consumerd: cleanup: use buffer view interface for mmap read subbuf
[lttng-tools.git] / src / common / consumer / consumer.c
index 09f0f0983a37cef21893e263d0ab2528b1d709f5..d70a5d1d406b758e1b02cc61f22b440ee006a7b1 100644 (file)
@@ -1,20 +1,10 @@
 /*
- * Copyright (C) 2011 Julien Desfossez <julien.desfossez@polymtl.ca>
- *                      Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
- *               2012 - David Goulet <dgoulet@efficios.com>
+ * Copyright (C) 2011 Julien Desfossez <julien.desfossez@polymtl.ca>
+ * Copyright (C) 2011 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * Copyright (C) 2012 David Goulet <dgoulet@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.
+ * SPDX-License-Identifier: GPL-2.0-only
  *
- * 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 _LGPL_SOURCE
@@ -91,6 +81,20 @@ int consumer_quit;
 static struct lttng_ht *metadata_ht;
 static struct lttng_ht *data_ht;
 
+static const char *get_consumer_domain(void)
+{
+       switch (consumer_data.type) {
+       case LTTNG_CONSUMER_KERNEL:
+               return DEFAULT_KERNEL_TRACE_DIR;
+       case LTTNG_CONSUMER64_UST:
+               /* Fall-through. */
+       case LTTNG_CONSUMER32_UST:
+               return DEFAULT_UST_TRACE_DIR;
+       default:
+               abort();
+       }
+}
+
 /*
  * Notify a thread lttng pipe to poll back again. This usually means that some
  * global state has changed so we just send back the thread in a poll wait
@@ -603,6 +607,7 @@ struct lttng_consumer_stream *consumer_allocate_stream(uint64_t channel_key,
        stream->endpoint_status = CONSUMER_ENDPOINT_ACTIVE;
        stream->index_file = NULL;
        stream->last_sequence_number = -1ULL;
+       stream->rotate_position = -1ULL;
        pthread_mutex_init(&stream->lock, NULL);
        pthread_mutex_init(&stream->metadata_timer_lock, NULL);
 
@@ -709,11 +714,6 @@ void consumer_add_data_stream(struct lttng_consumer_stream *stream)
        pthread_mutex_unlock(&consumer_data.lock);
 }
 
-void consumer_del_data_stream(struct lttng_consumer_stream *stream)
-{
-       consumer_del_stream(stream, data_ht);
-}
-
 /*
  * Add relayd socket to global consumer data hashtable. RCU read side lock MUST
  * be acquired before calling this.
@@ -820,7 +820,7 @@ int consumer_send_relayd_stream(struct lttng_consumer_stream *stream,
                /* Add stream on the relayd */
                pthread_mutex_lock(&relayd->ctrl_sock_mutex);
                ret = relayd_add_stream(&relayd->control_sock, stream->name,
-                               path, &stream->relayd_stream_id,
+                               get_consumer_domain(), path, &stream->relayd_stream_id,
                                stream->chan->tracefile_size,
                                stream->chan->tracefile_count,
                                stream->trace_chunk);
@@ -1014,13 +1014,6 @@ int lttng_consumer_channel_set_trace_chunk(
                struct lttng_consumer_channel *channel,
                struct lttng_trace_chunk *new_trace_chunk)
 {
-       int ret = 0;
-       const bool is_local_trace = channel->relayd_id == -1ULL;
-       bool update_stream_trace_chunk;
-       struct cds_lfht_iter iter;
-       struct lttng_consumer_stream *stream;
-       unsigned long channel_hash;
-
        pthread_mutex_lock(&channel->lock);
        if (channel->is_deleted) {
                /*
@@ -1032,24 +1025,6 @@ int lttng_consumer_channel_set_trace_chunk(
                 */
                goto end;
        }
-       /*
-        * A stream can transition to a state where it and its channel
-        * no longer belong to a trace chunk. For instance, this happens when
-        * a session is rotated while it is inactive. After the rotation
-        * of an inactive session completes, the channel and its streams no
-        * longer belong to a trace chunk.
-        *
-        * However, if a session is stopped, rotated, and started again,
-        * the session daemon will create a new chunk and send it to its peers.
-        * In that case, the streams' transition to a new chunk can be performed
-        * immediately.
-        *
-        * This trace chunk transition could also be performed lazily when
-        * a buffer is consumed. However, creating the files here allows the
-        * consumer daemon to report any creation error to the session daemon
-        * and cause the start of the tracing session to fail.
-        */
-       update_stream_trace_chunk = !channel->trace_chunk && new_trace_chunk;
 
