[lttng-tools.git] / src / common / kernel-consumer / kernel-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, version 2 only,
 * as published by the Free Software Foundation.
 *
 * 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.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#define _GNU_SOURCE
#include <assert.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 <inttypes.h>
#include <unistd.h>
#include <sys/stat.h>

#include <common/common.h>
#include <common/kernel-ctl/kernel-ctl.h>
#include <common/sessiond-comm/sessiond-comm.h>
#include <common/sessiond-comm/relayd.h>
#include <common/compat/fcntl.h>
#include <common/pipe.h>
#include <common/relayd/relayd.h>
#include <common/utils.h>
#include <common/consumer-stream.h>
#include <common/index/index.h>
#include <common/consumer-timer.h>

#include "kernel-consumer.h"

extern struct lttng_consumer_global_data consumer_data;
extern int consumer_poll_timeout;
extern volatile int consumer_quit;

/*
 * Take a snapshot for a specific fd
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_kconsumer_take_snapshot(struct lttng_consumer_stream *stream)
{
        int ret = 0;
        int infd = stream->wait_fd;

        ret = kernctl_snapshot(infd);
        if (ret != 0) {
                perror("Getting sub-buffer snapshot.");
                ret = -errno;
        }

        return ret;
}

/*
 * Get the produced position
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_kconsumer_get_produced_snapshot(struct lttng_consumer_stream *stream,
                unsigned long *pos)
{
        int ret;
        int infd = stream->wait_fd;

        ret = kernctl_snapshot_get_produced(infd, pos);
        if (ret != 0) {
                perror("kernctl_snapshot_get_produced");
                ret = -errno;
        }

        return ret;
}

/*
 * Get the consumerd position
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_kconsumer_get_consumed_snapshot(struct lttng_consumer_stream *stream,
                unsigned long *pos)
{
        int ret;
        int infd = stream->wait_fd;

        ret = kernctl_snapshot_get_consumed(infd, pos);
        if (ret != 0) {
                perror("kernctl_snapshot_get_consumed");
                ret = -errno;
        }

        return ret;
}

/*
 * Take a snapshot of all the stream of a channel
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_kconsumer_snapshot_channel(uint64_t key, char *path,
                uint64_t relayd_id, uint64_t max_stream_size,
                struct lttng_consumer_local_data *ctx)
{
        int ret;
        unsigned long consumed_pos, produced_pos;
        struct lttng_consumer_channel *channel;
        struct lttng_consumer_stream *stream;

        DBG("Kernel consumer snapshot channel %" PRIu64, key);

        rcu_read_lock();

        channel = consumer_find_channel(key);
        if (!channel) {
                ERR("No channel found for key %" PRIu64, key);
                ret = -1;
                goto end;
        }

        /* Splice is not supported yet for channel snapshot. */
        if (channel->output != CONSUMER_CHANNEL_MMAP) {
                ERR("Unsupported output %d", channel->output);
                ret = -1;
                goto end;
        }

        cds_list_for_each_entry(stream, &channel->streams.head, send_node) {
                /*
                 * Lock stream because we are about to change its state.
                 */
                pthread_mutex_lock(&stream->lock);

                /*
                 * Assign the received relayd ID so we can use it for streaming. The streams
                 * are not visible to anyone so this is OK to change it.
                 */
                stream->net_seq_idx = relayd_id;
                channel->relayd_id = relayd_id;
                if (relayd_id != (uint64_t) -1ULL) {
                        ret = consumer_send_relayd_stream(stream, path);
                        if (ret < 0) {
                                ERR("sending stream to relayd");
                                goto end_unlock;
                        }
                } else {
                        ret = utils_create_stream_file(path, stream->name,
                                        stream->chan->tracefile_size,
                                        stream->tracefile_count_current,
                                        stream->uid, stream->gid, NULL);
                        if (ret < 0) {
                                ERR("utils_create_stream_file");
                                goto end_unlock;
                        }

                        stream->out_fd = ret;
                        stream->tracefile_size_current = 0;

