cmd.c: fix typos in snapshot commands
[lttng-tools.git] / src / bin / lttng-sessiond / cmd.c
index d36966322fc7278617109b9df471bda8196ea5cc..a351d63de706b8843c7b16059f45ba2173b91e6c 100644 (file)
@@ -17,6 +17,7 @@
 
 #define _GNU_SOURCE
 #include <assert.h>
+#include <inttypes.h>
 #include <urcu/list.h>
 #include <urcu/uatomic.h>
 
 #include <common/common.h>
 #include <common/sessiond-comm/sessiond-comm.h>
 #include <common/relayd/relayd.h>
+#include <common/utils.h>
 
 #include "channel.h"
 #include "consumer.h"
 #include "event.h"
+#include "health.h"
 #include "kernel.h"
 #include "kernel-consumer.h"
 #include "lttng-sessiond.h"
 /*
  * Used to keep a unique index for each relayd socket created where this value
  * is associated with streams on the consumer so it can match the right relayd
- * to send to.
- *
- * This value should be incremented atomically for safety purposes and future
- * possible concurrent access.
+ * to send to. It must be accessed with the relayd_net_seq_idx_lock
+ * held.
  */
-static unsigned int relayd_net_seq_idx;
+static pthread_mutex_t relayd_net_seq_idx_lock = PTHREAD_MUTEX_INITIALIZER;
+static uint64_t relayd_net_seq_idx;
 
 /*
  * Create a session path used by list_lttng_sessions for the case that the
@@ -101,11 +103,22 @@ static int build_network_session_path(char *dst, size_t size,
                goto error;
        }
 
-       if (strlen(tmp_uurl) > 0) {
+       /*
+        * Do we have a UST url set. If yes, this means we have both kernel and UST
+        * to print.
+        */
+       if (*tmp_uurl != '\0') {
                ret = snprintf(dst, size, "[K]: %s [data: %d] -- [U]: %s [data: %d]",
                                tmp_urls, kdata_port, tmp_uurl, udata_port);
        } else {
-               ret = snprintf(dst, size, "%s [data: %d]", tmp_urls, kdata_port);
+               int dport;
+               if (kuri || (!kuri && !uuri)) {
+                       dport = kdata_port;
+               } else {
+                       /* No kernel URI, use the UST port. */
+                       dport = udata_port;
+               }
+               ret = snprintf(dst, size, "%s [data: %d]", tmp_urls, dport);
        }
 
 error:
@@ -141,6 +154,7 @@ static void list_lttng_channels(int domain, struct ltt_session *session,
                struct lttng_ht_iter iter;
                struct ltt_ust_channel *uchan;
 
+               rcu_read_lock();
                cds_lfht_for_each_entry(session->ust_session->domain_global.channels->ht,
                                &iter.iter, uchan, node.node) {
                        strncpy(channels[i].name, uchan->name, LTTNG_SYMBOL_NAME_LEN);
@@ -160,6 +174,7 @@ static void list_lttng_channels(int domain, struct ltt_session *session,
                        }
                        i++;
                }
+               rcu_read_unlock();
                break;
        }
        default:
@@ -188,7 +203,7 @@ static int list_lttng_ust_global_events(char *channel_name,
        lttng_ht_lookup(ust_global->channels, (void *)channel_name, &iter);
        node = lttng_ht_iter_get_node_str(&iter);
        if (node == NULL) {
-               ret = -LTTCOMM_UST_CHAN_NOT_FOUND;
+               ret = LTTNG_ERR_UST_CHAN_NOT_FOUND;
                goto error;
        }
 
@@ -205,7 +220,7 @@ static int list_lttng_ust_global_events(char *channel_name,
 
        tmp = zmalloc(nb_event * sizeof(struct lttng_event));
        if (tmp == NULL) {
-               ret = -LTTCOMM_FATAL;
+               ret = LTTNG_ERR_FATAL;
                goto error;
        }
 
@@ -265,7 +280,7 @@ static int list_lttng_kernel_events(char *channel_name,
 
        kchan = trace_kernel_get_channel_by_name(channel_name, kernel_session);
        if (kchan == NULL) {
-               ret = LTTCOMM_KERN_CHAN_NOT_FOUND;
+               ret = LTTNG_ERR_KERN_CHAN_NOT_FOUND;
                goto error;
        }
 
@@ -274,13 +289,12 @@ static int list_lttng_kernel_events(char *channel_name,
        DBG("Listing events for channel %s", kchan->channel->name);
 
        if (nb_event == 0) {
-               ret = nb_event;
-               goto error;
+               goto end;
        }
 
        *events = zmalloc(nb_event * sizeof(struct lttng_event));
        if (*events == NULL) {
-               ret = LTTCOMM_FATAL;
+               ret = LTTNG_ERR_FATAL;
                goto error;
        }
 
@@ -294,8 +308,12 @@ static int list_lttng_kernel_events(char *channel_name,
                case LTTNG_KERNEL_TRACEPOINT:
                        (*events)[i].type = LTTNG_EVENT_TRACEPOINT;
                        break;
-               case LTTNG_KERNEL_KPROBE:
                case LTTNG_KERNEL_KRETPROBE:
+                       (*events)[i].type = LTTNG_EVENT_FUNCTION;
+                       memcpy(&(*events)[i].attr.probe, &event->event->u.kprobe,
+                                       sizeof(struct lttng_kernel_kprobe));
+                       break;
+               case LTTNG_KERNEL_KPROBE:
                        (*events)[i].type = LTTNG_EVENT_PROBE;
                        memcpy(&(*events)[i].attr.probe, &event->event->u.kprobe,
                                        sizeof(struct lttng_kernel_kprobe));
@@ -318,10 +336,12 @@ static int list_lttng_kernel_events(char *channel_name,
                i++;
        }
 
+end:
        return nb_event;
 
 error:
-       return ret;
+       /* Negate the error code to differentiate the size from an error */
+       return -ret;
 }
 
 /*
@@ -331,14 +351,14 @@ error:
 static int add_uri_to_consumer(struct consumer_output *consumer,
                struct lttng_uri *uri, int domain, const char *session_name)
 {
-       int ret = LTTCOMM_OK;
+       int ret = LTTNG_OK;
        const char *default_trace_dir;
 
        assert(uri);
 
        if (consumer == NULL) {
                DBG("No consumer detected. Don't add URI. Stopping.");
-               ret = LTTCOMM_NO_CONSUMER;
+               ret = LTTNG_ERR_NO_CONSUMER;
                goto error;
        }
 
@@ -362,10 +382,24 @@ static int add_uri_to_consumer(struct consumer_output *consumer,
        case LTTNG_DST_IPV6:
                DBG2("Setting network URI to consumer");
 
+               if (consumer->type == CONSUMER_DST_NET) {
+                       if ((uri->stype == LTTNG_STREAM_CONTROL &&
+                               consumer->dst.net.control_isset) ||
+                               (uri->stype == LTTNG_STREAM_DATA &&
+                               consumer->dst.net.data_isset)) {
+                               ret = LTTNG_ERR_URL_EXIST;
+                               goto error;
+                       }
+               } else {
+                       memset(&consumer->dst.net, 0, sizeof(consumer->dst.net));
+               }
+
+               consumer->type = CONSUMER_DST_NET;
+
                /* Set URI into consumer output object */
                ret = consumer_set_network_uri(consumer, uri);
                if (ret < 0) {
-                       ret = LTTCOMM_FATAL;
+                       ret = -ret;
                        goto error;
                } else if (ret == 1) {
                        /*
@@ -378,14 +412,15 @@ static int add_uri_to_consumer(struct consumer_output *consumer,
                if (uri->stype == LTTNG_STREAM_CONTROL && strlen(uri->subdir) == 0) {
                        ret = consumer_set_subdir(consumer, session_name);
                        if (ret < 0) {
-                               ret = LTTCOMM_FATAL;
+                               ret = LTTNG_ERR_FATAL;
                                goto error;
                        }
                }
 
                if (uri->stype == LTTNG_STREAM_CONTROL) {
                        /* On a new subdir, reappend the default trace dir. */
-                       strncat(consumer->subdir, default_trace_dir, sizeof(consumer->subdir));
+                       strncat(consumer->subdir, default_trace_dir,
+                                       sizeof(consumer->subdir) - strlen(consumer->subdir) - 1);
                        DBG3("Append domain trace name to subdir %s", consumer->subdir);
                }
 
@@ -398,12 +433,15 @@ static int add_uri_to_consumer(struct consumer_output *consumer,
                                sizeof(consumer->dst.trace_path));
                /* Append default trace dir */
                strncat(consumer->dst.trace_path, default_trace_dir,
-                               sizeof(consumer->dst.trace_path));
+                               sizeof(consumer->dst.trace_path) -
+                               strlen(consumer->dst.trace_path) - 1);
                /* Flag consumer as local. */
                consumer->type = CONSUMER_DST_LOCAL;
                break;
        }
 
+       ret = LTTNG_OK;
+
 error:
        return ret;
 }
@@ -419,6 +457,8 @@ static int init_kernel_tracing(struct ltt_kernel_session *session)
 
        assert(session);
 
+       rcu_read_lock();
+
        if (session->consumer_fds_sent == 0 && session->consumer != NULL) {
                cds_lfht_for_each_entry(session->consumer->socks->ht, &iter.iter,
                                socket, node.node) {
@@ -426,16 +466,17 @@ static int init_kernel_tracing(struct ltt_kernel_session *session)
                        assert(socket->fd >= 0);
 
                        pthread_mutex_lock(socket->lock);
-                       ret = kernel_consumer_send_session(socket->fd, session);
+                       ret = kernel_consumer_send_session(socket, session);
                        pthread_mutex_unlock(socket->lock);
                        if (ret < 0) {
-                               ret = LTTCOMM_KERN_CONSUMER_FAIL;
+                               ret = LTTNG_ERR_KERN_CONSUMER_FAIL;
                                goto error;
                        }
                }
        }
 
 error:
+       rcu_read_unlock();
        return ret;
 }
 
@@ -445,31 +486,30 @@ error:
  * On success, the relayd_sock pointer is set to the created socket.
  * Else, it's stays untouched and a lttcomm error code is returned.
  */
-static int create_connect_relayd(struct consumer_output *output,
-               const char *session_name, struct lttng_uri *uri,
-               struct lttcomm_sock **relayd_sock)
+static int create_connect_relayd(struct lttng_uri *uri,
+               struct lttcomm_relayd_sock **relayd_sock)
 {
        int ret;
-       struct lttcomm_sock *sock;
-
-       /* Create socket object from URI */
-       sock = lttcomm_alloc_sock_from_uri(uri);
-       if (sock == NULL) {
-               ret = LTTCOMM_FATAL;
-               goto error;
-       }
+       struct lttcomm_relayd_sock *rsock;
 
-       ret = lttcomm_create_sock(sock);
-       if (ret < 0) {
-               ret = LTTCOMM_FATAL;
+       rsock = lttcomm_alloc_relayd_sock(uri, RELAYD_VERSION_COMM_MAJOR,
+                       RELAYD_VERSION_COMM_MINOR);
+       if (!rsock) {
+               ret = LTTNG_ERR_FATAL;
                goto error;
        }
 
-       /* Connect to relayd so we can proceed with a session creation. */
-       ret = relayd_connect(sock);
+       /*
+        * Connect to relayd so we can proceed with a session creation. This call
+        * can possibly block for an arbitrary amount of time to set the health
+        * state to be in poll execution.
+        */
+       health_poll_entry();
+       ret = relayd_connect(rsock);
+       health_poll_exit();
        if (ret < 0) {
                ERR("Unable to reach lttng-relayd");
-               ret = LTTCOMM_RELAYD_SESSION_FAIL;
+               ret = LTTNG_ERR_RELAYD_CONNECT_FAIL;
                goto free_sock;
        }
 
