[lttng-tools.git] / liblttng-consumer / lttng-consumer.c

/*
 * Copyright (C) 2011 - Julien Desfossez <julien.desfossez@polymtl.ca>
 *                      Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; only version 2
 * of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */

#define _GNU_SOURCE
#include <assert.h>
#include <fcntl.h>
#include <poll.h>
#include <pthread.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>

#include <lttng-kernel-ctl.h>
#include <lttng-sessiond-comm.h>
#include <lttng/lttng-consumer.h>
#include <lttng/lttng-kconsumer.h>
#include <lttng/lttng-ustconsumer.h>
#include <lttngerr.h>

struct lttng_consumer_global_data consumer_data = {
        .stream_list.head = CDS_LIST_HEAD_INIT(consumer_data.stream_list.head),
        .channel_list.head = CDS_LIST_HEAD_INIT(consumer_data.channel_list.head),
        .stream_count = 0,
        .need_update = 1,
        .type = LTTNG_CONSUMER_UNKNOWN,
};

/* timeout parameter, to control the polling thread grace period. */
int consumer_poll_timeout = -1;

/*
 * Flag to inform the polling thread to quit when all fd hung up. Updated by
 * the consumer_thread_receive_fds when it notices that all fds has hung up.
 * Also updated by the signal handler (consumer_should_exit()). Read by the
 * polling threads.
 */
volatile int consumer_quit = 0;

/*
 * Find a stream. The consumer_data.lock must be locked during this
 * call.
 */
static struct lttng_consumer_stream *consumer_find_stream(int key)
{
        struct lttng_consumer_stream *iter;

        /* Negative keys are lookup failures */
        if (key < 0)
                return NULL;
        cds_list_for_each_entry(iter, &consumer_data.stream_list.head, list) {
                if (iter->key == key) {
                        DBG("Found stream key %d", key);
                        return iter;
                }
        }
        return NULL;
}

static void consumer_steal_stream_key(int key)
{
        struct lttng_consumer_stream *stream;

        stream = consumer_find_stream(key);
        if (stream)
                stream->key = -1;
}

static struct lttng_consumer_channel *consumer_find_channel(int key)
{
        struct lttng_consumer_channel *iter;

        /* Negative keys are lookup failures */
        if (key < 0)
                return NULL;
        cds_list_for_each_entry(iter, &consumer_data.channel_list.head, list) {
                if (iter->key == key) {
                        DBG("Found channel key %d", key);
                        return iter;
                }
        }
        return NULL;
}

static void consumer_steal_channel_key(int key)
{
        struct lttng_consumer_channel *channel;

        channel = consumer_find_channel(key);
        if (channel)
                channel->key = -1;
}

/*
 * Remove a stream from the global list protected by a mutex. This
 * function is also responsible for freeing its data structures.
 */
void consumer_del_stream(struct lttng_consumer_stream *stream)
{
        int ret;
        struct lttng_consumer_channel *free_chan = NULL;

        pthread_mutex_lock(&consumer_data.lock);

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                if (stream->mmap_base != NULL) {
                        ret = munmap(stream->mmap_base, stream->mmap_len);
                        if (ret != 0) {
                                perror("munmap");
                        }
                }
                break;
        case LTTNG_CONSUMER_UST:
                lttng_ustconsumer_del_stream(stream);
                break;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                goto end;
        }

        cds_list_del(&stream->list);
        if (consumer_data.stream_count <= 0) {
                goto end;
        }
        consumer_data.stream_count--;
        if (!stream) {
                goto end;
        }
        if (stream->out_fd >= 0) {
                close(stream->out_fd);
        }
        if (stream->wait_fd >= 0 && !stream->wait_fd_is_copy) {
                close(stream->wait_fd);
        }
        if (stream->shm_fd >= 0 && stream->wait_fd != stream->shm_fd
                        && !stream->shm_fd_is_copy) {
                close(stream->shm_fd);
        }
        if (!--stream->chan->refcount)
                free_chan = stream->chan;
        free(stream);
end:
        consumer_data.need_update = 1;
        pthread_mutex_unlock(&consumer_data.lock);

        if (free_chan)
                consumer_del_channel(free_chan);
}

struct lttng_consumer_stream *consumer_allocate_stream(
                int channel_key, int stream_key,
                int shm_fd, int wait_fd,
                enum lttng_consumer_stream_state state,
                uint64_t mmap_len,
                enum lttng_event_output output,
                const char *path_name)
{
        struct lttng_consumer_stream *stream;
        int ret;

