SoW-2019-0002: Dynamic Snapshot
[lttng-tools.git] / src / bin / lttng-sessiond / kernel.c
index 19a325da1f1421b27c73bfb7866ae5204b87ca7b..646da3ba83affd3463a30dd7e2efb7a43b05535c 100644 (file)
@@ -1,18 +1,8 @@
 /*
- * Copyright (C) 2011 David Goulet <david.goulet@polymtl.ca>
+ * Copyright (C) 2011 David Goulet <david.goulet@polymtl.ca>
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License, version 2 only,
- * as published by the Free Software Foundation.
+ * SPDX-License-Identifier: GPL-2.0-only
  *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along
- * with this program; if not, write to the Free Software Foundation, Inc.,
- * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
 #define _LGPL_SOURCE
 #include <string.h>
 #include <unistd.h>
 #include <inttypes.h>
+#include <sys/types.h>
 
 #include <common/common.h>
+#include <common/hashtable/utils.h>
+#include <common/trace-chunk.h>
 #include <common/kernel-ctl/kernel-ctl.h>
 #include <common/kernel-ctl/kernel-ioctl.h>
 #include <common/sessiond-comm/sessiond-comm.h>
 
+#include <lttng/userspace-probe.h>
+#include <lttng/userspace-probe-internal.h>
+#include <lttng/condition/event-rule.h>
+#include <lttng/condition/event-rule-internal.h>
+#include <lttng/event-rule/event-rule.h>
+#include <lttng/event-rule/event-rule-internal.h>
+#include <lttng/event-rule/uprobe-internal.h>
+
+#include "lttng-sessiond.h"
+#include "lttng-syscall.h"
 #include "consumer.h"
 #include "kernel.h"
 #include "kernel-consumer.h"
 #include "kern-modules.h"
 #include "utils.h"
 #include "rotate.h"
+#include "modprobe.h"
+#include "notification-thread-commands.h"
 
 /*
  * Key used to reference a channel between the sessiond and the consumer. This
  */
 static uint64_t next_kernel_channel_key;
 
+static const char *module_proc_lttng = "/proc/lttng";
+
+static int kernel_tracer_fd = -1;
+static int kernel_tracer_trigger_group_fd = -1;
+static int kernel_tracer_trigger_group_notification_fd = -1;
+static struct ltt_kernel_token_event_rule_list kernel_tracer_token_list;
+
 /*
  * Add context on a kernel channel.
  *
@@ -89,7 +101,7 @@ error:
  * Create a new kernel session, register it to the kernel tracer and add it to
  * the session daemon session.
  */
-int kernel_create_session(struct ltt_session *session, int tracer_fd)
+int kernel_create_session(struct ltt_session *session)
 {
        int ret;
        struct ltt_kernel_session *lks;
@@ -104,7 +116,7 @@ int kernel_create_session(struct ltt_session *session, int tracer_fd)
        }
 
        /* Kernel tracer session creation */
-       ret = kernctl_create_session(tracer_fd);
+       ret = kernctl_create_session(kernel_tracer_fd);
        if (ret < 0) {
                PERROR("ioctl kernel create session");
                goto error;
@@ -123,11 +135,32 @@ int kernel_create_session(struct ltt_session *session, int tracer_fd)
 
        DBG("Kernel session created (fd: %d)", lks->fd);
 
+       /*
+        * This is necessary since the creation time is present in the session
+        * name when it is generated.
+        */
+       if (session->has_auto_generated_name) {
+               ret = kernctl_session_set_name(lks->fd, DEFAULT_SESSION_NAME);
+       } else {
+               ret = kernctl_session_set_name(lks->fd, session->name);
+       }
+       if (ret) {
+               WARN("Could not set kernel session name for session %" PRIu64 " name: %s",
+                       session->id, session->name);
+       }
+
+       ret = kernctl_session_set_creation_time(lks->fd, session->creation_time);
+       if (ret) {
+               WARN("Could not set kernel session creation time for session %" PRIu64 " name: %s",
+                       session->id, session->name);
+       }
+
        return 0;
 
 error:
        if (lks) {
                trace_kernel_destroy_session(lks);
+               trace_kernel_free_session(lks);
        }
        return ret;
 }
@@ -191,6 +224,325 @@ error:
        return -1;
 }
 