                        DBG("Kernel consumer snapshot stream %s/%s (%" PRIu64 ")",
                                        path, stream->name, stream->key);
                }

                ret = kernctl_buffer_flush(stream->wait_fd);
                if (ret < 0) {
                        ERR("Failed to flush kernel stream");
                        ret = -errno;
                        goto end_unlock;
                }

                ret = lttng_kconsumer_take_snapshot(stream);
                if (ret < 0) {
                        ERR("Taking kernel snapshot");
                        goto end_unlock;
                }

                ret = lttng_kconsumer_get_produced_snapshot(stream, &produced_pos);
                if (ret < 0) {
                        ERR("Produced kernel snapshot position");
                        goto end_unlock;
                }

                ret = lttng_kconsumer_get_consumed_snapshot(stream, &consumed_pos);
                if (ret < 0) {
                        ERR("Consumerd kernel snapshot position");
                        goto end_unlock;
                }

                if (stream->max_sb_size == 0) {
                        ret = kernctl_get_max_subbuf_size(stream->wait_fd,
                                        &stream->max_sb_size);
                        if (ret < 0) {
                                ERR("Getting kernel max_sb_size");
                                ret = -errno;
                                goto end_unlock;
                        }
                }

                /*
                 * The original value is sent back if max stream size is larger than
                 * the possible size of the snapshot. Also, we asume that the session
                 * daemon should never send a maximum stream size that is lower than
                 * subbuffer size.
                 */
                consumed_pos = consumer_get_consumed_maxsize(consumed_pos,
                                produced_pos, max_stream_size);

                while (consumed_pos < produced_pos) {
                        ssize_t read_len;
                        unsigned long len, padded_len;

                        DBG("Kernel consumer taking snapshot at pos %lu", consumed_pos);

                        ret = kernctl_get_subbuf(stream->wait_fd, &consumed_pos);
                        if (ret < 0) {
                                if (errno != EAGAIN) {
                                        PERROR("kernctl_get_subbuf snapshot");
                                        ret = -errno;
                                        goto end_unlock;
                                }
                                DBG("Kernel consumer get subbuf failed. Skipping it.");
                                consumed_pos += stream->max_sb_size;
                                continue;
                        }

                        ret = kernctl_get_subbuf_size(stream->wait_fd, &len);
                        if (ret < 0) {
                                ERR("Snapshot kernctl_get_subbuf_size");
                                ret = -errno;
                                goto error_put_subbuf;
                        }

                        ret = kernctl_get_padded_subbuf_size(stream->wait_fd, &padded_len);
                        if (ret < 0) {
                                ERR("Snapshot kernctl_get_padded_subbuf_size");
                                ret = -errno;
                                goto error_put_subbuf;
                        }

                        read_len = lttng_consumer_on_read_subbuffer_mmap(ctx, stream, len,
                                        padded_len - len, NULL);
                        /*
                         * We write the padded len in local tracefiles but the data len
                         * when using a relay. Display the error but continue processing
                         * to try to release the subbuffer.
                         */
                        if (relayd_id != (uint64_t) -1ULL) {
                                if (read_len != len) {
                                        ERR("Error sending to the relay (ret: %zd != len: %lu)",
                                                        read_len, len);
                                }
                        } else {
                                if (read_len != padded_len) {
                                        ERR("Error writing to tracefile (ret: %zd != len: %lu)",
                                                        read_len, padded_len);
                                }
                        }

                        ret = kernctl_put_subbuf(stream->wait_fd);
                        if (ret < 0) {
                                ERR("Snapshot kernctl_put_subbuf");
                                ret = -errno;
                                goto end_unlock;
                        }
                        consumed_pos += stream->max_sb_size;
                }

                if (relayd_id == (uint64_t) -1ULL) {
                        if (stream->out_fd >= 0) {
                                ret = close(stream->out_fd);
                                if (ret < 0) {
                                        PERROR("Kernel consumer snapshot close out_fd");
                                        goto end_unlock;
                                }
                                stream->out_fd = -1;
                        }
                } else {
                        close_relayd_stream(stream);
                        stream->net_seq_idx = (uint64_t) -1ULL;
                }
                pthread_mutex_unlock(&stream->lock);
        }

        /* All good! */
        ret = 0;
        goto end;

error_put_subbuf:
        ret = kernctl_put_subbuf(stream->wait_fd);
        if (ret < 0) {
                ret = -errno;
                ERR("Snapshot kernctl_put_subbuf error path");
        }
end_unlock:
        pthread_mutex_unlock(&stream->lock);
end:
        rcu_read_unlock();
        return ret;
}