@@ -478,10 +518,9 @@ static int create_connect_relayd(struct consumer_output *output,
                DBG3("Creating relayd stream socket from URI");
 
                /* Check relayd version */
-               ret = relayd_version_check(sock, RELAYD_VERSION_COMM_MAJOR,
-                               RELAYD_VERSION_COMM_MINOR);
+               ret = relayd_version_check(rsock);
                if (ret < 0) {
-                       ret = LTTCOMM_RELAYD_VERSION_FAIL;
+                       ret = LTTNG_ERR_RELAYD_VERSION_FAIL;
                        goto close_sock;
                }
        } else if (uri->stype == LTTNG_STREAM_DATA) {
@@ -489,22 +528,19 @@ static int create_connect_relayd(struct consumer_output *output,
        } else {
                /* Command is not valid */
                ERR("Relayd invalid stream type: %d", uri->stype);
-               ret = LTTCOMM_INVALID;
+               ret = LTTNG_ERR_INVALID;
                goto close_sock;
        }
 
-       *relayd_sock = sock;
+       *relayd_sock = rsock;
 
-       return LTTCOMM_OK;
+       return LTTNG_OK;
 
 close_sock:
-       if (sock) {
-               (void) relayd_close(sock);
-       }
+       /* The returned value is not useful since we are on an error path. */
+       (void) relayd_close(rsock);
 free_sock:
-       if (sock) {
-               lttcomm_destroy_sock(sock);
-       }
+       free(rsock);
 error:
        return ret;
 }
@@ -512,45 +548,48 @@ error:
 /*
  * Connect to the relayd using URI and send the socket to the right consumer.
  */
-static int send_consumer_relayd_socket(int domain, struct ltt_session *session,
+static int send_consumer_relayd_socket(int domain, unsigned int session_id,
                struct lttng_uri *relayd_uri, struct consumer_output *consumer,
-               int consumer_fd)
+               struct consumer_socket *consumer_sock)
 {
        int ret;
-       struct lttcomm_sock *sock = NULL;
+       struct lttcomm_relayd_sock *rsock = NULL;
+
+       /* Connect to relayd and make version check if uri is the control. */
+       ret = create_connect_relayd(relayd_uri, &rsock);
+       if (ret != LTTNG_OK) {
+               goto error;
+       }
+       assert(rsock);
 
        /* Set the network sequence index if not set. */
-       if (consumer->net_seq_index == -1) {
+       if (consumer->net_seq_index == (uint64_t) -1ULL) {
+               pthread_mutex_lock(&relayd_net_seq_idx_lock);
                /*
                 * Increment net_seq_idx because we are about to transfer the
                 * new relayd socket to the consumer.
+                * Assign unique key so the consumer can match streams.
                 */
-               uatomic_inc(&relayd_net_seq_idx);
-               /* Assign unique key so the consumer can match streams */
-               uatomic_set(&consumer->net_seq_index,
-                               uatomic_read(&relayd_net_seq_idx));
+               consumer->net_seq_index = ++relayd_net_seq_idx;
+               pthread_mutex_unlock(&relayd_net_seq_idx_lock);
        }
 
-       /* Connect to relayd and make version check if uri is the control. */
-       ret = create_connect_relayd(consumer, session->name, relayd_uri, &sock);
-       if (ret != LTTCOMM_OK) {
+       /* Send relayd socket to consumer. */
+       ret = consumer_send_relayd_socket(consumer_sock, rsock, consumer,
+                       relayd_uri->stype, session_id);
+       if (ret < 0) {
+               ret = LTTNG_ERR_ENABLE_CONSUMER_FAIL;
                goto close_sock;
        }
 
-       /* If the control socket is connected, network session is ready */
+       /* Flag that the corresponding socket was sent. */
        if (relayd_uri->stype == LTTNG_STREAM_CONTROL) {
-               session->net_handle = 1;
-       }
-
-       /* Send relayd socket to consumer. */
-       ret = consumer_send_relayd_socket(consumer_fd, sock,
-                       consumer, relayd_uri->stype);
-       if (ret < 0) {
-               ret = LTTCOMM_ENABLE_CONSUMER_FAIL;
-               goto close_sock;
+               consumer_sock->control_sock_sent = 1;
+       } else if (relayd_uri->stype == LTTNG_STREAM_DATA) {
+               consumer_sock->data_sock_sent = 1;
        }
 
-       ret = LTTCOMM_OK;
+       ret = LTTNG_OK;
 
        /*
         * Close socket which was dup on the consumer side. The session daemon does
@@ -558,11 +597,18 @@ static int send_consumer_relayd_socket(int domain, struct ltt_session *session,
         */
 
 close_sock:
-       if (sock) {
-               (void) relayd_close(sock);
-               lttcomm_destroy_sock(sock);
-       }
+       (void) relayd_close(rsock);
+       free(rsock);
 
+error:
+       if (ret != LTTNG_OK) {
+               /*
+                * The consumer output for this session should not be used anymore
+                * since the relayd connection failed thus making any tracing or/and
+                * streaming not usable.
+                */
+               consumer->enabled = 0;
+       }
        return ret;
 }
 
@@ -571,37 +617,32 @@ close_sock:
  * helper function to facilitate sending the information to the consumer for a
  * session.
  */
-static int send_consumer_relayd_sockets(int domain,
-               struct ltt_session *session, struct consumer_output *consumer, int fd)
+static int send_consumer_relayd_sockets(int domain, unsigned int session_id,
+               struct consumer_output *consumer, struct consumer_socket *sock)
 {
-       int ret;
+       int ret = LTTNG_OK;
 
-       assert(session);
        assert(consumer);
-
-       /* Don't resend the sockets to the consumer. */
-       if (consumer->dst.net.relayd_socks_sent) {
-               ret = LTTCOMM_OK;
-               goto error;
-       }
+       assert(sock);
 
        /* Sending control relayd socket. */
-       ret = send_consumer_relayd_socket(domain, session,
-                       &consumer->dst.net.control, consumer, fd);
-       if (ret != LTTCOMM_OK) {
-               goto error;
+       if (!sock->control_sock_sent) {
+               ret = send_consumer_relayd_socket(domain, session_id,
+                               &consumer->dst.net.control, consumer, sock);
+               if (ret != LTTNG_OK) {
+                       goto error;
+               }
        }
 
        /* Sending data relayd socket. */
-       ret = send_consumer_relayd_socket(domain, session,
-                       &consumer->dst.net.data, consumer, fd);
-       if (ret != LTTCOMM_OK) {
-               goto error;
+       if (!sock->data_sock_sent) {
+               ret = send_consumer_relayd_socket(domain, session_id,
+                               &consumer->dst.net.data, consumer, sock);
+               if (ret != LTTNG_OK) {
+                       goto error;
+               }
        }
 
-       /* Flag that all relayd sockets were sent to the consumer. */
-       consumer->dst.net.relayd_socks_sent = 1;
-
 error:
        return ret;
 }
@@ -611,9 +652,9 @@ error:
  * the relayd and send them to the right domain consumer. Consumer type MUST be
  * network.
  */
-static int setup_relayd(struct ltt_session *session)
+int cmd_setup_relayd(struct ltt_session *session)
 {
-       int ret = LTTCOMM_OK;
+       int ret = LTTNG_OK;
        struct ltt_ust_session *usess;
        struct ltt_kernel_session *ksess;
        struct consumer_socket *socket;
@@ -624,7 +665,9 @@ static int setup_relayd(struct ltt_session *session)
        usess = session->ust_session;
        ksess = session->kernel_session;
 
-       DBG2("Setting relayd for session %s", session->name);
+       DBG("Setting relayd for session %s", session->name);
+
+       rcu_read_lock();
 
        if (usess && usess->consumer && usess->consumer->type == CONSUMER_DST_NET
                        && usess->consumer->enabled) {
@@ -635,12 +678,14 @@ static int setup_relayd(struct ltt_session *session)
                        assert(socket->fd >= 0);
 
                        pthread_mutex_lock(socket->lock);
-                       send_consumer_relayd_sockets(LTTNG_DOMAIN_UST, session,
-                                       usess->consumer, socket->fd);
+                       ret = send_consumer_relayd_sockets(LTTNG_DOMAIN_UST, session->id,
+                                       usess->consumer, socket);
                        pthread_mutex_unlock(socket->lock);
-                       if (ret != LTTCOMM_OK) {
+                       if (ret != LTTNG_OK) {
                                goto error;
                        }
+                       /* Session is now ready for network streaming. */
+                       session->net_handle = 1;
                }
        }
 
@@ -652,15 +697,83 @@ static int setup_relayd(struct ltt_session *session)
                        assert(socket->fd >= 0);
 
                        pthread_mutex_lock(socket->lock);
-                       send_consumer_relayd_sockets(LTTNG_DOMAIN_KERNEL, session,
-                                       ksess->consumer, socket->fd);
+                       ret = send_consumer_relayd_sockets(LTTNG_DOMAIN_KERNEL, session->id,
+                                       ksess->consumer, socket);
                        pthread_mutex_unlock(socket->lock);
-                       if (ret != LTTCOMM_OK) {
+                       if (ret != LTTNG_OK) {
+                               goto error;
+                       }
+                       /* Session is now ready for network streaming. */
+                       session->net_handle = 1;
+               }
+       }
+
+error:
+       rcu_read_unlock();
+       return ret;
+}
+
+/*
+ * Start a kernel session by opening all necessary streams.
+ */
+static int start_kernel_session(struct ltt_kernel_session *ksess, int wpipe)
+{
+       int ret;
+       struct ltt_kernel_channel *kchan;
+
+       /* Open kernel metadata */
+       if (ksess->metadata == NULL && ksess->output_traces) {
+               ret = kernel_open_metadata(ksess);
+               if (ret < 0) {
+                       ret = LTTNG_ERR_KERN_META_FAIL;
+                       goto error;
+               }
+       }
+
+       /* Open kernel metadata stream */
+       if (ksess->metadata && ksess->metadata_stream_fd < 0) {
+               ret = kernel_open_metadata_stream(ksess);
+               if (ret < 0) {
+                       ERR("Kernel create metadata stream failed");
+                       ret = LTTNG_ERR_KERN_STREAM_FAIL;
+                       goto error;
+               }
+       }
+
+       /* For each channel */
+       cds_list_for_each_entry(kchan, &ksess->channel_list.head, list) {
+               if (kchan->stream_count == 0) {
+                       ret = kernel_open_channel_stream(kchan);
+                       if (ret < 0) {
+                               ret = LTTNG_ERR_KERN_STREAM_FAIL;
                                goto error;
                        }
+                       /* Update the stream global counter */
+                       ksess->stream_count_global += ret;
                }
        }
 
+       /* Setup kernel consumer socket and send fds to it */
+       ret = init_kernel_tracing(ksess);
+       if (ret != 0) {
+               ret = LTTNG_ERR_KERN_START_FAIL;
+               goto error;
+       }
+
+       /* This start the kernel tracing */
+       ret = kernel_start_session(ksess);
+       if (ret < 0) {
+               ret = LTTNG_ERR_KERN_START_FAIL;
+               goto error;
+       }
+
+       /* Quiescent wait after starting trace */
+       kernel_wait_quiescent(kernel_tracer_fd);
+
+       ksess->started = 1;
+
+       ret = LTTNG_OK;
+
 error:
        return ret;
 }
@@ -676,12 +789,14 @@ int cmd_disable_channel(struct ltt_session *session, int domain,
 
        usess = session->ust_session;
 