+/*
+ * Create a kernel channel, register it to the kernel tracer and add it to the
+ * kernel session.
+ */
+static
+int kernel_create_trigger_group(int *trigger_group_fd)
+{
+       int ret;
+       int local_fd = -1;
+
+       assert(trigger_group_fd);
+
+       /* Kernel tracer channel creation */
+       ret = kernctl_create_trigger_group(kernel_tracer_fd);
+       if (ret < 0) {
+               PERROR("ioctl kernel create trigger group");
+               ret = -1;
+               goto error;
+       }
+
+       /* Store locally */
+       local_fd = ret;
+
+       /* Prevent fd duplication after execlp() */
+       ret = fcntl(local_fd, F_SETFD, FD_CLOEXEC);
+       if (ret < 0) {
+               PERROR("fcntl session fd");
+       }
+
+       DBG("Kernel trigger group created (fd: %d)",
+                       local_fd);
+       ret = 0;
+
+error:
+       *trigger_group_fd = local_fd;
+       return ret;
+}
+
+/*
+ * Compute the offset of the instrumentation byte in the binary based on the
+ * function probe location using the ELF lookup method.
+ *
+ * Returns 0 on success and set the offset out parameter to the offset of the
+ * elf symbol
+ * Returns -1 on error
+ */
+static
+int extract_userspace_probe_offset_function_elf(
+               const struct lttng_userspace_probe_location *probe_location,
+               uid_t uid, gid_t gid, uint64_t *offset)
+{
+       int fd;
+       int ret = 0;
+       const char *symbol = NULL;
+       const struct lttng_userspace_probe_location_lookup_method *lookup = NULL;
+       enum lttng_userspace_probe_location_lookup_method_type lookup_method_type;
+
+       assert(lttng_userspace_probe_location_get_type(probe_location) ==
+                       LTTNG_USERSPACE_PROBE_LOCATION_TYPE_FUNCTION);
+
+       lookup = lttng_userspace_probe_location_get_lookup_method(
+                       probe_location);
+       if (!lookup) {
+               ret = -1;
+               goto end;
+       }
+
+       lookup_method_type =
+                       lttng_userspace_probe_location_lookup_method_get_type(lookup);
+
+       assert(lookup_method_type ==
+                       LTTNG_USERSPACE_PROBE_LOCATION_LOOKUP_METHOD_TYPE_FUNCTION_ELF);
+
+       symbol = lttng_userspace_probe_location_function_get_function_name(
+                       probe_location);
+       if (!symbol) {
+               ret = -1;
+               goto end;
+       }
+
+       fd = lttng_userspace_probe_location_function_get_binary_fd(probe_location);
+       if (fd < 0) {
+               ret = -1;
+               goto end;
+       }
+
+       ret = run_as_extract_elf_symbol_offset(fd, symbol, uid, gid, offset);
+       if (ret < 0) {
+               DBG("userspace probe offset calculation failed for "
+                               "function %s", symbol);
+               goto end;
+       }
+
+       DBG("userspace probe elf offset for %s is 0x%jd", symbol, (intmax_t)(*offset));
+end:
+       return ret;
+}
+
+/*
+ * Compute the offsets of the instrumentation bytes in the binary based on the
+ * tracepoint probe location using the SDT lookup method. This function
+ * allocates the offsets buffer, the caller must free it.
+ *
+ * Returns 0 on success and set the offset out parameter to the offsets of the
+ * SDT tracepoint.
+ * Returns -1 on error.
+ */
+static
+int extract_userspace_probe_offset_tracepoint_sdt(
+               const struct lttng_userspace_probe_location *probe_location,
+               uid_t uid, gid_t gid, uint64_t **offsets,
+               uint32_t *offsets_count)
+{
+       enum lttng_userspace_probe_location_lookup_method_type lookup_method_type;
+       const struct lttng_userspace_probe_location_lookup_method *lookup = NULL;
+       const char *probe_name = NULL, *provider_name = NULL;
+       int ret = 0;
+       int fd, i;
+
+       assert(lttng_userspace_probe_location_get_type(probe_location) ==
+                       LTTNG_USERSPACE_PROBE_LOCATION_TYPE_TRACEPOINT);
+
+       lookup = lttng_userspace_probe_location_get_lookup_method(probe_location);
+       if (!lookup) {
+               ret = -1;
+               goto end;
+       }
+
+       lookup_method_type =
+                       lttng_userspace_probe_location_lookup_method_get_type(lookup);
+
+       assert(lookup_method_type ==
+                       LTTNG_USERSPACE_PROBE_LOCATION_LOOKUP_METHOD_TYPE_TRACEPOINT_SDT);
+
+
+       probe_name = lttng_userspace_probe_location_tracepoint_get_probe_name(
+                       probe_location);
+       if (!probe_name) {
+               ret = -1;
+               goto end;
+       }
+
+       provider_name = lttng_userspace_probe_location_tracepoint_get_provider_name(
+                       probe_location);
+       if (!provider_name) {
+               ret = -1;
+               goto end;
+       }
+
+       fd = lttng_userspace_probe_location_tracepoint_get_binary_fd(probe_location);
+       if (fd < 0) {
+               ret = -1;
+               goto end;
+       }
+
+       ret = run_as_extract_sdt_probe_offsets(fd, provider_name, probe_name,
+                       uid, gid, offsets, offsets_count);
+       if (ret < 0) {
+               DBG("userspace probe offset calculation failed for sdt "
+                               "probe %s:%s", provider_name, probe_name);
+               goto end;
+       }
+
+       if (*offsets_count == 0) {
+               DBG("no userspace probe offset found");
+               goto end;
+       }
+
+       DBG("%u userspace probe SDT offsets found for %s:%s at:",
+                       *offsets_count, provider_name, probe_name);
+       for (i = 0; i < *offsets_count; i++) {
+               DBG("\t0x%jd", (intmax_t)((*offsets)[i]));
+       }
+end:
+       return ret;
+}
+
+static
+int userspace_probe_add_callsite(
+               const struct lttng_userspace_probe_location *location,
+               uid_t uid, gid_t gid, int fd)
+{
+       const struct lttng_userspace_probe_location_lookup_method *lookup_method = NULL;
+       enum lttng_userspace_probe_location_lookup_method_type type;
+       int ret;
+
+       lookup_method = lttng_userspace_probe_location_get_lookup_method(location);
+       if (!lookup_method) {
+               ret = -1;
+               goto end;
+       }
+
+       type = lttng_userspace_probe_location_lookup_method_get_type(lookup_method);
+       switch (type) {
+       case LTTNG_USERSPACE_PROBE_LOCATION_LOOKUP_METHOD_TYPE_FUNCTION_ELF:
+       {
+               struct lttng_kernel_event_callsite callsite;
+               uint64_t offset;
+
+               ret = extract_userspace_probe_offset_function_elf(location,
+                               uid, gid, &offset);
+               if (ret) {
+                       ret = LTTNG_ERR_PROBE_LOCATION_INVAL;
+                       goto end;
+               }
+
+               callsite.u.uprobe.offset = offset;
+               ret = kernctl_add_callsite(fd, &callsite);
+               if (ret) {
+                       WARN("Adding callsite to ELF userspace probe failed.");
+                       ret = LTTNG_ERR_KERN_ENABLE_FAIL;
+                       goto end;
+               }
+               break;
+       }
+       case LTTNG_USERSPACE_PROBE_LOCATION_LOOKUP_METHOD_TYPE_TRACEPOINT_SDT:
+       {
+               int i;
+               uint64_t *offsets = NULL;
+               uint32_t offsets_count;
+               struct lttng_kernel_event_callsite callsite;
+
+               /*
+                * This call allocates the offsets buffer. This buffer must be freed
+                * by the caller
+                */
+               ret = extract_userspace_probe_offset_tracepoint_sdt(location,
+                               uid, gid, &offsets, &offsets_count);
+               if (ret) {
+                       ret = LTTNG_ERR_PROBE_LOCATION_INVAL;
+                       goto end;
+               }
+               for (i = 0; i < offsets_count; i++) {
+                       callsite.u.uprobe.offset = offsets[i];
+                       ret = kernctl_add_callsite(fd, &callsite);
+                       if (ret) {
+                               WARN("Adding callsite to SDT userspace probe "
+                                       "failed.");
+                               ret = LTTNG_ERR_KERN_ENABLE_FAIL;
+                               free(offsets);
+                               goto end;
+                       }
+               }
+               free(offsets);
+               break;
+       }
+       default:
+               ret = LTTNG_ERR_PROBE_LOCATION_INVAL;
+               goto end;
+       }
+end:
+       return ret;
+}
+
+/*
+ * Extract the offsets of the instrumentation point for the different lookup
+ * methods.
+ */
+static
+int userspace_probe_event_add_callsites(struct lttng_event *ev,
+                       struct ltt_kernel_session *session, int fd)
+{
+       const struct lttng_userspace_probe_location *location = NULL;
+       int ret;
+
+       assert(ev);
+       assert(ev->type == LTTNG_EVENT_USERSPACE_PROBE);
+
+       location = lttng_event_get_userspace_probe_location(ev);
+       if (!location) {
+               ret = -1;
+               goto end;
+       }
+
+       ret = userspace_probe_add_callsite(location, session->uid, session->gid,
+               fd);
+       if (ret) {
+               WARN("Adding callsite to userspace probe event \"%s\" "
+                       "failed.", ev->name);
+       }
+
+end:
+       return ret;
+}
+
+/*
+ * Extract the offsets of the instrumentation point for the different lookup
+ * methods.
+ */
+static int userspace_probe_event_rule_add_callsites(
+               const struct lttng_event_rule *rule,
+               const struct lttng_credentials *creds,
+               int fd)
+{
+       const struct lttng_userspace_probe_location *location = NULL;
+       enum lttng_event_rule_status status;
+       int ret;
+
+       assert(rule);
+       assert(creds);
+       assert(lttng_event_rule_get_type(rule) == LTTNG_EVENT_RULE_TYPE_UPROBE);
+
+       status = lttng_event_rule_uprobe_get_location(rule, &location);
+       if (status != LTTNG_EVENT_RULE_STATUS_OK || !location) {
+               ret = -1;
+               goto end;
+       }
+
+       ret = userspace_probe_add_callsite(location, creds->uid, creds->gid,
+               fd);
+       if (ret) {
+               WARN("Adding callsite to userspace probe object %d"
+                       "failed.", fd);
+       }
+
+end:
+       return ret;
+}
+
 /*
  * Create a kernel event, enable it to the kernel tracer and add it to the
  * channel event list of the kernel session.
@@ -201,60 +553,81 @@ int kernel_create_event(struct lttng_event *ev,
                char *filter_expression,
                struct lttng_filter_bytecode *filter)
 {
-       int ret;
+       int err, fd;
+       enum lttng_error_code ret;
        struct ltt_kernel_event *event;
 