        /*
         * The acquisition of the reference cannot fail (barring
@@ -1065,59 +1040,9 @@ int lttng_consumer_channel_set_trace_chunk(
 
        lttng_trace_chunk_put(channel->trace_chunk);
        channel->trace_chunk = new_trace_chunk;
-       if (!is_local_trace || !new_trace_chunk) {
-               /* Not an error. */
-               goto end;
-       }
-
-       if (!update_stream_trace_chunk) {
-               goto end;
-       }
-
-       channel_hash = consumer_data.stream_per_chan_id_ht->hash_fct(
-                       &channel->key, lttng_ht_seed);
-       rcu_read_lock();
-       cds_lfht_for_each_entry_duplicate(consumer_data.stream_per_chan_id_ht->ht,
-                       channel_hash,
-                       consumer_data.stream_per_chan_id_ht->match_fct,
-                       &channel->key, &iter, stream, node_channel_id.node) {
-               bool acquired_reference, should_regenerate_metadata = false;
-
-               acquired_reference = lttng_trace_chunk_get(channel->trace_chunk);
-               assert(acquired_reference);
-
-               pthread_mutex_lock(&stream->lock);
-
-               /*
-                * On a transition from "no-chunk" to a new chunk, a metadata
-                * stream's content must be entirely dumped. This must occcur
-                * _after_ the creation of the metadata stream's output files
-                * as the consumption thread (not necessarily the one executing
-                * this) may start to consume during the call to
-                * consumer_metadata_stream_dump().
-                */
-               should_regenerate_metadata =
-                       stream->metadata_flag &&
-                       !stream->trace_chunk && channel->trace_chunk;
-               stream->trace_chunk = channel->trace_chunk;
-               ret = consumer_stream_create_output_files(stream, true);
-               if (ret) {
-                       pthread_mutex_unlock(&stream->lock);
-                       goto end_rcu_unlock;
-               }
-               if (should_regenerate_metadata) {
-                       ret = consumer_metadata_stream_dump(stream);
-               }
-               pthread_mutex_unlock(&stream->lock);
-               if (ret) {
-                       goto end_rcu_unlock;
-               }
-       }
-end_rcu_unlock:
-       rcu_read_unlock();
 end:
        pthread_mutex_unlock(&channel->lock);
-       return ret;
+       return 0;
 }
 
 /*
@@ -1745,18 +1670,19 @@ end:
  */
 ssize_t lttng_consumer_on_read_subbuffer_mmap(
                struct lttng_consumer_local_data *ctx,
-               struct lttng_consumer_stream *stream, unsigned long len,
+               struct lttng_consumer_stream *stream,
+               const struct lttng_buffer_view *buffer,
                unsigned long padding,
                struct ctf_packet_index *index)
 {
-       unsigned long mmap_offset;
-       void *mmap_base;
        ssize_t ret = 0;
        off_t orig_offset = stream->out_fd_offset;
        /* Default is on the disk */
        int outfd = stream->out_fd;
        struct consumer_relayd_sock_pair *relayd = NULL;
        unsigned int relayd_hang_up = 0;
+       const size_t subbuf_content_size = buffer->size - padding;
+       size_t write_len;
 
        /* RCU lock for the relayd pointer */
        rcu_read_lock();
@@ -1772,39 +1698,9 @@ ssize_t lttng_consumer_on_read_subbuffer_mmap(
                }
        }
 
-       /* get the offset inside the fd to mmap */
-       switch (consumer_data.type) {
-       case LTTNG_CONSUMER_KERNEL:
-               mmap_base = stream->mmap_base;
-               ret = kernctl_get_mmap_read_offset(stream->wait_fd, &mmap_offset);
-               if (ret < 0) {
-                       PERROR("tracer ctl get_mmap_read_offset");
-                       goto end;
-               }
-               break;
-       case LTTNG_CONSUMER32_UST:
-       case LTTNG_CONSUMER64_UST:
-               mmap_base = lttng_ustctl_get_mmap_base(stream);
-               if (!mmap_base) {
-                       ERR("read mmap get mmap base for stream %s", stream->name);
-                       ret = -EPERM;
-                       goto end;
-               }
-               ret = lttng_ustctl_get_mmap_read_offset(stream, &mmap_offset);
-               if (ret != 0) {
-                       PERROR("tracer ctl get_mmap_read_offset");
-                       ret = -EINVAL;
-                       goto end;
-               }
-               break;
-       default:
-               ERR("Unknown consumer_data type");
-               assert(0);
-       }
-
        /* Handle stream on the relayd if the output is on the network */
        if (relayd) {
-               unsigned long netlen = len;
+               unsigned long netlen = subbuf_content_size;
 