/*
 * Read the whole metadata available for a snapshot.
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_kconsumer_snapshot_metadata(uint64_t key, char *path,
                uint64_t relayd_id, struct lttng_consumer_local_data *ctx)
{
        int ret, use_relayd = 0;
        ssize_t ret_read;
        struct lttng_consumer_channel *metadata_channel;
        struct lttng_consumer_stream *metadata_stream;

        assert(ctx);

        DBG("Kernel consumer snapshot metadata with key %" PRIu64 " at path %s",
                        key, path);

        rcu_read_lock();

        metadata_channel = consumer_find_channel(key);
        if (!metadata_channel) {
                ERR("Kernel snapshot metadata not found for key %" PRIu64, key);
                ret = -1;
                goto error;
        }

        metadata_stream = metadata_channel->metadata_stream;
        assert(metadata_stream);

        /* Flag once that we have a valid relayd for the stream. */
        if (relayd_id != (uint64_t) -1ULL) {
                use_relayd = 1;
        }

        if (use_relayd) {
                ret = consumer_send_relayd_stream(metadata_stream, path);
                if (ret < 0) {
                        goto error;
                }
        } else {
                ret = utils_create_stream_file(path, metadata_stream->name,
                                metadata_stream->chan->tracefile_size,
                                metadata_stream->tracefile_count_current,
                                metadata_stream->uid, metadata_stream->gid, NULL);
                if (ret < 0) {
                        goto error;
                }
                metadata_stream->out_fd = ret;
        }

        do {
                ret_read = lttng_kconsumer_read_subbuffer(metadata_stream, ctx);
                if (ret_read < 0) {
                        if (ret_read != -EAGAIN) {
                                ERR("Kernel snapshot reading metadata subbuffer (ret: %zd)",
                                                ret_read);
                                goto error;
                        }
                        /* ret_read is negative at this point so we will exit the loop. */
                        continue;
                }
        } while (ret_read >= 0);

        if (use_relayd) {
                close_relayd_stream(metadata_stream);
                metadata_stream->net_seq_idx = (uint64_t) -1ULL;
        } else {
                if (metadata_stream->out_fd >= 0) {
                        ret = close(metadata_stream->out_fd);
                        if (ret < 0) {
                                PERROR("Kernel consumer snapshot metadata close out_fd");
                                /*
                                 * Don't go on error here since the snapshot was successful at this
                                 * point but somehow the close failed.
                                 */
                        }
                        metadata_stream->out_fd = -1;
                }
        }

        ret = 0;

        cds_list_del(&metadata_stream->send_node);
        consumer_stream_destroy(metadata_stream, NULL);
        metadata_channel->metadata_stream = NULL;
error:
        rcu_read_unlock();
        return ret;
}

/*
 * Receive command from session daemon and process it.
 *
 * Return 1 on success else a negative value or 0.
 */
int lttng_kconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
                int sock, struct pollfd *consumer_sockpoll)
{
        ssize_t ret;
        enum lttng_error_code ret_code = LTTNG_OK;
        struct lttcomm_consumer_msg msg;

        ret = lttcomm_recv_unix_sock(sock, &msg, sizeof(msg));
        if (ret != sizeof(msg)) {
                if (ret > 0) {
                        lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_ERROR_RECV_CMD);
                        ret = -1;
                }
                return ret;
        }
        if (msg.cmd_type == LTTNG_CONSUMER_STOP) {
                /*
                 * Notify the session daemon that the command is completed.
                 *
                 * On transport layer error, the function call will print an error
                 * message so handling the returned code is a bit useless since we
                 * return an error code anyway.
                 */
                (void) consumer_send_status_msg(sock, ret_code);
                return -ENOENT;
        }

        /* relayd needs RCU read-side protection */
        rcu_read_lock();

        switch (msg.cmd_type) {
        case LTTNG_CONSUMER_ADD_RELAYD_SOCKET:
        {
                /* Session daemon status message are handled in the following call. */
                ret = consumer_add_relayd_socket(msg.u.relayd_sock.net_index,
                                msg.u.relayd_sock.type, ctx, sock, consumer_sockpoll,
                                &msg.u.relayd_sock.sock, msg.u.relayd_sock.session_id,
                                 msg.u.relayd_sock.relayd_session_id);
                goto end_nosignal;
        }
        case LTTNG_CONSUMER_ADD_CHANNEL:
        {
                struct lttng_consumer_channel *new_channel;
                int ret_recv;