        assert(ev);
        assert(channel);
 
        /* We pass ownership of filter_expression and filter */
-       event = trace_kernel_create_event(ev, filter_expression,
-                       filter);
-       if (event == NULL) {
-               ret = -1;
+       ret = trace_kernel_create_event(ev, filter_expression,
+                       filter, &event);
+       if (ret != LTTNG_OK) {
                goto error;
        }
 
-       ret = kernctl_create_event(channel->fd, event->event);
-       if (ret < 0) {
-               switch (-ret) {
+       fd = kernctl_create_event(channel->fd, event->event);
+       if (fd < 0) {
+               switch (-fd) {
                case EEXIST:
+                       ret = LTTNG_ERR_KERN_EVENT_EXIST;
                        break;
                case ENOSYS:
                        WARN("Event type not implemented");
+                       ret = LTTNG_ERR_KERN_EVENT_ENOSYS;
                        break;
                case ENOENT:
                        WARN("Event %s not found!", ev->name);
+                       ret = LTTNG_ERR_KERN_ENABLE_FAIL;
                        break;
                default:
+                       ret = LTTNG_ERR_KERN_ENABLE_FAIL;
                        PERROR("create event ioctl");
                }
                goto free_event;
        }
 
        event->type = ev->type;
-       event->fd = ret;
+       event->fd = fd;
        /* Prevent fd duplication after execlp() */
-       ret = fcntl(event->fd, F_SETFD, FD_CLOEXEC);
-       if (ret < 0) {
+       err = fcntl(event->fd, F_SETFD, FD_CLOEXEC);
+       if (err < 0) {
                PERROR("fcntl session fd");
        }
 
        if (filter) {
-               ret = kernctl_filter(event->fd, filter);
-               if (ret) {
+               err = kernctl_filter(event->fd, filter);
+               if (err < 0) {
+                       switch (-err) {
+                       case ENOMEM:
+                               ret = LTTNG_ERR_FILTER_NOMEM;
+                               break;
+                       default:
+                               ret = LTTNG_ERR_FILTER_INVAL;
+                               break;
+                       }
                        goto filter_error;
                }
        }
 
-       ret = kernctl_enable(event->fd);
-       if (ret < 0) {
-               switch (-ret) {
+       if (ev->type == LTTNG_EVENT_USERSPACE_PROBE) {
+               ret = userspace_probe_event_add_callsites(ev, channel->session,
+                       event->fd);
+               if (ret) {
+                       goto add_callsite_error;
+               }
+       }
+
+       err = kernctl_enable(event->fd);
+       if (err < 0) {
+               switch (-err) {
                case EEXIST:
                        ret = LTTNG_ERR_KERN_EVENT_EXIST;
                        break;
                default:
                        PERROR("enable kernel event");
+                       ret = LTTNG_ERR_KERN_ENABLE_FAIL;
                        break;
                }
                goto enable_error;
@@ -268,6 +641,7 @@ int kernel_create_event(struct lttng_event *ev,
 
        return 0;
 
+add_callsite_error:
 enable_error:
 filter_error:
        {
@@ -396,120 +770,311 @@ error:
        return ret;
 }
 
-
-int kernel_track_pid(struct ltt_kernel_session *session, int pid)
+/*
+ * Disable a kernel trigger.
+ */
+int kernel_disable_token_event_rule(struct ltt_kernel_token_event_rule *event)
 {
        int ret;
 
-       DBG("Kernel track PID %d for session id %" PRIu64 ".",
-                       pid, session->id);
-       ret = kernctl_track_pid(session->fd, pid);
-       if (!ret) {
-               return LTTNG_OK;
-       }
-       switch (-ret) {
-       case EINVAL:
-               return LTTNG_ERR_INVALID;
-       case ENOMEM:
-               return LTTNG_ERR_NOMEM;
-       case EEXIST:
-               return LTTNG_ERR_PID_TRACKED;
-       default:
-               return LTTNG_ERR_UNK;
+       assert(event);
+
+       ret = kernctl_disable(event->fd);
+       if (ret < 0) {
+               switch (-ret) {
+               case EEXIST:
+                       ret = LTTNG_ERR_KERN_EVENT_EXIST;
+                       break;
+               default:
+                       PERROR("disable kernel event");
+                       break;
+               }
+               goto error;
        }
-}
 
