
+               ret = -1;
+               goto end_no_session;
+       }
+
+       ret = cmd->sock->ops->recvmsg(cmd->sock, &msg, sizeof(msg), 0);
+       if (ret < sizeof(msg)) {
+               if (ret == 0) {
+                       /* Orderly shutdown. Not necessary to print an error. */
+                       DBG("Socket %d did an orderly shutdown", cmd->sock->fd);
+               } else {
+                       ERR("Relay didn't receive valid begin data_pending struct size: %d",
+                                       ret);
+               }
+               ret = -1;
+               goto end_no_session;
+       }
+
+       session_id = be64toh(msg.session_id);
+
+       /*
+        * Iterate over all streams to set the begin data pending flag. For now, the
+        * streams are indexed by stream handle so we have to iterate over all
+        * streams to find the one associated with the right session_id.
+        */
+       rcu_read_lock();
+       cds_lfht_for_each_entry(streams_ht->ht, &iter.iter, stream, stream_n.node) {
+               if (stream->session->id == session_id) {
+                       stream->data_pending_check_done = 0;
+                       DBG("Set begin data pending flag to stream %" PRIu64,
+                                       stream->stream_handle);
+               }
+       }
+       rcu_read_unlock();
+
+       /* All good, send back reply. */
        reply.ret_code = htobe32(LTTNG_OK);
+
+       ret = cmd->sock->ops->sendmsg(cmd->sock, &reply, sizeof(reply), 0);
+       if (ret < 0) {
+               ERR("Relay begin data pending send reply failed");
+       }
+
+end_no_session:
+       return ret;
+}
+
+/*
+ * End data pending command. This will check, for a given session id, if each
+ * stream associated with it has its data_pending_check_done flag set. If not,
+ * this means that the client lost track of the stream but the data is still
+ * being streamed on our side. In this case, we inform the client that data is
+ * inflight.
+ *
+ * Return to the client if there is data in flight or not with a ret_code.
+ */
+static
+int relay_end_data_pending(struct lttcomm_relayd_hdr *recv_hdr,
+               struct relay_command *cmd, struct lttng_ht *streams_ht)
+{
+       int ret;
+       struct lttng_ht_iter iter;
+       struct lttcomm_relayd_end_data_pending msg;
+       struct lttcomm_relayd_generic_reply reply;
+       struct relay_stream *stream;
+       uint64_t session_id;
+       uint32_t is_data_inflight = 0;
+
+       assert(recv_hdr);
+       assert(cmd);
+       assert(streams_ht);
+
+       DBG("End data pending command");
+
+       if (!cmd->session || cmd->version_check_done == 0) {
+               ERR("Trying to check for data before version check");
+               ret = -1;
+               goto end_no_session;
+       }
+
+       ret = cmd->sock->ops->recvmsg(cmd->sock, &msg, sizeof(msg), 0);
+       if (ret < sizeof(msg)) {
+               if (ret == 0) {
+                       /* Orderly shutdown. Not necessary to print an error. */
+                       DBG("Socket %d did an orderly shutdown", cmd->sock->fd);
+               } else {
+                       ERR("Relay didn't receive valid end data_pending struct size: %d",
+                                       ret);
+               }
+               ret = -1;
+               goto end_no_session;
+       }
+
+       session_id = be64toh(msg.session_id);
+
+       /* Iterate over all streams to see if the begin data pending flag is set. */
+       rcu_read_lock();
+       cds_lfht_for_each_entry(streams_ht->ht, &iter.iter, stream, stream_n.node) {
+               if (stream->session->id == session_id &&
+                               !stream->data_pending_check_done) {
+                       is_data_inflight = 1;
+                       DBG("Data is still in flight for stream %" PRIu64,
+                                       stream->stream_handle);
+                       break;
+               }
+       }
+       rcu_read_unlock();
+
+       /* All good, send back reply. */
+       reply.ret_code = htobe32(is_data_inflight);
+
        ret = cmd->sock->ops->sendmsg(cmd->sock, &reply, sizeof(reply), 0);
        if (ret < 0) {
-               ERR("Relay data available ret code failed");
+               ERR("Relay end data pending send reply failed");
        }
 