+       rcu_read_lock();
+
        switch (domain) {
        case LTTNG_DOMAIN_KERNEL:
        {
                ret = channel_kernel_disable(session->kernel_session,
                                channel_name);
-               if (ret != LTTCOMM_OK) {
+               if (ret != LTTNG_OK) {
                        goto error;
                }
 
@@ -697,12 +812,12 @@ int cmd_disable_channel(struct ltt_session *session, int domain,
 
                uchan = trace_ust_find_channel_by_name(chan_ht, channel_name);
                if (uchan == NULL) {
-                       ret = LTTCOMM_UST_CHAN_NOT_FOUND;
+                       ret = LTTNG_ERR_UST_CHAN_NOT_FOUND;
                        goto error;
                }
 
-               ret = channel_ust_disable(usess, domain, uchan);
-               if (ret != LTTCOMM_OK) {
+               ret = channel_ust_disable(usess, uchan);
+               if (ret != LTTNG_OK) {
                        goto error;
                }
                break;
@@ -713,13 +828,14 @@ int cmd_disable_channel(struct ltt_session *session, int domain,
        case LTTNG_DOMAIN_UST_PID:
 #endif
        default:
-               ret = LTTCOMM_UNKNOWN_DOMAIN;
+               ret = LTTNG_ERR_UNKNOWN_DOMAIN;
                goto error;
        }
 
-       ret = LTTCOMM_OK;
+       ret = LTTNG_OK;
 
 error:
+       rcu_read_unlock();
        return ret;
 }
 
@@ -729,7 +845,7 @@ error:
  * The wpipe arguments is used as a notifier for the kernel thread.
  */
 int cmd_enable_channel(struct ltt_session *session,
-               int domain, struct lttng_channel *attr, int wpipe)
+               struct lttng_domain *domain, struct lttng_channel *attr, int wpipe)
 {
        int ret;
        struct ltt_ust_session *usess = session->ust_session;
@@ -737,17 +853,26 @@ int cmd_enable_channel(struct ltt_session *session,
 
        assert(session);
        assert(attr);
+       assert(domain);
 
        DBG("Enabling channel %s for session %s", attr->name, session->name);
 
-       switch (domain) {
+       rcu_read_lock();
+
+       /*
+        * Don't try to enable a channel if the session has been started at
+        * some point in time before. The tracer does not allow it.
+        */
+       if (session->started) {
+               ret = LTTNG_ERR_TRACE_ALREADY_STARTED;
+               goto error;
+       }
+
+       switch (domain->type) {
        case LTTNG_DOMAIN_KERNEL:
        {
                struct ltt_kernel_channel *kchan;
 
-               /* Mandatory for a kernel channel. */
-               assert(wpipe > 0);
-
                kchan = trace_kernel_get_channel_by_name(attr->name,
                                session->kernel_session);
                if (kchan == NULL) {
@@ -756,7 +881,7 @@ int cmd_enable_channel(struct ltt_session *session,
                        ret = channel_kernel_enable(session->kernel_session, kchan);
                }
 
-               if (ret != LTTCOMM_OK) {
+               if (ret != LTTNG_OK) {
                        goto error;
                }
 
@@ -771,23 +896,19 @@ int cmd_enable_channel(struct ltt_session *session,
 
                uchan = trace_ust_find_channel_by_name(chan_ht, attr->name);
                if (uchan == NULL) {
-                       ret = channel_ust_create(usess, domain, attr);
+                       ret = channel_ust_create(usess, attr, domain->buf_type);
                } else {
-                       ret = channel_ust_enable(usess, domain, uchan);
+                       ret = channel_ust_enable(usess, uchan);
                }
                break;
        }
-#if 0
-       case LTTNG_DOMAIN_UST_PID_FOLLOW_CHILDREN:
-       case LTTNG_DOMAIN_UST_EXEC_NAME:
-       case LTTNG_DOMAIN_UST_PID:
-#endif
        default:
-               ret = LTTCOMM_UNKNOWN_DOMAIN;
+               ret = LTTNG_ERR_UNKNOWN_DOMAIN;
                goto error;
        }
 
 error:
+       rcu_read_unlock();
        return ret;
 }
 
@@ -800,6 +921,8 @@ int cmd_disable_event(struct ltt_session *session, int domain,
 {
        int ret;
 
+       rcu_read_lock();
+
        switch (domain) {
        case LTTNG_DOMAIN_KERNEL:
        {
@@ -810,12 +933,12 @@ int cmd_disable_event(struct ltt_session *session, int domain,
 
                kchan = trace_kernel_get_channel_by_name(channel_name, ksess);
                if (kchan == NULL) {
-                       ret = LTTCOMM_KERN_CHAN_NOT_FOUND;
+                       ret = LTTNG_ERR_KERN_CHAN_NOT_FOUND;
                        goto error;
                }
 
-               ret = event_kernel_disable_tracepoint(ksess, kchan, event_name);
-               if (ret != LTTCOMM_OK) {
+               ret = event_kernel_disable_tracepoint(kchan, event_name);
+               if (ret != LTTNG_OK) {
                        goto error;
                }
 
@@ -832,12 +955,12 @@ int cmd_disable_event(struct ltt_session *session, int domain,
                uchan = trace_ust_find_channel_by_name(usess->domain_global.channels,
                                channel_name);
                if (uchan == NULL) {
-                       ret = LTTCOMM_UST_CHAN_NOT_FOUND;
+                       ret = LTTNG_ERR_UST_CHAN_NOT_FOUND;
                        goto error;
                }
 
-               ret = event_ust_disable_tracepoint(usess, domain, uchan, event_name);
-               if (ret != LTTCOMM_OK) {
+               ret = event_ust_disable_tracepoint(usess, uchan, event_name);
+               if (ret != LTTNG_OK) {
                        goto error;
                }
 
@@ -851,13 +974,14 @@ int cmd_disable_event(struct ltt_session *session, int domain,
        case LTTNG_DOMAIN_UST_PID_FOLLOW_CHILDREN:
 #endif
        default:
-               ret = LTTCOMM_UND;
+               ret = LTTNG_ERR_UND;
                goto error;
        }
 
-       ret = LTTCOMM_OK;
+       ret = LTTNG_OK;
 
 error:
+       rcu_read_unlock();
        return ret;
 }
 
@@ -869,6 +993,8 @@ int cmd_disable_event_all(struct ltt_session *session, int domain,
 {
        int ret;
 
+       rcu_read_lock();
+
        switch (domain) {
        case LTTNG_DOMAIN_KERNEL:
        {
@@ -879,12 +1005,12 @@ int cmd_disable_event_all(struct ltt_session *session, int domain,
 
                kchan = trace_kernel_get_channel_by_name(channel_name, ksess);
                if (kchan == NULL) {
-                       ret = LTTCOMM_KERN_CHAN_NOT_FOUND;
+                       ret = LTTNG_ERR_KERN_CHAN_NOT_FOUND;
                        goto error;
                }
 
-               ret = event_kernel_disable_all(ksess, kchan);
-               if (ret != LTTCOMM_OK) {
+               ret = event_kernel_disable_all(kchan);
+               if (ret != LTTNG_OK) {
                        goto error;
                }
 
@@ -901,11 +1027,11 @@ int cmd_disable_event_all(struct ltt_session *session, int domain,
                uchan = trace_ust_find_channel_by_name(usess->domain_global.channels,
                                channel_name);
                if (uchan == NULL) {
-                       ret = LTTCOMM_UST_CHAN_NOT_FOUND;
+                       ret = LTTNG_ERR_UST_CHAN_NOT_FOUND;
                        goto error;
                }
 
-               ret = event_ust_disable_all_tracepoints(usess, domain, uchan);
+               ret = event_ust_disable_all_tracepoints(usess, uchan);
                if (ret != 0) {
                        goto error;
                }
@@ -920,13 +1046,14 @@ int cmd_disable_event_all(struct ltt_session *session, int domain,
        case LTTNG_DOMAIN_UST_PID_FOLLOW_CHILDREN:
 #endif
        default:
-               ret = LTTCOMM_UND;
+               ret = LTTNG_ERR_UND;
                goto error;
        }
 
-       ret = LTTCOMM_OK;
+       ret = LTTNG_OK;
 
 error:
+       rcu_read_unlock();
        return ret;
 }
 
@@ -934,66 +1061,56 @@ error:
  * Command LTTNG_ADD_CONTEXT processed by the client thread.
  */
 int cmd_add_context(struct ltt_session *session, int domain,
-               char *channel_name, char *event_name, struct lttng_event_context *ctx)
+               char *channel_name, struct lttng_event_context *ctx, int kwpipe)
 {
-       int ret;
+       int ret, chan_kern_created = 0, chan_ust_created = 0;
 
        switch (domain) {
        case LTTNG_DOMAIN_KERNEL:
+               assert(session->kernel_session);
+
+               if (session->kernel_session->channel_count == 0) {
+                       /* Create default channel */
+                       ret = channel_kernel_create(session->kernel_session, NULL, kwpipe);
+                       if (ret != LTTNG_OK) {
+                               goto error;
+                       }
+                       chan_kern_created = 1;
+               }
+
                /* Add kernel context to kernel tracer */
-               ret = context_kernel_add(session->kernel_session, ctx,
-                               event_name, channel_name);
-               if (ret != LTTCOMM_OK) {
+               ret = context_kernel_add(session->kernel_session, ctx, channel_name);
+               if (ret != LTTNG_OK) {
                        goto error;
                }
                break;
        case LTTNG_DOMAIN_UST:
        {
                struct ltt_ust_session *usess = session->ust_session;
-
                assert(usess);
 
-               ret = context_ust_add(usess, domain, ctx, event_name, channel_name);
-               if (ret != LTTCOMM_OK) {
-                       goto error;
-               }
-               break;
-       }
-#if 0
-       case LTTNG_DOMAIN_UST_EXEC_NAME:
-       case LTTNG_DOMAIN_UST_PID:
-       case LTTNG_DOMAIN_UST_PID_FOLLOW_CHILDREN:
-#endif
-       default:
-               ret = LTTCOMM_UND;
-               goto error;
-       }
-
-       ret = LTTCOMM_OK;
-
-error:
-       return ret;
-}
-
-/*
- * Command LTTNG_SET_FILTER processed by the client thread.
- */
-int cmd_set_filter(struct ltt_session *session, int domain,
-               char *channel_name, char *event_name,
-               struct lttng_filter_bytecode *bytecode)
-{
-       int ret;
+               unsigned int chan_count =
+                       lttng_ht_get_count(usess->domain_global.channels);
+               if (chan_count == 0) {
+                       struct lttng_channel *attr;
+                       /* Create default channel */
+                       attr = channel_new_default_attr(domain, usess->buffer_type);
+                       if (attr == NULL) {
+                               ret = LTTNG_ERR_FATAL;
+                               goto error;
+                       }
 
-       switch (domain) {
-       case LTTNG_DOMAIN_KERNEL:
-               ret = LTTCOMM_FATAL;
-               break;
-       case LTTNG_DOMAIN_UST:
-       {
-               struct ltt_ust_session *usess = session->ust_session;
+                       ret = channel_ust_create(usess, attr, usess->buffer_type);
+                       if (ret != LTTNG_OK) {
+                               free(attr);
+                               goto error;
+                       }
+                       free(attr);
+                       chan_ust_created = 1;
+               }
 
-               ret = filter_ust_set(usess, domain, bytecode, event_name, channel_name);
-               if (ret != LTTCOMM_OK) {
+               ret = context_ust_add(usess, domain, ctx, channel_name);
+               if (ret != LTTNG_OK) {
                        goto error;
                }
                break;
@@ -1004,32 +1121,54 @@ int cmd_set_filter(struct ltt_session *session, int domain,
        case LTTNG_DOMAIN_UST_PID_FOLLOW_CHILDREN:
 #endif
        default:
-               ret = LTTCOMM_UND;
+               ret = LTTNG_ERR_UND;
                goto error;
        }
 