        stream = zmalloc(sizeof(*stream));
        if (stream == NULL) {
                perror("malloc struct lttng_consumer_stream");
                goto end;
        }
        stream->chan = consumer_find_channel(channel_key);
        if (!stream->chan) {
                perror("Unable to find channel key");
                goto end;
        }
        stream->chan->refcount++;
        stream->key = stream_key;
        stream->shm_fd = shm_fd;
        stream->wait_fd = wait_fd;
        stream->out_fd = -1;
        stream->out_fd_offset = 0;
        stream->state = state;
        stream->mmap_len = mmap_len;
        stream->mmap_base = NULL;
        stream->output = output;
        strncpy(stream->path_name, path_name, PATH_MAX - 1);
        stream->path_name[PATH_MAX - 1] = '\0';

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                break;
        case LTTNG_CONSUMER_UST:
                stream->cpu = stream->chan->cpucount++;
                ret = lttng_ustconsumer_allocate_stream(stream);
                if (ret) {
                        free(stream);
                        return NULL;
                }
                break;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                goto end;
        }
        DBG("Allocated stream %s (key %d, shm_fd %d, wait_fd %d, mmap_len %llu, out_fd %d)",
                        stream->path_name, stream->key,
                        stream->shm_fd,
                        stream->wait_fd,
                        (unsigned long long) stream->mmap_len,
                        stream->out_fd);
end:
        return stream;
}

/*
 * Add a stream to the global list protected by a mutex.
 */
int consumer_add_stream(struct lttng_consumer_stream *stream)
{
        int ret = 0;

        pthread_mutex_lock(&consumer_data.lock);
        /* Steal stream identifier, for UST */
        consumer_steal_stream_key(stream->key);
        cds_list_add(&stream->list, &consumer_data.stream_list.head);
        consumer_data.stream_count++;
        consumer_data.need_update = 1;

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                break;
        case LTTNG_CONSUMER_UST:
                /* Streams are in CPU number order (we rely on this) */
                stream->cpu = stream->chan->nr_streams++;
                break;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                goto end;
        }

end:
        pthread_mutex_unlock(&consumer_data.lock);
        return ret;
}

/*
 * Update a stream according to what we just received.
 */
void consumer_change_stream_state(int stream_key,
                enum lttng_consumer_stream_state state)
{
        struct lttng_consumer_stream *stream;

        pthread_mutex_lock(&consumer_data.lock);
        stream = consumer_find_stream(stream_key);
        if (stream) {
                stream->state = state;
        }
        consumer_data.need_update = 1;
        pthread_mutex_unlock(&consumer_data.lock);
}

/*
 * Remove a channel from the global list protected by a mutex. This
 * function is also responsible for freeing its data structures.
 */
void consumer_del_channel(struct lttng_consumer_channel *channel)
{
        int ret;

        pthread_mutex_lock(&consumer_data.lock);

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                break;
        case LTTNG_CONSUMER_UST:
                lttng_ustconsumer_del_channel(channel);
                break;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                goto end;
        }

        cds_list_del(&channel->list);
        if (channel->mmap_base != NULL) {
                ret = munmap(channel->mmap_base, channel->mmap_len);
                if (ret != 0) {
                        perror("munmap");
                }
        }
        if (channel->wait_fd >= 0 && !channel->wait_fd_is_copy) {
                close(channel->wait_fd);
        }
        if (channel->shm_fd >= 0 && channel->wait_fd != channel->shm_fd
                        && !channel->shm_fd_is_copy) {
                close(channel->shm_fd);
        }
        free(channel);
end:
        pthread_mutex_unlock(&consumer_data.lock);
}

struct lttng_consumer_channel *consumer_allocate_channel(
                int channel_key,
                int shm_fd, int wait_fd,
                uint64_t mmap_len,
                uint64_t max_sb_size)
{
        struct lttng_consumer_channel *channel;
        int ret;

        channel = zmalloc(sizeof(*channel));
        if (channel == NULL) {
                perror("malloc struct lttng_consumer_channel");
                goto end;
        }
        channel->key = channel_key;
        channel->shm_fd = shm_fd;
        channel->wait_fd = wait_fd;
        channel->mmap_len = mmap_len;
        channel->max_sb_size = max_sb_size;
        channel->refcount = 0;
        channel->nr_streams = 0;

