Fix: relayd: live client not notified of inactive streams

[lttng-tools.git] / src / bin / lttng-relayd / live.cpp

/*
 * Copyright (C) 2013 Julien Desfossez <jdesfossez@efficios.com>
 * Copyright (C) 2013 David Goulet <dgoulet@efficios.com>
 * Copyright (C) 2015 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 */

#define _LGPL_SOURCE
#include "cmd.hpp"
#include "connection.hpp"
#include "ctf-trace.hpp"
#include "health-relayd.hpp"
#include "live.hpp"
#include "lttng-relayd.hpp"
#include "session.hpp"
#include "stream.hpp"
#include "testpoint.hpp"
#include "utils.hpp"
#include "viewer-session.hpp"
#include "viewer-stream.hpp"

#include <common/common.hpp>
#include <common/compat/endian.hpp>
#include <common/compat/poll.hpp>
#include <common/compat/socket.hpp>
#include <common/defaults.hpp>
#include <common/fd-tracker/utils.hpp>
#include <common/fs-handle.hpp>
#include <common/futex.hpp>
#include <common/index/index.hpp>
#include <common/sessiond-comm/inet.hpp>
#include <common/sessiond-comm/relayd.hpp>
#include <common/sessiond-comm/sessiond-comm.hpp>
#include <common/urcu.hpp>
#include <common/uri.hpp>
#include <common/utils.hpp>

#include <lttng/lttng.h>

#include <fcntl.h>
#include <getopt.h>
#include <grp.h>
#include <inttypes.h>
#include <limits.h>
#include <pthread.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <string>
#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/resource.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <urcu/futex.h>
#include <urcu/rculist.h>
#include <urcu/uatomic.h>

#define SESSION_BUF_DEFAULT_COUNT 16

static struct lttng_uri *live_uri;

/*
 * This pipe is used to inform the worker thread that a command is queued and
 * ready to be processed.
 */
static int live_conn_pipe[2] = { -1, -1 };

/* Shared between threads */
static int live_dispatch_thread_exit;

static pthread_t live_listener_thread;
static pthread_t live_dispatcher_thread;
static pthread_t live_worker_thread;

/*
 * Relay command queue.
 *
 * The live_thread_listener and live_thread_dispatcher communicate with this
 * queue.
 */
static struct relay_conn_queue viewer_conn_queue;

static uint64_t last_relay_viewer_session_id;
static pthread_mutex_t last_relay_viewer_session_id_lock = PTHREAD_MUTEX_INITIALIZER;

static const char *lttng_viewer_command_str(lttng_viewer_command cmd)
{
        switch (cmd) {
        case LTTNG_VIEWER_CONNECT:
                return "CONNECT";
        case LTTNG_VIEWER_LIST_SESSIONS:
                return "LIST_SESSIONS";
        case LTTNG_VIEWER_ATTACH_SESSION:
                return "ATTACH_SESSION";
        case LTTNG_VIEWER_GET_NEXT_INDEX:
                return "GET_NEXT_INDEX";
        case LTTNG_VIEWER_GET_PACKET:
                return "GET_PACKET";
        case LTTNG_VIEWER_GET_METADATA:
                return "GET_METADATA";
        case LTTNG_VIEWER_GET_NEW_STREAMS:
                return "GET_NEW_STREAMS";
        case LTTNG_VIEWER_CREATE_SESSION:
                return "CREATE_SESSION";
        case LTTNG_VIEWER_DETACH_SESSION:
                return "DETACH_SESSION";
        default:
                abort();
        }
}

static const char *
lttng_viewer_next_index_return_code_str(enum lttng_viewer_next_index_return_code code)
{
        switch (code) {
        case LTTNG_VIEWER_INDEX_OK:
                return "INDEX_OK";
        case LTTNG_VIEWER_INDEX_RETRY:
                return "INDEX_RETRY";
        case LTTNG_VIEWER_INDEX_HUP:
                return "INDEX_HUP";
        case LTTNG_VIEWER_INDEX_ERR:
                return "INDEX_ERR";
        case LTTNG_VIEWER_INDEX_INACTIVE:
                return "INDEX_INACTIVE";
        case LTTNG_VIEWER_INDEX_EOF:
                return "INDEX_EOF";
        default:
                abort();
        }
}

static const char *lttng_viewer_attach_return_code_str(enum lttng_viewer_attach_return_code code)
{
        switch (code) {
        case LTTNG_VIEWER_ATTACH_OK:
                return "ATTACH_OK";
        case LTTNG_VIEWER_ATTACH_ALREADY:
                return "ATTACH_ALREADY";
        case LTTNG_VIEWER_ATTACH_UNK:
                return "ATTACH_UNK";
        case LTTNG_VIEWER_ATTACH_NOT_LIVE:
                return "ATTACH_NOT_LIVE";
        case LTTNG_VIEWER_ATTACH_SEEK_ERR:
                return "ATTACH_SEEK_ERR";
        case LTTNG_VIEWER_ATTACH_NO_SESSION:
                return "ATTACH_NO_SESSION";
        default:
                abort();
        }
};

static const char *
lttng_viewer_get_packet_return_code_str(enum lttng_viewer_get_packet_return_code code)
{
        switch (code) {
        case LTTNG_VIEWER_GET_PACKET_OK:
                return "GET_PACKET_OK";
        case LTTNG_VIEWER_GET_PACKET_RETRY:
                return "GET_PACKET_RETRY";
        case LTTNG_VIEWER_GET_PACKET_ERR:
                return "GET_PACKET_ERR";
        case LTTNG_VIEWER_GET_PACKET_EOF:
                return "GET_PACKET_EOF";
        default:
                abort();
        }
};

/*
 * Cleanup the daemon
 */
static void cleanup_relayd_live()
{
        DBG("Cleaning up");

        free(live_uri);
}

/*
 * Receive a request buffer using a given socket, destination allocated buffer
 * of length size.
 *
 * Return the size of the received message or else a negative value on error
 * with errno being set by recvmsg() syscall.
 */
static ssize_t recv_request(struct lttcomm_sock *sock, void *buf, size_t size)
{
        ssize_t ret;

        ret = sock->ops->recvmsg(sock, buf, size, 0);
        if (ret < 0 || ret != size) {
                if (ret == 0) {
                        /* Orderly shutdown. Not necessary to print an error. */
                        DBG("Socket %d did an orderly shutdown", sock->fd);
                } else {
                        ERR("Relay failed to receive request.");
                }
                ret = -1;
        }

        return ret;
}

/*
 * Send a response buffer using a given socket, source allocated buffer of
 * length size.
 *
 * Return the size of the sent message or else a negative value on error with
 * errno being set by sendmsg() syscall.
 */
static ssize_t send_response(struct lttcomm_sock *sock, void *buf, size_t size)
{
        ssize_t ret;

        ret = sock->ops->sendmsg(sock, buf, size, 0);
        if (ret < 0) {
                ERR("Relayd failed to send response.");
        }

        return ret;
}

/*
 * Atomically check if new streams got added in one of the sessions attached
 * and reset the flag to 0.
 *
 * Returns 1 if new streams got added, 0 if nothing changed, a negative value
 * on error.
 */
static int check_new_streams(struct relay_connection *conn)
{
        struct relay_session *session;
        int ret = 0;

        if (!conn->viewer_session) {
                goto end;
        }

        {
                lttng::urcu::read_lock_guard read_lock;
                cds_list_for_each_entry_rcu(
                        session, &conn->viewer_session->session_list, viewer_session_node)
                {
                        if (!session_get(session)) {
                                continue;
                        }

                        ret = uatomic_read(&session->new_streams);
                        session_put(session);
                        if (ret == 1) {
                                goto end;
                        }
                }
        }

end:
        DBG("Viewer connection has%s new streams: socket_fd = %d", ret == 0 ? " no" : "", conn->sock->fd);
        return ret;
}

/*
 * Send viewer streams to the given socket. The ignore_sent_flag indicates if
 * this function should ignore the sent flag or not.
 *
 * Return 0 on success or else a negative value.
 */
static ssize_t
send_viewer_streams(struct lttcomm_sock *sock, uint64_t session_id, unsigned int ignore_sent_flag)
{
        ssize_t ret;
        struct lttng_ht_iter iter;
        struct relay_viewer_stream *vstream;

        {
                lttng::urcu::read_lock_guard read_lock;

                cds_lfht_for_each_entry (
                        viewer_streams_ht->ht, &iter.iter, vstream, stream_n.node) {
                        struct ctf_trace *ctf_trace;
                        struct lttng_viewer_stream send_stream = {};

                        health_code_update();

                        if (!viewer_stream_get(vstream)) {
                                continue;
                        }

                        pthread_mutex_lock(&vstream->stream->lock);
                        /* Ignore if not the same session. */
                        if (vstream->stream->trace->session->id != session_id ||
                            (!ignore_sent_flag && vstream->sent_flag)) {
                                pthread_mutex_unlock(&vstream->stream->lock);
                                viewer_stream_put(vstream);
                                continue;
                        }

                        ctf_trace = vstream->stream->trace;
                        send_stream.id = htobe64(vstream->stream->stream_handle);
                        send_stream.ctf_trace_id = htobe64(ctf_trace->id);
                        send_stream.metadata_flag = htobe32(vstream->stream->is_metadata);
                        if (lttng_strncpy(send_stream.path_name,
                                          vstream->path_name,
                                          sizeof(send_stream.path_name))) {
                                pthread_mutex_unlock(&vstream->stream->lock);
                                viewer_stream_put(vstream);
                                ret = -1; /* Error. */
                                goto end;
                        }
                        if (lttng_strncpy(send_stream.channel_name,
                                          vstream->channel_name,
                                          sizeof(send_stream.channel_name))) {
                                pthread_mutex_unlock(&vstream->stream->lock);
                                viewer_stream_put(vstream);
                                ret = -1; /* Error. */
                                goto end;
                        }

                        DBG("Sending stream %" PRIu64 " to viewer", vstream->stream->stream_handle);
                        vstream->sent_flag = true;
                        pthread_mutex_unlock(&vstream->stream->lock);

                        ret = send_response(sock, &send_stream, sizeof(send_stream));
                        viewer_stream_put(vstream);
                        if (ret < 0) {
                                goto end;
                        }
                }
        }

        ret = 0;

end:
        return ret;
}

/*
 * Create every viewer stream possible for the given session with the seek
 * type. Three counters *can* be return which are in order the total amount of
 * viewer stream of the session, the number of unsent stream and the number of
 * stream created. Those counters can be NULL and thus will be ignored.
 *
 * session must be locked to ensure that we see either none or all initial
 * streams for a session, but no intermediate state..
 *
 * Return 0 on success or else a negative value.
 */
static int make_viewer_streams(struct relay_session *relay_session,
                               struct relay_viewer_session *viewer_session,
                               enum lttng_viewer_seek seek_t,
                               uint32_t *nb_total,
                               uint32_t *nb_unsent,
                               uint32_t *nb_created,
                               bool *closed)
{
        int ret;
        struct lttng_ht_iter iter;
        struct ctf_trace *ctf_trace;
        struct relay_stream *relay_stream = nullptr;

        LTTNG_ASSERT(relay_session);
        ASSERT_LOCKED(relay_session->lock);

        if (relay_session->connection_closed) {
                *closed = true;
        }

        /*
         * Create viewer streams for relay streams that are ready to be
         * used for a the given session id only.
         */
        {
                lttng::urcu::read_lock_guard read_lock;

                cds_lfht_for_each_entry (
                        relay_session->ctf_traces_ht->ht, &iter.iter, ctf_trace, node.node) {
                        bool trace_has_metadata_stream = false;

                        health_code_update();

                        if (!ctf_trace_get(ctf_trace)) {
                                continue;
                        }