-       ret = LTTCOMM_OK;
+       return LTTNG_OK;
 
 error:
+       if (chan_kern_created) {
+               struct ltt_kernel_channel *kchan =
+                       trace_kernel_get_channel_by_name(DEFAULT_CHANNEL_NAME,
+                                       session->kernel_session);
+               /* Created previously, this should NOT fail. */
+               assert(kchan);
+               kernel_destroy_channel(kchan);
+       }
+
+       if (chan_ust_created) {
+               struct ltt_ust_channel *uchan =
+                       trace_ust_find_channel_by_name(
+                                       session->ust_session->domain_global.channels,
+                                       DEFAULT_CHANNEL_NAME);
+               /* Created previously, this should NOT fail. */
+               assert(uchan);
+               /* Remove from the channel list of the session. */
+               trace_ust_delete_channel(session->ust_session->domain_global.channels,
+                               uchan);
+               trace_ust_destroy_channel(uchan);
+       }
        return ret;
-
 }
 
-
 /*
  * Command LTTNG_ENABLE_EVENT processed by the client thread.
  */
-int cmd_enable_event(struct ltt_session *session, int domain,
-               char *channel_name, struct lttng_event *event, int wpipe)
+int cmd_enable_event(struct ltt_session *session, struct lttng_domain *domain,
+               char *channel_name, struct lttng_event *event,
+               struct lttng_filter_bytecode *filter, int wpipe)
 {
-       int ret;
+       int ret, channel_created = 0;
        struct lttng_channel *attr;
 
        assert(session);
        assert(event);
        assert(channel_name);
 
-       switch (domain) {
+       rcu_read_lock();
+
+       switch (domain->type) {
        case LTTNG_DOMAIN_KERNEL:
        {
                struct ltt_kernel_channel *kchan;
@@ -1037,19 +1176,22 @@ int cmd_enable_event(struct ltt_session *session, int domain,
                kchan = trace_kernel_get_channel_by_name(channel_name,
                                session->kernel_session);
                if (kchan == NULL) {
-                       attr = channel_new_default_attr(domain);
+                       attr = channel_new_default_attr(LTTNG_DOMAIN_KERNEL,
+                                       LTTNG_BUFFER_GLOBAL);
                        if (attr == NULL) {
-                               ret = LTTCOMM_FATAL;
+                               ret = LTTNG_ERR_FATAL;
                                goto error;
                        }
                        strncpy(attr->name, channel_name, sizeof(attr->name));
 
                        ret = cmd_enable_channel(session, domain, attr, wpipe);
-                       if (ret != LTTCOMM_OK) {
+                       if (ret != LTTNG_OK) {
                                free(attr);
                                goto error;
                        }
                        free(attr);
+
+                       channel_created = 1;
                }
 
                /* Get the newly created kernel channel pointer */
@@ -1057,13 +1199,16 @@ int cmd_enable_event(struct ltt_session *session, int domain,
                                session->kernel_session);
                if (kchan == NULL) {
                        /* This sould not happen... */
-                       ret = LTTCOMM_FATAL;
+                       ret = LTTNG_ERR_FATAL;
                        goto error;
                }
 
-               ret = event_kernel_enable_tracepoint(session->kernel_session, kchan,
-                               event);
-               if (ret != LTTCOMM_OK) {
+               ret = event_kernel_enable_tracepoint(kchan, event);
+               if (ret != LTTNG_OK) {
+                       if (channel_created) {
+                               /* Let's not leak a useless channel. */
+                               kernel_destroy_channel(kchan);
+                       }
                        goto error;
                }
 
@@ -1082,15 +1227,16 @@ int cmd_enable_event(struct ltt_session *session, int domain,
                                channel_name);
                if (uchan == NULL) {
                        /* Create default channel */
-                       attr = channel_new_default_attr(domain);
+                       attr = channel_new_default_attr(LTTNG_DOMAIN_UST,
+                                       usess->buffer_type);
                        if (attr == NULL) {
-                               ret = LTTCOMM_FATAL;
+                               ret = LTTNG_ERR_FATAL;
                                goto error;
                        }
                        strncpy(attr->name, channel_name, sizeof(attr->name));
 
                        ret = cmd_enable_channel(session, domain, attr, wpipe);
-                       if (ret != LTTCOMM_OK) {
+                       if (ret != LTTNG_OK) {
                                free(attr);
                                goto error;
                        }
@@ -1103,8 +1249,8 @@ int cmd_enable_event(struct ltt_session *session, int domain,
                }
 
                /* At this point, the session and channel exist on the tracer */
-               ret = event_ust_enable_tracepoint(usess, domain, uchan, event);
-               if (ret != LTTCOMM_OK) {
+               ret = event_ust_enable_tracepoint(usess, uchan, event, filter);
+               if (ret != LTTNG_OK) {
                        goto error;
                }
                break;
@@ -1115,21 +1261,23 @@ int cmd_enable_event(struct ltt_session *session, int domain,
        case LTTNG_DOMAIN_UST_PID_FOLLOW_CHILDREN:
 #endif
        default:
-               ret = LTTCOMM_UND;
+               ret = LTTNG_ERR_UND;
                goto error;
        }
 
-       ret = LTTCOMM_OK;
+       ret = LTTNG_OK;
 
 error:
+       rcu_read_unlock();
        return ret;
 }
 
 /*
  * Command LTTNG_ENABLE_ALL_EVENT processed by the client thread.
  */
-int cmd_enable_event_all(struct ltt_session *session, int domain,
-               char *channel_name, int event_type, int wpipe)
+int cmd_enable_event_all(struct ltt_session *session,
+               struct lttng_domain *domain, char *channel_name, int event_type,
+               struct lttng_filter_bytecode *filter, int wpipe)
 {
        int ret;
        struct lttng_channel *attr;
@@ -1137,7 +1285,9 @@ int cmd_enable_event_all(struct ltt_session *session, int domain,
        assert(session);
        assert(channel_name);
 
-       switch (domain) {
+       rcu_read_lock();
+
+       switch (domain->type) {
        case LTTNG_DOMAIN_KERNEL:
        {
                struct ltt_kernel_channel *kchan;
@@ -1148,15 +1298,16 @@ int cmd_enable_event_all(struct ltt_session *session, int domain,
                                session->kernel_session);
                if (kchan == NULL) {
                        /* Create default channel */
-                       attr = channel_new_default_attr(domain);
+                       attr = channel_new_default_attr(LTTNG_DOMAIN_KERNEL,
+                                       LTTNG_BUFFER_GLOBAL);
                        if (attr == NULL) {
-                               ret = LTTCOMM_FATAL;
+                               ret = LTTNG_ERR_FATAL;
                                goto error;
                        }
                        strncpy(attr->name, channel_name, sizeof(attr->name));
 
                        ret = cmd_enable_channel(session, domain, attr, wpipe);
-                       if (ret != LTTCOMM_OK) {
+                       if (ret != LTTNG_OK) {
                                free(attr);
                                goto error;
                        }
@@ -1170,29 +1321,30 @@ int cmd_enable_event_all(struct ltt_session *session, int domain,
 
                switch (event_type) {
                case LTTNG_EVENT_SYSCALL:
-                       ret = event_kernel_enable_all_syscalls(session->kernel_session,
-                                       kchan, kernel_tracer_fd);
+                       ret = event_kernel_enable_all_syscalls(kchan, kernel_tracer_fd);
                        break;
                case LTTNG_EVENT_TRACEPOINT:
                        /*
                         * This call enables all LTTNG_KERNEL_TRACEPOINTS and
                         * events already registered to the channel.
                         */
-                       ret = event_kernel_enable_all_tracepoints(session->kernel_session,
-                                       kchan, kernel_tracer_fd);
+                       ret = event_kernel_enable_all_tracepoints(kchan, kernel_tracer_fd);
                        break;
                case LTTNG_EVENT_ALL:
                        /* Enable syscalls and tracepoints */
-                       ret = event_kernel_enable_all(session->kernel_session,
-                                       kchan, kernel_tracer_fd);
+                       ret = event_kernel_enable_all(kchan, kernel_tracer_fd);
                        break;
                default:
-                       ret = LTTCOMM_KERN_ENABLE_FAIL;
+                       ret = LTTNG_ERR_KERN_ENABLE_FAIL;
                        goto error;
                }
 
                /* Manage return value */
-               if (ret != LTTCOMM_OK) {
+               if (ret != LTTNG_OK) {
+                       /*
+                        * On error, cmd_enable_channel call will take care of destroying
+                        * the created channel if it was needed.
+                        */
                        goto error;
                }
 
@@ -1211,15 +1363,16 @@ int cmd_enable_event_all(struct ltt_session *session, int domain,
                                channel_name);
                if (uchan == NULL) {
                        /* Create default channel */
-                       attr = channel_new_default_attr(domain);
+                       attr = channel_new_default_attr(LTTNG_DOMAIN_UST,
+                                       usess->buffer_type);
                        if (attr == NULL) {
-                               ret = LTTCOMM_FATAL;
+                               ret = LTTNG_ERR_FATAL;
                                goto error;
                        }
                        strncpy(attr->name, channel_name, sizeof(attr->name));
 
                        ret = cmd_enable_channel(session, domain, attr, wpipe);
-                       if (ret != LTTCOMM_OK) {
+                       if (ret != LTTNG_OK) {
                                free(attr);
                                goto error;
                        }
@@ -1236,18 +1389,18 @@ int cmd_enable_event_all(struct ltt_session *session, int domain,
                switch (event_type) {
                case LTTNG_EVENT_ALL:
                case LTTNG_EVENT_TRACEPOINT:
-                       ret = event_ust_enable_all_tracepoints(usess, domain, uchan);
-                       if (ret != LTTCOMM_OK) {
+                       ret = event_ust_enable_all_tracepoints(usess, uchan, filter);
+                       if (ret != LTTNG_OK) {
                                goto error;
                        }
                        break;
                default:
-                       ret = LTTCOMM_UST_ENABLE_FAIL;
+                       ret = LTTNG_ERR_UST_ENABLE_FAIL;
                        goto error;
                }
 
                /* Manage return value */
-               if (ret != LTTCOMM_OK) {
+               if (ret != LTTNG_OK) {
                        goto error;
                }
 
@@ -1259,13 +1412,14 @@ int cmd_enable_event_all(struct ltt_session *session, int domain,
        case LTTNG_DOMAIN_UST_PID_FOLLOW_CHILDREN:
 #endif
        default:
-               ret = LTTCOMM_UND;
+               ret = LTTNG_ERR_UND;
                goto error;
        }
 
-       ret = LTTCOMM_OK;
+       ret = LTTNG_OK;
 
 error:
+       rcu_read_unlock();
        return ret;
 }
 
@@ -1282,19 +1436,19 @@ ssize_t cmd_list_tracepoints(int domain, struct lttng_event **events)
        case LTTNG_DOMAIN_KERNEL:
                nb_events = kernel_list_events(kernel_tracer_fd, events);
                if (nb_events < 0) {
-                       ret = LTTCOMM_KERN_LIST_FAIL;
+                       ret = LTTNG_ERR_KERN_LIST_FAIL;
                        goto error;
                }
                break;
        case LTTNG_DOMAIN_UST:
                nb_events = ust_app_list_events(events);
                if (nb_events < 0) {
-                       ret = LTTCOMM_UST_LIST_FAIL;
+                       ret = LTTNG_ERR_UST_LIST_FAIL;
                        goto error;
                }
                break;
        default:
-               ret = LTTCOMM_UND;
+               ret = LTTNG_ERR_UND;
                goto error;
        }
 