                /* First send a status message before receiving the fds. */
                ret = consumer_send_status_msg(sock, ret_code);
                if (ret < 0) {
                        /* Somehow, the session daemon is not responding anymore. */
                        goto error_fatal;
                }
                DBG("consumer_add_channel %" PRIu64, msg.u.channel.channel_key);
                new_channel = consumer_allocate_channel(msg.u.channel.channel_key,
                                msg.u.channel.session_id, msg.u.channel.pathname,
                                msg.u.channel.name, msg.u.channel.uid, msg.u.channel.gid,
                                msg.u.channel.relayd_id, msg.u.channel.output,
                                msg.u.channel.tracefile_size,
                                msg.u.channel.tracefile_count, 0,
                                msg.u.channel.monitor,
                                msg.u.channel.live_timer_interval);
                if (new_channel == NULL) {
                        lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_OUTFD_ERROR);
                        goto end_nosignal;
                }
                new_channel->nb_init_stream_left = msg.u.channel.nb_init_streams;
                switch (msg.u.channel.output) {
                case LTTNG_EVENT_SPLICE:
                        new_channel->output = CONSUMER_CHANNEL_SPLICE;
                        break;
                case LTTNG_EVENT_MMAP:
                        new_channel->output = CONSUMER_CHANNEL_MMAP;
                        break;
                default:
                        ERR("Channel output unknown %d", msg.u.channel.output);
                        goto end_nosignal;
                }

                /* Translate and save channel type. */
                switch (msg.u.channel.type) {
                case CONSUMER_CHANNEL_TYPE_DATA:
                case CONSUMER_CHANNEL_TYPE_METADATA:
                        new_channel->type = msg.u.channel.type;
                        break;
                default:
                        assert(0);
                        goto end_nosignal;
                };

                if (ctx->on_recv_channel != NULL) {
                        ret_recv = ctx->on_recv_channel(new_channel);
                        if (ret_recv == 0) {
                                ret = consumer_add_channel(new_channel, ctx);
                        } else if (ret_recv < 0) {
                                goto end_nosignal;
                        }
                } else {
                        ret = consumer_add_channel(new_channel, ctx);
                }
                consumer_timer_live_start(new_channel, msg.u.channel.live_timer_interval);

                /* If we received an error in add_channel, we need to report it. */
                if (ret < 0) {
                        ret = consumer_send_status_msg(sock, ret);
                        if (ret < 0) {
                                goto error_fatal;
                        }
                        goto end_nosignal;
                }

                goto end_nosignal;
        }
        case LTTNG_CONSUMER_ADD_STREAM:
        {
                int fd;
                struct lttng_pipe *stream_pipe;
                struct lttng_consumer_stream *new_stream;
                struct lttng_consumer_channel *channel;
                int alloc_ret = 0;

                /*
                 * Get stream's channel reference. Needed when adding the stream to the
                 * global hash table.
                 */
                channel = consumer_find_channel(msg.u.stream.channel_key);
                if (!channel) {
                        /*
                         * We could not find the channel. Can happen if cpu hotplug
                         * happens while tearing down.
                         */
                        ERR("Unable to find channel key %" PRIu64, msg.u.stream.channel_key);
                        ret_code = LTTNG_ERR_KERN_CHAN_NOT_FOUND;
                }

                /* First send a status message before receiving the fds. */
                ret = consumer_send_status_msg(sock, ret_code);
                if (ret < 0) {
                        /* Somehow, the session daemon is not responding anymore. */
                        goto error_fatal;
                }
                if (ret_code != LTTNG_OK) {
                        /* Channel was not found. */
                        goto end_nosignal;
                }

                /* Blocking call */
                if (lttng_consumer_poll_socket(consumer_sockpoll) < 0) {
                        rcu_read_unlock();
                        return -EINTR;
                }

                /* Get stream file descriptor from socket */
                ret = lttcomm_recv_fds_unix_sock(sock, &fd, 1);
                if (ret != sizeof(fd)) {
                        lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_ERROR_RECV_FD);
                        rcu_read_unlock();
                        return ret;
                }