                        /*
                         * Iterate over all the streams of the trace to see if we have a
                         * metadata stream.
                         */
                        cds_list_for_each_entry_rcu(
                                relay_stream, &ctf_trace->stream_list, stream_node)
                        {
                                bool is_metadata_stream;

                                pthread_mutex_lock(&relay_stream->lock);
                                is_metadata_stream = relay_stream->is_metadata;
                                pthread_mutex_unlock(&relay_stream->lock);

                                if (is_metadata_stream) {
                                        trace_has_metadata_stream = true;
                                        break;
                                }
                        }

                        relay_stream = nullptr;

                        /*
                         * If there is no metadata stream in this trace at the moment
                         * and we never sent one to the viewer, skip the trace. We
                         * accept that the viewer will not see this trace at all.
                         */
                        if (!trace_has_metadata_stream &&
                            !ctf_trace->metadata_stream_sent_to_viewer) {
                                ctf_trace_put(ctf_trace);
                                continue;
                        }

                        cds_list_for_each_entry_rcu(
                                relay_stream, &ctf_trace->stream_list, stream_node)
                        {
                                struct relay_viewer_stream *viewer_stream;

                                if (!stream_get(relay_stream)) {
                                        continue;
                                }

                                pthread_mutex_lock(&relay_stream->lock);
                                /*
                                 * stream published is protected by the session lock.
                                 */
                                if (!relay_stream->published) {
                                        goto next;
                                }
                                viewer_stream =
                                        viewer_stream_get_by_id(relay_stream->stream_handle);
                                if (!viewer_stream) {
                                        struct lttng_trace_chunk *viewer_stream_trace_chunk =
                                                nullptr;

                                        /*
                                         * Save that we sent the metadata stream to the
                                         * viewer. So that we know what trace the viewer
                                         * is aware of.
                                         */
                                        if (relay_stream->is_metadata) {
                                                ctf_trace->metadata_stream_sent_to_viewer = true;
                                        }

                                        /*
                                         * If a rotation is ongoing, use a copy of the
                                         * relay stream's chunk to ensure the stream
                                         * files exist.
                                         *
                                         * Otherwise, the viewer session's current trace
                                         * chunk can be used safely.
                                         */
                                        if ((relay_stream->ongoing_rotation.is_set ||
                                             session_has_ongoing_rotation(relay_session)) &&
                                            relay_stream->trace_chunk) {
                                                viewer_stream_trace_chunk = lttng_trace_chunk_copy(
                                                        relay_stream->trace_chunk);
                                                if (!viewer_stream_trace_chunk) {
                                                        ret = -1;
                                                        ctf_trace_put(ctf_trace);
                                                        goto error_unlock;
                                                }
                                        } else {
                                                /*
                                                 * Transition the viewer session into the newest
                                                 * trace chunk available.
                                                 */
                                                if (!lttng_trace_chunk_ids_equal(
                                                            viewer_session->current_trace_chunk,
                                                            relay_stream->trace_chunk)) {
                                                        ret = viewer_session_set_trace_chunk_copy(
                                                                viewer_session,
                                                                relay_stream->trace_chunk);
                                                        if (ret) {
                                                                ret = -1;
                                                                ctf_trace_put(ctf_trace);
                                                                goto error_unlock;
                                                        }
                                                }

                                                if (relay_stream->trace_chunk) {
                                                        /*
                                                         * If the corresponding relay
                                                         * stream's trace chunk is set,
                                                         * the viewer stream will be
                                                         * created under it.
                                                         *
                                                         * Note that a relay stream can
                                                         * have a NULL output trace
                                                         * chunk (for instance, after a
                                                         * clear against a stopped
                                                         * session).
                                                         */
                                                        const bool reference_acquired =
                                                                lttng_trace_chunk_get(
                                                                        viewer_session
                                                                                ->current_trace_chunk);

                                                        LTTNG_ASSERT(reference_acquired);
                                                        viewer_stream_trace_chunk =
                                                                viewer_session->current_trace_chunk;
                                                }
                                        }

                                        viewer_stream = viewer_stream_create(
                                                relay_stream, viewer_stream_trace_chunk, seek_t);
                                        lttng_trace_chunk_put(viewer_stream_trace_chunk);
                                        viewer_stream_trace_chunk = nullptr;
                                        if (!viewer_stream) {
                                                ret = -1;
                                                ctf_trace_put(ctf_trace);
                                                goto error_unlock;
                                        }

                                        if (nb_created) {
                                                /* Update number of created stream counter. */
                                                (*nb_created)++;
                                        }
                                        /*
                                         * Ensure a self-reference is preserved even
                                         * after we have put our local reference.
                                         */
                                        if (!viewer_stream_get(viewer_stream)) {
                                                ERR("Unable to get self-reference on viewer stream, logic error.");
                                                abort();
                                        }
                                } else {
                                        if (!viewer_stream->sent_flag && nb_unsent) {
                                                /* Update number of unsent stream counter. */
                                                (*nb_unsent)++;
                                        }
                                }
                                /* Update number of total stream counter. */
                                if (nb_total) {
                                        if (relay_stream->is_metadata) {
                                                if (!relay_stream->closed ||
                                                    relay_stream->metadata_received >
                                                            viewer_stream->metadata_sent) {
                                                        (*nb_total)++;
                                                }
                                        } else {
                                                if (!relay_stream->closed ||
                                                    !(((int64_t) (relay_stream->prev_data_seq -
                                                                  relay_stream->last_net_seq_num)) >=
                                                      0)) {
                                                        (*nb_total)++;
                                                }
                                        }
                                }
                                /* Put local reference. */
                                viewer_stream_put(viewer_stream);
                        next:
                                pthread_mutex_unlock(&relay_stream->lock);
                                stream_put(relay_stream);
                        }
                        relay_stream = nullptr;
                        ctf_trace_put(ctf_trace);
                }
        }

        ret = 0;

error_unlock:

        if (relay_stream) {
                pthread_mutex_unlock(&relay_stream->lock);
                stream_put(relay_stream);
        }

        return ret;
}

int relayd_live_stop()
{
        /* Stop dispatch thread */
        CMM_STORE_SHARED(live_dispatch_thread_exit, 1);
        futex_nto1_wake(&viewer_conn_queue.futex);
        return 0;
}

static int create_sock(void *data, int *out_fd)
{
        int ret;
        struct lttcomm_sock *sock = (lttcomm_sock *) data;

        ret = lttcomm_create_sock(sock);
        if (ret < 0) {
                goto end;
        }

        *out_fd = sock->fd;
end:
        return ret;
}

static int close_sock(void *data, int *in_fd __attribute__((unused)))
{
        struct lttcomm_sock *sock = (lttcomm_sock *) data;

        return sock->ops->close(sock);
}

static int accept_sock(void *data, int *out_fd)
{
        int ret = 0;
        /* Socks is an array of in_sock, out_sock. */
        struct lttcomm_sock **socks = (lttcomm_sock **) data;
        struct lttcomm_sock *in_sock = socks[0];

        socks[1] = in_sock->ops->accept(in_sock);
        if (!socks[1]) {
                ret = -1;
                goto end;
        }
        *out_fd = socks[1]->fd;
end:
        return ret;
}

static struct lttcomm_sock *accept_live_sock(struct lttcomm_sock *listening_sock, const char *name)
{
        int out_fd, ret;
        struct lttcomm_sock *socks[2] = { listening_sock, nullptr };
        struct lttcomm_sock *new_sock = nullptr;

        ret = fd_tracker_open_unsuspendable_fd(
                the_fd_tracker, &out_fd, (const char **) &name, 1, accept_sock, &socks);
        if (ret) {
                goto end;
        }
        new_sock = socks[1];
        DBG("%s accepted, socket %d", name, new_sock->fd);
end:
        return new_sock;
}

/*
 * Create and init socket from uri.
 */
static struct lttcomm_sock *init_socket(struct lttng_uri *uri, const char *name)
{
        int ret, sock_fd;
        struct lttcomm_sock *sock = nullptr;
        char uri_str[LTTNG_PATH_MAX];
        char *formated_name = nullptr;

        sock = lttcomm_alloc_sock_from_uri(uri);
        if (sock == nullptr) {
                ERR("Allocating socket");
                goto error;
        }

        /*
         * Don't fail to create the socket if the name can't be built as it is
         * only used for debugging purposes.
         */
        ret = uri_to_str_url(uri, uri_str, sizeof(uri_str));
        uri_str[sizeof(uri_str) - 1] = '\0';
        if (ret >= 0) {
                ret = asprintf(&formated_name, "%s socket @ %s", name, uri_str);
                if (ret < 0) {
                        formated_name = nullptr;
                }
        }

        ret = fd_tracker_open_unsuspendable_fd(the_fd_tracker,
                                               &sock_fd,
                                               (const char **) (formated_name ? &formated_name :
                                                                                nullptr),
                                               1,
                                               create_sock,
                                               sock);
        if (ret) {
                PERROR("Failed to create \"%s\" socket", formated_name ?: "Unknown");
                goto error;
        }
        DBG("Listening on %s socket %d", name, sock->fd);

        ret = sock->ops->bind(sock);
        if (ret < 0) {
                PERROR("Failed to bind lttng-live socket");
                goto error;
        }

        ret = sock->ops->listen(sock, -1);
        if (ret < 0) {
                goto error;
        }

        free(formated_name);
        return sock;

error:
        if (sock) {
                lttcomm_destroy_sock(sock);
        }
        free(formated_name);
        return nullptr;
}

/*
 * This thread manages the listening for new connections on the network
 */
static void *thread_listener(void *data __attribute__((unused)))
{
        int i, ret, err = -1;
        uint32_t nb_fd;
        struct lttng_poll_event events;
        struct lttcomm_sock *live_control_sock;

        DBG("[thread] Relay live listener started");

        rcu_register_thread();
        health_register(health_relayd, HEALTH_RELAYD_TYPE_LIVE_LISTENER);

        health_code_update();

        live_control_sock = init_socket(live_uri, "Live listener");
        if (!live_control_sock) {
                goto error_sock_control;
        }

        /* Pass 2 as size here for the thread quit pipe and control sockets. */
        ret = create_named_thread_poll_set(&events, 2, "Live listener thread epoll");
        if (ret < 0) {
                goto error_create_poll;
        }

        /* Add the control socket */
        ret = lttng_poll_add(&events, live_control_sock->fd, LPOLLIN | LPOLLRDHUP);
        if (ret < 0) {
                goto error_poll_add;
        }

        lttng_relay_notify_ready();

        if (testpoint(relayd_thread_live_listener)) {
                goto error_testpoint;
        }

        while (true) {
                health_code_update();

                DBG("Listener accepting live viewers connections");

        restart:
                health_poll_entry();
                ret = lttng_poll_wait(&events, -1);
                health_poll_exit();
                if (ret < 0) {
                        /*
                         * Restart interrupted system call.
                         */
                        if (errno == EINTR) {
                                goto restart;
                        }
                        goto error;
                }
                nb_fd = ret;

                DBG("Relay new viewer connection received");
                for (i = 0; i < nb_fd; i++) {
                        /* Fetch once the poll data */
                        const auto revents = LTTNG_POLL_GETEV(&events, i);
                        const auto pollfd = LTTNG_POLL_GETFD(&events, i);

                        health_code_update();

                        /* Activity on thread quit pipe, exiting. */
                        if (relayd_is_thread_quit_pipe(pollfd)) {
                                DBG("Activity on thread quit pipe");
                                err = 0;
                                goto exit;
                        }

                        if (revents & LPOLLIN) {
                                /*
                                 * A new connection is requested, therefore a
                                 * viewer connection is allocated in this
                                 * thread, enqueued to a global queue and
                                 * dequeued (and freed) in the worker thread.
                                 */
                                int val = 1;
                                struct relay_connection *new_conn;
                                struct lttcomm_sock *newsock;