+end_no_session:
        return ret;
 }
 
@@ -1415,11 +1696,9 @@ int relay_process_control(struct lttcomm_relayd_hdr *recv_hdr,
        int ret = 0;
 
        switch (be32toh(recv_hdr->cmd)) {
-               /*
        case RELAYD_CREATE_SESSION:
                ret = relay_create_session(recv_hdr, cmd);
                break;
-               */
        case RELAYD_ADD_STREAM:
                ret = relay_add_stream(recv_hdr, cmd, streams_ht);
                break;
@@ -1435,11 +1714,17 @@ int relay_process_control(struct lttcomm_relayd_hdr *recv_hdr,
        case RELAYD_CLOSE_STREAM:
                ret = relay_close_stream(recv_hdr, cmd, streams_ht);
                break;
-       case RELAYD_DATA_AVAILABLE:
-               ret = relay_data_available(recv_hdr, cmd, streams_ht);
+       case RELAYD_DATA_PENDING:
+               ret = relay_data_pending(recv_hdr, cmd, streams_ht);
                break;
        case RELAYD_QUIESCENT_CONTROL:
-               ret = relay_quiescent_control(recv_hdr, cmd);
+               ret = relay_quiescent_control(recv_hdr, cmd, streams_ht);
+               break;
+       case RELAYD_BEGIN_DATA_PENDING:
+               ret = relay_begin_data_pending(recv_hdr, cmd, streams_ht);
+               break;
+       case RELAYD_END_DATA_PENDING:
+               ret = relay_end_data_pending(recv_hdr, cmd, streams_ht);
                break;
        case RELAYD_UPDATE_SYNC_INFO:
        default:
@@ -1467,9 +1752,14 @@ int relay_process_data(struct relay_command *cmd, struct lttng_ht *streams_ht)
        uint32_t data_size;
 
        ret = cmd->sock->ops->recvmsg(cmd->sock, &data_hdr,
-                       sizeof(struct lttcomm_relayd_data_hdr), MSG_WAITALL);
+                       sizeof(struct lttcomm_relayd_data_hdr), 0);
        if (ret <= 0) {
-               ERR("Connections seems to be closed");
+               if (ret == 0) {
+                       /* Orderly shutdown. Not necessary to print an error. */
+                       DBG("Socket %d did an orderly shutdown", cmd->sock->fd);
+               } else {
+                       ERR("Unable to receive data header on sock %d", cmd->sock->fd);
+               }
                ret = -1;
                goto end;
        }
@@ -1485,14 +1775,16 @@ int relay_process_data(struct relay_command *cmd, struct lttng_ht *streams_ht)
 
        data_size = be32toh(data_hdr.data_size);
        if (data_buffer_size < data_size) {
-               char *tmp_data_ptr = data_buffer;
-               data_buffer = realloc(data_buffer, data_size);
-               if (!data_buffer) {
+               char *tmp_data_ptr;
+
+               tmp_data_ptr = realloc(data_buffer, data_size);
+               if (!tmp_data_ptr) {
                        ERR("Allocating data buffer");
-                       free(tmp_data_ptr);
+                       free(data_buffer);
                        ret = -1;
                        goto end_unlock;
                }
+               data_buffer = tmp_data_ptr;
                data_buffer_size = data_size;
        }
        memset(data_buffer, 0, data_size);
@@ -1501,8 +1793,12 @@ int relay_process_data(struct relay_command *cmd, struct lttng_ht *streams_ht)
 
        DBG3("Receiving data of size %u for stream id %" PRIu64 " seqnum %" PRIu64,
                data_size, stream_id, net_seq_num);
-       ret = cmd->sock->ops->recvmsg(cmd->sock, data_buffer, data_size, MSG_WAITALL);
+       ret = cmd->sock->ops->recvmsg(cmd->sock, data_buffer, data_size, 0);
        if (ret <= 0) {
+               if (ret == 0) {
+                       /* Orderly shutdown. Not necessary to print an error. */
+                       DBG("Socket %d did an orderly shutdown", cmd->sock->fd);
+               }
                ret = -1;
                goto end_unlock;
        }
@@ -1510,7 +1806,7 @@ int relay_process_data(struct relay_command *cmd, struct lttng_ht *streams_ht)
        do {
                ret = write(stream->fd, data_buffer, data_size);
        } while (ret < 0 && errno == EINTR);
-       if (ret < data_size) {
+       if (ret < 0 || ret != data_size) {
                ERR("Relay error writing data to file");
                ret = -1;
                goto end_unlock;
@@ -1528,9 +1824,13 @@ int relay_process_data(struct relay_command *cmd, struct lttng_ht *streams_ht)
 
        /* Check if we need to close the FD */
        if (close_stream_check(stream)) {
+               int cret;
                struct lttng_ht_iter iter;
 