@@ -1318,13 +1472,13 @@ ssize_t cmd_list_tracepoint_fields(int domain,
        case LTTNG_DOMAIN_UST:
                nb_fields = ust_app_list_event_fields(fields);
                if (nb_fields < 0) {
-                       ret = LTTCOMM_UST_LIST_FAIL;
+                       ret = LTTNG_ERR_UST_LIST_FAIL;
                        goto error;
                }
                break;
        case LTTNG_DOMAIN_KERNEL:
        default:        /* fall-through */
-               ret = LTTCOMM_UND;
+               ret = LTTNG_ERR_UND;
                goto error;
        }
 
@@ -1343,7 +1497,6 @@ int cmd_start_trace(struct ltt_session *session)
        int ret;
        struct ltt_kernel_session *ksession;
        struct ltt_ust_session *usess;
-       struct ltt_kernel_channel *kchan;
 
        assert(session);
 
@@ -1353,68 +1506,18 @@ int cmd_start_trace(struct ltt_session *session)
 
        if (session->enabled) {
                /* Already started. */
-               ret = LTTCOMM_TRACE_ALREADY_STARTED;
+               ret = LTTNG_ERR_TRACE_ALREADY_STARTED;
                goto error;
        }
 
        session->enabled = 1;
 
-       ret = setup_relayd(session);
-       if (ret != LTTCOMM_OK) {
-               ERR("Error setting up relayd for session %s", session->name);
-               goto error;
-       }
-
        /* Kernel tracing */
        if (ksession != NULL) {
-               /* Open kernel metadata */
-               if (ksession->metadata == NULL) {
-                       ret = kernel_open_metadata(ksession);
-                       if (ret < 0) {
-                               ret = LTTCOMM_KERN_META_FAIL;
-                               goto error;
-                       }
-               }
-
-               /* Open kernel metadata stream */
-               if (ksession->metadata_stream_fd < 0) {
-                       ret = kernel_open_metadata_stream(ksession);
-                       if (ret < 0) {
-                               ERR("Kernel create metadata stream failed");
-                               ret = LTTCOMM_KERN_STREAM_FAIL;
-                               goto error;
-                       }
-               }
-
-               /* For each channel */
-               cds_list_for_each_entry(kchan, &ksession->channel_list.head, list) {
-                       if (kchan->stream_count == 0) {
-                               ret = kernel_open_channel_stream(kchan);
-                               if (ret < 0) {
-                                       ret = LTTCOMM_KERN_STREAM_FAIL;
-                                       goto error;
-                               }
-                               /* Update the stream global counter */
-                               ksession->stream_count_global += ret;
-                       }
-               }
-
-               /* Setup kernel consumer socket and send fds to it */
-               ret = init_kernel_tracing(ksession);
-               if (ret < 0) {
-                       ret = LTTCOMM_KERN_START_FAIL;
-                       goto error;
-               }
-
-               /* This start the kernel tracing */
-               ret = kernel_start_session(ksession);
-               if (ret < 0) {
-                       ret = LTTCOMM_KERN_START_FAIL;
+               ret = start_kernel_session(ksession, kernel_tracer_fd);
+               if (ret != LTTNG_OK) {
                        goto error;
                }
-
-               /* Quiescent wait after starting trace */
-               kernel_wait_quiescent(kernel_tracer_fd);
        }
 
        /* Flag session that trace should start automatically */
@@ -1423,12 +1526,14 @@ int cmd_start_trace(struct ltt_session *session)
 
                ret = ust_app_start_trace_all(usess);
                if (ret < 0) {
-                       ret = LTTCOMM_UST_START_FAIL;
+                       ret = LTTNG_ERR_UST_START_FAIL;
                        goto error;
                }
        }
 
-       ret = LTTCOMM_OK;
+       session->started = 1;
+
+       ret = LTTNG_OK;
 
 error:
        return ret;
@@ -1451,14 +1556,14 @@ int cmd_stop_trace(struct ltt_session *session)
        usess = session->ust_session;
 
        if (!session->enabled) {
-               ret = LTTCOMM_TRACE_ALREADY_STOPPED;
+               ret = LTTNG_ERR_TRACE_ALREADY_STOPPED;
                goto error;
        }
 
        session->enabled = 0;
 
        /* Kernel tracer */
-       if (ksession) {
+       if (ksession && ksession->started) {
                DBG("Stop kernel tracing");
 
                /* Flush metadata if exist */
@@ -1479,24 +1584,26 @@ int cmd_stop_trace(struct ltt_session *session)
 
                ret = kernel_stop_session(ksession);
                if (ret < 0) {
-                       ret = LTTCOMM_KERN_STOP_FAIL;
+                       ret = LTTNG_ERR_KERN_STOP_FAIL;
                        goto error;
                }
 
                kernel_wait_quiescent(kernel_tracer_fd);
+
+               ksession->started = 0;
        }
 
-       if (usess) {
+       if (usess && usess->start_trace) {
                usess->start_trace = 0;
 
                ret = ust_app_stop_trace_all(usess);
                if (ret < 0) {
-                       ret = LTTCOMM_UST_STOP_FAIL;
+                       ret = LTTNG_ERR_UST_STOP_FAIL;
                        goto error;
                }
        }
 
-       ret = LTTCOMM_OK;
+       ret = LTTNG_OK;
 
 error:
        return ret;
@@ -1519,12 +1626,7 @@ int cmd_set_consumer_uri(int domain, struct ltt_session *session,
 
        /* Can't enable consumer after session started. */
        if (session->enabled) {
-               ret = LTTCOMM_TRACE_ALREADY_STARTED;
-               goto error;
-       }
-
-       if (!session->start_consumer) {
-               ret = LTTCOMM_NO_CONSUMER;
+               ret = LTTNG_ERR_TRACE_ALREADY_STARTED;
                goto error;
        }
 
@@ -1545,85 +1647,30 @@ int cmd_set_consumer_uri(int domain, struct ltt_session *session,
        case LTTNG_DOMAIN_KERNEL:
                /* Code flow error if we don't have a kernel session here. */
                assert(ksess);
-
-               /* Create consumer output if none exists */
-               consumer = ksess->tmp_consumer;
-               if (consumer == NULL) {
-                       consumer = consumer_copy_output(ksess->consumer);
-                       if (consumer == NULL) {
-                               ret = LTTCOMM_FATAL;
-                               goto error;
-                       }
-                       /* Trash the consumer subdir, we are about to set a new one. */
-                       memset(consumer->subdir, 0, sizeof(consumer->subdir));
-                       ksess->tmp_consumer = consumer;
-               }
-
+               assert(ksess->consumer);
+               consumer = ksess->consumer;
                break;
        case LTTNG_DOMAIN_UST:
                /* Code flow error if we don't have a kernel session here. */
                assert(usess);
-
-               /* Create consumer output if none exists */
-               consumer = usess->tmp_consumer;
-               if (consumer == NULL) {
-                       consumer = consumer_copy_output(usess->consumer);
-                       if (consumer == NULL) {
-                               ret = LTTCOMM_FATAL;
-                               goto error;
-                       }
-                       /* Trash the consumer subdir, we are about to set a new one. */
-                       memset(consumer->subdir, 0, sizeof(consumer->subdir));
-                       usess->tmp_consumer = consumer;
-               }
-
+               assert(usess->consumer);
+               consumer = usess->consumer;
                break;
        }
 
        for (i = 0; i < nb_uri; i++) {
-               struct consumer_socket *socket;
-               struct lttng_ht_iter iter;
-
                ret = add_uri_to_consumer(consumer, &uris[i], domain, session->name);
-               if (ret < 0) {
+               if (ret != LTTNG_OK) {
                        goto error;
                }
+       }
 
-               /*
-                * Don't send relayd socket if URI is NOT remote or if the relayd
-                * sockets for the session are already sent.
-                */
-               if (uris[i].dtype == LTTNG_DST_PATH ||
-                               consumer->dst.net.relayd_socks_sent) {
-                       continue;
-               }
-
-               /* Try to send relayd URI to the consumer if exist. */
-               rcu_read_lock();
-               cds_lfht_for_each_entry(consumer->socks->ht, &iter.iter,
-                               socket, node.node) {
+       /* All good! */
+       ret = LTTNG_OK;
 
-                       /* A socket in the HT should never have a negative fd */
-                       assert(socket->fd >= 0);
-
-                       pthread_mutex_lock(socket->lock);
-                       ret = send_consumer_relayd_socket(domain, session, &uris[i],
-                                       consumer, socket->fd);
-                       pthread_mutex_unlock(socket->lock);
-                       if (ret != LTTCOMM_OK) {
-                               rcu_read_unlock();
-                               goto error;
-                       }
-               }
-               rcu_read_unlock();
-       }
-
-       /* All good! */
-       ret = LTTCOMM_OK;
-
-error:
-       return ret;
-}
+error:
+       return ret;
+}
 
 /*
  * Command LTTNG_CREATE_SESSION processed by the client thread.
@@ -1632,10 +1679,10 @@ int cmd_create_session_uri(char *name, struct lttng_uri *uris,
                size_t nb_uri, lttng_sock_cred *creds)
 {
        int ret;
-       char *path = NULL;
        struct ltt_session *session;
 
        assert(name);
+       assert(creds);
 
        /*
         * Verify if the session already exist
@@ -1646,14 +1693,14 @@ int cmd_create_session_uri(char *name, struct lttng_uri *uris,
         */
        session = session_find_by_name(name);
        if (session != NULL) {
-               ret = LTTCOMM_EXIST_SESS;
+               ret = LTTNG_ERR_EXIST_SESS;
                goto find_error;
        }
 
        /* Create tracing session in the registry */
-       ret = session_create(name, path, LTTNG_SOCK_GET_UID_CRED(creds),
+       ret = session_create(name, LTTNG_SOCK_GET_UID_CRED(creds),
                        LTTNG_SOCK_GET_GID_CRED(creds));
-       if (ret != LTTCOMM_OK) {
+       if (ret != LTTNG_OK) {
                goto session_error;
        }
 
@@ -1670,40 +1717,95 @@ int cmd_create_session_uri(char *name, struct lttng_uri *uris,
        /* Create default consumer output for the session not yet created. */
        session->consumer = consumer_create_output(CONSUMER_DST_LOCAL);
        if (session->consumer == NULL) {
-               ret = LTTCOMM_FATAL;
+               ret = LTTNG_ERR_FATAL;
                goto consumer_error;
        }
 
+       if (uris) {
+               ret = cmd_set_consumer_uri(0, session, nb_uri, uris);
+               if (ret != LTTNG_OK) {
+                       goto consumer_error;
+               }
+               session->output_traces = 1;
+       } else {
+               session->output_traces = 0;
+               DBG2("Session %s created with no output", session->name);
+       }
+
+       session->consumer->enabled = 1;
+
+       return LTTNG_OK;
+
+consumer_error:
+       session_destroy(session);
+session_error:
+find_error:
+       return ret;
+}
+
+/*
+ * Command LTTNG_CREATE_SESSION_SNAPSHOT processed by the client thread.
+ */
+int cmd_create_session_snapshot(char *name, struct lttng_uri *uris,
+               size_t nb_uri, lttng_sock_cred *creds)
+{
+       int ret;
+       struct ltt_session *session;
+       struct snapshot_output *new_output = NULL;
+
+       assert(name);
+       assert(creds);
+
        /*
-        * This means that the lttng_create_session call was called with the _path_
-        * argument set to NULL.
+        * Create session in no output mode with URIs set to NULL. The uris we've
+        * received are for a default snapshot output if one.
         */
-       if (uris == NULL) {
-               /*
-                * At this point, we'll skip the consumer URI setup and create a
-                * session with a NULL path which will flag the session to NOT spawn a
-                * consumer.
-                */
-               DBG("Create session %s with NO uri, skipping consumer setup", name);
+       ret = cmd_create_session_uri(name, NULL, 0, creds);
+       if (ret != LTTNG_OK) {
+               goto error;
+       }
+
+       /* Get the newly created session pointer back. This should NEVER fail. */
+       session = session_find_by_name(name);
+       assert(session);
+
+       /* Flag session for snapshot mode. */
+       session->snapshot_mode = 1;
+
+       /* Skip snapshot output creation if no URI is given. */
+       if (nb_uri == 0) {
                goto end;
        }
 