                                newsock = accept_live_sock(live_control_sock,
                                                           "Live socket to client");
                                if (!newsock) {
                                        PERROR("accepting control sock");
                                        goto error;
                                }
                                DBG("Relay viewer connection accepted socket %d", newsock->fd);

                                ret = setsockopt(
                                        newsock->fd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
                                if (ret < 0) {
                                        PERROR("setsockopt inet");
                                        lttcomm_destroy_sock(newsock);
                                        goto error;
                                }
                                new_conn = connection_create(newsock, RELAY_CONNECTION_UNKNOWN);
                                if (!new_conn) {
                                        lttcomm_destroy_sock(newsock);
                                        goto error;
                                }
                                /* Ownership assumed by the connection. */
                                newsock = nullptr;

                                /* Enqueue request for the dispatcher thread. */
                                cds_wfcq_head_ptr_t head;
                                head.h = &viewer_conn_queue.head;
                                cds_wfcq_enqueue(head, &viewer_conn_queue.tail, &new_conn->qnode);

                                /*
                                 * Wake the dispatch queue futex.
                                 * Implicit memory barrier with the
                                 * exchange in cds_wfcq_enqueue.
                                 */
                                futex_nto1_wake(&viewer_conn_queue.futex);
                        } else if (revents & (LPOLLERR | LPOLLHUP | LPOLLRDHUP)) {
                                ERR("socket poll error");
                                goto error;
                        } else {
                                ERR("Unexpected poll events %u for sock %d", revents, pollfd);
                                goto error;
                        }
                }
        }

exit:
error:
error_poll_add:
error_testpoint:
        (void) fd_tracker_util_poll_clean(the_fd_tracker, &events);
error_create_poll:
        if (live_control_sock->fd >= 0) {
                int sock_fd = live_control_sock->fd;

                ret = fd_tracker_close_unsuspendable_fd(
                        the_fd_tracker, &sock_fd, 1, close_sock, live_control_sock);
                if (ret) {
                        PERROR("close");
                }
                live_control_sock->fd = -1;
        }
        lttcomm_destroy_sock(live_control_sock);
error_sock_control:
        if (err) {
                health_error();
                DBG("Live viewer listener thread exited with error");
        }
        health_unregister(health_relayd);
        rcu_unregister_thread();
        DBG("Live viewer listener thread cleanup complete");
        if (lttng_relay_stop_threads()) {
                ERR("Error stopping threads");
        }
        return nullptr;
}

/*
 * This thread manages the dispatching of the requests to worker threads
 */
static void *thread_dispatcher(void *data __attribute__((unused)))
{
        int err = -1;
        ssize_t ret;
        struct cds_wfcq_node *node;
        struct relay_connection *conn = nullptr;

        DBG("[thread] Live viewer relay dispatcher started");

        health_register(health_relayd, HEALTH_RELAYD_TYPE_LIVE_DISPATCHER);

        if (testpoint(relayd_thread_live_dispatcher)) {
                goto error_testpoint;
        }

        health_code_update();

        for (;;) {
                health_code_update();

                /* Atomically prepare the queue futex */
                futex_nto1_prepare(&viewer_conn_queue.futex);

                if (CMM_LOAD_SHARED(live_dispatch_thread_exit)) {
                        break;
                }

                do {
                        health_code_update();

                        /* Dequeue commands */
                        node = cds_wfcq_dequeue_blocking(&viewer_conn_queue.head,
                                                         &viewer_conn_queue.tail);
                        if (node == nullptr) {
                                DBG("Woken up but nothing in the live-viewer "
                                    "relay command queue");
                                /* Continue thread execution */
                                break;
                        }
                        conn = lttng::utils::container_of(node, &relay_connection::qnode);
                        DBG("Dispatching viewer request waiting on sock %d", conn->sock->fd);

                        /*
                         * Inform worker thread of the new request. This
                         * call is blocking so we can be assured that
                         * the data will be read at some point in time
                         * or wait to the end of the world :)
                         */
                        ret = lttng_write(live_conn_pipe[1], &conn, sizeof(conn)); /* NOLINT sizeof
                                                                                      used on a
                                                                                      pointer. */
                        if (ret < 0) {
                                PERROR("write conn pipe");
                                connection_put(conn);
                                goto error;
                        }
                } while (node != nullptr);

                /* Futex wait on queue. Blocking call on futex() */
                health_poll_entry();
                futex_nto1_wait(&viewer_conn_queue.futex);
                health_poll_exit();
        }

        /* Normal exit, no error */
        err = 0;

error:
error_testpoint:
        if (err) {
                health_error();
                ERR("Health error occurred in %s", __func__);
        }
        health_unregister(health_relayd);
        DBG("Live viewer dispatch thread dying");
        if (lttng_relay_stop_threads()) {
                ERR("Error stopping threads");
        }
        return nullptr;
}

/*
 * Establish connection with the viewer and check the versions.
 *
 * Return 0 on success or else negative value.
 */
static int viewer_connect(struct relay_connection *conn)
{
        int ret;
        struct lttng_viewer_connect reply, msg;

        conn->version_check_done = true;

        health_code_update();

        ret = recv_request(conn->sock, &msg, sizeof(msg));
        if (ret < 0) {
                goto end;
        }

        health_code_update();

        memset(&reply, 0, sizeof(reply));
        reply.major = RELAYD_VERSION_COMM_MAJOR;
        reply.minor = RELAYD_VERSION_COMM_MINOR;

        /* Major versions must be the same */
        if (reply.major != be32toh(msg.major)) {
                DBG("Incompatible major versions ([relayd] %u vs [client] %u)",
                    reply.major,
                    be32toh(msg.major));
                ret = -1;
                goto end;
        }

        conn->major = reply.major;
        /* We adapt to the lowest compatible version */
        if (reply.minor <= be32toh(msg.minor)) {
                conn->minor = reply.minor;
        } else {
                conn->minor = be32toh(msg.minor);
        }

        if (be32toh(msg.type) == LTTNG_VIEWER_CLIENT_COMMAND) {
                conn->type = RELAY_VIEWER_COMMAND;
        } else if (be32toh(msg.type) == LTTNG_VIEWER_CLIENT_NOTIFICATION) {
                conn->type = RELAY_VIEWER_NOTIFICATION;
        } else {
                ERR("Unknown connection type : %u", be32toh(msg.type));
                ret = -1;
                goto end;
        }

        reply.major = htobe32(reply.major);
        reply.minor = htobe32(reply.minor);
        if (conn->type == RELAY_VIEWER_COMMAND) {
                /*
                 * Increment outside of htobe64 macro, because the argument can
                 * be used more than once within the macro, and thus the
                 * operation may be undefined.
                 */
                pthread_mutex_lock(&last_relay_viewer_session_id_lock);
                last_relay_viewer_session_id++;
                pthread_mutex_unlock(&last_relay_viewer_session_id_lock);
                reply.viewer_session_id = htobe64(last_relay_viewer_session_id);
        }

        health_code_update();

        ret = send_response(conn->sock, &reply, sizeof(reply));
        if (ret < 0) {
                goto end;
        }

        health_code_update();

        DBG("Version check done using protocol %u.%u", conn->major, conn->minor);
        ret = 0;

end:
        return ret;
}

/*
 * Send the viewer the list of current sessions.
 * We need to create a copy of the hash table content because otherwise
 * we cannot assume the number of entries stays the same between getting
 * the number of HT elements and iteration over the HT.
 *
 * Return 0 on success or else a negative value.
 */
static int viewer_list_sessions(struct relay_connection *conn)
{
        int ret = 0;
        struct lttng_viewer_list_sessions session_list;
        struct lttng_ht_iter iter;
        struct relay_session *session;
        struct lttng_viewer_session *send_session_buf = nullptr;
        uint32_t buf_count = SESSION_BUF_DEFAULT_COUNT;
        uint32_t count = 0;

        send_session_buf = calloc<lttng_viewer_session>(SESSION_BUF_DEFAULT_COUNT);
        if (!send_session_buf) {
                return -1;
        }

        {
                lttng::urcu::read_lock_guard read_lock;

                cds_lfht_for_each_entry (sessions_ht->ht, &iter.iter, session, session_n.node) {
                        struct lttng_viewer_session *send_session;

                        health_code_update();

                        pthread_mutex_lock(&session->lock);
                        if (session->connection_closed) {
                                /* Skip closed session */
                                goto next_session;
                        }

                        if (count >= buf_count) {
                                struct lttng_viewer_session *newbuf;
                                uint32_t new_buf_count = buf_count << 1;

                                newbuf = (lttng_viewer_session *) realloc(
                                        send_session_buf,
                                        new_buf_count * sizeof(*send_session_buf));
                                if (!newbuf) {
                                        ret = -1;
                                        goto break_loop;
                                }
                                send_session_buf = newbuf;
                                buf_count = new_buf_count;
                        }
                        send_session = &send_session_buf[count];
                        if (lttng_strncpy(send_session->session_name,
                                          session->session_name,
                                          sizeof(send_session->session_name))) {
                                ret = -1;
                                goto break_loop;
                        }
                        if (lttng_strncpy(send_session->hostname,
                                          session->hostname,
                                          sizeof(send_session->hostname))) {
                                ret = -1;
                                goto break_loop;
                        }
                        send_session->id = htobe64(session->id);
                        send_session->live_timer = htobe32(session->live_timer);
                        if (session->viewer_attached) {
                                send_session->clients = htobe32(1);
                        } else {
                                send_session->clients = htobe32(0);
                        }
                        send_session->streams = htobe32(session->stream_count);
                        count++;
                next_session:
                        pthread_mutex_unlock(&session->lock);
                        continue;
                break_loop:
                        pthread_mutex_unlock(&session->lock);
                        break;
                }
        }

        if (ret < 0) {
                goto end_free;
        }

        session_list.sessions_count = htobe32(count);

        health_code_update();

        ret = send_response(conn->sock, &session_list, sizeof(session_list));
        if (ret < 0) {
                goto end_free;
        }

        health_code_update();

        ret = send_response(conn->sock, send_session_buf, count * sizeof(*send_session_buf));
        if (ret < 0) {
                goto end_free;
        }
        health_code_update();

        ret = 0;
end_free:
        free(send_session_buf);
        return ret;
}

/*
 * Send the viewer the list of current streams.
 */
static int viewer_get_new_streams(struct relay_connection *conn)
{
        int ret, send_streams = 0;
        uint32_t nb_created = 0, nb_unsent = 0, nb_streams = 0, nb_total = 0;
        struct lttng_viewer_new_streams_request request;
        struct lttng_viewer_new_streams_response response;
        struct relay_session *session = nullptr;
        uint64_t session_id;
        bool closed = false;

        LTTNG_ASSERT(conn);

        health_code_update();

        /* Receive the request from the connected client. */
        ret = recv_request(conn->sock, &request, sizeof(request));
        if (ret < 0) {
                goto error;
        }
        session_id = be64toh(request.session_id);

        health_code_update();

        memset(&response, 0, sizeof(response));

        session = session_get_by_id(session_id);
        if (!session) {
                DBG("Relay session %" PRIu64 " not found", session_id);
                response.status = htobe32(LTTNG_VIEWER_NEW_STREAMS_ERR);
                goto send_reply;
        }

        if (!viewer_session_is_attached(conn->viewer_session, session)) {
                response.status = htobe32(LTTNG_VIEWER_NEW_STREAMS_ERR);
                goto send_reply;
        }