-int kernel_untrack_pid(struct ltt_kernel_session *session, int pid)
-{
-       int ret;
+       event->enabled = 0;
+       DBG("Kernel trigger token %" PRIu64" disabled (fd: %d)", event->token, event->fd);
 
-       DBG("Kernel untrack PID %d for session id %" PRIu64 ".",
-                       pid, session->id);
-       ret = kernctl_untrack_pid(session->fd, pid);
-       if (!ret) {
-               return LTTNG_OK;
-       }
-       switch (-ret) {
-       case EINVAL:
-               return LTTNG_ERR_INVALID;
-       case ENOMEM:
-               return LTTNG_ERR_NOMEM;
-       case ENOENT:
-               return LTTNG_ERR_PID_NOT_TRACKED;
+       return 0;
+
+error:
+       return ret;
+}
+static struct lttng_tracker_list *get_id_tracker_list(
+               struct ltt_kernel_session *session,
+               enum lttng_tracker_type tracker_type)
+{
+       switch (tracker_type) {
+       case LTTNG_TRACKER_PID:
+               return session->tracker_list_pid;
+       case LTTNG_TRACKER_VPID:
+               return session->tracker_list_vpid;
+       case LTTNG_TRACKER_UID:
+               return session->tracker_list_uid;
+       case LTTNG_TRACKER_VUID:
+               return session->tracker_list_vuid;
+       case LTTNG_TRACKER_GID:
+               return session->tracker_list_gid;
+       case LTTNG_TRACKER_VGID:
+               return session->tracker_list_vgid;
        default:
-               return LTTNG_ERR_UNK;
+               return NULL;
        }
 }
 
-ssize_t kernel_list_tracker_pids(struct ltt_kernel_session *session,
-               int **_pids)
+int kernel_track_id(enum lttng_tracker_type tracker_type,
+               struct ltt_kernel_session *session,
+               const struct lttng_tracker_id *id)
 {
-       int fd, ret;
-       int pid;
-       ssize_t nbmem, count = 0;
-       FILE *fp;
-       int *pids;
+       int ret, value;
+       struct lttng_tracker_list *tracker_list;
+       struct lttng_tracker_ids *saved_ids;
 
-       fd = kernctl_list_tracker_pids(session->fd);
-       if (fd < 0) {
-               PERROR("kernel tracker pids list");
-               goto error;
+       ret = lttng_tracker_id_lookup_string(tracker_type, id, &value);
+       if (ret != LTTNG_OK) {
+               return ret;
        }
 
-       fp = fdopen(fd, "r");
-       if (fp == NULL) {
-               PERROR("kernel tracker pids list fdopen");
-               goto error_fp;
+       tracker_list = get_id_tracker_list(session, tracker_type);
+       if (!tracker_list) {
+               return LTTNG_ERR_INVALID;
        }
 
-       nbmem = KERNEL_TRACKER_PIDS_INIT_LIST_SIZE;
-       pids = zmalloc(sizeof(*pids) * nbmem);
-       if (pids == NULL) {
-               PERROR("alloc list pids");
-               count = -ENOMEM;
-               goto end;
+       /* Save list for restore on error. */
+       ret = lttng_tracker_id_get_list(tracker_list, &saved_ids);
+       if (ret != LTTNG_OK) {
+               return LTTNG_ERR_INVALID;
        }
 
-       while (fscanf(fp, "process { pid = %u; };\n", &pid) == 1) {
-               if (count >= nbmem) {
-                       int *new_pids;
-                       size_t new_nbmem;
-
-                       new_nbmem = nbmem << 1;
-                       DBG("Reallocating pids list from %zu to %zu entries",
-                                       nbmem, new_nbmem);
-                       new_pids = realloc(pids, new_nbmem * sizeof(*new_pids));
-                       if (new_pids == NULL) {
-                               PERROR("realloc list events");
-                               free(pids);
-                               count = -ENOMEM;
-                               goto end;
-                       }
-                       /* Zero the new memory */
-                       memset(new_pids + nbmem, 0,
-                               (new_nbmem - nbmem) * sizeof(*new_pids));
-                       nbmem = new_nbmem;
-                       pids = new_pids;
-               }
-               pids[count++] = pid;
+       /* Add to list. */
+       ret = lttng_tracker_list_add(tracker_list, id);
+       if (ret != LTTNG_OK) {
+               goto end;
        }
 
-       *_pids = pids;
-       DBG("Kernel list tracker pids done (%zd pids)", count);
+       switch (tracker_type) {
+       case LTTNG_TRACKER_PID:
+               DBG("Kernel track PID %d for session id %" PRIu64 ".", value,
+                               session->id);
+               ret = kernctl_track_pid(session->fd, value);
+               if (!ret) {
+                       ret = LTTNG_OK;
+                       goto end;
+               }
+               break;
+       case LTTNG_TRACKER_VPID:
+               DBG("Kernel track VPID %d for session id %" PRIu64 ".", value,
+                               session->id);
+               ret = kernctl_track_id(session->fd, LTTNG_TRACKER_VPID, value);
+               if (!ret) {
+                       ret = LTTNG_OK;
+                       goto end;
+               }
+               break;
+       case LTTNG_TRACKER_UID:
+               DBG("Kernel track UID %d for session id %" PRIu64 ".", value,
+                               session->id);
+               ret = kernctl_track_id(session->fd, LTTNG_TRACKER_UID, value);
+               if (!ret) {
+                       ret = LTTNG_OK;
+                       goto end;
+               }
+               break;
+       case LTTNG_TRACKER_GID:
+               DBG("Kernel track GID %d for session id %" PRIu64 ".", value,
+                               session->id);
+               ret = kernctl_track_id(session->fd, LTTNG_TRACKER_GID, value);
+               if (!ret) {
+                       ret = LTTNG_OK;
+                       goto end;
+               }
+               break;
+       case LTTNG_TRACKER_VUID:
+               DBG("Kernel track VUID %d for session id %" PRIu64 ".", value,
+                               session->id);
+               ret = kernctl_track_id(session->fd, LTTNG_TRACKER_VUID, value);
+               if (!ret) {
+                       ret = LTTNG_OK;
+                       goto end;
+               }
+               break;
+       case LTTNG_TRACKER_VGID:
+               DBG("Kernel track VGID %d for session id %" PRIu64 ".", value,
+                               session->id);
+               ret = kernctl_track_id(session->fd, LTTNG_TRACKER_VGID, value);
+               if (!ret) {
+                       ret = LTTNG_OK;
+                       goto end;
+               }
+               break;
+       default:
+               ret = -EINVAL;
+               break;
+       }
+
+       /* Error handling. */
+       switch (-ret) {
+       case EINVAL:
+               ret = LTTNG_ERR_INVALID;
+               break;
+       case ENOMEM:
+               ret = LTTNG_ERR_NOMEM;
+               break;
+       case EEXIST:
+               ret = LTTNG_ERR_ID_TRACKED;
+               break;
+       default:
+               ret = LTTNG_ERR_UNK;
+               break;
+       }
+
+       if (lttng_tracker_id_set_list(tracker_list, saved_ids) != LTTNG_OK) {
+               ERR("Error on tracker add error handling.\n");
+       }
 end:
-       ret = fclose(fp);       /* closes both fp and fd */
-       if (ret) {
-               PERROR("fclose");
+       lttng_tracker_ids_destroy(saved_ids);
+       return ret;
+}
+
+int kernel_untrack_id(enum lttng_tracker_type tracker_type,
+               struct ltt_kernel_session *session,
+               const struct lttng_tracker_id *id)
+{
+       int ret, value;
+       struct lttng_tracker_list *tracker_list;
+       struct lttng_tracker_ids *saved_ids;
+
+       ret = lttng_tracker_id_lookup_string(tracker_type, id, &value);
+       if (ret != LTTNG_OK) {
+               return ret;
        }
-       return count;
 