                /*
                 * Send status code to session daemon only if the recv works. If the
                 * above recv() failed, the session daemon is notified through the
                 * error socket and the teardown is eventually done.
                 */
                ret = consumer_send_status_msg(sock, ret_code);
                if (ret < 0) {
                        /* Somehow, the session daemon is not responding anymore. */
                        goto end_nosignal;
                }

                new_stream = consumer_allocate_stream(channel->key,
                                fd,
                                LTTNG_CONSUMER_ACTIVE_STREAM,
                                channel->name,
                                channel->uid,
                                channel->gid,
                                channel->relayd_id,
                                channel->session_id,
                                msg.u.stream.cpu,
                                &alloc_ret,
                                channel->type,
                                channel->monitor);
                if (new_stream == NULL) {
                        switch (alloc_ret) {
                        case -ENOMEM:
                        case -EINVAL:
                        default:
                                lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_OUTFD_ERROR);
                                break;
                        }
                        goto end_nosignal;
                }

                new_stream->chan = channel;
                new_stream->wait_fd = fd;
                switch (channel->output) {
                case CONSUMER_CHANNEL_SPLICE:
                        new_stream->output = LTTNG_EVENT_SPLICE;
                        break;
                case CONSUMER_CHANNEL_MMAP:
                        new_stream->output = LTTNG_EVENT_MMAP;
                        break;
                default:
                        ERR("Stream output unknown %d", channel->output);
                        goto end_nosignal;
                }

                /*
                 * We've just assigned the channel to the stream so increment the
                 * refcount right now. We don't need to increment the refcount for
                 * streams in no monitor because we handle manually the cleanup of
                 * those. It is very important to make sure there is NO prior
                 * consumer_del_stream() calls or else the refcount will be unbalanced.
                 */
                if (channel->monitor) {
                        uatomic_inc(&new_stream->chan->refcount);
                }

                /*
                 * The buffer flush is done on the session daemon side for the kernel
                 * so no need for the stream "hangup_flush_done" variable to be
                 * tracked. This is important for a kernel stream since we don't rely
                 * on the flush state of the stream to read data. It's not the case for
                 * user space tracing.
                 */
                new_stream->hangup_flush_done = 0;

                if (ctx->on_recv_stream) {
                        ret = ctx->on_recv_stream(new_stream);
                        if (ret < 0) {
                                consumer_stream_free(new_stream);
                                goto end_nosignal;
                        }
                }

                if (new_stream->metadata_flag) {
                        channel->metadata_stream = new_stream;
                }

                /* Do not monitor this stream. */
                if (!channel->monitor) {
                        DBG("Kernel consumer add stream %s in no monitor mode with "
                                        "relayd id %" PRIu64, new_stream->name,
                                        new_stream->net_seq_idx);
                        cds_list_add(&new_stream->send_node, &channel->streams.head);
                        break;
                }

                /* Send stream to relayd if the stream has an ID. */
                if (new_stream->net_seq_idx != (uint64_t) -1ULL) {
                        ret = consumer_send_relayd_stream(new_stream,
                                        new_stream->chan->pathname);
                        if (ret < 0) {
                                consumer_stream_free(new_stream);
                                goto end_nosignal;
                        }
                }

                /* Get the right pipe where the stream will be sent. */
                if (new_stream->metadata_flag) {
                        ret = consumer_add_metadata_stream(new_stream);
                        if (ret) {
                                ERR("Consumer add metadata stream %" PRIu64 " failed. Continuing",
                                                new_stream->key);
                                consumer_stream_free(new_stream);
                                goto end_nosignal;
                        }
                        stream_pipe = ctx->consumer_metadata_pipe;
                } else {
                        ret = consumer_add_data_stream(new_stream);
                        if (ret) {
                                ERR("Consumer add stream %" PRIu64 " failed. Continuing",
                                                new_stream->key);
                                consumer_stream_free(new_stream);
                                goto end_nosignal;
                        }
                        stream_pipe = ctx->consumer_data_pipe;
                }

                /* Vitible to other threads */
                new_stream->globally_visible = 1;

                ret = lttng_pipe_write(stream_pipe, &new_stream, sizeof(new_stream));
                if (ret < 0) {
                        ERR("Consumer write %s stream to pipe %d",
                                        new_stream->metadata_flag ? "metadata" : "data",
                                        lttng_pipe_get_writefd(stream_pipe));
                        if (new_stream->metadata_flag) {
                                consumer_del_stream_for_metadata(new_stream);
                        } else {
                                consumer_del_stream_for_data(new_stream);
                        }
                        goto end_nosignal;
                }