        /*
         * For any new stream, create it with LTTNG_VIEWER_SEEK_BEGINNING since
         * that at this point the client is already attached to the session.Aany
         * initial stream will have been created with the seek type at attach
         * time (for now most readers use the LTTNG_VIEWER_SEEK_LAST on attach).
         * Otherwise any event happening in a new stream between the attach and
         * a call to viewer_get_new_streams will be "lost" (never received) from
         * the viewer's point of view.
         */
        pthread_mutex_lock(&session->lock);
        /*
         * If a session rotation is ongoing, do not attempt to open any
         * stream, because the chunk can be in an intermediate state
         * due to directory renaming.
         */
        if (session_has_ongoing_rotation(session)) {
                DBG("Relay session %" PRIu64 " rotation ongoing", session_id);
                response.status = htobe32(LTTNG_VIEWER_NEW_STREAMS_NO_NEW);
                goto send_reply_unlock;
        }
        ret = make_viewer_streams(session,
                                  conn->viewer_session,
                                  LTTNG_VIEWER_SEEK_BEGINNING,
                                  &nb_total,
                                  &nb_unsent,
                                  &nb_created,
                                  &closed);
        if (ret < 0) {
                /*
                 * This is caused by an internal error; propagate the negative
                 * 'ret' to close the connection.
                 */
                response.status = htobe32(LTTNG_VIEWER_NEW_STREAMS_ERR);
                goto send_reply_unlock;
        }

        uatomic_set(&session->new_streams, 0);
        send_streams = 1;
        response.status = htobe32(LTTNG_VIEWER_NEW_STREAMS_OK);

        /* Only send back the newly created streams with the unsent ones. */
        nb_streams = nb_created + nb_unsent;
        response.streams_count = htobe32(nb_streams);

        /*
         * If the session is closed, HUP when there are no more streams
         * with data.
         */
        if (closed && nb_total == 0) {
                send_streams = 0;
                response.streams_count = 0;
                response.status = htobe32(LTTNG_VIEWER_NEW_STREAMS_HUP);
                goto send_reply_unlock;
        }
send_reply_unlock:
        pthread_mutex_unlock(&session->lock);

send_reply:
        health_code_update();
        ret = send_response(conn->sock, &response, sizeof(response));
        if (ret < 0) {
                goto end_put_session;
        }
        health_code_update();

        /*
         * Unknown or empty session, just return gracefully, the viewer
         * knows what is happening.
         */
        if (!send_streams || !nb_streams) {
                ret = 0;
                goto end_put_session;
        }

        /*
         * Send stream and *DON'T* ignore the sent flag so every viewer
         * streams that were not sent from that point will be sent to
         * the viewer.
         */
        ret = send_viewer_streams(conn->sock, session_id, 0);
        if (ret < 0) {
                goto end_put_session;
        }

end_put_session:
        if (session) {
                session_put(session);
        }
error:
        return ret;
}

/*
 * Send the viewer the list of current sessions.
 */
static int viewer_attach_session(struct relay_connection *conn)
{
        int send_streams = 0;
        ssize_t ret;
        uint32_t nb_streams = 0;
        enum lttng_viewer_seek seek_type;
        struct lttng_viewer_attach_session_request request;
        struct lttng_viewer_attach_session_response response;
        struct relay_session *session = nullptr;
        enum lttng_viewer_attach_return_code viewer_attach_status;
        bool closed = false;
        uint64_t session_id;

        LTTNG_ASSERT(conn);

        health_code_update();

        /* Receive the request from the connected client. */
        ret = recv_request(conn->sock, &request, sizeof(request));
        if (ret < 0) {
                goto error;
        }

        session_id = be64toh(request.session_id);

        health_code_update();

        memset(&response, 0, sizeof(response));

        if (!conn->viewer_session) {
                viewer_attach_status = LTTNG_VIEWER_ATTACH_NO_SESSION;
                DBG("Client trying to attach before creating a live viewer session, returning status=%s",
                    lttng_viewer_attach_return_code_str(viewer_attach_status));
                goto send_reply;
        }

        session = session_get_by_id(session_id);
        if (!session) {
                viewer_attach_status = LTTNG_VIEWER_ATTACH_UNK;
                DBG("Relay session %" PRIu64 " not found, returning status=%s",
                    session_id,
                    lttng_viewer_attach_return_code_str(viewer_attach_status));
                goto send_reply;
        }
        DBG("Attach relay session ID %" PRIu64 " received", session_id);

        pthread_mutex_lock(&session->lock);
        if (session->live_timer == 0) {
                viewer_attach_status = LTTNG_VIEWER_ATTACH_NOT_LIVE;
                DBG("Relay session ID %" PRIu64 " is not a live session, returning status=%s",
                    session_id,
                    lttng_viewer_attach_return_code_str(viewer_attach_status));
                goto send_reply;
        }

        send_streams = 1;
        viewer_attach_status = viewer_session_attach(conn->viewer_session, session);
        if (viewer_attach_status != LTTNG_VIEWER_ATTACH_OK) {
                DBG("Error attaching to relay session %" PRIu64 ", returning status=%s",
                    session_id,
                    lttng_viewer_attach_return_code_str(viewer_attach_status));
                goto send_reply;
        }

        switch (be32toh(request.seek)) {
        case LTTNG_VIEWER_SEEK_BEGINNING:
        case LTTNG_VIEWER_SEEK_LAST:
                viewer_attach_status = LTTNG_VIEWER_ATTACH_OK;
                seek_type = (lttng_viewer_seek) be32toh(request.seek);
                break;
        default:
                ERR("Wrong seek parameter for relay session %" PRIu64 ", returning status=%s",
                    session_id,
                    lttng_viewer_attach_return_code_str(viewer_attach_status));
                viewer_attach_status = LTTNG_VIEWER_ATTACH_SEEK_ERR;
                send_streams = 0;
                goto send_reply;
        }

        /*
         * If a session rotation is ongoing, do not attempt to open any
         * stream, because the chunk can be in an intermediate state
         * due to directory renaming.
         */
        if (session_has_ongoing_rotation(session)) {
                DBG("Relay session %" PRIu64 " rotation ongoing", session_id);
                send_streams = 0;
                goto send_reply;
        }

        ret = make_viewer_streams(
                session, conn->viewer_session, seek_type, &nb_streams, nullptr, nullptr, &closed);
        if (ret < 0) {
                goto end_put_session;
        }
        pthread_mutex_unlock(&session->lock);
        session_put(session);
        session = nullptr;

        response.streams_count = htobe32(nb_streams);
        /*
         * If the session is closed when the viewer is attaching, it
         * means some of the streams may have been concurrently removed,
         * so we don't allow the viewer to attach, even if there are
         * streams available.
         */
        if (closed) {
                send_streams = 0;
                response.streams_count = 0;
                viewer_attach_status = LTTNG_VIEWER_ATTACH_UNK;
                ERR("Session %" PRIu64 " is closed, returning status=%s",
                    session_id,
                    lttng_viewer_attach_return_code_str(viewer_attach_status));
                goto send_reply;
        }

send_reply:
        health_code_update();

        response.status = htobe32((uint32_t) viewer_attach_status);

        ret = send_response(conn->sock, &response, sizeof(response));
        if (ret < 0) {
                goto end_put_session;
        }
        health_code_update();

        /*
         * Unknown or empty session, just return gracefully, the viewer
         * knows what is happening.
         */
        if (!send_streams || !nb_streams) {
                ret = 0;
                goto end_put_session;
        }

        /* Send stream and ignore the sent flag. */
        ret = send_viewer_streams(conn->sock, session_id, 1);
        if (ret < 0) {
                goto end_put_session;
        }

end_put_session:
        if (session) {
                pthread_mutex_unlock(&session->lock);
                session_put(session);
        }
error:
        return ret;
}

/*
 * Open the index file if needed for the given vstream.
 *
 * If an index file is successfully opened, the vstream will set it as its
 * current index file.
 *
 * Return 0 on success, a negative value on error (-ENOENT if not ready yet).
 *
 * Called with rstream lock held.
 */
static int try_open_index(struct relay_viewer_stream *vstream, struct relay_stream *rstream)
{
        int ret = 0;
        const uint32_t connection_major = rstream->trace->session->major;
        const uint32_t connection_minor = rstream->trace->session->minor;
        enum lttng_trace_chunk_status chunk_status;

        if (vstream->index_file) {
                goto end;
        }

        /*
         * First time, we open the index file and at least one index is ready.
         */
        if (rstream->index_received_seqcount == 0 || !vstream->stream_file.trace_chunk) {
                ret = -ENOENT;
                goto end;
        }

        chunk_status = lttng_index_file_create_from_trace_chunk_read_only(
                vstream->stream_file.trace_chunk,
                rstream->path_name,
                rstream->channel_name,
                rstream->tracefile_size,
                vstream->current_tracefile_id,
                lttng_to_index_major(connection_major, connection_minor),
                lttng_to_index_minor(connection_major, connection_minor),
                true,
                &vstream->index_file);
        if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                if (chunk_status == LTTNG_TRACE_CHUNK_STATUS_NO_FILE) {
                        ret = -ENOENT;
                } else {
                        ret = -1;
                }
        }

end:
        return ret;
}

/*
 * Check the status of the index for the given stream. This function
 * updates the index structure if needed and can put (close) the vstream
 * in the HUP situation.
 *
 * Return 0 means that we can proceed with the index. A value of 1 means
 * that the index has been updated and is ready to be sent to the
 * client. A negative value indicates an error that can't be handled.
 *
 * Called with rstream lock held.
 */
static int check_index_status(struct relay_viewer_stream *vstream,
                              struct relay_stream *rstream,
                              struct ctf_trace *trace,
                              struct lttng_viewer_index *index)
{
        int ret;