-error_fp:
-       ret = close(fd);
-       if (ret) {
-               PERROR("close");
+       tracker_list = get_id_tracker_list(session, tracker_type);
+       if (!tracker_list) {
+               return LTTNG_ERR_INVALID;
        }
-error:
-       return -1;
+       /* Save list for restore on error. */
+       ret = lttng_tracker_id_get_list(tracker_list, &saved_ids);
+       if (ret != LTTNG_OK) {
+               return LTTNG_ERR_INVALID;
+       }
+       /* Remove from list. */
+       ret = lttng_tracker_list_remove(tracker_list, id);
+       if (ret != LTTNG_OK) {
+               goto end;
+       }
+
+       switch (tracker_type) {
+       case LTTNG_TRACKER_PID:
+               DBG("Kernel untrack PID %d for session id %" PRIu64 ".", value,
+                               session->id);
+               ret = kernctl_untrack_pid(session->fd, value);
+               if (!ret) {
+                       ret = LTTNG_OK;
+                       goto end;
+               }
+               break;
+       case LTTNG_TRACKER_VPID:
+               DBG("Kernel untrack VPID %d for session id %" PRIu64 ".", value,
+                               session->id);
+               ret = kernctl_untrack_id(
+                               session->fd, LTTNG_TRACKER_VPID, value);
+               if (!ret) {
+                       ret = LTTNG_OK;
+                       goto end;
+               }
+               break;
+       case LTTNG_TRACKER_UID:
+               DBG("Kernel untrack UID %d for session id %" PRIu64 ".", value,
+                               session->id);
+               ret = kernctl_untrack_id(session->fd, LTTNG_TRACKER_UID, value);
+               if (!ret) {
+                       ret = LTTNG_OK;
+                       goto end;
+               }
+               break;
+       case LTTNG_TRACKER_GID:
+               DBG("Kernel untrack GID %d for session id %" PRIu64 ".", value,
+                               session->id);
+               ret = kernctl_untrack_id(session->fd, LTTNG_TRACKER_GID, value);
+               if (!ret) {
+                       ret = LTTNG_OK;
+                       goto end;
+               }
+               break;
+       case LTTNG_TRACKER_VUID:
+               DBG("Kernel untrack VUID %d for session id %" PRIu64 ".", value,
+                               session->id);
+               ret = kernctl_untrack_id(
+                               session->fd, LTTNG_TRACKER_VUID, value);
+               if (!ret) {
+                       ret = LTTNG_OK;
+                       goto end;
+               }
+               break;
+       case LTTNG_TRACKER_VGID:
+               DBG("Kernel untrack VGID %d for session id %" PRIu64 ".", value,
+                               session->id);
+               ret = kernctl_untrack_id(
+                               session->fd, LTTNG_TRACKER_VGID, value);
+               if (!ret) {
+                       ret = LTTNG_OK;
+                       goto end;
+               }
+               break;
+       default:
+               ret = -EINVAL;
+               break;
+       }
+
+       /* Error handling. */
+       switch (-ret) {
+       case EINVAL:
+               ret = LTTNG_ERR_INVALID;
+               break;
+       case ENOMEM:
+               ret = LTTNG_ERR_NOMEM;
+               break;
+       case EEXIST:
+               ret = LTTNG_ERR_ID_TRACKED;
+               break;
+       default:
+               ret = LTTNG_ERR_UNK;
+               break;
+       }
+
+       if (lttng_tracker_id_set_list(tracker_list, saved_ids) != LTTNG_OK) {
+               ERR("Error on tracker remove error handling.\n");
+       }
+end:
+       lttng_tracker_ids_destroy(saved_ids);
+       return ret;
+}
+
+/*
+ * Called with session lock held.
+ */
+int kernel_list_tracker_ids(enum lttng_tracker_type tracker_type,
+               struct ltt_kernel_session *session,
+               struct lttng_tracker_ids **_ids)
+{
+       int ret = 0;
+       struct lttng_tracker_list *tracker_list;
+
+       tracker_list = get_id_tracker_list(session, tracker_type);
+       if (!tracker_list) {
+               ret = -LTTNG_ERR_INVALID;
+               goto end;
+       }
+
+       ret = lttng_tracker_id_get_list(tracker_list, _ids);
+       if (ret != LTTNG_OK) {
+               ret = -LTTNG_ERR_INVALID;
+               goto end;
+       }
+
+end:
+       return ret;
 }
 
 /*
@@ -581,9 +1146,10 @@ error:
 /*
  * Make a kernel wait to make sure in-flight probe have completed.
  */
-void kernel_wait_quiescent(int fd)
+void kernel_wait_quiescent(void)
 {
        int ret;
+       int fd = kernel_tracer_fd;
 