-       session->start_consumer = 1;
+       new_output = snapshot_output_alloc();
+       if (!new_output) {
+               ret = LTTNG_ERR_NOMEM;
+               goto error_snapshot_alloc;
+       }
 
-       ret = cmd_set_consumer_uri(0, session, nb_uri, uris);
-       if (ret != LTTCOMM_OK) {
-               goto consumer_error;
+       ret = snapshot_output_init_with_uri(DEFAULT_SNAPSHOT_MAX_SIZE, NULL,
+                       uris, nb_uri, session->consumer, new_output, &session->snapshot);
+       if (ret < 0) {
+               if (ret == -ENOMEM) {
+                       ret = LTTNG_ERR_NOMEM;
+               } else {
+                       ret = LTTNG_ERR_INVALID;
+               }
+               goto error_snapshot;
        }
 
-       session->consumer->enabled = 1;
+       rcu_read_lock();
+       snapshot_add_output(&session->snapshot, new_output);
+       rcu_read_unlock();
 
 end:
-       return LTTCOMM_OK;
+       return LTTNG_OK;
 
-consumer_error:
+error_snapshot:
+       snapshot_output_destroy(new_output);
+error_snapshot_alloc:
        session_destroy(session);
-session_error:
-find_error:
+error:
        return ret;
 }
 
@@ -1769,7 +1871,7 @@ int cmd_calibrate(int domain, struct lttng_calibrate *calibrate)
                kcalibrate.type = calibrate->type;
                ret = kernel_calibrate(kernel_tracer_fd, &kcalibrate);
                if (ret < 0) {
-                       ret = LTTCOMM_KERN_ENABLE_FAIL;
+                       ret = LTTNG_ERR_KERN_ENABLE_FAIL;
                        goto error;
                }
                break;
@@ -1781,17 +1883,17 @@ int cmd_calibrate(int domain, struct lttng_calibrate *calibrate)
                ucalibrate.type = calibrate->type;
                ret = ust_app_calibrate_glb(&ucalibrate);
                if (ret < 0) {
-                       ret = LTTCOMM_UST_CALIBRATE_FAIL;
+                       ret = LTTNG_ERR_UST_CALIBRATE_FAIL;
                        goto error;
                }
                break;
        }
        default:
-               ret = LTTCOMM_UND;
+               ret = LTTNG_ERR_UND;
                goto error;
        }
 
-       ret = LTTCOMM_OK;
+       ret = LTTNG_OK;
 
 error:
        return ret;
@@ -1804,7 +1906,7 @@ int cmd_register_consumer(struct ltt_session *session, int domain,
                const char *sock_path, struct consumer_data *cdata)
 {
        int ret, sock;
-       struct consumer_socket *socket;
+       struct consumer_socket *socket = NULL;
 
        assert(session);
        assert(cdata);
@@ -1819,27 +1921,30 @@ int cmd_register_consumer(struct ltt_session *session, int domain,
 
                /* Can't register a consumer if there is already one */
                if (ksess->consumer_fds_sent != 0) {
-                       ret = LTTCOMM_KERN_CONSUMER_FAIL;
+                       ret = LTTNG_ERR_KERN_CONSUMER_FAIL;
                        goto error;
                }
 
                sock = lttcomm_connect_unix_sock(sock_path);
                if (sock < 0) {
-                       ret = LTTCOMM_CONNECT_FAIL;
+                       ret = LTTNG_ERR_CONNECT_FAIL;
                        goto error;
                }
 
                socket = consumer_allocate_socket(sock);
                if (socket == NULL) {
-                       ret = LTTCOMM_FATAL;
-                       close(sock);
+                       ret = close(sock);
+                       if (ret < 0) {
+                               PERROR("close register consumer");
+                       }
+                       ret = LTTNG_ERR_FATAL;
                        goto error;
                }
 
                socket->lock = zmalloc(sizeof(pthread_mutex_t));
                if (socket->lock == NULL) {
                        PERROR("zmalloc pthread mutex");
-                       ret = LTTCOMM_FATAL;
+                       ret = LTTNG_ERR_FATAL;
                        goto error;
                }
                pthread_mutex_init(socket->lock, NULL);
@@ -1857,13 +1962,16 @@ int cmd_register_consumer(struct ltt_session *session, int domain,
        }
        default:
                /* TODO: Userspace tracing */
-               ret = LTTCOMM_UND;
+               ret = LTTNG_ERR_UND;
                goto error;
        }
 
-       ret = LTTCOMM_OK;
+       return LTTNG_OK;
 
 error:
+       if (socket) {
+               consumer_destroy_socket(socket);
+       }
        return ret;
 }
 
@@ -1888,7 +1996,7 @@ ssize_t cmd_list_domains(struct ltt_session *session,
 
        *domains = zmalloc(nb_dom * sizeof(struct lttng_domain));
        if (*domains == NULL) {
-               ret = -LTTCOMM_FATAL;
+               ret = LTTNG_ERR_FATAL;
                goto error;
        }
 
@@ -1899,13 +2007,15 @@ ssize_t cmd_list_domains(struct ltt_session *session,
 
        if (session->ust_session != NULL) {
                (*domains)[index].type = LTTNG_DOMAIN_UST;
+               (*domains)[index].buf_type = session->ust_session->buffer_type;
                index++;
        }
 
        return nb_dom;
 
 error:
-       return ret;
+       /* Return negative value to differentiate return code */
+       return -ret;
 }
 
 
@@ -1924,6 +2034,9 @@ ssize_t cmd_list_channels(int domain, struct ltt_session *session,
                        nb_chan = session->kernel_session->channel_count;
                }
                DBG3("Number of kernel channels %zd", nb_chan);
+               if (nb_chan <= 0) {
+                       ret = LTTNG_ERR_KERN_CHAN_NOT_FOUND;
+               }
                break;
        case LTTNG_DOMAIN_UST:
                if (session->ust_session != NULL) {
@@ -1931,29 +2044,35 @@ ssize_t cmd_list_channels(int domain, struct ltt_session *session,
                                        session->ust_session->domain_global.channels);
                }
                DBG3("Number of UST global channels %zd", nb_chan);
+               if (nb_chan <= 0) {
+                       ret = LTTNG_ERR_UST_CHAN_NOT_FOUND;
+               }
                break;
        default:
                *channels = NULL;
-               ret = -LTTCOMM_UND;
+               ret = LTTNG_ERR_UND;
                goto error;
        }
 
        if (nb_chan > 0) {
                *channels = zmalloc(nb_chan * sizeof(struct lttng_channel));
                if (*channels == NULL) {
-                       ret = -LTTCOMM_FATAL;
+                       ret = LTTNG_ERR_FATAL;
                        goto error;
                }
 
                list_lttng_channels(domain, session, *channels);
        } else {
                *channels = NULL;
+               /* Ret value was set in the domain switch case */
+               goto error;
        }
 
        return nb_chan;
 
 error:
-       return ret;
+       /* Return negative value to differentiate return code */
+       return -ret;
 }
 
 /*
@@ -1981,14 +2100,15 @@ ssize_t cmd_list_events(int domain, struct ltt_session *session,
                break;
        }
        default:
-               ret = -LTTCOMM_UND;
+               ret = LTTNG_ERR_UND;
                goto error;
        }
 
-       ret = nb_event;
+       return nb_event;
 
 error:
-       return ret;
+       /* Return negative value to differentiate return code */
+       return -ret;
 }
 
 /*
@@ -2027,9 +2147,9 @@ void cmd_list_lttng_sessions(struct lttng_session *sessions, uid_t uid,
                                (ksess && ksess->consumer->type == CONSUMER_DST_NET) ||
                                (usess && usess->consumer->type == CONSUMER_DST_NET)) {
                        ret = build_network_session_path(sessions[i].path,
-                                       sizeof(session[i].path), session);
+                                       sizeof(sessions[i].path), session);
                } else {
-                       ret = snprintf(sessions[i].path, sizeof(session[i].path), "%s",
+                       ret = snprintf(sessions[i].path, sizeof(sessions[i].path), "%s",
                                        session->consumer->dst.trace_path);
                }
                if (ret < 0) {
@@ -2040,273 +2160,581 @@ void cmd_list_lttng_sessions(struct lttng_session *sessions, uid_t uid,
                strncpy(sessions[i].name, session->name, NAME_MAX);
                sessions[i].name[NAME_MAX - 1] = '\0';
                sessions[i].enabled = session->enabled;
+               sessions[i].snapshot_mode = session->snapshot_mode;
                i++;
        }
 }
 
 /*
- * Command LTTNG_DISABLE_CONSUMER processed by the client thread.
+ * Command LTTNG_DATA_PENDING returning 0 if the data is NOT pending meaning
+ * ready for trace analysis (or any kind of reader) or else 1 for pending data.
  */
-int cmd_disable_consumer(int domain, struct ltt_session *session)
+int cmd_data_pending(struct ltt_session *session)
 {
        int ret;
        struct ltt_kernel_session *ksess = session->kernel_session;
        struct ltt_ust_session *usess = session->ust_session;
-       struct consumer_output *consumer;
 
        assert(session);
 
+       /* Session MUST be stopped to ask for data availability. */
        if (session->enabled) {
-               /* Can't disable consumer on an already started session */
-               ret = LTTCOMM_TRACE_ALREADY_STARTED;
+               ret = LTTNG_ERR_SESSION_STARTED;
                goto error;
        }
 
-       if (!session->start_consumer) {
-               ret = LTTCOMM_NO_CONSUMER;
-               goto error;
+       if (ksess && ksess->consumer) {
+               ret = consumer_is_data_pending(ksess->id, ksess->consumer);
+               if (ret == 1) {
+                       /* Data is still being extracted for the kernel. */
+                       goto error;
+               }
        }
 
-       switch (domain) {
-       case 0:
-               DBG("Disable tracing session %s consumer", session->name);
-               consumer = session->consumer;
-               break;
-       case LTTNG_DOMAIN_KERNEL:
-               /* Code flow error if we don't have a kernel session here. */
-               assert(ksess);
+       if (usess && usess->consumer) {
+               ret = consumer_is_data_pending(usess->id, usess->consumer);
+               if (ret == 1) {
+                       /* Data is still being extracted for the kernel. */
+                       goto error;
+               }
+       }
 
-               DBG("Disabling kernel consumer");
-               consumer = ksess->consumer;
+       /* Data is ready to be read by a viewer */
+       ret = 0;
 
-               break;
-       case LTTNG_DOMAIN_UST:
-               /* Code flow error if we don't have a UST session here. */
-               assert(usess);
+error:
+       return ret;
+}
 
-               DBG("Disabling UST consumer");
-               consumer = usess->consumer;
+/*
+ * Command LTTNG_SNAPSHOT_ADD_OUTPUT from the lttng ctl library.
+ *
+ * Return LTTNG_OK on success or else a LTTNG_ERR code.
+ */
+int cmd_snapshot_add_output(struct ltt_session *session,
+               struct lttng_snapshot_output *output, uint32_t *id)
+{
+       int ret;
+       struct snapshot_output *new_output;
 