        DBG("Check index status: index_received_seqcount %" PRIu64 " "
            "index_sent_seqcount %" PRIu64 " "
            "for stream %" PRIu64,
            rstream->index_received_seqcount,
            vstream->index_sent_seqcount,
            vstream->stream->stream_handle);
        if ((trace->session->connection_closed || rstream->closed) &&
            rstream->index_received_seqcount == vstream->index_sent_seqcount) {
                /*
                 * Last index sent and session connection or relay
                 * stream are closed.
                 */
                index->status = LTTNG_VIEWER_INDEX_HUP;
                DBG("Check index status: Connection or stream are closed, stream %" PRIu64
                    ",connection-closed=%d, relay-stream-closed=%d, returning status=%s",
                    vstream->stream->stream_handle,
                    trace->session->connection_closed,
                    rstream->closed,
                    lttng_viewer_next_index_return_code_str(
                            (enum lttng_viewer_next_index_return_code) index->status));
                goto hup;
        } else if (rstream->beacon_ts_end != -1ULL &&
                   (rstream->index_received_seqcount == 0 ||
                    (vstream->index_sent_seqcount != 0 &&
                     rstream->index_received_seqcount <= vstream->index_sent_seqcount))) {
                /*
                 * We've received a synchronization beacon and the last index
                 * available has been sent, the index for now is inactive.
                 *
                 * In this case, we have received a beacon which allows us to
                 * inform the client of a time interval during which we can
                 * guarantee that there are no events to read (and never will
                 * be).
                 *
                 * The sent seqcount can grow higher than receive seqcount on
                 * clear because the rotation performed by clear will push
                 * the index_sent_seqcount ahead (see
                 * viewer_stream_sync_tracefile_array_tail) and skip over
                 * packet sequence numbers.
                 */
                index->status = LTTNG_VIEWER_INDEX_INACTIVE;
                index->timestamp_end = htobe64(rstream->beacon_ts_end);
                index->stream_id = htobe64(rstream->ctf_stream_id);
                DBG("Check index status: inactive with beacon, for stream %" PRIu64
                    ", returning status=%s",
                    vstream->stream->stream_handle,
                    lttng_viewer_next_index_return_code_str(
                            (enum lttng_viewer_next_index_return_code) index->status));
                goto index_ready;
        } else if (rstream->index_received_seqcount == 0 ||
                   (vstream->index_sent_seqcount != 0 &&
                    rstream->index_received_seqcount <= vstream->index_sent_seqcount)) {
                /*
                 * This checks whether received <= sent seqcount. In
                 * this case, we have not received a beacon. Therefore,
                 * we can only ask the client to retry later.
                 *
                 * The sent seqcount can grow higher than receive seqcount on
                 * clear because the rotation performed by clear will push
                 * the index_sent_seqcount ahead (see
                 * viewer_stream_sync_tracefile_array_tail) and skip over
                 * packet sequence numbers.
                 */
                index->status = LTTNG_VIEWER_INDEX_RETRY;
                DBG("Check index status:"
                    "did not received beacon for stream %" PRIu64 ", returning status=%s",
                    vstream->stream->stream_handle,
                    lttng_viewer_next_index_return_code_str(
                            (enum lttng_viewer_next_index_return_code) index->status));
                goto index_ready;
        } else if (!tracefile_array_seq_in_file(rstream->tfa,
                                                vstream->current_tracefile_id,
                                                vstream->index_sent_seqcount)) {
                /*
                 * The next index we want to send cannot be read either
                 * because we need to perform a rotation, or due to
                 * the producer having overwritten its trace file.
                 */
                DBG("Viewer stream %" PRIu64 " rotation", vstream->stream->stream_handle);
                ret = viewer_stream_rotate(vstream);
                if (ret == 1) {
                        /* EOF across entire stream. */
                        index->status = LTTNG_VIEWER_INDEX_HUP;
                        DBG("Check index status:"
                            "reached end of file for stream %" PRIu64 ", returning status=%s",
                            vstream->stream->stream_handle,
                            lttng_viewer_next_index_return_code_str(
                                    (enum lttng_viewer_next_index_return_code) index->status));
                        goto hup;
                }
                /*
                 * If we have been pushed due to overwrite, it
                 * necessarily means there is data that can be read in
                 * the stream. If we rotated because we reached the end
                 * of a tracefile, it means the following tracefile
                 * needs to contain at least one index, else we would
                 * have already returned LTTNG_VIEWER_INDEX_RETRY to the
                 * viewer. The updated index_sent_seqcount needs to
                 * point to a readable index entry now.
                 *
                 * In the case where we "rotate" on a single file, we
                 * can end up in a case where the requested index is
                 * still unavailable.
                 */
                if (rstream->tracefile_count == 1 &&
                    !tracefile_array_seq_in_file(rstream->tfa,
                                                 vstream->current_tracefile_id,
                                                 vstream->index_sent_seqcount)) {
                        index->status = LTTNG_VIEWER_INDEX_RETRY;
                        DBG("Check index status:"
                            "tracefile array sequence number %" PRIu64
                            " not in file for stream %" PRIu64 ", returning status=%s",
                            vstream->index_sent_seqcount,
                            vstream->stream->stream_handle,
                            lttng_viewer_next_index_return_code_str(
                                    (enum lttng_viewer_next_index_return_code) index->status));
                        goto index_ready;
                }
                LTTNG_ASSERT(tracefile_array_seq_in_file(
                        rstream->tfa, vstream->current_tracefile_id, vstream->index_sent_seqcount));
        }
        /* ret == 0 means successful so we continue. */
        ret = 0;
        return ret;

hup:
        viewer_stream_put(vstream);
index_ready:
        return 1;
}

static void viewer_stream_rotate_to_trace_chunk(struct relay_viewer_stream *vstream,
                                                struct lttng_trace_chunk *new_trace_chunk)
{
        lttng_trace_chunk_put(vstream->stream_file.trace_chunk);

        if (new_trace_chunk) {
                const bool acquired_reference = lttng_trace_chunk_get(new_trace_chunk);

                LTTNG_ASSERT(acquired_reference);
        }

        vstream->stream_file.trace_chunk = new_trace_chunk;
        viewer_stream_sync_tracefile_array_tail(vstream);
        viewer_stream_close_files(vstream);
}

/*
 * Send the next index for a stream.
 *
 * Return 0 on success or else a negative value.
 */
static int viewer_get_next_index(struct relay_connection *conn)
{
        int ret;
        struct lttng_viewer_get_next_index request_index;
        struct lttng_viewer_index viewer_index;
        struct ctf_packet_index packet_index;
        struct relay_viewer_stream *vstream = nullptr;
        struct relay_stream *rstream = nullptr;
        struct ctf_trace *ctf_trace = nullptr;
        struct relay_viewer_stream *metadata_viewer_stream = nullptr;
        bool viewer_stream_and_session_in_same_chunk, viewer_stream_one_rotation_behind;
        uint64_t stream_file_chunk_id = -1ULL, viewer_session_chunk_id = -1ULL;
        enum lttng_trace_chunk_status status;
        bool attached_sessions_have_new_streams = false;

        LTTNG_ASSERT(conn);

        memset(&viewer_index, 0, sizeof(viewer_index));
        health_code_update();

        ret = recv_request(conn->sock, &request_index, sizeof(request_index));
        if (ret < 0) {
                goto end;
        }
        health_code_update();

        vstream = viewer_stream_get_by_id(be64toh(request_index.stream_id));
        if (!vstream) {
                viewer_index.status = LTTNG_VIEWER_INDEX_ERR;
                DBG("Client requested index of unknown stream id %" PRIu64 ", returning status=%s",
                    (uint64_t) be64toh(request_index.stream_id),
                    lttng_viewer_next_index_return_code_str(
                            (enum lttng_viewer_next_index_return_code) viewer_index.status));
                goto send_reply;
        }

        /* Use back. ref. Protected by refcounts. */
        rstream = vstream->stream;
        ctf_trace = rstream->trace;

        /* metadata_viewer_stream may be NULL. */
        metadata_viewer_stream = ctf_trace_get_viewer_metadata_stream(ctf_trace);

        /*
         * Hold the session lock to protect against concurrent changes
         * to the chunk files (e.g. rename done by clear), which are
         * protected by the session ongoing rotation state. Those are
         * synchronized with the session lock.
         */
        pthread_mutex_lock(&rstream->trace->session->lock);
        pthread_mutex_lock(&rstream->lock);

        /*
         * The viewer should not ask for index on metadata stream.
         */
        if (rstream->is_metadata) {
                viewer_index.status = LTTNG_VIEWER_INDEX_HUP;
                DBG("Client requested index of a metadata stream id %" PRIu64
                    ", returning status=%s",
                    (uint64_t) be64toh(request_index.stream_id),
                    lttng_viewer_next_index_return_code_str(
                            (enum lttng_viewer_next_index_return_code) viewer_index.status));
                goto send_reply;
        }

        ret = check_new_streams(conn);
        if (ret < 0) {
                viewer_index.status = LTTNG_VIEWER_INDEX_ERR;
                ERR("Error checking for new streams in the attached sessions, returning status=%s",
                    lttng_viewer_next_index_return_code_str(
                            (enum lttng_viewer_next_index_return_code) viewer_index.status));
                goto send_reply;
        } else if (ret == 1) {
                attached_sessions_have_new_streams = true;
        }

        if (rstream->ongoing_rotation.is_set) {
                /* Rotation is ongoing, try again later. */
                viewer_index.status = LTTNG_VIEWER_INDEX_RETRY;
                DBG("Client requested index for stream id %" PRIu64
                    " while a stream rotation is ongoing, returning status=%s",
                    (uint64_t) be64toh(request_index.stream_id),
                    lttng_viewer_next_index_return_code_str(
                            (enum lttng_viewer_next_index_return_code) viewer_index.status));
                goto send_reply;
        }

        if (session_has_ongoing_rotation(rstream->trace->session)) {
                /* Rotation is ongoing, try again later. */
                viewer_index.status = LTTNG_VIEWER_INDEX_RETRY;
                DBG("Client requested index for stream id %" PRIu64
                    " while a session rotation is ongoing, returning status=%s",
                    (uint64_t) be64toh(request_index.stream_id),
                    lttng_viewer_next_index_return_code_str(
                            (enum lttng_viewer_next_index_return_code) viewer_index.status));
                goto send_reply;
        }

        /*
         * Transition the viewer session into the newest trace chunk available.
         */
        if (!lttng_trace_chunk_ids_equal(conn->viewer_session->current_trace_chunk,
                                         rstream->trace_chunk)) {
                DBG("Relay stream and viewer chunk ids differ");

                ret = viewer_session_set_trace_chunk_copy(conn->viewer_session,
                                                          rstream->trace_chunk);
                if (ret) {
                        viewer_index.status = LTTNG_VIEWER_INDEX_ERR;
                        ERR("Error copying trace chunk for stream id %" PRIu64
                            ", returning status=%s",
                            (uint64_t) be64toh(request_index.stream_id),
                            lttng_viewer_next_index_return_code_str(
                                    (enum lttng_viewer_next_index_return_code) viewer_index.status));
                        goto send_reply;
                }
        }

        /*
         * Transition the viewer stream into the latest trace chunk available.
         *
         * Note that the stream must _not_ rotate in one precise condition:
         * the relay stream has rotated to a NULL trace chunk and the viewer
         * stream is consuming the trace chunk that was active just before
         * that rotation to NULL.
         *
         * This allows clients to consume all the packets of a trace chunk
         * after a session's destruction.
         */
        if (vstream->stream_file.trace_chunk) {
                status = lttng_trace_chunk_get_id(vstream->stream_file.trace_chunk,
                                                  &stream_file_chunk_id);
                LTTNG_ASSERT(status == LTTNG_TRACE_CHUNK_STATUS_OK);
        }
        if (conn->viewer_session->current_trace_chunk) {
                status = lttng_trace_chunk_get_id(conn->viewer_session->current_trace_chunk,
                                                  &viewer_session_chunk_id);
                LTTNG_ASSERT(status == LTTNG_TRACE_CHUNK_STATUS_OK);
        }

        viewer_stream_and_session_in_same_chunk = lttng_trace_chunk_ids_equal(
                conn->viewer_session->current_trace_chunk, vstream->stream_file.trace_chunk);
        viewer_stream_one_rotation_behind = rstream->completed_rotation_count ==
                vstream->last_seen_rotation_count + 1;

        if (viewer_stream_and_session_in_same_chunk) {
                DBG("Transition to latest chunk check (%s -> %s): Same chunk, no need to rotate",
                    vstream->stream_file.trace_chunk ?
                            std::to_string(stream_file_chunk_id).c_str() :
                            "None",
                    conn->viewer_session->current_trace_chunk ?
                            std::to_string(viewer_session_chunk_id).c_str() :
                            "None");
        } else if (viewer_stream_one_rotation_behind && !rstream->trace_chunk) {
                DBG("Transition to latest chunk check (%s -> %s): One chunk behind relay stream which is being destroyed, no need to rotate",
                    vstream->stream_file.trace_chunk ?
                            std::to_string(stream_file_chunk_id).c_str() :
                            "None",
                    conn->viewer_session->current_trace_chunk ?
                            std::to_string(viewer_session_chunk_id).c_str() :
                            "None");
        } else {
                DBG("Transition to latest chunk check (%s -> %s): Viewer stream chunk ID and viewer session chunk ID differ, rotating viewer stream",
                    vstream->stream_file.trace_chunk ?
                            std::to_string(stream_file_chunk_id).c_str() :
                            "None",
                    conn->viewer_session->current_trace_chunk ?
                            std::to_string(viewer_session_chunk_id).c_str() :
                            "None");

                viewer_stream_rotate_to_trace_chunk(vstream,
                                                    conn->viewer_session->current_trace_chunk);
                vstream->last_seen_rotation_count = rstream->completed_rotation_count;
        }

        ret = check_index_status(vstream, rstream, ctf_trace, &viewer_index);
        if (ret < 0) {
                goto error_put;
        } else if (ret == 1) {
                /*
                 * We have no index to send and check_index_status has populated
                 * viewer_index's status.
                 */
                goto send_reply;
        }