        DBG("Kernel quiescent wait on %d", fd);
 
@@ -742,7 +1308,7 @@ error:
 /*
  * Get the event list from the kernel tracer and return the number of elements.
  */
-ssize_t kernel_list_events(int tracer_fd, struct lttng_event **events)
+ssize_t kernel_list_events(struct lttng_event **events)
 {
        int fd, ret;
        char *event;
@@ -752,7 +1318,7 @@ ssize_t kernel_list_events(int tracer_fd, struct lttng_event **events)
 
        assert(events);
 
-       fd = kernctl_tracepoint_list(tracer_fd);
+       fd = kernctl_tracepoint_list(kernel_tracer_fd);
        if (fd < 0) {
                PERROR("kernel tracepoint list");
                goto error;
@@ -826,13 +1392,12 @@ error:
 /*
  * Get kernel version and validate it.
  */
-int kernel_validate_version(int tracer_fd,
-               struct lttng_kernel_tracer_version *version,
+int kernel_validate_version(struct lttng_kernel_tracer_version *version,
                struct lttng_kernel_tracer_abi_version *abi_version)
 {
        int ret;
 
-       ret = kernctl_tracer_version(tracer_fd, version);
+       ret = kernctl_tracer_version(kernel_tracer_fd, version);
        if (ret < 0) {
                ERR("Failed to retrieve the lttng-modules version");
                goto error;
@@ -844,7 +1409,7 @@ int kernel_validate_version(int tracer_fd,
                        version->major, VERSION_MAJOR);
                goto error_version;
        }
-       ret = kernctl_tracer_abi_version(tracer_fd, abi_version);
+       ret = kernctl_tracer_abi_version(kernel_tracer_fd, abi_version);
        if (ret < 0) {
                ERR("Failed to retrieve lttng-modules ABI version");
                goto error;
@@ -902,16 +1467,19 @@ end_boot_id:
 }
 
 /*
- * Complete teardown of a kernel session.
+ * Teardown of a kernel session, keeping data required by destroy notifiers.
  */
 void kernel_destroy_session(struct ltt_kernel_session *ksess)
 {
+       struct lttng_trace_chunk *trace_chunk;
+
        if (ksess == NULL) {
                DBG3("No kernel session when tearing down session");
                return;
        }
 
        DBG("Tearing down kernel session");
+       trace_chunk = ksess->current_trace_chunk;
 
        /*
         * Destroy channels on the consumer if at least one FD has been sent and we
@@ -945,6 +1513,16 @@ void kernel_destroy_session(struct ltt_kernel_session *ksess)
        consumer_output_send_destroy_relayd(ksess->consumer);
 
        trace_kernel_destroy_session(ksess);
+       lttng_trace_chunk_put(trace_chunk);
+}
+
+/* Teardown of data required by destroy notifiers. */
+void kernel_free_session(struct ltt_kernel_session *ksess)
+{
+       if (ksess == NULL) {
+               return;
+       }
+       trace_kernel_free_session(ksess);
 }
 
 /*
@@ -980,16 +1558,20 @@ void kernel_destroy_channel(struct ltt_kernel_channel *kchan)
 /*
  * Take a snapshot for a given kernel session.
  *
- * Return 0 on success or else return a LTTNG_ERR code.
+ * Return LTTNG_OK on success or else return a LTTNG_ERR code.
  */
-int kernel_snapshot_record(struct ltt_kernel_session *ksess,
-               struct snapshot_output *output, int wait,
+enum lttng_error_code kernel_snapshot_record(
+               struct ltt_kernel_session *ksess,
+               const struct consumer_output *output, int wait,
                uint64_t nb_packets_per_stream)
 {
        int err, ret, saved_metadata_fd;
+       enum lttng_error_code status = LTTNG_OK;
        struct consumer_socket *socket;
        struct lttng_ht_iter iter;
        struct ltt_kernel_metadata *saved_metadata;
+       char *trace_path = NULL;
+       size_t consumer_path_offset = 0;
 
        assert(ksess);
        assert(ksess->consumer);
@@ -1005,48 +1587,43 @@ int kernel_snapshot_record(struct ltt_kernel_session *ksess,
 
        ret = kernel_open_metadata(ksess);
        if (ret < 0) {
-               ret = LTTNG_ERR_KERN_META_FAIL;
+               status = LTTNG_ERR_KERN_META_FAIL;
                goto error;
        }
 
        ret = kernel_open_metadata_stream(ksess);
        if (ret < 0) {
-               ret = LTTNG_ERR_KERN_META_FAIL;
+               status = LTTNG_ERR_KERN_META_FAIL;
                goto error_open_stream;
        }
 
+       trace_path = setup_channel_trace_path(ksess->consumer,
+                       DEFAULT_KERNEL_TRACE_DIR, &consumer_path_offset);
+       if (!trace_path) {
+               status = LTTNG_ERR_INVALID;
+               goto error;
+       }
        /* Send metadata to consumer and snapshot everything. */
-       cds_lfht_for_each_entry(ksess->consumer->socks->ht, &iter.iter,
+       cds_lfht_for_each_entry(output->socks->ht, &iter.iter,
                        socket, node.node) {
-               struct consumer_output *saved_output;
                struct ltt_kernel_channel *chan;
 
-               /*
-                * Temporarly switch consumer output for our snapshot output. As long
-                * as the session lock is taken, this is safe.
-                */
-               saved_output = ksess->consumer;
-               ksess->consumer = output->consumer;
-
                pthread_mutex_lock(socket->lock);
                /* This stream must not be monitored by the consumer. */
                ret = kernel_consumer_add_metadata(socket, ksess, 0);
                pthread_mutex_unlock(socket->lock);
-               /* Put back the saved consumer output into the session. */
-               ksess->consumer = saved_output;
                if (ret < 0) {
-                       ret = LTTNG_ERR_KERN_CONSUMER_FAIL;
+                       status = LTTNG_ERR_KERN_META_FAIL;
                        goto error_consumer;
                }
 
                /* For each channel, ask the consumer to snapshot it. */
                cds_list_for_each_entry(chan, &ksess->channel_list.head, list) {
-                       ret = consumer_snapshot_channel(socket, chan->key, output, 0,
+                       status = consumer_snapshot_channel(socket, chan->key, output, 0,
                                        ksess->uid, ksess->gid,
-                                       DEFAULT_KERNEL_TRACE_DIR, wait,
+                                       &trace_path[consumer_path_offset], wait,
                                        nb_packets_per_stream);
-                       if (ret < 0) {
-                               ret = LTTNG_ERR_KERN_CONSUMER_FAIL;
+                       if (status != LTTNG_OK) {
                                (void) kernel_consumer_destroy_metadata(socket,
                                                ksess->metadata);
                                goto error_consumer;
@@ -1054,11 +1631,10 @@ int kernel_snapshot_record(struct ltt_kernel_session *ksess,
                }
 