                /*
                 * Lock the control socket for the complete duration of the function
@@ -1842,10 +1738,10 @@ ssize_t lttng_consumer_on_read_subbuffer_mmap(
                                goto write_error;
                        }
                }
-       } else {
-               /* No streaming, we have to set the len with the full padding */
-               len += padding;
 
+               write_len = subbuf_content_size;
+       } else {
+               /* No streaming; we have to write the full padding. */
                if (stream->metadata_flag && stream->reset_metadata_flag) {
                        ret = utils_truncate_stream_file(stream->out_fd, 0);
                        if (ret < 0) {
@@ -1859,7 +1755,7 @@ ssize_t lttng_consumer_on_read_subbuffer_mmap(
                 * Check if we need to change the tracefile before writing the packet.
                 */
                if (stream->chan->tracefile_size > 0 &&
-                               (stream->tracefile_size_current + len) >
+                               (stream->tracefile_size_current + buffer->size) >
                                stream->chan->tracefile_size) {
                        ret = consumer_stream_rotate_output_files(stream);
                        if (ret) {
@@ -1868,19 +1764,21 @@ ssize_t lttng_consumer_on_read_subbuffer_mmap(
                        outfd = stream->out_fd;
                        orig_offset = 0;
                }
-               stream->tracefile_size_current += len;
+               stream->tracefile_size_current += buffer->size;
                if (index) {
                        index->offset = htobe64(stream->out_fd_offset);
                }
+
+               write_len = buffer->size;
        }
 
        /*
         * This call guarantee that len or less is returned. It's impossible to
         * receive a ret value that is bigger than len.
         */
-       ret = lttng_write(outfd, mmap_base + mmap_offset, len);
-       DBG("Consumer mmap write() ret %zd (len %lu)", ret, len);
-       if (ret < 0 || ((size_t) ret != len)) {
+       ret = lttng_write(outfd, buffer->data, write_len);
+       DBG("Consumer mmap write() ret %zd (len %lu)", ret, write_len);
+       if (ret < 0 || ((size_t) ret != write_len)) {
                /*
                 * Report error to caller if nothing was written else at least send the
                 * amount written.
@@ -1901,7 +1799,8 @@ ssize_t lttng_consumer_on_read_subbuffer_mmap(
                        DBG("Consumer mmap write detected relayd hang up");
                } else {
                        /* Unhandled error, print it and stop function right now. */
-                       PERROR("Error in write mmap (ret %zd != len %lu)", ret, len);
+                       PERROR("Error in write mmap (ret %zd != write_len %zu)", ret,
+                                       write_len);
                }
                goto write_error;
        }
@@ -1910,9 +1809,9 @@ ssize_t lttng_consumer_on_read_subbuffer_mmap(
        /* This call is useless on a socket so better save a syscall. */
        if (!relayd) {
                /* This won't block, but will start writeout asynchronously */
-               lttng_sync_file_range(outfd, stream->out_fd_offset, len,
+               lttng_sync_file_range(outfd, stream->out_fd_offset, write_len,
                                SYNC_FILE_RANGE_WRITE);
-               stream->out_fd_offset += len;
+               stream->out_fd_offset += write_len;
                lttng_consumer_sync_trace_file(stream, orig_offset);
        }
 
@@ -2254,6 +2153,7 @@ int lttng_consumer_recv_cmd(struct lttng_consumer_local_data *ctx,
        }
 }
 
+static
 void lttng_consumer_close_all_metadata(void)
 {
        switch (consumer_data.type) {
@@ -4018,15 +3918,33 @@ int consumer_flush_buffer(struct lttng_consumer_stream *stream, int producer_act
 