        /* At this point, ret is 0 thus we will be able to read the index. */
        LTTNG_ASSERT(!ret);

        /* Try to open an index if one is needed for that stream. */
        ret = try_open_index(vstream, rstream);
        if (ret == -ENOENT) {
                if (rstream->closed) {
                        viewer_index.status = LTTNG_VIEWER_INDEX_HUP;
                        DBG("Cannot open index for stream id %" PRIu64
                            "stream is closed, returning status=%s",
                            (uint64_t) be64toh(request_index.stream_id),
                            lttng_viewer_next_index_return_code_str(
                                    (enum lttng_viewer_next_index_return_code) viewer_index.status));
                        goto send_reply;
                } else {
                        viewer_index.status = LTTNG_VIEWER_INDEX_RETRY;
                        DBG("Cannot open index for stream id %" PRIu64 ", returning status=%s",
                            (uint64_t) be64toh(request_index.stream_id),
                            lttng_viewer_next_index_return_code_str(
                                    (enum lttng_viewer_next_index_return_code) viewer_index.status));
                        goto send_reply;
                }
        }
        if (ret < 0) {
                viewer_index.status = LTTNG_VIEWER_INDEX_ERR;
                ERR("Error opening index for stream id %" PRIu64 ", returning status=%s",
                    (uint64_t) be64toh(request_index.stream_id),
                    lttng_viewer_next_index_return_code_str(
                            (enum lttng_viewer_next_index_return_code) viewer_index.status));
                goto send_reply;
        }

        /*
         * vstream->stream_fd may be NULL if it has been closed by
         * tracefile rotation, or if we are at the beginning of the
         * stream. We open the data stream file here to protect against
         * overwrite caused by tracefile rotation (in association with
         * unlink performed before overwrite).
         */
        if (!vstream->stream_file.handle) {
                char file_path[LTTNG_PATH_MAX];
                struct fs_handle *fs_handle;

                ret = utils_stream_file_path(rstream->path_name,
                                             rstream->channel_name,
                                             rstream->tracefile_size,
                                             vstream->current_tracefile_id,
                                             nullptr,
                                             file_path,
                                             sizeof(file_path));
                if (ret < 0) {
                        goto error_put;
                }

                /*
                 * It is possible the the file we are trying to open is
                 * missing if the stream has been closed (application exits with
                 * per-pid buffers) and a clear command has been performed.
                 */
                status = lttng_trace_chunk_open_fs_handle(
                        vstream->stream_file.trace_chunk, file_path, O_RDONLY, 0, &fs_handle, true);
                if (status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                        if (status == LTTNG_TRACE_CHUNK_STATUS_NO_FILE && rstream->closed) {
                                viewer_index.status = LTTNG_VIEWER_INDEX_HUP;
                                DBG("Cannot find trace chunk file and stream is closed for stream id %" PRIu64
                                    ", returning status=%s",
                                    (uint64_t) be64toh(request_index.stream_id),
                                    lttng_viewer_next_index_return_code_str(
                                            (enum lttng_viewer_next_index_return_code)
                                                    viewer_index.status));
                                goto send_reply;
                        }
                        PERROR("Failed to open trace file for viewer stream");
                        goto error_put;
                }
                vstream->stream_file.handle = fs_handle;
        }

        ret = lttng_index_file_read(vstream->index_file, &packet_index);
        if (ret) {
                viewer_index.status = LTTNG_VIEWER_INDEX_ERR;
                ERR("Relay error reading index file for stream id %" PRIu64 ", returning status=%s",
                    (uint64_t) be64toh(request_index.stream_id),
                    lttng_viewer_next_index_return_code_str(
                            (enum lttng_viewer_next_index_return_code) viewer_index.status));
                goto send_reply;
        } else {
                viewer_index.status = LTTNG_VIEWER_INDEX_OK;
                DBG("Read index file for stream id %" PRIu64 ", returning status=%s",
                    (uint64_t) be64toh(request_index.stream_id),
                    lttng_viewer_next_index_return_code_str(
                            (enum lttng_viewer_next_index_return_code) viewer_index.status));
                vstream->index_sent_seqcount++;
        }

        /*
         * Indexes are stored in big endian, no need to switch before sending.
         */
        DBG("Sending viewer index for stream %" PRIu64 " offset %" PRIu64,
            rstream->stream_handle,
            (uint64_t) be64toh(packet_index.offset));
        viewer_index.offset = packet_index.offset;
        viewer_index.packet_size = packet_index.packet_size;
        viewer_index.content_size = packet_index.content_size;
        viewer_index.timestamp_begin = packet_index.timestamp_begin;
        viewer_index.timestamp_end = packet_index.timestamp_end;
        viewer_index.events_discarded = packet_index.events_discarded;
        viewer_index.stream_id = packet_index.stream_id;

send_reply:
        if (rstream) {
                pthread_mutex_unlock(&rstream->lock);
                pthread_mutex_unlock(&rstream->trace->session->lock);
        }

        if (metadata_viewer_stream) {
                pthread_mutex_lock(&metadata_viewer_stream->stream->lock);
                DBG("get next index metadata check: recv %" PRIu64 " sent %" PRIu64,
                    metadata_viewer_stream->stream->metadata_received,
                    metadata_viewer_stream->metadata_sent);
                if (!metadata_viewer_stream->stream->metadata_received ||
                    metadata_viewer_stream->stream->metadata_received >
                            metadata_viewer_stream->metadata_sent) {
                        viewer_index.flags |= LTTNG_VIEWER_FLAG_NEW_METADATA;
                }
                pthread_mutex_unlock(&metadata_viewer_stream->stream->lock);
        }

        if (attached_sessions_have_new_streams) {
                viewer_index.flags |= LTTNG_VIEWER_FLAG_NEW_STREAM;
        }

        viewer_index.flags = htobe32(viewer_index.flags);
        viewer_index.status = htobe32(viewer_index.status);
        health_code_update();

        ret = send_response(conn->sock, &viewer_index, sizeof(viewer_index));
        if (ret < 0) {
                goto end;
        }
        health_code_update();

        if (vstream) {
                DBG("Index %" PRIu64 " for stream %" PRIu64 " sent",
                    vstream->index_sent_seqcount,
                    vstream->stream->stream_handle);
        }
end:
        if (metadata_viewer_stream) {
                viewer_stream_put(metadata_viewer_stream);
        }
        if (vstream) {
                viewer_stream_put(vstream);
        }
        return ret;

error_put:
        pthread_mutex_unlock(&rstream->lock);
        pthread_mutex_unlock(&rstream->trace->session->lock);
        if (metadata_viewer_stream) {
                viewer_stream_put(metadata_viewer_stream);
        }
        viewer_stream_put(vstream);
        return ret;
}

/*
 * Send the next index for a stream
 *
 * Return 0 on success or else a negative value.
 */
static int viewer_get_packet(struct relay_connection *conn)
{
        int ret;
        off_t lseek_ret;
        char *reply = nullptr;
        struct lttng_viewer_get_packet get_packet_info;
        struct lttng_viewer_trace_packet reply_header;
        struct relay_viewer_stream *vstream = nullptr;
        uint32_t reply_size = sizeof(reply_header);
        uint32_t packet_data_len = 0;
        ssize_t read_len;
        uint64_t stream_id;
        enum lttng_viewer_get_packet_return_code get_packet_status;

        health_code_update();

        ret = recv_request(conn->sock, &get_packet_info, sizeof(get_packet_info));
        if (ret < 0) {
                goto end;
        }
        health_code_update();

        /* From this point on, the error label can be reached. */
        memset(&reply_header, 0, sizeof(reply_header));
        stream_id = (uint64_t) be64toh(get_packet_info.stream_id);

        vstream = viewer_stream_get_by_id(stream_id);
        if (!vstream) {
                get_packet_status = LTTNG_VIEWER_GET_PACKET_ERR;
                DBG("Client requested packet of unknown stream id %" PRIu64 ", returning status=%s",
                    stream_id,
                    lttng_viewer_get_packet_return_code_str(get_packet_status));
                goto send_reply_nolock;
        } else {
                packet_data_len = be32toh(get_packet_info.len);
                reply_size += packet_data_len;
        }

        reply = zmalloc<char>(reply_size);
        if (!reply) {
                get_packet_status = LTTNG_VIEWER_GET_PACKET_ERR;
                PERROR("Falled to allocate reply, returning status=%s",
                       lttng_viewer_get_packet_return_code_str(get_packet_status));
                goto error;
        }

        pthread_mutex_lock(&vstream->stream->lock);
        lseek_ret = fs_handle_seek(
                vstream->stream_file.handle, be64toh(get_packet_info.offset), SEEK_SET);
        if (lseek_ret < 0) {
                get_packet_status = LTTNG_VIEWER_GET_PACKET_ERR;
                PERROR("Failed to seek file system handle of viewer stream %" PRIu64
                       " to offset %" PRIu64 ", returning status=%s",
                       stream_id,
                       (uint64_t) be64toh(get_packet_info.offset),
                       lttng_viewer_get_packet_return_code_str(get_packet_status));
                goto error;
        }
        read_len = fs_handle_read(
                vstream->stream_file.handle, reply + sizeof(reply_header), packet_data_len);
        if (read_len < packet_data_len) {
                get_packet_status = LTTNG_VIEWER_GET_PACKET_ERR;
                PERROR("Failed to read from file system handle of viewer stream id %" PRIu64
                       ", offset: %" PRIu64 ", returning status=%s",
                       stream_id,
                       (uint64_t) be64toh(get_packet_info.offset),
                       lttng_viewer_get_packet_return_code_str(get_packet_status));
                goto error;
        }

        get_packet_status = LTTNG_VIEWER_GET_PACKET_OK;
        reply_header.len = htobe32(packet_data_len);
        goto send_reply;

error:
        /* No payload to send on error. */
        reply_size = sizeof(reply_header);

send_reply:
        if (vstream) {
                pthread_mutex_unlock(&vstream->stream->lock);
        }
send_reply_nolock:

        health_code_update();

        reply_header.status = htobe32(get_packet_status);
        if (reply) {
                memcpy(reply, &reply_header, sizeof(reply_header));
                ret = send_response(conn->sock, reply, reply_size);
        } else {
                /* No reply to send. */
                ret = send_response(conn->sock, &reply_header, reply_size);
        }

        health_code_update();
        if (ret < 0) {
                PERROR("sendmsg of packet data failed");
                goto end_free;
        }

        DBG("Sent %u bytes for stream %" PRIu64, reply_size, stream_id);

end_free:
        free(reply);
end:
        if (vstream) {
                viewer_stream_put(vstream);
        }
        return ret;
}

/*
 * Send the session's metadata
 *
 * Return 0 on success else a negative value.
 */
static int viewer_get_metadata(struct relay_connection *conn)
{
        int ret = 0;
        int fd = -1;
        ssize_t read_len;
        uint64_t len = 0;
        char *data = nullptr;
        struct lttng_viewer_get_metadata request;
        struct lttng_viewer_metadata_packet reply;
        struct relay_viewer_stream *vstream = nullptr;
        bool dispose_of_stream = false;