                /* Snapshot metadata, */
-               ret = consumer_snapshot_channel(socket, ksess->metadata->key, output,
-                               1, ksess->uid, ksess->gid,
-                               DEFAULT_KERNEL_TRACE_DIR, wait, 0);
-               if (ret < 0) {
-                       ret = LTTNG_ERR_KERN_CONSUMER_FAIL;
+               status = consumer_snapshot_channel(socket, ksess->metadata->key, output,
+                               1, ksess->uid, ksess->gid, &trace_path[consumer_path_offset],
+                               wait, 0);
+               if (status != LTTNG_OK) {
                        goto error_consumer;
                }
 
@@ -1069,8 +1645,6 @@ int kernel_snapshot_record(struct ltt_kernel_session *ksess,
                (void) kernel_consumer_destroy_metadata(socket, ksess->metadata);
        }
 
-       ret = LTTNG_OK;
-
 error_consumer:
        /* Close newly opened metadata stream. It's now on the consumer side. */
        err = close(ksess->metadata_stream_fd);
@@ -1084,9 +1658,9 @@ error:
        /* Restore metadata state.*/
        ksess->metadata = saved_metadata;
        ksess->metadata_stream_fd = saved_metadata_fd;
-
        rcu_read_unlock();
-       return ret;
+       free(trace_path);
+       return status;
 }
 
 /*
@@ -1110,12 +1684,12 @@ int kernel_syscall_mask(int chan_fd, char **syscall_mask, uint32_t *nr_bits)
  * Return 1 on success, 0 when feature is not supported, negative value in case
  * of errors.
  */
-int kernel_supports_ring_buffer_snapshot_sample_positions(int tracer_fd)
+int kernel_supports_ring_buffer_snapshot_sample_positions(void)
 {
        int ret = 0; // Not supported by default
        struct lttng_kernel_tracer_abi_version abi;
 
-       ret = kernctl_tracer_abi_version(tracer_fd, &abi);
+       ret = kernctl_tracer_abi_version(kernel_tracer_fd, &abi);
        if (ret < 0) {
                ERR("Failed to retrieve lttng-modules ABI version");
                goto error;
@@ -1135,14 +1709,47 @@ error:
        return ret;
 }
 
+/*
+ * Check for the support of the packet sequence number via abi version number.
+ *
+ * Return 1 on success, 0 when feature is not supported, negative value in case
+ * of errors.
+ */
+int kernel_supports_ring_buffer_packet_sequence_number(void)
+{
+       int ret = 0; // Not supported by default
+       struct lttng_kernel_tracer_abi_version abi;
+
+       ret = kernctl_tracer_abi_version(kernel_tracer_fd, &abi);
+       if (ret < 0) {
+               ERR("Failed to retrieve lttng-modules ABI version");
+               goto error;
+       }
+
+       /*
+        * Packet sequence number was introduced in LTTng 2.8,
+        * lttng-modules ABI 2.1.
+        */
+       if (abi.major >= 2 && abi.minor >= 1) {
+               /* Supported */
+               ret = 1;
+       } else {
+               /* Not supported */
+               ret = 0;
+       }
+error:
+       return ret;
+}
+
 /*
  * Rotate a kernel session.
  *
- * Return 0 on success or else return a LTTNG_ERR code.
+ * Return LTTNG_OK on success or else an LTTng error code.
  */
-int kernel_rotate_session(struct ltt_session *session)
+enum lttng_error_code kernel_rotate_session(struct ltt_session *session)
 {
        int ret;
+       enum lttng_error_code status = LTTNG_OK;
        struct consumer_socket *socket;
        struct lttng_ht_iter iter;
        struct ltt_kernel_session *ksess = session->kernel_session;
@@ -1163,59 +1770,558 @@ int kernel_rotate_session(struct ltt_session *session)
                        socket, node.node) {
                struct ltt_kernel_channel *chan;
 