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
-               ret = kernctl_buffer_flush(stream->wait_fd);
-               if (ret < 0) {
-                       ERR("Failed to flush kernel stream");
-                       goto end;
+               if (producer_active) {
+                       ret = kernctl_buffer_flush(stream->wait_fd);
+                       if (ret < 0) {
+                               ERR("Failed to flush kernel stream");
+                               goto end;
+                       }
+               } else {
+                       ret = kernctl_buffer_flush_empty(stream->wait_fd);
+                       if (ret < 0) {
+                               /*
+                                * Doing a buffer flush which does not take into
+                                * account empty packets. This is not perfect,
+                                * but required as a fall-back when
+                                * "flush_empty" is not implemented by
+                                * lttng-modules.
+                                */
+                               ret = kernctl_buffer_flush(stream->wait_fd);
+                               if (ret < 0) {
+                                       ERR("Failed to flush kernel stream");
+                                       goto end;
+                               }
+                       }
                }
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
-               lttng_ustctl_flush_buffer(stream, producer_active);
+               lttng_ustconsumer_flush_buffer(stream, producer_active);
                break;
        default:
                ERR("Unknown consumer_data type");
@@ -4081,7 +3999,7 @@ int lttng_consumer_rotate_channel(struct lttng_consumer_channel *channel,
                        ht->hash_fct(&channel->key, lttng_ht_seed),
                        ht->match_fct, &channel->key, &iter.iter,
                        stream, node_channel_id.node) {
-               unsigned long consumed_pos;
+               unsigned long produced_pos = 0, consumed_pos = 0;
 
                health_code_update();
 
@@ -4094,65 +4012,95 @@ int lttng_consumer_rotate_channel(struct lttng_consumer_channel *channel,
                        rotating_to_new_chunk = false;
                }
 
-               ret = lttng_consumer_sample_snapshot_positions(stream);
-               if (ret < 0) {
-                       ERR("Failed to sample snapshot position during channel rotation");
-                       goto end_unlock_stream;
+               /*
+                * Do not flush an empty packet when rotating from a NULL trace
+                * chunk. The stream has no means to output data, and the prior
+                * rotation which rotated to NULL performed that side-effect already.
+                */
+               if (stream->trace_chunk) {
+                       /*
+                        * For metadata stream, do an active flush, which does not
+                        * produce empty packets. For data streams, empty-flush;
+                        * ensures we have at least one packet in each stream per trace
+                        * chunk, even if no data was produced.
+                        */
+                       ret = consumer_flush_buffer(stream, stream->metadata_flag ? 1 : 0);
+                       if (ret < 0) {
+                               ERR("Failed to flush stream %" PRIu64 " during channel rotation",
+                                               stream->key);
+                               goto end_unlock_stream;
+                       }
                }
 
-               ret = lttng_consumer_get_produced_snapshot(stream,
-                               &stream->rotate_position);
-               if (ret < 0) {
-                       ERR("Failed to sample produced position during channel rotation");
+               ret = lttng_consumer_take_snapshot(stream);
+               if (ret < 0 && ret != -ENODATA && ret != -EAGAIN) {
+                       ERR("Failed to sample snapshot position during channel rotation");
                        goto end_unlock_stream;
                }
+               if (!ret) {
+                       ret = lttng_consumer_get_produced_snapshot(stream,
+                                       &produced_pos);
+                       if (ret < 0) {
+                               ERR("Failed to sample produced position during channel rotation");
+                               goto end_unlock_stream;
+                       }
 