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                channel->mmap_base = NULL;
                channel->mmap_len = 0;
                break;
        case LTTNG_CONSUMER_UST:
                ret = lttng_ustconsumer_allocate_channel(channel);
                if (ret) {
                        free(channel);
                        return NULL;
                }
                break;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                goto end;
        }
        DBG("Allocated channel (key %d, shm_fd %d, wait_fd %d, mmap_len %llu, max_sb_size %llu)",
                        channel->key,
                        channel->shm_fd,
                        channel->wait_fd,
                        (unsigned long long) channel->mmap_len,
                        (unsigned long long) channel->max_sb_size);
end:
        return channel;
}

/*
 * Add a channel to the global list protected by a mutex.
 */
int consumer_add_channel(struct lttng_consumer_channel *channel)
{
        pthread_mutex_lock(&consumer_data.lock);
        /* Steal channel identifier, for UST */
        consumer_steal_channel_key(channel->key);
        cds_list_add(&channel->list, &consumer_data.channel_list.head);
        pthread_mutex_unlock(&consumer_data.lock);
        return 0;
}

/*
 * Allocate the pollfd structure and the local view of the out fds to avoid
 * doing a lookup in the linked list and concurrency issues when writing is
 * needed. Called with consumer_data.lock held.
 *
 * Returns the number of fds in the structures.
 */
int consumer_update_poll_array(
                struct lttng_consumer_local_data *ctx, struct pollfd **pollfd,
                struct lttng_consumer_stream **local_stream)
{
        struct lttng_consumer_stream *iter;
        int i = 0;

        DBG("Updating poll fd array");
        cds_list_for_each_entry(iter, &consumer_data.stream_list.head, list) {
                if (iter->state != LTTNG_CONSUMER_ACTIVE_STREAM) {
                        continue;
                }
                DBG("Active FD %d", iter->wait_fd);
                (*pollfd)[i].fd = iter->wait_fd;
                (*pollfd)[i].events = POLLIN | POLLPRI;
                local_stream[i] = iter;
                i++;
        }

        /*
         * Insert the consumer_poll_pipe at the end of the array and don't
         * increment i so nb_fd is the number of real FD.
         */
        (*pollfd)[i].fd = ctx->consumer_poll_pipe[0];
        (*pollfd)[i].events = POLLIN;
        return i;
}

/*
 * Poll on the should_quit pipe and the command socket return -1 on error and
 * should exit, 0 if data is available on the command socket
 */
int lttng_consumer_poll_socket(struct pollfd *consumer_sockpoll)
{
        int num_rdy;

        num_rdy = poll(consumer_sockpoll, 2, -1);
        if (num_rdy == -1) {
                perror("Poll error");
                goto exit;
        }
        if (consumer_sockpoll[0].revents == POLLIN) {
                DBG("consumer_should_quit wake up");
                goto exit;
        }
        return 0;

exit:
        return -1;
}

/*
 * Set the error socket.
 */
void lttng_consumer_set_error_sock(
                struct lttng_consumer_local_data *ctx, int sock)
{
        ctx->consumer_error_socket = sock;
}

/*
 * Set the command socket path.
 */

void lttng_consumer_set_command_sock_path(
                struct lttng_consumer_local_data *ctx, char *sock)
{
        ctx->consumer_command_sock_path = sock;
}

/*
 * Send return code to the session daemon.
 * If the socket is not defined, we return 0, it is not a fatal error
 */
int lttng_consumer_send_error(
                struct lttng_consumer_local_data *ctx, int cmd)
{
        if (ctx->consumer_error_socket > 0) {
                return lttcomm_send_unix_sock(ctx->consumer_error_socket, &cmd,
                                sizeof(enum lttcomm_sessiond_command));
        }

        return 0;
}

/*
 * Close all the tracefiles and stream fds, should be called when all instances
 * are destroyed.
 */
void lttng_consumer_cleanup(void)
{
        struct lttng_consumer_stream *iter, *tmp;
        struct lttng_consumer_channel *citer, *ctmp;

        /*
         * close all outfd. Called when there are no more threads
         * running (after joining on the threads), no need to protect
         * list iteration with mutex.
         */
        cds_list_for_each_entry_safe(iter, tmp,
                        &consumer_data.stream_list.head, list) {
                consumer_del_stream(iter);
        }
        cds_list_for_each_entry_safe(citer, ctmp,
                        &consumer_data.channel_list.head, list) {
                consumer_del_channel(citer);
        }
}