        LTTNG_ASSERT(conn);

        health_code_update();

        ret = recv_request(conn->sock, &request, sizeof(request));
        if (ret < 0) {
                goto end;
        }
        health_code_update();

        memset(&reply, 0, sizeof(reply));

        vstream = viewer_stream_get_by_id(be64toh(request.stream_id));
        if (!vstream) {
                /*
                 * The metadata stream can be closed by a CLOSE command
                 * just before we attach. It can also be closed by
                 * per-pid tracing during tracing. Therefore, it is
                 * possible that we cannot find this viewer stream.
                 * Reply back to the client with an error if we cannot
                 * find it.
                 */
                DBG("Client requested metadata of unknown stream id %" PRIu64,
                    (uint64_t) be64toh(request.stream_id));
                reply.status = htobe32(LTTNG_VIEWER_METADATA_ERR);
                goto send_reply;
        }

        pthread_mutex_lock(&vstream->stream->trace->session->lock);
        pthread_mutex_lock(&vstream->stream->trace->lock);
        pthread_mutex_lock(&vstream->stream->lock);
        if (!vstream->stream->is_metadata) {
                ERR("Invalid metadata stream");
                goto error;
        }

        if (vstream->metadata_sent >= vstream->stream->metadata_received) {
                /*
                 * Clear feature resets the metadata_received to 0 until the
                 * same metadata is received again.
                 */
                reply.status = htobe32(LTTNG_VIEWER_NO_NEW_METADATA);
                /*
                 * The live viewer considers a closed 0 byte metadata stream as
                 * an error.
                 */
                dispose_of_stream = vstream->metadata_sent > 0 && vstream->stream->closed;
                goto send_reply;
        }

        if (vstream->stream->trace_chunk &&
            !lttng_trace_chunk_ids_equal(conn->viewer_session->current_trace_chunk,
                                         vstream->stream->trace_chunk)) {
                /* A rotation has occurred on the relay stream. */
                DBG("Metadata relay stream and viewer chunk ids differ");

                ret = viewer_session_set_trace_chunk_copy(conn->viewer_session,
                                                          vstream->stream->trace_chunk);
                if (ret) {
                        reply.status = htobe32(LTTNG_VIEWER_METADATA_ERR);
                        goto send_reply;
                }
        }

        if (conn->viewer_session->current_trace_chunk &&
            !lttng_trace_chunk_ids_equal(conn->viewer_session->current_trace_chunk,
                                         vstream->stream_file.trace_chunk)) {
                bool acquired_reference;

                DBG("Viewer session and viewer stream chunk differ: "
                    "vsession chunk %p vstream chunk %p",
                    conn->viewer_session->current_trace_chunk,
                    vstream->stream_file.trace_chunk);
                lttng_trace_chunk_put(vstream->stream_file.trace_chunk);
                acquired_reference =
                        lttng_trace_chunk_get(conn->viewer_session->current_trace_chunk);
                LTTNG_ASSERT(acquired_reference);
                vstream->stream_file.trace_chunk = conn->viewer_session->current_trace_chunk;
                viewer_stream_close_files(vstream);
        }

        len = vstream->stream->metadata_received - vstream->metadata_sent;

        if (!vstream->stream_file.trace_chunk) {
                if (vstream->stream->trace->session->connection_closed) {
                        /*
                         * If the connection is closed, there is no way for the metadata stream
                         * to ever transition back to an active chunk. As such, signal to the viewer
                         * that there is no new metadata available.
                         *
                         * The stream can be disposed-of. On the next execution of this command,
                         * the relay daemon will reply with an error status since the stream can't
                         * be found.
                         */
                        dispose_of_stream = true;
                }

                reply.status = htobe32(LTTNG_VIEWER_NO_NEW_METADATA);
                len = 0;
                goto send_reply;
        } else if (vstream->stream_file.trace_chunk && !vstream->stream_file.handle && len > 0) {
                /*
                 * Either this is the first time the metadata file is read, or a
                 * rotation of the corresponding relay stream has occurred.
                 */
                struct fs_handle *fs_handle;
                char file_path[LTTNG_PATH_MAX];
                enum lttng_trace_chunk_status status;
                struct relay_stream *rstream = vstream->stream;

                ret = utils_stream_file_path(rstream->path_name,
                                             rstream->channel_name,
                                             rstream->tracefile_size,
                                             vstream->current_tracefile_id,
                                             nullptr,
                                             file_path,
                                             sizeof(file_path));
                if (ret < 0) {
                        goto error;
                }

                /*
                 * It is possible the the metadata file we are trying to open is
                 * missing if the stream has been closed (application exits with
                 * per-pid buffers) and a clear command has been performed.
                 */
                status = lttng_trace_chunk_open_fs_handle(
                        vstream->stream_file.trace_chunk, file_path, O_RDONLY, 0, &fs_handle, true);
                if (status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                        if (status == LTTNG_TRACE_CHUNK_STATUS_NO_FILE) {
                                reply.status = htobe32(LTTNG_VIEWER_NO_NEW_METADATA);
                                len = 0;
                                if (vstream->stream->closed) {
                                        viewer_stream_put(vstream);
                                }
                                goto send_reply;
                        }
                        PERROR("Failed to open metadata file for viewer stream");
                        goto error;
                }
                vstream->stream_file.handle = fs_handle;

                if (vstream->metadata_sent != 0) {
                        /*
                         * The client does not expect to receive any metadata
                         * it has received and metadata files in successive
                         * chunks must be a strict superset of one another.
                         *
                         * Skip the first `metadata_sent` bytes to ensure
                         * they are not sent a second time to the client.
                         *
                         * Baring a block layer error or an internal error,
                         * this seek should not fail as
                         * `vstream->stream->metadata_received` is reset when
                         * a relay stream is rotated. If this is reached, it is
                         * safe to assume that
                         * `metadata_received` > `metadata_sent`.
                         */
                        const off_t seek_ret =
                                fs_handle_seek(fs_handle, vstream->metadata_sent, SEEK_SET);

                        if (seek_ret < 0) {
                                PERROR("Failed to seek metadata viewer stream file to `sent` position: pos = %" PRId64,
                                       vstream->metadata_sent);
                                reply.status = htobe32(LTTNG_VIEWER_METADATA_ERR);
                                goto send_reply;
                        }
                }
        }

        reply.len = htobe64(len);
        data = zmalloc<char>(len);
        if (!data) {
                PERROR("viewer metadata zmalloc");
                goto error;
        }

        fd = fs_handle_get_fd(vstream->stream_file.handle);
        if (fd < 0) {
                ERR("Failed to restore viewer stream file system handle");
                goto error;
        }
        read_len = lttng_read(fd, data, len);
        fs_handle_put_fd(vstream->stream_file.handle);
        fd = -1;
        if (read_len < len) {
                if (read_len < 0) {
                        PERROR("Failed to read metadata file");
                        goto error;
                } else {
                        /*
                         * A clear has been performed which prevents the relay
                         * from sending `len` bytes of metadata.
                         *
                         * It is important not to send any metadata if we
                         * couldn't read all the available metadata in one shot:
                         * sending partial metadata can cause the client to
                         * attempt to parse an incomplete (incoherent) metadata
                         * stream, which would result in an error.
                         */
                        const off_t seek_ret =
                                fs_handle_seek(vstream->stream_file.handle, -read_len, SEEK_CUR);

                        DBG("Failed to read metadata: requested = %" PRIu64 ", got = %zd",
                            len,
                            read_len);
                        read_len = 0;
                        len = 0;
                        if (seek_ret < 0) {
                                PERROR("Failed to restore metadata file position after partial read");
                                ret = -1;
                                goto error;
                        }
                }
        }
        vstream->metadata_sent += read_len;
        reply.status = htobe32(LTTNG_VIEWER_METADATA_OK);

        goto send_reply;

error:
        reply.status = htobe32(LTTNG_VIEWER_METADATA_ERR);

send_reply:
        health_code_update();
        if (vstream) {
                pthread_mutex_unlock(&vstream->stream->lock);
                pthread_mutex_unlock(&vstream->stream->trace->lock);
                pthread_mutex_unlock(&vstream->stream->trace->session->lock);
        }
        ret = send_response(conn->sock, &reply, sizeof(reply));
        if (ret < 0) {
                goto end_free;
        }
        health_code_update();

        if (len > 0) {
                ret = send_response(conn->sock, data, len);
                if (ret < 0) {
                        goto end_free;
                }
        }

        DBG("Sent %" PRIu64 " bytes of metadata for stream %" PRIu64,
            len,
            (uint64_t) be64toh(request.stream_id));

        DBG("Metadata sent");

end_free:
        free(data);
end:
        if (vstream) {
                viewer_stream_put(vstream);
                if (dispose_of_stream) {
                        /*
                         * Trigger the destruction of the viewer stream
                         * by releasing its global reference.
                         *
                         * The live viewers expect to receive a NO_NEW_METADATA
                         * status before a stream disappears, otherwise they abort the
                         * entire live connection when receiving an error status.
                         *
                         * On the next query for this stream, an error will be reported to the
                         * client.
                         */
                        viewer_stream_put(vstream);
                }
        }

        return ret;
}

/*
 * Create a viewer session.
 *
 * Return 0 on success or else a negative value.
 */
static int viewer_create_session(struct relay_connection *conn)
{
        int ret;
        struct lttng_viewer_create_session_response resp;

        memset(&resp, 0, sizeof(resp));
        resp.status = htobe32(LTTNG_VIEWER_CREATE_SESSION_OK);
        conn->viewer_session = viewer_session_create();
        if (!conn->viewer_session) {
                ERR("Allocation viewer session");
                resp.status = htobe32(LTTNG_VIEWER_CREATE_SESSION_ERR);
                goto send_reply;
        }

send_reply:
        health_code_update();
        ret = send_response(conn->sock, &resp, sizeof(resp));
        if (ret < 0) {
                goto end;
        }
        health_code_update();
        ret = 0;

end:
        return ret;
}

/*
 * Detach a viewer session.
 *
 * Return 0 on success or else a negative value.
 */
static int viewer_detach_session(struct relay_connection *conn)
{
        int ret;
        struct lttng_viewer_detach_session_response response;
        struct lttng_viewer_detach_session_request request;
        struct relay_session *session = nullptr;
        uint64_t viewer_session_to_close;

        LTTNG_ASSERT(conn);

        health_code_update();

        /* Receive the request from the connected client. */
        ret = recv_request(conn->sock, &request, sizeof(request));
        if (ret < 0) {
                goto end;
        }
        viewer_session_to_close = be64toh(request.session_id);

        if (!conn->viewer_session) {
                DBG("Client trying to detach before creating a live viewer session");
                response.status = htobe32(LTTNG_VIEWER_DETACH_SESSION_ERR);
                goto send_reply;
        }

        health_code_update();

        memset(&response, 0, sizeof(response));
        DBG("Detaching from session ID %" PRIu64, viewer_session_to_close);

        session = session_get_by_id(be64toh(request.session_id));
        if (!session) {
                DBG("Relay session %" PRIu64 " not found", (uint64_t) be64toh(request.session_id));
                response.status = htobe32(LTTNG_VIEWER_DETACH_SESSION_UNK);
                goto send_reply;
        }

        ret = viewer_session_is_attached(conn->viewer_session, session);
        if (ret != 1) {
                DBG("Not attached to this session");
                response.status = htobe32(LTTNG_VIEWER_DETACH_SESSION_ERR);
                goto send_reply_put;
        }

        viewer_session_close_one_session(conn->viewer_session, session);
        response.status = htobe32(LTTNG_VIEWER_DETACH_SESSION_OK);
        DBG("Session %" PRIu64 " detached.", viewer_session_to_close);

send_reply_put:
        session_put(session);

send_reply:
        health_code_update();
        ret = send_response(conn->sock, &response, sizeof(response));
        if (ret < 0) {
                goto end;
        }
        health_code_update();
        ret = 0;

end:
        return ret;
}

/*
 * live_relay_unknown_command: send -1 if received unknown command
 */
static void live_relay_unknown_command(struct relay_connection *conn)
{
        struct lttcomm_relayd_generic_reply reply;

        memset(&reply, 0, sizeof(reply));
        reply.ret_code = htobe32(LTTNG_ERR_UNK);
        (void) send_response(conn->sock, &reply, sizeof(reply));
}