-               lttng_consumer_get_consumed_snapshot(stream,
-                               &consumed_pos);
-               if (consumed_pos == stream->rotate_position) {
+                       ret = lttng_consumer_get_consumed_snapshot(stream,
+                                       &consumed_pos);
+                       if (ret < 0) {
+                               ERR("Failed to sample consumed position during channel rotation");
+                               goto end_unlock_stream;
+                       }
+               }
+               /*
+                * Align produced position on the start-of-packet boundary of the first
+                * packet going into the next trace chunk.
+                */
+               produced_pos = ALIGN_FLOOR(produced_pos, stream->max_sb_size);
+               if (consumed_pos == produced_pos) {
+                       DBG("Set rotate ready for stream %" PRIu64 " produced = %lu consumed = %lu",
+                                       stream->key, produced_pos, consumed_pos);
                        stream->rotate_ready = true;
+               } else {
+                       DBG("Different consumed and produced positions "
+                                       "for stream %" PRIu64 " produced = %lu consumed = %lu",
+                                       stream->key, produced_pos, consumed_pos);
                }
-
                /*
-                * Active flush; has no effect if the production position
-                * is at a packet boundary.
+                * The rotation position is based on the packet_seq_num of the
+                * packet following the last packet that was consumed for this
+                * stream, incremented by the offset between produced and
+                * consumed positions. This rotation position is a lower bound
+                * (inclusive) at which the next trace chunk starts. Since it
+                * is a lower bound, it is OK if the packet_seq_num does not
+                * correspond exactly to the same packet identified by the
+                * consumed_pos, which can happen in overwrite mode.
                 */
-               ret = consumer_flush_buffer(stream, 1);
-               if (ret < 0) {
-                       ERR("Failed to flush stream %" PRIu64 " during channel rotation",
+               if (stream->sequence_number_unavailable) {
+                       /*
+                        * Rotation should never be performed on a session which
+                        * interacts with a pre-2.8 lttng-modules, which does
+                        * not implement packet sequence number.
+                        */
+                       ERR("Failure to rotate stream %" PRIu64 ": sequence number unavailable",
                                        stream->key);
+                       ret = -1;
                        goto end_unlock_stream;
                }
+               stream->rotate_position = stream->last_sequence_number + 1 +
+                               ((produced_pos - consumed_pos) / stream->max_sb_size);
+               DBG("Set rotation position for stream %" PRIu64 " at position %" PRIu64,
+                               stream->key, stream->rotate_position);
 
                if (!is_local_trace) {
                        /*
                         * The relay daemon control protocol expects a rotation
                         * position as "the sequence number of the first packet
-                        * _after_ the current trace chunk.
-                        *
-                        * At the moment when the positions of the buffers are
-                        * sampled, the production position does not necessarily
-                        * sit at a packet boundary. The 'active' flush
-                        * operation above will push the production position to
-                        * the next packet boundary _if_ it is not already
-                        * sitting at such a boundary.
-                        *
-                        * Assuming a current production position that is not
-                        * on the bound of a packet, the 'target' sequence
-                        * number is
-                        *   (consumed_pos / subbuffer_size) + 1
-                        * Note the '+ 1' to ensure the current packet is
-                        * part of the current trace chunk.
-                        *
-                        * However, if the production position is already at
-                        * a packet boundary, the '+ 1' is not necessary as the
-                        * last packet of the current chunk is already
-                        * 'complete'.
+                        * _after_ the current trace chunk".
                         */
                        const struct relayd_stream_rotation_position position = {
                                .stream_id = stream->relayd_stream_id,
-                               .rotate_at_seq_num = (stream->rotate_position / stream->max_sb_size) +
-                                       !!(stream->rotate_position % stream->max_sb_size),
+                               .rotate_at_seq_num = stream->rotate_position,
                        };
 
                        ret = lttng_dynamic_array_add_element(
@@ -4207,60 +4155,172 @@ end:
        return ret;
 }
 
-/*
- * Check if a stream is ready to be rotated after extracting it.
- *
- * Return 1 if it is ready for rotation, 0 if it is not, a negative value on
- * error. Stream lock must be held.
- */
-int lttng_consumer_stream_is_rotate_ready(struct lttng_consumer_stream *stream)
+static
+int consumer_clear_buffer(struct lttng_consumer_stream *stream)
 {
-       int ret;
-       unsigned long consumed_pos;
+       int ret = 0;
+       unsigned long consumed_pos_before, consumed_pos_after;
 
-       if (!stream->rotate_position && !stream->rotate_ready) {
-               ret = 0;
+       ret = lttng_consumer_sample_snapshot_positions(stream);
+       if (ret < 0) {
+               ERR("Taking snapshot positions");
                goto end;
        }
 
-       if (stream->rotate_ready) {
-               ret = 1;
+       ret = lttng_consumer_get_consumed_snapshot(stream, &consumed_pos_before);
+       if (ret < 0) {
+               ERR("Consumed snapshot position");
                goto end;
        }
 