/*
 * Called from signal handler.
 */
void lttng_consumer_should_exit(struct lttng_consumer_local_data *ctx)
{
        int ret;
        consumer_quit = 1;
        ret = write(ctx->consumer_should_quit[1], "4", 1);
        if (ret < 0) {
                perror("write consumer quit");
        }
}

void lttng_consumer_sync_trace_file(
                struct lttng_consumer_stream *stream, off_t orig_offset)
{
        int outfd = stream->out_fd;

        /*
         * This does a blocking write-and-wait on any page that belongs to the
         * subbuffer prior to the one we just wrote.
         * Don't care about error values, as these are just hints and ways to
         * limit the amount of page cache used.
         */
        if (orig_offset < stream->chan->max_sb_size) {
                return;
        }
        sync_file_range(outfd, orig_offset - stream->chan->max_sb_size,
                        stream->chan->max_sb_size,
                        SYNC_FILE_RANGE_WAIT_BEFORE
                        | SYNC_FILE_RANGE_WRITE
                        | SYNC_FILE_RANGE_WAIT_AFTER);
        /*
         * Give hints to the kernel about how we access the file:
         * POSIX_FADV_DONTNEED : we won't re-access data in a near future after
         * we write it.
         *
         * We need to call fadvise again after the file grows because the
         * kernel does not seem to apply fadvise to non-existing parts of the
         * file.
         *
         * Call fadvise _after_ having waited for the page writeback to
         * complete because the dirty page writeback semantic is not well
         * defined. So it can be expected to lead to lower throughput in
         * streaming.
         */
        posix_fadvise(outfd, orig_offset - stream->chan->max_sb_size,
                        stream->chan->max_sb_size, POSIX_FADV_DONTNEED);
}

/*
 * Initialise the necessary environnement :
 * - create a new context
 * - create the poll_pipe
 * - create the should_quit pipe (for signal handler)
 * - create the thread pipe (for splice)
 *
 * Takes a function pointer as argument, this function is called when data is
 * available on a buffer. This function is responsible to do the
 * kernctl_get_next_subbuf, read the data with mmap or splice depending on the
 * buffer configuration and then kernctl_put_next_subbuf at the end.
 *
 * Returns a pointer to the new context or NULL on error.
 */
struct lttng_consumer_local_data *lttng_consumer_create(
                enum lttng_consumer_type type,
                int (*buffer_ready)(struct lttng_consumer_stream *stream,
                        struct lttng_consumer_local_data *ctx),
                int (*recv_channel)(struct lttng_consumer_channel *channel),
                int (*recv_stream)(struct lttng_consumer_stream *stream),
                int (*update_stream)(int stream_key, uint32_t state))
{
        int ret, i;
        struct lttng_consumer_local_data *ctx;

        assert(consumer_data.type == LTTNG_CONSUMER_UNKNOWN ||
                consumer_data.type == type);
        consumer_data.type = type;

        ctx = zmalloc(sizeof(struct lttng_consumer_local_data));
        if (ctx == NULL) {
                perror("allocating context");
                goto error;
        }

        ctx->consumer_error_socket = -1;
        /* assign the callbacks */
        ctx->on_buffer_ready = buffer_ready;
        ctx->on_recv_channel = recv_channel;
        ctx->on_recv_stream = recv_stream;
        ctx->on_update_stream = update_stream;

        ret = pipe(ctx->consumer_poll_pipe);
        if (ret < 0) {
                perror("Error creating poll pipe");
                goto error_poll_pipe;
        }

        ret = pipe(ctx->consumer_should_quit);
        if (ret < 0) {
                perror("Error creating recv pipe");
                goto error_quit_pipe;
        }

        ret = pipe(ctx->consumer_thread_pipe);
        if (ret < 0) {
                perror("Error creating thread pipe");
                goto error_thread_pipe;
        }

        return ctx;


error_thread_pipe:
        for (i = 0; i < 2; i++) {
                int err;

                err = close(ctx->consumer_should_quit[i]);
                assert(!err);
        }
error_quit_pipe:
        for (i = 0; i < 2; i++) {
                int err;

                err = close(ctx->consumer_poll_pipe[i]);
                assert(!err);
        }
error_poll_pipe:
        free(ctx);
error:
        return NULL;
}