-               close(stream->fd);
+               cret = close(stream->fd);
+               if (cret < 0) {
+                       PERROR("close stream process data");
+               }
                iter.iter.node = &stream->stream_n.node;
                ret = lttng_ht_del(streams_ht, &iter);
                assert(!ret);
@@ -1570,7 +1870,9 @@ int relay_add_connection(int fd, struct lttng_poll_event *events,
                PERROR("Relay command zmalloc");
                goto error;
        }
-       ret = read(fd, relay_connection, sizeof(struct relay_command));
+       do {
+               ret = read(fd, relay_connection, sizeof(struct relay_command));
+       } while (ret < 0 && errno == EINTR);
        if (ret < 0 || ret < sizeof(struct relay_command)) {
                PERROR("read relay cmd pipe");
                goto error_read;
@@ -1597,6 +1899,8 @@ void deferred_free_connection(struct rcu_head *head)
 {
        struct relay_command *relay_connection =
                caa_container_of(head, struct relay_command, rcu_node);
+
+       lttcomm_destroy_sock(relay_connection->sock);
        free(relay_connection);
 }
 
@@ -1612,6 +1916,7 @@ void relay_del_connection(struct lttng_ht *relay_connections_ht,
        if (relay_connection->type == RELAY_CONTROL) {
                relay_delete_session(relay_connection, streams_ht);
        }
+
        call_rcu(&relay_connection->rcu_node,
                deferred_free_connection);
 }
@@ -1622,8 +1927,8 @@ void relay_del_connection(struct lttng_ht *relay_connections_ht,
 static
 void *relay_thread_worker(void *data)
 {
-       int i, ret, pollfd, err = -1;
-       uint32_t revents, nb_fd;
+       int ret, err = -1, last_seen_data_fd = -1;
+       uint32_t nb_fd;
        struct relay_command *relay_connection;
        struct lttng_poll_event events;
        struct lttng_ht *relay_connections_ht;
@@ -1658,14 +1963,11 @@ void *relay_thread_worker(void *data)
                goto error;
        }
 
+restart:
        while (1) {
-               /* Zeroed the events structure */
-               lttng_poll_reset(&events);
-
-               nb_fd = LTTNG_POLL_GETNB(&events);
+               int idx = -1, i, seen_control = 0, last_notdel_data_fd = -1;
 
                /* Infinite blocking call, waiting for transmission */
-       restart:
                DBG3("Relayd worker thread polling...");
                ret = lttng_poll_wait(&events, -1);
                if (ret < 0) {
@@ -1678,10 +1980,17 @@ void *relay_thread_worker(void *data)
                        goto error;
                }
 
+               nb_fd = ret;
+
+               /*
+                * Process control. The control connection is prioritised so we don't
+                * starve it with high throughout put tracing data on the data
+                * connection.
+                */
                for (i = 0; i < nb_fd; i++) {
                        /* Fetch once the poll data */
-                       revents = LTTNG_POLL_GETEV(&events, i);
-                       pollfd = LTTNG_POLL_GETFD(&events, i);
+                       uint32_t revents = LTTNG_POLL_GETEV(&events, i);
+                       int pollfd = LTTNG_POLL_GETFD(&events, i);
 