-       /*
-        * If we don't have the rotate_ready flag, check the consumed position
-        * to determine if we need to rotate.
-        */
+       switch (consumer_data.type) {
+       case LTTNG_CONSUMER_KERNEL:
+               ret = kernctl_buffer_clear(stream->wait_fd);
+               if (ret < 0) {
+                       ERR("Failed to clear kernel stream (ret = %d)", ret);
+                       goto end;
+               }
+               break;
+       case LTTNG_CONSUMER32_UST:
+       case LTTNG_CONSUMER64_UST:
+               lttng_ustconsumer_clear_buffer(stream);
+               break;
+       default:
+               ERR("Unknown consumer_data type");
+               abort();
+       }
+
        ret = lttng_consumer_sample_snapshot_positions(stream);
        if (ret < 0) {
                ERR("Taking snapshot positions");
                goto end;
        }
-
-       ret = lttng_consumer_get_consumed_snapshot(stream, &consumed_pos);
+       ret = lttng_consumer_get_consumed_snapshot(stream, &consumed_pos_after);
        if (ret < 0) {
                ERR("Consumed snapshot position");
                goto end;
        }
+       DBG("clear: before: %lu after: %lu", consumed_pos_before, consumed_pos_after);
+end:
+       return ret;
+}
 
-       /* Rotate position not reached yet (with check for overflow). */
-       if ((long) (consumed_pos - stream->rotate_position) < 0) {
-               ret = 0;
-               goto end;
+static
+int consumer_clear_stream(struct lttng_consumer_stream *stream)
+{
+       int ret;
+
+       ret = consumer_flush_buffer(stream, 1);
+       if (ret < 0) {
+               ERR("Failed to flush stream %" PRIu64 " during channel clear",
+                               stream->key);
+               ret = LTTCOMM_CONSUMERD_FATAL;
+               goto error;
        }
-       ret = 1;
 
-end:
+       ret = consumer_clear_buffer(stream);
+       if (ret < 0) {
+               ERR("Failed to clear stream %" PRIu64 " during channel clear",
+                               stream->key);
+               ret = LTTCOMM_CONSUMERD_FATAL;
+               goto error;
+       }
+
+       ret = LTTCOMM_CONSUMERD_SUCCESS;
+error:
+       return ret;
+}
+
+static
+int consumer_clear_unmonitored_channel(struct lttng_consumer_channel *channel)
+{
+       int ret;
+       struct lttng_consumer_stream *stream;
+
+       rcu_read_lock();
+       pthread_mutex_lock(&channel->lock);
+       cds_list_for_each_entry(stream, &channel->streams.head, send_node) {
+               health_code_update();
+               pthread_mutex_lock(&stream->lock);
+               ret = consumer_clear_stream(stream);
+               if (ret) {
+                       goto error_unlock;
+               }
+               pthread_mutex_unlock(&stream->lock);
+       }
+       pthread_mutex_unlock(&channel->lock);
+       rcu_read_unlock();
+       return 0;
+
+error_unlock:
+       pthread_mutex_unlock(&stream->lock);
+       pthread_mutex_unlock(&channel->lock);
+       rcu_read_unlock();
        return ret;
 }
 
+/*
+ * Check if a stream is ready to be rotated after extracting it.
+ *
+ * Return 1 if it is ready for rotation, 0 if it is not, a negative value on
+ * error. Stream lock must be held.
+ */
+int lttng_consumer_stream_is_rotate_ready(struct lttng_consumer_stream *stream)
+{
+       DBG("Check is rotate ready for stream %" PRIu64
+                       " ready %u rotate_position %" PRIu64
+                       " last_sequence_number %" PRIu64,
+                       stream->key, stream->rotate_ready,
+                       stream->rotate_position, stream->last_sequence_number);
+       if (stream->rotate_ready) {
+               return 1;
+       }
+
+       /*
+        * If packet seq num is unavailable, it means we are interacting
+        * with a pre-2.8 lttng-modules which does not implement the
+        * sequence number. Rotation should never be used by sessiond in this
+        * scenario.
+        */
+       if (stream->sequence_number_unavailable) {
+               ERR("Internal error: rotation used on stream %" PRIu64
+                               " with unavailable sequence number",
+                               stream->key);
+               return -1;
+       }
+
+       if (stream->rotate_position == -1ULL ||
+                       stream->last_sequence_number == -1ULL) {
+               return 0;
+       }
+
+       /*
+        * Rotate position not reached yet. The stream rotate position is
+        * the position of the next packet belonging to the next trace chunk,
+        * but consumerd considers rotation ready when reaching the last
+        * packet of the current chunk, hence the "rotate_position - 1".
+        */
+
+       DBG("Check is rotate ready for stream %" PRIu64
+                       " last_sequence_number %" PRIu64
+                       " rotate_position %" PRIu64,
+                       stream->key, stream->last_sequence_number,
+                       stream->rotate_position);
+       if (stream->last_sequence_number >= stream->rotate_position - 1) {
+               return 1;
+       }
+
+       return 0;
+}
+
 /*
  * Reset the state for a stream after a rotation occurred.
  */
 void lttng_consumer_reset_stream_rotate_state(struct lttng_consumer_stream *stream)
 {
-       stream->rotate_position = 0;
+       DBG("lttng_consumer_reset_stream_rotate_state for stream %" PRIu64,
+                       stream->key);
+       stream->rotate_position = -1ULL;
        stream->rotate_ready = false;
 }
 