/*
 * Close all fds associated with the instance and free the context.
 */
void lttng_consumer_destroy(struct lttng_consumer_local_data *ctx)
{
        close(ctx->consumer_error_socket);
        close(ctx->consumer_thread_pipe[0]);
        close(ctx->consumer_thread_pipe[1]);
        close(ctx->consumer_poll_pipe[0]);
        close(ctx->consumer_poll_pipe[1]);
        close(ctx->consumer_should_quit[0]);
        close(ctx->consumer_should_quit[1]);
        unlink(ctx->consumer_command_sock_path);
        free(ctx);
}

/*
 * Mmap the ring buffer, read it and write the data to the tracefile.
 *
 * Returns the number of bytes written
 */
int lttng_consumer_on_read_subbuffer_mmap(
                struct lttng_consumer_local_data *ctx,
                struct lttng_consumer_stream *stream, unsigned long len)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_on_read_subbuffer_mmap(ctx, stream, len);
        case LTTNG_CONSUMER_UST:
                return lttng_ustconsumer_on_read_subbuffer_mmap(ctx, stream, len);
        default:
                ERR("Unknown consumer_data type");
                assert(0);
        }
}

/*
 * Splice the data from the ring buffer to the tracefile.
 *
 * Returns the number of bytes spliced.
 */
int lttng_consumer_on_read_subbuffer_splice(
                struct lttng_consumer_local_data *ctx,
                struct lttng_consumer_stream *stream, unsigned long len)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_on_read_subbuffer_splice(ctx, stream, len);
        case LTTNG_CONSUMER_UST:
                return -ENOSYS;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                return -ENOSYS;
        }

}

/*
 * Take a snapshot for a specific fd
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_consumer_take_snapshot(struct lttng_consumer_local_data *ctx,
                struct lttng_consumer_stream *stream)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_take_snapshot(ctx, stream);
        case LTTNG_CONSUMER_UST:
                return lttng_ustconsumer_take_snapshot(ctx, stream);
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                return -ENOSYS;
        }

}

/*
 * Get the produced position
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_consumer_get_produced_snapshot(
                struct lttng_consumer_local_data *ctx,
                struct lttng_consumer_stream *stream,
                unsigned long *pos)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_get_produced_snapshot(ctx, stream, pos);
        case LTTNG_CONSUMER_UST:
                return lttng_ustconsumer_get_produced_snapshot(ctx, stream, pos);
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                return -ENOSYS;
        }
}

int lttng_consumer_recv_cmd(struct lttng_consumer_local_data *ctx,
                int sock, struct pollfd *consumer_sockpoll)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_recv_cmd(ctx, sock, consumer_sockpoll);
        case LTTNG_CONSUMER_UST:
                return lttng_ustconsumer_recv_cmd(ctx, sock, consumer_sockpoll);
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                return -ENOSYS;
        }
}

/*
 * This thread polls the fds in the ltt_fd_list to consume the data and write
 * it to tracefile if necessary.
 */
void *lttng_consumer_thread_poll_fds(void *data)
{
        int num_rdy, num_hup, high_prio, ret, i;
        struct pollfd *pollfd = NULL;
        /* local view of the streams */
        struct lttng_consumer_stream **local_stream = NULL;
        /* local view of consumer_data.fds_count */
        int nb_fd = 0;
        char tmp;
        int tmp2;
        struct lttng_consumer_local_data *ctx = data;

        local_stream = zmalloc(sizeof(struct lttng_consumer_stream));

        while (1) {
                high_prio = 0;
                num_hup = 0;

                /*
                 * the ltt_fd_list has been updated, we need to update our
                 * local array as well
                 */
                pthread_mutex_lock(&consumer_data.lock);
                if (consumer_data.need_update) {
                        if (pollfd != NULL) {
                                free(pollfd);
                                pollfd = NULL;
                        }
                        if (local_stream != NULL) {
                                free(local_stream);
                                local_stream = NULL;
                        }

                        /* allocate for all fds + 1 for the consumer_poll_pipe */
                        pollfd = zmalloc((consumer_data.stream_count + 1) * sizeof(struct pollfd));
                        if (pollfd == NULL) {
                                perror("pollfd malloc");
                                pthread_mutex_unlock(&consumer_data.lock);
                                goto end;
                        }