-               break;
-       default:
-               ret = LTTCOMM_UNKNOWN_DOMAIN;
+       assert(session);
+       assert(output);
+
+       DBG("Cmd snapshot add output for session %s", session->name);
+
+       /*
+        * Permission denied to create an output if the session is not
+        * set in no output mode.
+        */
+       if (session->output_traces) {
+               ret = LTTNG_ERR_EPERM;
                goto error;
        }
 
-       if (consumer) {
-               consumer->enabled = 0;
-               /* Success at this point */
-               ret = LTTCOMM_OK;
-       } else {
-               ret = LTTCOMM_NO_CONSUMER;
+       /* Only one output is allowed until we have the "tee" feature. */
+       if (session->snapshot.nb_output == 1) {
+               ret = LTTNG_ERR_SNAPSHOT_OUTPUT_EXIST;
+               goto error;
+       }
+
+       new_output = snapshot_output_alloc();
+       if (!new_output) {
+               ret = LTTNG_ERR_NOMEM;
+               goto error;
        }
 
+       ret = snapshot_output_init(output->max_size, output->name,
+                       output->ctrl_url, output->data_url, session->consumer, new_output,
+                       &session->snapshot);
+       if (ret < 0) {
+               if (ret == -ENOMEM) {
+                       ret = LTTNG_ERR_NOMEM;
+               } else {
+                       ret = LTTNG_ERR_INVALID;
+               }
+               goto free_error;
+       }
+
+       rcu_read_lock();
+       snapshot_add_output(&session->snapshot, new_output);
+       if (id) {
+               *id = new_output->id;
+       }
+       rcu_read_unlock();
+
+       return LTTNG_OK;
+
+free_error:
+       snapshot_output_destroy(new_output);
 error:
        return ret;
 }
 
 /*
- * Command LTTNG_ENABLE_CONSUMER processed by the client thread.
+ * Command LTTNG_SNAPSHOT_DEL_OUTPUT from lib lttng ctl.
+ *
+ * Return LTTNG_OK on success or else a LTTNG_ERR code.
  */
-int cmd_enable_consumer(int domain, struct ltt_session *session)
+int cmd_snapshot_del_output(struct ltt_session *session,
+               struct lttng_snapshot_output *output)
 {
        int ret;
-       struct ltt_kernel_session *ksess = session->kernel_session;
-       struct ltt_ust_session *usess = session->ust_session;
-       struct consumer_output *consumer = NULL;
+       struct snapshot_output *sout = NULL;
 
        assert(session);
+       assert(output);
 
-       /* Can't enable consumer after session started. */
-       if (session->enabled) {
-               ret = LTTCOMM_TRACE_ALREADY_STARTED;
+       rcu_read_lock();
+
+       /*
+        * Permission denied to create an output if the session is not
+        * set in no output mode.
+        */
+       if (session->output_traces) {
+               ret = LTTNG_ERR_EPERM;
                goto error;
        }
 
-       if (!session->start_consumer) {
-               ret = LTTCOMM_NO_CONSUMER;
+       if (output->id) {
+               DBG("Cmd snapshot del output id %" PRIu32 " for session %s", output->id,
+                               session->name);
+               sout = snapshot_find_output_by_id(output->id, &session->snapshot);
+       } else if (*output->name != '\0') {
+               DBG("Cmd snapshot del output name %s for session %s", output->name,
+                               session->name);
+               sout = snapshot_find_output_by_name(output->name, &session->snapshot);
+       }
+       if (!sout) {
+               ret = LTTNG_ERR_INVALID;
                goto error;
        }
 
-       switch (domain) {
-       case 0:
-               assert(session->consumer);
-               consumer = session->consumer;
-               break;
-       case LTTNG_DOMAIN_KERNEL:
-               /* Code flow error if we don't have a kernel session here. */
-               assert(ksess);
+       snapshot_delete_output(&session->snapshot, sout);
+       snapshot_output_destroy(sout);
+       ret = LTTNG_OK;
 
-               /*
-                * Check if we have already sent fds to the consumer. In that case,
-                * the enable-consumer command can't be used because a start trace
-                * had previously occured.
-                */
-               if (ksess->consumer_fds_sent) {
-                       ret = LTTCOMM_ENABLE_CONSUMER_FAIL;
-                       goto error;
-               }
+error:
+       rcu_read_unlock();
+       return ret;
+}
 
-               consumer = ksess->tmp_consumer;
-               if (consumer == NULL) {
-                       ret = LTTCOMM_OK;
-                       /* No temp. consumer output exists. Using the current one. */
-                       DBG3("No temporary consumer. Using default");
-                       consumer = ksess->consumer;
-                       goto error;
-               }
+/*
+ * Command LTTNG_SNAPSHOT_LIST_OUTPUT from lib lttng ctl.
+ *
+ * If no output is available, outputs is untouched and 0 is returned.
+ *
+ * Return the size of the newly allocated outputs or a negative LTTNG_ERR code.
+ */
+ssize_t cmd_snapshot_list_outputs(struct ltt_session *session,
+               struct lttng_snapshot_output **outputs)
+{
+       int ret, idx = 0;
+       struct lttng_snapshot_output *list;
+       struct lttng_ht_iter iter;
+       struct snapshot_output *output;
+
+       assert(session);
+       assert(outputs);
 
-               switch (consumer->type) {
-               case CONSUMER_DST_LOCAL:
-                       DBG2("Consumer output is local. Creating directory(ies)");
+       DBG("Cmd snapshot list outputs for session %s", session->name);
 
-                       /* Create directory(ies) */
-                       ret = run_as_mkdir_recursive(consumer->dst.trace_path,
-                                       S_IRWXU | S_IRWXG, session->uid, session->gid);
+       /*
+        * Permission denied to create an output if the session is not
+        * set in no output mode.
+        */
+       if (session->output_traces) {
+               ret = LTTNG_ERR_EPERM;
+               goto error;
+       }
+
+       if (session->snapshot.nb_output == 0) {
+               ret = 0;
+               goto error;
+       }
+
+       list = zmalloc(session->snapshot.nb_output * sizeof(*list));
+       if (!list) {
+               ret = LTTNG_ERR_NOMEM;
+               goto error;
+       }
+
+       /* Copy list from session to the new list object. */
+       cds_lfht_for_each_entry(session->snapshot.output_ht->ht, &iter.iter,
+                       output, node.node) {
+               assert(output->consumer);
+               list[idx].id = output->id;
+               list[idx].max_size = output->max_size;
+               strncpy(list[idx].name, output->name, sizeof(list[idx].name));
+               if (output->consumer->type == CONSUMER_DST_LOCAL) {
+                       strncpy(list[idx].ctrl_url, output->consumer->dst.trace_path,
+                                       sizeof(list[idx].ctrl_url));
+               } else {
+                       /* Control URI. */
+                       ret = uri_to_str_url(&output->consumer->dst.net.control,
+                                       list[idx].ctrl_url, sizeof(list[idx].ctrl_url));
                        if (ret < 0) {
-                               if (ret != -EEXIST) {
-                                       ERR("Trace directory creation error");
-                                       ret = LTTCOMM_FATAL;
-                                       goto error;
-                               }
-                       }
-                       break;
-               case CONSUMER_DST_NET:
-                       DBG2("Consumer output is network. Validating URIs");
-                       /* Validate if we have both control and data path set. */
-                       if (!consumer->dst.net.control_isset) {
-                               ret = LTTCOMM_URL_CTRL_MISS;
-                               goto error;
+                               ret = LTTNG_ERR_NOMEM;
+                               goto free_error;
                        }
 
-                       if (!consumer->dst.net.data_isset) {
-                               ret = LTTCOMM_URL_DATA_MISS;
-                               goto error;
+                       /* Data URI. */
+                       ret = uri_to_str_url(&output->consumer->dst.net.data,
+                                       list[idx].data_url, sizeof(list[idx].data_url));
+                       if (ret < 0) {
+                               ret = LTTNG_ERR_NOMEM;
+                               goto free_error;
                        }
+               }
+               idx++;
+       }
 
-                       /* Check established network session state */
-                       if (session->net_handle == 0) {
-                               ret = LTTCOMM_ENABLE_CONSUMER_FAIL;
-                               ERR("Session network handle is not set on enable-consumer");
-                               goto error;
-                       }
+       *outputs = list;
+       return session->snapshot.nb_output;
 
-                       break;
-               }
+free_error:
+       free(list);
+error:
+       return -ret;
+}
+
+/*
+ * Send relayd sockets from snapshot output to consumer. Ignore request if the
+ * snapshot output is *not* set with a remote destination.
+ *
+ * Return 0 on success or a LTTNG_ERR code.
+ */
+static int set_relayd_for_snapshot(struct consumer_output *consumer,
+               struct snapshot_output *snap_output, struct ltt_session *session)
+{
+       int ret = LTTNG_OK;
+       struct lttng_ht_iter iter;
+       struct consumer_socket *socket;
 
-               /* Append default kernel trace dir to subdir */
-               strncat(ksess->consumer->subdir, DEFAULT_KERNEL_TRACE_DIR,
-                               sizeof(ksess->consumer->subdir));
+       assert(consumer);
+       assert(snap_output);
+       assert(session);
 
-               /*
-                * @session-lock
-                * This is race free for now since the session lock is acquired before
-                * ending up in this function. No other threads can access this kernel
-                * session without this lock hence freeing the consumer output object
-                * is valid.
-                */
-               rcu_read_lock();
-               consumer_destroy_output(ksess->consumer);
-               rcu_read_unlock();
-               ksess->consumer = consumer;
-               ksess->tmp_consumer = NULL;
+       DBG2("Set relayd object from snapshot output");
 
-               break;
-       case LTTNG_DOMAIN_UST:
-               /* Code flow error if we don't have a UST session here. */
-               assert(usess);
+       /* Ignore if snapshot consumer output is not network. */
+       if (snap_output->consumer->type != CONSUMER_DST_NET) {
+               goto error;
+       }
 
-               /*
-                * Check if we have already sent fds to the consumer. In that case,
-                * the enable-consumer command can't be used because a start trace
-                * had previously occured.
-                */
-               if (usess->start_trace) {
-                       ret = LTTCOMM_ENABLE_CONSUMER_FAIL;
+       /*
+        * For each consumer socket, create and send the relayd object of the
+        * snapshot output.
+        */
+       rcu_read_lock();
+       cds_lfht_for_each_entry(snap_output->consumer->socks->ht, &iter.iter,
+                       socket, node.node) {
+               ret = send_consumer_relayd_sockets(0, session->id,
+                               snap_output->consumer, socket);
+               if (ret != LTTNG_OK) {
+                       rcu_read_unlock();
                        goto error;
                }
+       }
+       rcu_read_unlock();
 