@@ -4435,7 +4495,7 @@ enum lttcomm_return_code lttng_consumer_init_command(
                const lttng_uuid sessiond_uuid)
 {
        enum lttcomm_return_code ret;
-       char uuid_str[UUID_STR_LEN];
+       char uuid_str[LTTNG_UUID_STR_LEN];
 
        if (ctx->sessiond_uuid.is_set) {
                ret = LTTCOMM_CONSUMERD_ALREADY_SET;
@@ -4512,7 +4572,7 @@ enum lttcomm_return_code lttng_consumer_create_trace_chunk(
         * and LTTNG_CONSUMER_DESTROY_TRACE_CHUNK commands.
         */
        created_chunk = lttng_trace_chunk_create(chunk_id,
-                       chunk_creation_timestamp);
+                       chunk_creation_timestamp, NULL);
        if (!created_chunk) {
                ERR("Failed to create trace chunk");
                ret_code = LTTCOMM_CONSUMERD_CREATE_TRACE_CHUNK_FAILED;
@@ -4542,6 +4602,7 @@ enum lttcomm_return_code lttng_consumer_create_trace_chunk(
                 */
                chunk_status = lttng_trace_chunk_set_as_user(created_chunk,
                                chunk_directory_handle);
+               chunk_directory_handle = NULL;
                if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                        ERR("Failed to set trace chunk's directory handle");
                        ret_code = LTTCOMM_CONSUMERD_CREATE_TRACE_CHUNK_FAILED;
@@ -4842,3 +4903,67 @@ end_rcu_unlock:
 end:
        return ret_code;
 }
+
+static
+int consumer_clear_monitored_channel(struct lttng_consumer_channel *channel)
+{
+       struct lttng_ht *ht;
+       struct lttng_consumer_stream *stream;
+       struct lttng_ht_iter iter;
+       int ret;
+
+       ht = consumer_data.stream_per_chan_id_ht;
+
+       rcu_read_lock();
+       cds_lfht_for_each_entry_duplicate(ht->ht,
+                       ht->hash_fct(&channel->key, lttng_ht_seed),
+                       ht->match_fct, &channel->key,
+                       &iter.iter, stream, node_channel_id.node) {
+               /*
+                * Protect against teardown with mutex.
+                */
+               pthread_mutex_lock(&stream->lock);
+               if (cds_lfht_is_node_deleted(&stream->node.node)) {
+                       goto next;
+               }
+               ret = consumer_clear_stream(stream);
+               if (ret) {
+                       goto error_unlock;
+               }
+       next:
+               pthread_mutex_unlock(&stream->lock);
+       }
+       rcu_read_unlock();
+       return LTTCOMM_CONSUMERD_SUCCESS;
+
+error_unlock:
+       pthread_mutex_unlock(&stream->lock);
+       rcu_read_unlock();
+       return ret;
+}
+
+int lttng_consumer_clear_channel(struct lttng_consumer_channel *channel)
+{
+       int ret;
+
+       DBG("Consumer clear channel %" PRIu64, channel->key);
+
+       if (channel->type == CONSUMER_CHANNEL_TYPE_METADATA) {
+               /*
+                * Nothing to do for the metadata channel/stream.
+                * Snapshot mechanism already take care of the metadata
+                * handling/generation, and monitored channels only need to
+                * have their data stream cleared..
+                */
+               ret = LTTCOMM_CONSUMERD_SUCCESS;
+               goto end;
+       }
+
+       if (!channel->monitor) {
+               ret = consumer_clear_unmonitored_channel(channel);
+       } else {
+               ret = consumer_clear_monitored_channel(channel);
+       }
+end:
+       return ret;
+}
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