                        /* Thread quit pipe has been closed. Killing thread. */
                        ret = check_thread_quit_pipe(pollfd, revents);
@@ -1703,7 +2012,7 @@ void *relay_thread_worker(void *data)
                                                goto error;
                                        }
                                }
-                       } else if (revents > 0) {
+                       } else if (revents) {
                                rcu_read_lock();
                                lttng_ht_lookup(relay_connections_ht,
                                                (void *)((unsigned long) pollfd),
@@ -1723,18 +2032,24 @@ void *relay_thread_worker(void *data)
                                        relay_del_connection(relay_connections_ht,
                                                        streams_ht, &iter,
                                                        relay_connection);
+                                       if (last_seen_data_fd == pollfd) {
+                                               last_seen_data_fd = last_notdel_data_fd;
+                                       }
                                } else if (revents & (LPOLLHUP | LPOLLRDHUP)) {
                                        DBG("Socket %d hung up", pollfd);
                                        relay_cleanup_poll_connection(&events, pollfd);
                                        relay_del_connection(relay_connections_ht,
                                                        streams_ht, &iter,
                                                        relay_connection);
+                                       if (last_seen_data_fd == pollfd) {
+                                               last_seen_data_fd = last_notdel_data_fd;
+                                       }
                                } else if (revents & LPOLLIN) {
                                        /* control socket */
                                        if (relay_connection->type == RELAY_CONTROL) {
                                                ret = relay_connection->sock->ops->recvmsg(
                                                                relay_connection->sock, &recv_hdr,
-                                                               sizeof(struct lttcomm_relayd_hdr), MSG_WAITALL);
+                                                               sizeof(struct lttcomm_relayd_hdr), 0);
                                                /* connection closed */
                                                if (ret <= 0) {
                                                        relay_cleanup_poll_connection(&events, pollfd);
@@ -1750,34 +2065,101 @@ void *relay_thread_worker(void *data)
                                                        ret = relay_process_control(&recv_hdr,
                                                                        relay_connection,
                                                                        streams_ht);
-                                                       /*
-                                                        * there was an error in processing a control
-                                                        * command: clear the session
-                                                        * */
                                                        if (ret < 0) {
+                                                               /* Clear the session on error. */
                                                                relay_cleanup_poll_connection(&events, pollfd);
                                                                relay_del_connection(relay_connections_ht,
                                                                                streams_ht, &iter,
                                                                                relay_connection);
                                                                DBG("Connection closed with %d", pollfd);
                                                        }
+                                                       seen_control = 1;
                                                }
-                                               /* data socket */
-                                       } else if (relay_connection->type == RELAY_DATA) {
-                                               ret = relay_process_data(relay_connection, streams_ht);
-                                               /* connection closed */
-                                               if (ret < 0) {
-                                                       relay_cleanup_poll_connection(&events, pollfd);
-                                                       relay_del_connection(relay_connections_ht,
-                                                                       streams_ht, &iter,
-                                                                       relay_connection);
-                                                       DBG("Data connection closed with %d", pollfd);
-                                               }
+                                       } else {
+                                               /*
+                                                * Flag the last seen data fd not deleted. It will be
+                                                * used as the last seen fd if any fd gets deleted in
+                                                * this first loop.
+                                                */
+                                               last_notdel_data_fd = pollfd;
+                                       }
+                               }
+                               rcu_read_unlock();
+                       }
+               }
+
+               /*
+                * The last loop handled a control request, go back to poll to make
+                * sure we prioritise the control socket.
+                */
+               if (seen_control) {
+                       continue;
+               }
+
+               if (last_seen_data_fd >= 0) {
+                       for (i = 0; i < nb_fd; i++) {
+                               int pollfd = LTTNG_POLL_GETFD(&events, i);
+                               if (last_seen_data_fd == pollfd) {
+                                       idx = i;
+                                       break;
+                               }
+                       }
+               }
+
+               /* Process data connection. */
+               for (i = idx + 1; i < nb_fd; i++) {
+                       /* Fetch the poll data. */
+                       uint32_t revents = LTTNG_POLL_GETEV(&events, i);
+                       int pollfd = LTTNG_POLL_GETFD(&events, i);
+
+                       /* Skip the command pipe. It's handled in the first loop. */
+                       if (pollfd == relay_cmd_pipe[0]) {
+                               continue;
+                       }
+
+                       if (revents) {
+                               rcu_read_lock();
+                               lttng_ht_lookup(relay_connections_ht,
+                                               (void *)((unsigned long) pollfd),
+                                               &iter);
+                               node = lttng_ht_iter_get_node_ulong(&iter);
+                               if (node == NULL) {
+                                       /* Skip it. Might be removed before. */
+                                       rcu_read_unlock();
+                                       continue;
+                               }
+                               relay_connection = caa_container_of(node,
+                                               struct relay_command, sock_n);
+
+                               if (revents & LPOLLIN) {
+                                       if (relay_connection->type != RELAY_DATA) {
+                                               continue;
+                                       }
+
+                                       ret = relay_process_data(relay_connection, streams_ht);
+                                       /* connection closed */
+                                       if (ret < 0) {
+                                               relay_cleanup_poll_connection(&events, pollfd);
+                                               relay_del_connection(relay_connections_ht,
+                                                               streams_ht, &iter,
+                                                               relay_connection);
+                                               DBG("Data connection closed with %d", pollfd);
+                                               /*
+                                                * Every goto restart call sets the last seen fd where
+                                                * here we don't really care since we gracefully
+                                                * continue the loop after the connection is deleted.
+                                                */
+                                       } else {
+                                               /* Keep last seen port. */
+                                               last_seen_data_fd = pollfd;
+                                               rcu_read_unlock();
+                                               goto restart;
                                        }
                                }
                                rcu_read_unlock();
                        }
                }
+               last_seen_data_fd = -1;
        }
 
 exit:
@@ -1802,6 +2184,8 @@ error_poll_create:
 streams_ht_error:
        lttng_ht_destroy(relay_connections_ht);
 relay_connections_ht_error:
+       /* Close relay cmd pipes */
+       utils_close_pipe(relay_cmd_pipe);
        if (err) {
                DBG("Thread exited with error");
        }
@@ -1840,7 +2224,7 @@ int main(int argc, char **argv)
 
        /* Parse arguments */
        progname = argv[0];
-       if ((ret = parse_args(argc, argv) < 0)) {
+       if ((ret = parse_args(argc, argv)) < 0) {
                goto exit;
        }
 
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