                        /* allocate for all fds + 1 for the consumer_poll_pipe */
                        local_stream = zmalloc((consumer_data.stream_count + 1) *
                                        sizeof(struct lttng_consumer_stream));
                        if (local_stream == NULL) {
                                perror("local_stream malloc");
                                pthread_mutex_unlock(&consumer_data.lock);
                                goto end;
                        }
                        ret = consumer_update_poll_array(ctx, &pollfd, local_stream);
                        if (ret < 0) {
                                ERR("Error in allocating pollfd or local_outfds");
                                lttng_consumer_send_error(ctx, CONSUMERD_POLL_ERROR);
                                pthread_mutex_unlock(&consumer_data.lock);
                                goto end;
                        }
                        nb_fd = ret;
                        consumer_data.need_update = 0;
                }
                pthread_mutex_unlock(&consumer_data.lock);

                /* poll on the array of fds */
                DBG("polling on %d fd", nb_fd + 1);
                num_rdy = poll(pollfd, nb_fd + 1, consumer_poll_timeout);
                DBG("poll num_rdy : %d", num_rdy);
                if (num_rdy == -1) {
                        perror("Poll error");
                        lttng_consumer_send_error(ctx, CONSUMERD_POLL_ERROR);
                        goto end;
                } else if (num_rdy == 0) {
                        DBG("Polling thread timed out");
                        goto end;
                }

                /* No FDs and consumer_quit, consumer_cleanup the thread */
                if (nb_fd == 0 && consumer_quit == 1) {
                        goto end;
                }

                /*
                 * If the consumer_poll_pipe triggered poll go
                 * directly to the beginning of the loop to update the
                 * array. We want to prioritize array update over
                 * low-priority reads.
                 */
                if (pollfd[nb_fd].revents & POLLIN) {
                        DBG("consumer_poll_pipe wake up");
                        tmp2 = read(ctx->consumer_poll_pipe[0], &tmp, 1);
                        if (tmp2 < 0) {
                                perror("read consumer poll");
                        }
                        continue;
                }

                /* Take care of high priority channels first. */
                for (i = 0; i < nb_fd; i++) {
                        if (pollfd[i].revents & POLLPRI) {
                                DBG("Urgent read on fd %d", pollfd[i].fd);
                                high_prio = 1;
                                ret = ctx->on_buffer_ready(local_stream[i], ctx);
                                /* it's ok to have an unavailable sub-buffer */
                                if (ret == EAGAIN) {
                                        ret = 0;
                                }
                        } else if (pollfd[i].revents & POLLERR) {
                                ERR("Error returned in polling fd %d.", pollfd[i].fd);
                                consumer_del_stream(local_stream[i]);
                                num_hup++;
                        } else if (pollfd[i].revents & POLLNVAL) {
                                ERR("Polling fd %d tells fd is not open.", pollfd[i].fd);
                                consumer_del_stream(local_stream[i]);
                                num_hup++;
                        } else if ((pollfd[i].revents & POLLHUP) &&
                                        !(pollfd[i].revents & POLLIN)) {
                                if (consumer_data.type == LTTNG_CONSUMER_UST) {
                                        DBG("Polling fd %d tells it has hung up. Attempting flush and read.",
                                                pollfd[i].fd);
                                        if (!local_stream[i]->hangup_flush_done) {
                                                lttng_ustconsumer_on_stream_hangup(local_stream[i]);
                                                /* read after flush */
                                                do {
                                                        ret = ctx->on_buffer_ready(local_stream[i], ctx);
                                                } while (ret == EAGAIN);
                                        }
                                } else {
                                        DBG("Polling fd %d tells it has hung up.", pollfd[i].fd);
                                }
                                consumer_del_stream(local_stream[i]);
                                num_hup++;
                        }
                }

                /* If every buffer FD has hung up, we end the read loop here */
                if (nb_fd > 0 && num_hup == nb_fd) {
                        DBG("every buffer FD has hung up\n");
                        if (consumer_quit == 1) {
                                goto end;
                        }
                        continue;
                }

                /* Take care of low priority channels. */
                if (high_prio == 0) {
                        for (i = 0; i < nb_fd; i++) {
                                if (pollfd[i].revents & POLLIN) {
                                        DBG("Normal read on fd %d", pollfd[i].fd);
                                        ret = ctx->on_buffer_ready(local_stream[i], ctx);
                                        /* it's ok to have an unavailable subbuffer */
                                        if (ret == EAGAIN) {
                                                ret = 0;
                                        }
                                }
                        }
                }
        }
end:
        DBG("polling thread exiting");
        if (pollfd != NULL) {
                free(pollfd);
                pollfd = NULL;
        }
        if (local_stream != NULL) {
                free(local_stream);
                local_stream = NULL;
        }
        return NULL;
}