/*
 * Process the commands received on the control socket
 */
static int process_control(struct lttng_viewer_cmd *recv_hdr, struct relay_connection *conn)
{
        int ret = 0;
        lttng_viewer_command cmd = (lttng_viewer_command) be32toh(recv_hdr->cmd);

        /*
         * Make sure we've done the version check before any command other then
         * a new client connection.
         */
        if (cmd != LTTNG_VIEWER_CONNECT && !conn->version_check_done) {
                ERR("Viewer on connection %d requested %s command before version check",
                    conn->sock->fd,
                    lttng_viewer_command_str(cmd));
                ret = -1;
                goto end;
        }

        DBG("Processing %s viewer command from connection %d",
            lttng_viewer_command_str(cmd),
            conn->sock->fd);

        switch (cmd) {
        case LTTNG_VIEWER_CONNECT:
                ret = viewer_connect(conn);
                break;
        case LTTNG_VIEWER_LIST_SESSIONS:
                ret = viewer_list_sessions(conn);
                break;
        case LTTNG_VIEWER_ATTACH_SESSION:
                ret = viewer_attach_session(conn);
                break;
        case LTTNG_VIEWER_GET_NEXT_INDEX:
                ret = viewer_get_next_index(conn);
                break;
        case LTTNG_VIEWER_GET_PACKET:
                ret = viewer_get_packet(conn);
                break;
        case LTTNG_VIEWER_GET_METADATA:
                ret = viewer_get_metadata(conn);
                break;
        case LTTNG_VIEWER_GET_NEW_STREAMS:
                ret = viewer_get_new_streams(conn);
                break;
        case LTTNG_VIEWER_CREATE_SESSION:
                ret = viewer_create_session(conn);
                break;
        case LTTNG_VIEWER_DETACH_SESSION:
                ret = viewer_detach_session(conn);
                break;
        default:
                ERR("Received unknown viewer command (%u)", be32toh(recv_hdr->cmd));
                live_relay_unknown_command(conn);
                ret = -1;
                goto end;
        }

end:
        return ret;
}

static void cleanup_connection_pollfd(struct lttng_poll_event *events, int pollfd)
{
        int ret;

        (void) lttng_poll_del(events, pollfd);

        ret = fd_tracker_close_unsuspendable_fd(
                the_fd_tracker, &pollfd, 1, fd_tracker_util_close_fd, nullptr);
        if (ret < 0) {
                ERR("Closing pollfd %d", pollfd);
        }
}

/*
 * This thread does the actual work
 */
static void *thread_worker(void *data __attribute__((unused)))
{
        int ret, err = -1;
        uint32_t nb_fd;
        struct lttng_poll_event events;
        struct lttng_ht *viewer_connections_ht;
        struct lttng_ht_iter iter;
        struct lttng_viewer_cmd recv_hdr;
        struct relay_connection *destroy_conn;

        DBG("[thread] Live viewer relay worker started");

        rcu_register_thread();

        health_register(health_relayd, HEALTH_RELAYD_TYPE_LIVE_WORKER);

        if (testpoint(relayd_thread_live_worker)) {
                goto error_testpoint;
        }

        /* table of connections indexed on socket */
        viewer_connections_ht = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
        if (!viewer_connections_ht) {
                goto viewer_connections_ht_error;
        }

        ret = create_named_thread_poll_set(&events, 2, "Live viewer worker thread epoll");
        if (ret < 0) {
                goto error_poll_create;
        }

        ret = lttng_poll_add(&events, live_conn_pipe[0], LPOLLIN | LPOLLRDHUP);
        if (ret < 0) {
                goto error;
        }

restart:
        while (true) {
                int i;

                health_code_update();

                /* Infinite blocking call, waiting for transmission */
                DBG3("Relayd live viewer worker thread polling...");
                health_poll_entry();
                ret = lttng_poll_wait(&events, -1);
                health_poll_exit();
                if (ret < 0) {
                        /*
                         * Restart interrupted system call.
                         */
                        if (errno == EINTR) {
                                goto restart;
                        }
                        goto error;
                }

                nb_fd = ret;

                /*
                 * Process control. The control connection is prioritised so we don't
                 * starve it with high throughput tracing data on the data
                 * connection.
                 */
                for (i = 0; i < nb_fd; i++) {
                        /* Fetch once the poll data */
                        const auto revents = LTTNG_POLL_GETEV(&events, i);
                        const auto pollfd = LTTNG_POLL_GETFD(&events, i);

                        health_code_update();

                        /* Activity on thread quit pipe, exiting. */
                        if (relayd_is_thread_quit_pipe(pollfd)) {
                                DBG("Activity on thread quit pipe");
                                err = 0;
                                goto exit;
                        }

                        /* Inspect the relay conn pipe for new connection. */
                        if (pollfd == live_conn_pipe[0]) {
                                if (revents & LPOLLIN) {
                                        struct relay_connection *conn;

                                        ret = lttng_read(live_conn_pipe[0],
                                                         &conn,
                                                         sizeof(conn)); /* NOLINT sizeof used on a
                                                                           pointer. */
                                        if (ret < 0) {
                                                goto error;
                                        }
                                        ret = lttng_poll_add(
                                                &events, conn->sock->fd, LPOLLIN | LPOLLRDHUP);
                                        if (ret) {
                                                ERR("Failed to add new live connection file descriptor to poll set");
                                                goto error;
                                        }
                                        connection_ht_add(viewer_connections_ht, conn);
                                        DBG("Connection socket %d added to poll", conn->sock->fd);
                                } else if (revents & (LPOLLERR | LPOLLHUP | LPOLLRDHUP)) {
                                        ERR("Relay live pipe error");
                                        goto error;
                                } else {
                                        ERR("Unexpected poll events %u for sock %d",
                                            revents,
                                            pollfd);
                                        goto error;
                                }
                        } else {
                                /* Connection activity. */
                                struct relay_connection *conn;

                                conn = connection_get_by_sock(viewer_connections_ht, pollfd);
                                if (!conn) {
                                        continue;
                                }

                                if (revents & LPOLLIN) {
                                        ret = conn->sock->ops->recvmsg(
                                                conn->sock, &recv_hdr, sizeof(recv_hdr), 0);
                                        if (ret <= 0) {
                                                /* Connection closed. */
                                                cleanup_connection_pollfd(&events, pollfd);
                                                /* Put "create" ownership reference. */
                                                connection_put(conn);
                                                DBG("Viewer control conn closed with %d", pollfd);
                                        } else {
                                                ret = process_control(&recv_hdr, conn);
                                                if (ret < 0) {
                                                        /* Clear the session on error. */
                                                        cleanup_connection_pollfd(&events, pollfd);
                                                        /* Put "create" ownership reference. */
                                                        connection_put(conn);
                                                        DBG("Viewer connection closed with %d",
                                                            pollfd);
                                                }
                                        }
                                } else if (revents & (LPOLLERR | LPOLLHUP | LPOLLRDHUP)) {
                                        cleanup_connection_pollfd(&events, pollfd);
                                        /* Put "create" ownership reference. */
                                        connection_put(conn);
                                } else {
                                        ERR("Unexpected poll events %u for sock %d",
                                            revents,
                                            pollfd);
                                        connection_put(conn);
                                        goto error;
                                }
                                /* Put local "get_by_sock" reference. */
                                connection_put(conn);
                        }
                }
        }

exit:
error:
        (void) fd_tracker_util_poll_clean(the_fd_tracker, &events);

        /* Cleanup remaining connection object. */
        {
                lttng::urcu::read_lock_guard read_lock;

                cds_lfht_for_each_entry (
                        viewer_connections_ht->ht, &iter.iter, destroy_conn, sock_n.node) {
                        health_code_update();
                        connection_put(destroy_conn);
                }
        }
error_poll_create:
        lttng_ht_destroy(viewer_connections_ht);
viewer_connections_ht_error:
        /* Close relay conn pipes */
        (void) fd_tracker_util_pipe_close(the_fd_tracker, live_conn_pipe);
        if (err) {
                DBG("Viewer worker thread exited with error");
        }
        DBG("Viewer worker thread cleanup complete");
error_testpoint:
        if (err) {
                health_error();
                ERR("Health error occurred in %s", __func__);
        }
        health_unregister(health_relayd);
        if (lttng_relay_stop_threads()) {
                ERR("Error stopping threads");
        }
        rcu_unregister_thread();
        return nullptr;
}

/*
 * Create the relay command pipe to wake thread_manage_apps.
 * Closed in cleanup().
 */
static int create_conn_pipe()
{
        return fd_tracker_util_pipe_open_cloexec(
                the_fd_tracker, "Live connection pipe", live_conn_pipe);
}

int relayd_live_join()
{
        int ret, retval = 0;
        void *status;

        ret = pthread_join(live_listener_thread, &status);
        if (ret) {
                errno = ret;
                PERROR("pthread_join live listener");
                retval = -1;
        }

        ret = pthread_join(live_worker_thread, &status);
        if (ret) {
                errno = ret;
                PERROR("pthread_join live worker");
                retval = -1;
        }

        ret = pthread_join(live_dispatcher_thread, &status);
        if (ret) {
                errno = ret;
                PERROR("pthread_join live dispatcher");
                retval = -1;
        }

        cleanup_relayd_live();

        return retval;
}

/*
 * main
 */
int relayd_live_create(struct lttng_uri *uri)
{
        int ret = 0, retval = 0;
        void *status;
        int is_root;

        if (!uri) {
                retval = -1;
                goto exit_init_data;
        }
        live_uri = uri;

        /* Check if daemon is UID = 0 */
        is_root = !getuid();

        if (!is_root) {
                if (live_uri->port < 1024) {
                        ERR("Need to be root to use ports < 1024");
                        retval = -1;
                        goto exit_init_data;
                }
        }

        /* Setup the thread apps communication pipe. */
        if (create_conn_pipe()) {
                retval = -1;
                goto exit_init_data;
        }

        /* Init relay command queue. */
        cds_wfcq_init(&viewer_conn_queue.head, &viewer_conn_queue.tail);

        /* Set up max poll set size */
        if (lttng_poll_set_max_size()) {
                retval = -1;
                goto exit_init_data;
        }

        /* Setup the dispatcher thread */
        ret = pthread_create(&live_dispatcher_thread,
                             default_pthread_attr(),
                             thread_dispatcher,
                             (void *) nullptr);
        if (ret) {
                errno = ret;
                PERROR("pthread_create viewer dispatcher");
                retval = -1;
                goto exit_dispatcher_thread;
        }

        /* Setup the worker thread */
        ret = pthread_create(&live_worker_thread, default_pthread_attr(), thread_worker, nullptr);
        if (ret) {
                errno = ret;
                PERROR("pthread_create viewer worker");
                retval = -1;
                goto exit_worker_thread;
        }

        /* Setup the listener thread */
        ret = pthread_create(
                &live_listener_thread, default_pthread_attr(), thread_listener, (void *) nullptr);
        if (ret) {
                errno = ret;
                PERROR("pthread_create viewer listener");
                retval = -1;
                goto exit_listener_thread;
        }

        /*
         * All OK, started all threads.
         */
        return retval;

        /*
         * Join on the live_listener_thread should anything be added after
         * the live_listener thread's creation.
         */

exit_listener_thread:

        ret = pthread_join(live_worker_thread, &status);
        if (ret) {
                errno = ret;
                PERROR("pthread_join live worker");
                retval = -1;
        }
exit_worker_thread:

        ret = pthread_join(live_dispatcher_thread, &status);
        if (ret) {
                errno = ret;
                PERROR("pthread_join live dispatcher");
                retval = -1;
        }
exit_dispatcher_thread:

exit_init_data:
        cleanup_relayd_live();

        return retval;
}