                DBG("Kernel consumer ADD_STREAM %s (fd: %d) with relayd id %" PRIu64,
                                new_stream->name, fd, new_stream->relayd_stream_id);
                break;
        }
        case LTTNG_CONSUMER_UPDATE_STREAM:
        {
                rcu_read_unlock();
                return -ENOSYS;
        }
        case LTTNG_CONSUMER_DESTROY_RELAYD:
        {
                uint64_t index = msg.u.destroy_relayd.net_seq_idx;
                struct consumer_relayd_sock_pair *relayd;

                DBG("Kernel consumer destroying relayd %" PRIu64, index);

                /* Get relayd reference if exists. */
                relayd = consumer_find_relayd(index);
                if (relayd == NULL) {
                        DBG("Unable to find relayd %" PRIu64, index);
                        ret_code = LTTNG_ERR_NO_CONSUMER;
                }

                /*
                 * Each relayd socket pair has a refcount of stream attached to it
                 * which tells if the relayd is still active or not depending on the
                 * refcount value.
                 *
                 * This will set the destroy flag of the relayd object and destroy it
                 * if the refcount reaches zero when called.
                 *
                 * The destroy can happen either here or when a stream fd hangs up.
                 */
                if (relayd) {
                        consumer_flag_relayd_for_destroy(relayd);
                }

                ret = consumer_send_status_msg(sock, ret_code);
                if (ret < 0) {
                        /* Somehow, the session daemon is not responding anymore. */
                        goto error_fatal;
                }

                goto end_nosignal;
        }
        case LTTNG_CONSUMER_DATA_PENDING:
        {
                int32_t ret;
                uint64_t id = msg.u.data_pending.session_id;

                DBG("Kernel consumer data pending command for id %" PRIu64, id);

                ret = consumer_data_pending(id);

                /* Send back returned value to session daemon */
                ret = lttcomm_send_unix_sock(sock, &ret, sizeof(ret));
                if (ret < 0) {
                        PERROR("send data pending ret code");
                        goto error_fatal;
                }

                /*
                 * No need to send back a status message since the data pending
                 * returned value is the response.
                 */
                break;
        }
        case LTTNG_CONSUMER_SNAPSHOT_CHANNEL:
        {
                if (msg.u.snapshot_channel.metadata == 1) {
                        ret = lttng_kconsumer_snapshot_metadata(msg.u.snapshot_channel.key,
                                        msg.u.snapshot_channel.pathname,
                                        msg.u.snapshot_channel.relayd_id, ctx);
                        if (ret < 0) {
                                ERR("Snapshot metadata failed");
                                ret_code = LTTNG_ERR_KERN_META_FAIL;
                        }
                } else {
                        ret = lttng_kconsumer_snapshot_channel(msg.u.snapshot_channel.key,
                                        msg.u.snapshot_channel.pathname,
                                        msg.u.snapshot_channel.relayd_id,
                                        msg.u.snapshot_channel.max_stream_size,
                                        ctx);
                        if (ret < 0) {
                                ERR("Snapshot channel failed");
                                ret_code = LTTNG_ERR_KERN_CHAN_FAIL;
                        }
                }

                ret = consumer_send_status_msg(sock, ret_code);
                if (ret < 0) {
                        /* Somehow, the session daemon is not responding anymore. */
                        goto end_nosignal;
                }
                break;
        }
        case LTTNG_CONSUMER_DESTROY_CHANNEL:
        {
                uint64_t key = msg.u.destroy_channel.key;
                struct lttng_consumer_channel *channel;

                channel = consumer_find_channel(key);
                if (!channel) {
                        ERR("Kernel consumer destroy channel %" PRIu64 " not found", key);
                        ret_code = LTTNG_ERR_KERN_CHAN_NOT_FOUND;
                }

                ret = consumer_send_status_msg(sock, ret_code);
                if (ret < 0) {
                        /* Somehow, the session daemon is not responding anymore. */
                        goto end_nosignal;
                }

                /*
                 * This command should ONLY be issued for channel with streams set in
                 * no monitor mode.
                 */
                assert(!channel->monitor);

                /*
                 * The refcount should ALWAYS be 0 in the case of a channel in no
                 * monitor mode.
                 */
                assert(!uatomic_sub_return(&channel->refcount, 1));

                consumer_del_channel(channel);

                goto end_nosignal;
        }
        default:
                goto end_nosignal;
        }

end_nosignal:
        rcu_read_unlock();

        /*
         * Return 1 to indicate success since the 0 value can be a socket
         * shutdown during the recv() or send() call.
         */
        return 1;

error_fatal:
        rcu_read_unlock();
        /* This will issue a consumer stop. */
        return -1;
}