/*
 * This thread listens on the consumerd socket and receives the file
 * descriptors from the session daemon.
 */
void *lttng_consumer_thread_receive_fds(void *data)
{
        int sock, client_socket, ret;
        /*
         * structure to poll for incoming data on communication socket avoids
         * making blocking sockets.
         */
        struct pollfd consumer_sockpoll[2];
        struct lttng_consumer_local_data *ctx = data;

        DBG("Creating command socket %s", ctx->consumer_command_sock_path);
        unlink(ctx->consumer_command_sock_path);
        client_socket = lttcomm_create_unix_sock(ctx->consumer_command_sock_path);
        if (client_socket < 0) {
                ERR("Cannot create command socket");
                goto end;
        }

        ret = lttcomm_listen_unix_sock(client_socket);
        if (ret < 0) {
                goto end;
        }

        DBG("Sending ready command to lttng-sessiond");
        ret = lttng_consumer_send_error(ctx, CONSUMERD_COMMAND_SOCK_READY);
        /* return < 0 on error, but == 0 is not fatal */
        if (ret < 0) {
                ERR("Error sending ready command to lttng-sessiond");
                goto end;
        }

        ret = fcntl(client_socket, F_SETFL, O_NONBLOCK);
        if (ret < 0) {
                perror("fcntl O_NONBLOCK");
                goto end;
        }

        /* prepare the FDs to poll : to client socket and the should_quit pipe */
        consumer_sockpoll[0].fd = ctx->consumer_should_quit[0];
        consumer_sockpoll[0].events = POLLIN | POLLPRI;
        consumer_sockpoll[1].fd = client_socket;
        consumer_sockpoll[1].events = POLLIN | POLLPRI;

        if (lttng_consumer_poll_socket(consumer_sockpoll) < 0) {
                goto end;
        }
        DBG("Connection on client_socket");

        /* Blocking call, waiting for transmission */
        sock = lttcomm_accept_unix_sock(client_socket);
        if (sock <= 0) {
                WARN("On accept");
                goto end;
        }
        ret = fcntl(sock, F_SETFL, O_NONBLOCK);
        if (ret < 0) {
                perror("fcntl O_NONBLOCK");
                goto end;
        }

        /* update the polling structure to poll on the established socket */
        consumer_sockpoll[1].fd = sock;
        consumer_sockpoll[1].events = POLLIN | POLLPRI;

        while (1) {
                if (lttng_consumer_poll_socket(consumer_sockpoll) < 0) {
                        goto end;
                }
                DBG("Incoming command on sock");
                ret = lttng_consumer_recv_cmd(ctx, sock, consumer_sockpoll);
                if (ret == -ENOENT) {
                        DBG("Received STOP command");
                        goto end;
                }
                if (ret < 0) {
                        ERR("Communication interrupted on command socket");
                        goto end;
                }
                if (consumer_quit) {
                        DBG("consumer_thread_receive_fds received quit from signal");
                        goto end;
                }
                DBG("received fds on sock");
        }
end:
        DBG("consumer_thread_receive_fds exiting");

        /*
         * when all fds have hung up, the polling thread
         * can exit cleanly
         */
        consumer_quit = 1;

        /*
         * 2s of grace period, if no polling events occur during
         * this period, the polling thread will exit even if there
         * are still open FDs (should not happen, but safety mechanism).
         */
        consumer_poll_timeout = LTTNG_CONSUMER_POLL_TIMEOUT;

        /* wake up the polling thread */
        ret = write(ctx->consumer_poll_pipe[1], "4", 1);
        if (ret < 0) {
                perror("poll pipe write");
        }
        return NULL;
}

int lttng_consumer_read_subbuffer(struct lttng_consumer_stream *stream,
                struct lttng_consumer_local_data *ctx)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_read_subbuffer(stream, ctx);
        case LTTNG_CONSUMER_UST:
                return lttng_ustconsumer_read_subbuffer(stream, ctx);
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                return -ENOSYS;
        }
}

int lttng_consumer_on_recv_stream(struct lttng_consumer_stream *stream)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_on_recv_stream(stream);
        case LTTNG_CONSUMER_UST:
                return lttng_ustconsumer_on_recv_stream(stream);
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                return -ENOSYS;
        }
}