-               consumer = usess->tmp_consumer;
-               if (consumer == NULL) {
-                       ret = LTTCOMM_OK;
-                       /* No temp. consumer output exists. Using the current one. */
-                       DBG3("No temporary consumer. Using default");
-                       consumer = usess->consumer;
-                       goto error;
+error:
+       return ret;
+}
+
+/*
+ * Record a kernel snapshot.
+ *
+ * Return 0 on success or a LTTNG_ERR code.
+ */
+static int record_kernel_snapshot(struct ltt_kernel_session *ksess,
+               struct snapshot_output *output, struct ltt_session *session,
+               int wait, int nb_streams)
+{
+       int ret;
+
+       assert(ksess);
+       assert(output);
+       assert(session);
+
+       /* Get the datetime for the snapshot output directory. */
+       ret = utils_get_current_time_str("%Y%m%d-%H%M%S", output->datetime,
+                       sizeof(output->datetime));
+       if (!ret) {
+               ret = LTTNG_ERR_INVALID;
+               goto error;
+       }
+
+       /*
+        * Copy kernel session sockets so we can communicate with the right
+        * consumer for the snapshot record command.
+        */
+       ret = consumer_copy_sockets(output->consumer, ksess->consumer);
+       if (ret < 0) {
+               ret = LTTNG_ERR_NOMEM;
+               goto error;
+       }
+
+       ret = set_relayd_for_snapshot(ksess->consumer, output, session);
+       if (ret != LTTNG_OK) {
+               goto error_snapshot;
+       }
+
+       ret = kernel_snapshot_record(ksess, output, wait, nb_streams);
+       if (ret < 0) {
+               ret = LTTNG_ERR_SNAPSHOT_FAIL;
+               if (ret == -EINVAL) {
+                       ret = LTTNG_ERR_INVALID;
                }
+               goto error_snapshot;
+       }
 
-               switch (consumer->type) {
-               case CONSUMER_DST_LOCAL:
-                       DBG2("Consumer output is local. Creating directory(ies)");
+       ret = LTTNG_OK;
 
-                       /* Create directory(ies) */
-                       ret = run_as_mkdir_recursive(consumer->dst.trace_path,
-                                       S_IRWXU | S_IRWXG, session->uid, session->gid);
-                       if (ret < 0) {
-                               if (ret != -EEXIST) {
-                                       ERR("Trace directory creation error");
-                                       ret = LTTCOMM_FATAL;
-                                       goto error;
-                               }
-                       }
-                       break;
-               case CONSUMER_DST_NET:
-                       DBG2("Consumer output is network. Validating URIs");
-                       /* Validate if we have both control and data path set. */
-                       if (!consumer->dst.net.control_isset) {
-                               ret = LTTCOMM_URL_CTRL_MISS;
-                               goto error;
+error_snapshot:
+       /* Clean up copied sockets so this output can use some other later on. */
+       consumer_destroy_output_sockets(output->consumer);
+error:
+       return ret;
+}
+
+/*
+ * Record a UST snapshot.
+ *
+ * Return 0 on success or a LTTNG_ERR error code.
+ */
+static int record_ust_snapshot(struct ltt_ust_session *usess,
+               struct snapshot_output *output, struct ltt_session *session,
+               int wait, int nb_streams)
+{
+       int ret;
+
+       assert(usess);
+       assert(output);
+       assert(session);
+
+       /* Get the datetime for the snapshot output directory. */
+       ret = utils_get_current_time_str("%Y%m%d-%H%M%S", output->datetime,
+                       sizeof(output->datetime));
+       if (!ret) {
+               ret = LTTNG_ERR_INVALID;
+               goto error;
+       }
+
+       /*
+        * Copy UST session sockets so we can communicate with the right
+        * consumer for the snapshot record command.
+        */
+       ret = consumer_copy_sockets(output->consumer, usess->consumer);
+       if (ret < 0) {
+               ret = LTTNG_ERR_NOMEM;
+               goto error;
+       }
+
+       ret = set_relayd_for_snapshot(usess->consumer, output, session);
+       if (ret != LTTNG_OK) {
+               goto error_snapshot;
+       }
+
+       ret = ust_app_snapshot_record(usess, output, wait, nb_streams);
+       if (ret < 0) {
+               ret = LTTNG_ERR_SNAPSHOT_FAIL;
+               if (ret == -EINVAL) {
+                       ret = LTTNG_ERR_INVALID;
+               }
+               goto error_snapshot;
+       }
+
+       ret = LTTNG_OK;
+
+error_snapshot:
+       /* Clean up copied sockets so this output can use some other later on. */
+       consumer_destroy_output_sockets(output->consumer);
+error:
+       return ret;
+}
+
+/*
+ * Returns the total number of streams for a session or a negative value
+ * on error.
+ */
+static unsigned int get_total_nb_stream(struct ltt_session *session)
+{
+       unsigned int total_streams = 0;
+
+       if (session->kernel_session) {
+               struct ltt_kernel_session *ksess = session->kernel_session;
+
+               total_streams += ksess->stream_count_global;
+       }
+
+       if (session->ust_session) {
+               struct ltt_ust_session *usess = session->ust_session;
+
+               total_streams += ust_app_get_nb_stream(usess);
+       }
+
+       return total_streams;
+}
+
+/*
+ * Command LTTNG_SNAPSHOT_RECORD from lib lttng ctl.
+ *
+ * The wait parameter is ignored so this call always wait for the snapshot to
+ * complete before returning.
+ *
+ * Return LTTNG_OK on success or else a LTTNG_ERR code.
+ */
+int cmd_snapshot_record(struct ltt_session *session,
+               struct lttng_snapshot_output *output, int wait)
+{
+       int ret = LTTNG_OK;
+       unsigned int use_tmp_output = 0;
+       struct snapshot_output tmp_output;
+       unsigned int nb_streams, snapshot_success = 0;
+
+       assert(session);
+
+       DBG("Cmd snapshot record for session %s", session->name);
+
+       /*
+        * Permission denied to create an output if the session is not
+        * set in no output mode.
+        */
+       if (session->output_traces) {
+               ret = LTTNG_ERR_EPERM;
+               goto error;
+       }
+
+       /* The session needs to be started at least once. */
+       if (!session->started) {
+               ret = LTTNG_ERR_START_SESSION_ONCE;
+               goto error;
+       }
+
+       /* Use temporary output for the session. */
+       if (output && *output->ctrl_url != '\0') {
+               ret = snapshot_output_init(output->max_size, output->name,
+                               output->ctrl_url, output->data_url, session->consumer,
+                               &tmp_output, NULL);
+               if (ret < 0) {
+                       if (ret == -ENOMEM) {
+                               ret = LTTNG_ERR_NOMEM;
+                       } else {
+                               ret = LTTNG_ERR_INVALID;
                        }
+                       goto error;
+               }
+               /* Use the global session count for the temporary snapshot. */
+               tmp_output.nb_snapshot = session->snapshot.nb_snapshot;
+               use_tmp_output = 1;
+       }
+
+       /*
+        * Get the total number of stream of that session which is used by the
+        * maximum size of the snapshot feature.
+        */
+       nb_streams = get_total_nb_stream(session);
+
+       if (session->kernel_session) {
+               struct ltt_kernel_session *ksess = session->kernel_session;
 
-                       if (!consumer->dst.net.data_isset) {
-                               ret = LTTCOMM_URL_DATA_MISS;
+               if (use_tmp_output) {
+                       ret = record_kernel_snapshot(ksess, &tmp_output, session,
+                                       wait, nb_streams);
+                       if (ret != LTTNG_OK) {
                                goto error;
                        }
+                       snapshot_success = 1;
+               } else {
+                       struct snapshot_output *sout;
+                       struct lttng_ht_iter iter;
+
+                       rcu_read_lock();
+                       cds_lfht_for_each_entry(session->snapshot.output_ht->ht,
+                                       &iter.iter, sout, node.node) {
+                               /*
+                                * Make a local copy of the output and assign the possible
+                                * temporary value given by the caller.
+                                */
+                               memset(&tmp_output, 0, sizeof(tmp_output));
+                               memcpy(&tmp_output, sout, sizeof(tmp_output));
+
+                               /* Use temporary max size. */
+                               if (output->max_size != (uint64_t) -1ULL) {
+                                       tmp_output.max_size = output->max_size;
+                               }
 
-                       /* Check established network session state */
-                       if (session->net_handle == 0) {
-                               ret = LTTCOMM_ENABLE_CONSUMER_FAIL;
-                               DBG2("Session network handle is not set on enable-consumer");
-                               goto error;
+                               /* Use temporary name. */
+                               if (*output->name != '\0') {
+                                       strncpy(tmp_output.name, output->name,
+                                                       sizeof(tmp_output.name));
+                               }
+
+                               tmp_output.nb_snapshot = session->snapshot.nb_snapshot;
+
+                               ret = record_kernel_snapshot(ksess, &tmp_output,
+                                               session, wait, nb_streams);
+                               if (ret != LTTNG_OK) {
+                                       rcu_read_unlock();
+                                       goto error;
+                               }
+                               snapshot_success = 1;
                        }
+                       rcu_read_unlock();
+               }
+       }
 
-                       if (consumer->net_seq_index == -1) {
-                               ret = LTTCOMM_ENABLE_CONSUMER_FAIL;
-                               DBG2("Network index is not set on the consumer");
+       if (session->ust_session) {
+               struct ltt_ust_session *usess = session->ust_session;
+
+               if (use_tmp_output) {
+                       ret = record_ust_snapshot(usess, &tmp_output, session,
+                                       wait, nb_streams);
+                       if (ret != LTTNG_OK) {
                                goto error;
                        }
+                       snapshot_success = 1;
+               } else {
+                       struct snapshot_output *sout;
+                       struct lttng_ht_iter iter;
+
+                       rcu_read_lock();
+                       cds_lfht_for_each_entry(session->snapshot.output_ht->ht,
+                                       &iter.iter, sout, node.node) {
+                               /*
+                                * Make a local copy of the output and assign the possible
+                                * temporary value given by the caller.
+                                */
+                               memset(&tmp_output, 0, sizeof(tmp_output));
+                               memcpy(&tmp_output, sout, sizeof(tmp_output));
+
+                               /* Use temporary max size. */
+                               if (output->max_size != (uint64_t) -1ULL) {
+                                       tmp_output.max_size = output->max_size;
+                               }
 
-                       break;
-               }
+                               /* Use temporary name. */
+                               if (*output->name != '\0') {
+                                       strncpy(tmp_output.name, output->name,
+                                                       sizeof(tmp_output.name));
+                               }
 
-               /* Append default kernel trace dir to subdir */
-               strncat(usess->consumer->subdir, DEFAULT_UST_TRACE_DIR,
-                               sizeof(usess->consumer->subdir));
+                               tmp_output.nb_snapshot = session->snapshot.nb_snapshot;
 
-               /*
-                * @session-lock
-                * This is race free for now since the session lock is acquired before
-                * ending up in this function. No other threads can access this kernel
-                * session without this lock hence freeing the consumer output object
-                * is valid.
-                */
-               rcu_read_lock();
-               consumer_destroy_output(usess->consumer);
-               rcu_read_unlock();
-               usess->consumer = consumer;
-               usess->tmp_consumer = NULL;
-
-               break;
+                               ret = record_ust_snapshot(usess, &tmp_output, session,
+                                               wait, nb_streams);
+                               if (ret != LTTNG_OK) {
+                                       rcu_read_unlock();
+                                       goto error;
+                               }
+                               snapshot_success = 1;
+                       }
+                       rcu_read_unlock();
+               }
        }
 
-       /* Enable it */
-       if (consumer) {
-               consumer->enabled = 1;
-               /* Success at this point */
-               ret = LTTCOMM_OK;
-       } else {
-               /* Should not really happend... */
-               ret = LTTCOMM_NO_CONSUMER;
+       if (snapshot_success) {
+               session->snapshot.nb_snapshot++;
        }
 
 error:
@@ -2319,10 +2747,12 @@ error:
 void cmd_init(void)
 {
        /*
-        * Set network sequence index to 1 for streams to match a relayd socket on
-        * the consumer side.
+        * Set network sequence index to 1 for streams to match a relayd
+        * socket on the consumer side.
         */
-       uatomic_set(&relayd_net_seq_idx, 1);
+       pthread_mutex_lock(&relayd_net_seq_idx_lock);
+       relayd_net_seq_idx = 1;
+       pthread_mutex_unlock(&relayd_net_seq_idx_lock);
 
        DBG("Command subsystem initialized");
 }
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