/*
 * Populate index values of a kernel stream. Values are set in big endian order.
 *
 * Return 0 on success or else a negative value.
 */
static int get_index_values(struct lttng_packet_index *index, int infd)
{
        int ret;

        ret = kernctl_get_timestamp_begin(infd, &index->timestamp_begin);
        if (ret < 0) {
                PERROR("kernctl_get_timestamp_begin");
                goto error;
        }
        index->timestamp_begin = htobe64(index->timestamp_begin);

        ret = kernctl_get_timestamp_end(infd, &index->timestamp_end);
        if (ret < 0) {
                PERROR("kernctl_get_timestamp_end");
                goto error;
        }
        index->timestamp_end = htobe64(index->timestamp_end);

        ret = kernctl_get_events_discarded(infd, &index->events_discarded);
        if (ret < 0) {
                PERROR("kernctl_get_events_discarded");
                goto error;
        }
        index->events_discarded = htobe64(index->events_discarded);

        ret = kernctl_get_content_size(infd, &index->content_size);
        if (ret < 0) {
                PERROR("kernctl_get_content_size");
                goto error;
        }
        index->content_size = htobe64(index->content_size);

        ret = kernctl_get_packet_size(infd, &index->packet_size);
        if (ret < 0) {
                PERROR("kernctl_get_packet_size");
                goto error;
        }
        index->packet_size = htobe64(index->packet_size);

        ret = kernctl_get_stream_id(infd, &index->stream_id);
        if (ret < 0) {
                PERROR("kernctl_get_stream_id");
                goto error;
        }
        index->stream_id = htobe64(index->stream_id);

error:
        return ret;
}

/*
 * Consume data on a file descriptor and write it on a trace file.
 */
ssize_t lttng_kconsumer_read_subbuffer(struct lttng_consumer_stream *stream,
                struct lttng_consumer_local_data *ctx)
{
        unsigned long len, subbuf_size, padding;
        int err, write_index = 1;
        ssize_t ret = 0;
        int infd = stream->wait_fd;
        struct lttng_packet_index index;

        DBG("In read_subbuffer (infd : %d)", infd);

        /* Get the next subbuffer */
        err = kernctl_get_next_subbuf(infd);
        if (err != 0) {
                /*
                 * This is a debug message even for single-threaded consumer,
                 * because poll() have more relaxed criterions than get subbuf,
                 * so get_subbuf may fail for short race windows where poll()
                 * would issue wakeups.
                 */
                DBG("Reserving sub buffer failed (everything is normal, "
                                "it is due to concurrency)");
                ret = -errno;
                goto end;
        }

        /* Get the full subbuffer size including padding */
        err = kernctl_get_padded_subbuf_size(infd, &len);
        if (err != 0) {
                perror("Getting sub-buffer len failed.");
                ret = -errno;
                goto end;
        }

        if (!stream->metadata_flag) {
                ret = get_index_values(&index, infd);
                if (ret < 0) {
                        goto end;
                }
        } else {
                write_index = 0;
        }

        switch (stream->chan->output) {
        case CONSUMER_CHANNEL_SPLICE:
                /*
                 * XXX: The lttng-modules splice "actor" does not handle copying
                 * partial pages hence only using the subbuffer size without the
                 * padding makes the splice fail.
                 */
                subbuf_size = len;
                padding = 0;

                /* splice the subbuffer to the tracefile */
                ret = lttng_consumer_on_read_subbuffer_splice(ctx, stream, subbuf_size,
                                padding, &index);
                /*
                 * XXX: Splice does not support network streaming so the return value
                 * is simply checked against subbuf_size and not like the mmap() op.
                 */
                if (ret != subbuf_size) {
                        /*
                         * display the error but continue processing to try
                         * to release the subbuffer
                         */
                        ERR("Error splicing to tracefile (ret: %zd != len: %lu)",
                                        ret, subbuf_size);
                        write_index = 0;
                }
                break;
        case CONSUMER_CHANNEL_MMAP:
                /* Get subbuffer size without padding */
                err = kernctl_get_subbuf_size(infd, &subbuf_size);
                if (err != 0) {
                        perror("Getting sub-buffer len failed.");
                        ret = -errno;
                        goto end;
                }

                /* Make sure the tracer is not gone mad on us! */
                assert(len >= subbuf_size);

                padding = len - subbuf_size;

                /* write the subbuffer to the tracefile */
                ret = lttng_consumer_on_read_subbuffer_mmap(ctx, stream, subbuf_size,
                                padding, &index);
                /*
                 * The mmap operation should write subbuf_size amount of data when
                 * network streaming or the full padding (len) size when we are _not_
                 * streaming.
                 */
                if ((ret != subbuf_size && stream->net_seq_idx != (uint64_t) -1ULL) ||
                                (ret != len && stream->net_seq_idx == (uint64_t) -1ULL)) {
                        /*
                         * Display the error but continue processing to try to release the
                         * subbuffer
                         */
                        ERR("Error writing to tracefile "
                                        "(ret: %zd != len: %lu != subbuf_size: %lu)",
                                        ret, len, subbuf_size);
                        write_index = 0;
                }
                break;
        default:
                ERR("Unknown output method");
                ret = -EPERM;
        }

        err = kernctl_put_next_subbuf(infd);
        if (err != 0) {
                if (errno == EFAULT) {
                        perror("Error in unreserving sub buffer\n");
                } else if (errno == EIO) {
                        /* Should never happen with newer LTTng versions */
                        perror("Reader has been pushed by the writer, last sub-buffer corrupted.");
                }
                ret = -errno;
                goto end;
        }

        /* Write index if needed. */
        if (!write_index) {
                goto end;
        }

        err = consumer_stream_write_index(stream, &index);
        if (err < 0) {
                goto end;
        }

end:
        return ret;
}

int lttng_kconsumer_on_recv_stream(struct lttng_consumer_stream *stream)
{
        int ret;

        assert(stream);

        /*
         * Don't create anything if this is set for streaming or should not be
         * monitored.
         */
        if (stream->net_seq_idx == (uint64_t) -1ULL && stream->chan->monitor) {
                ret = utils_create_stream_file(stream->chan->pathname, stream->name,
                                stream->chan->tracefile_size, stream->tracefile_count_current,
                                stream->uid, stream->gid, NULL);
                if (ret < 0) {
                        goto error;
                }
                stream->out_fd = ret;
                stream->tracefile_size_current = 0;

                if (!stream->metadata_flag) {
                        ret = index_create_file(stream->chan->pathname,
                                        stream->name, stream->uid, stream->gid,
                                        stream->chan->tracefile_size,
                                        stream->tracefile_count_current);
                        if (ret < 0) {
                                goto error;
                        }
                        stream->index_fd = ret;
                }
        }

        if (stream->output == LTTNG_EVENT_MMAP) {
                /* get the len of the mmap region */
                unsigned long mmap_len;

                ret = kernctl_get_mmap_len(stream->wait_fd, &mmap_len);
                if (ret != 0) {
                        PERROR("kernctl_get_mmap_len");
                        ret = -errno;
                        goto error_close_fd;
                }
                stream->mmap_len = (size_t) mmap_len;

                stream->mmap_base = mmap(NULL, stream->mmap_len, PROT_READ,
                                MAP_PRIVATE, stream->wait_fd, 0);
                if (stream->mmap_base == MAP_FAILED) {
                        PERROR("Error mmaping");
                        ret = -1;
                        goto error_close_fd;
                }
        }

        /* we return 0 to let the library handle the FD internally */
        return 0;

error_close_fd:
        if (stream->out_fd >= 0) {
                int err;

                err = close(stream->out_fd);
                assert(!err);
                stream->out_fd = -1;
        }
error:
        return ret;
}

/*
 * Check if data is still being extracted from the buffers for a specific
 * stream. Consumer data lock MUST be acquired before calling this function
 * and the stream lock.
 *
 * Return 1 if the traced data are still getting read else 0 meaning that the
 * data is available for trace viewer reading.
 */
int lttng_kconsumer_data_pending(struct lttng_consumer_stream *stream)
{
        int ret;

        assert(stream);

        if (stream->endpoint_status != CONSUMER_ENDPOINT_ACTIVE) {
                ret = 0;
                goto end;
        }

        ret = kernctl_get_next_subbuf(stream->wait_fd);
        if (ret == 0) {
                /* There is still data so let's put back this subbuffer. */
                ret = kernctl_put_subbuf(stream->wait_fd);
                assert(ret == 0);
                ret = 1;   /* Data is pending */
                goto end;
        }

        /* Data is NOT pending and ready to be read. */
        ret = 0;

end:
        return ret;
}