+                /* For each channel, ask the consumer to rotate it. */
+               cds_list_for_each_entry(chan, &ksess->channel_list.head, list) {
+                       DBG("Rotate kernel channel %" PRIu64 ", session %s",
+                                       chan->key, session->name);
+                       ret = consumer_rotate_channel(socket, chan->key,
+                                       ksess->uid, ksess->gid, ksess->consumer,
+                                       /* is_metadata_channel */ false);
+                       if (ret < 0) {
+                               status = LTTNG_ERR_KERN_CONSUMER_FAIL;
+                               goto error;
+                       }
+               }
+
                /*
-                * Account the metadata channel first to make sure the
-                * number of channels waiting for a rotation cannot
-                * reach 0 before we complete the iteration over all
-                * the channels.
+                * Rotate the metadata channel.
                 */
-               ret = rotate_add_channel_pending(ksess->metadata->key,
-                               LTTNG_DOMAIN_KERNEL, session);
+               ret = consumer_rotate_channel(socket, ksess->metadata->key,
+                               ksess->uid, ksess->gid, ksess->consumer,
+                               /* is_metadata_channel */ true);
                if (ret < 0) {
-                       ret = LTTNG_ERR_KERN_CONSUMER_FAIL;
+                       status = LTTNG_ERR_KERN_CONSUMER_FAIL;
                        goto error;
                }
+       }
+
+error:
+       rcu_read_unlock();
+       return status;
+}
+
+enum lttng_error_code kernel_create_channel_subdirectories(
+               const struct ltt_kernel_session *ksess)
+{
+       enum lttng_error_code ret = LTTNG_OK;
+       enum lttng_trace_chunk_status chunk_status;
+
+       rcu_read_lock();
+       assert(ksess->current_trace_chunk);
+
+       /*
+        * Create the index subdirectory which will take care
+        * of implicitly creating the channel's path.
+        */
+       chunk_status = lttng_trace_chunk_create_subdirectory(
+                       ksess->current_trace_chunk,
+                       DEFAULT_KERNEL_TRACE_DIR "/" DEFAULT_INDEX_DIR);
+       if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
+               ret = LTTNG_ERR_CREATE_DIR_FAIL;
+               goto error;
+       }
+error:
+       rcu_read_unlock();
+       return ret;
+}
+
+/*
+ * Setup necessary data for kernel tracer action.
+ */
+LTTNG_HIDDEN
+int init_kernel_tracer(void)
+{
+       int ret;
+       bool is_root = !getuid();
+
+       /* Modprobe lttng kernel modules */
+       ret = modprobe_lttng_control();
+       if (ret < 0) {
+               goto error;
+       }
+
+       /* Open debugfs lttng */
+       kernel_tracer_fd = open(module_proc_lttng, O_RDWR);
+       if (kernel_tracer_fd < 0) {
+               DBG("Failed to open %s", module_proc_lttng);
+               goto error_open;
+       }
+
+       /* Validate kernel version */
+       ret = kernel_validate_version(&kernel_tracer_version,
+                       &kernel_tracer_abi_version);
+       if (ret < 0) {
+               goto error_version;
+       }
+
+       ret = modprobe_lttng_data();
+       if (ret < 0) {
+               goto error_modules;
+       }
+
+       ret = kernel_supports_ring_buffer_snapshot_sample_positions();
+       if (ret < 0) {
+               goto error_modules;
+       }
+       if (ret < 1) {
+               WARN("Kernel tracer does not support buffer monitoring. "
+                       "The monitoring timer of channels in the kernel domain "
+                       "will be set to 0 (disabled).");
+       }
+
+       ret = kernel_create_trigger_group(&kernel_tracer_trigger_group_fd);
+       if (ret < 0) {
+               /* TODO: error handling if it is not supported etc. */
+               WARN("Failed trigger group creation");
+               kernel_tracer_trigger_group_fd = -1;
+               /* This is not fatal */
+       } else {
+               ret = kernel_create_trigger_group_notification_fd(&kernel_tracer_trigger_group_notification_fd);
+               if (ret < 0) {
+                       goto error_modules;
+               }
+       }
+
+       CDS_INIT_LIST_HEAD(&kernel_tracer_token_list.head);
+
+       DBG("Kernel tracer fd %d", kernel_tracer_fd);
+       DBG("Kernel tracer trigger group fd %d", kernel_tracer_trigger_group_fd);
+       DBG("Kernel tracer trigger group notificationi fd %d", kernel_tracer_trigger_group_notification_fd);
+
+       ret = syscall_init_table(kernel_tracer_fd);
+       if (ret < 0) {
+               ERR("Unable to populate syscall table. Syscall tracing won't "
+                       "work for this session daemon.");
+       }
+
+       return 0;
+
+error_version:
+       modprobe_remove_lttng_control();
+       ret = close(kernel_tracer_fd);
+       if (ret) {
+               PERROR("close");
+       }
+       kernel_tracer_fd = -1;
+       return LTTNG_ERR_KERN_VERSION;
+
+error_modules:
+       ret = close(kernel_tracer_fd);
+       if (ret) {
+               PERROR("close");
+       }
+
+error_open:
+       modprobe_remove_lttng_control();
 
-               /* For each channel, ask the consumer to rotate it. */
+error:
+       WARN("No kernel tracer available");
+       kernel_tracer_fd = -1;
+       if (!is_root) {
+               return LTTNG_ERR_NEED_ROOT_SESSIOND;
+       } else {
+               return LTTNG_ERR_KERN_NA;
+       }
+}
+
+LTTNG_HIDDEN
+void cleanup_kernel_tracer(void)
+{
+       int ret;
+
+       struct ltt_kernel_token_event_rule *rule, *rtmp;
+        cds_list_for_each_entry_safe(rule, rtmp, &kernel_tracer_token_list.head, list) {
+               kernel_disable_token_event_rule(rule);
+               trace_kernel_destroy_token_event_rule(rule);
+       }
+
+       DBG2("Closing kernel trigger group notification fd");
+       if (kernel_tracer_trigger_group_notification_fd >= 0) {
+               ret = close(kernel_tracer_trigger_group_notification_fd);
+               if (ret) {
+                       PERROR("close");
+               }
+               kernel_tracer_trigger_group_notification_fd = -1;
+       }
+
+       /* TODO: do we iterate over the list to remove all token? */
+       DBG2("Closing kernel trigger group fd");
+       if (kernel_tracer_trigger_group_fd >= 0) {
+               ret = close(kernel_tracer_trigger_group_fd);
+               if (ret) {
+                       PERROR("close");
+               }
+               kernel_tracer_trigger_group_fd = -1;
+       }
+
+       DBG2("Closing kernel fd");
+       if (kernel_tracer_fd >= 0) {
+               ret = close(kernel_tracer_fd);
+               if (ret) {
+                       PERROR("close");
+               }
+               kernel_tracer_fd = -1;
+       }
+
+       
+       DBG("Unloading kernel modules");
+       modprobe_remove_lttng_all();
+       free(syscall_table);
+}
+
+LTTNG_HIDDEN
+bool kernel_tracer_is_initialized(void)
+{
+       return kernel_tracer_fd >= 0;
+}
+
+/*
+ *  Clear a kernel session.
+ *
+ * Return LTTNG_OK on success or else an LTTng error code.
+ */
+enum lttng_error_code kernel_clear_session(struct ltt_session *session)
+{
+       int ret;
+       enum lttng_error_code status = LTTNG_OK;
+       struct consumer_socket *socket;
+       struct lttng_ht_iter iter;
+       struct ltt_kernel_session *ksess = session->kernel_session;
+
+       assert(ksess);
+       assert(ksess->consumer);
+
+       DBG("Clear kernel session %s (session %" PRIu64 ")",
+                       session->name, session->id);
+
+       rcu_read_lock();
+
+       if (ksess->active) {
+               ERR("Expecting inactive session %s (%" PRIu64 ")", session->name, session->id);
+               status = LTTNG_ERR_FATAL;
+               goto end;
+       }
+
+       /*
+        * Note that this loop will end after one iteration given that there is
+        * only one kernel consumer.
+        */
+       cds_lfht_for_each_entry(ksess->consumer->socks->ht, &iter.iter,
+                       socket, node.node) {
+               struct ltt_kernel_channel *chan;
+
+               /* For each channel, ask the consumer to clear it. */
                cds_list_for_each_entry(chan, &ksess->channel_list.head, list) {
-                       ret = rotate_add_channel_pending(chan->key,
-                                       LTTNG_DOMAIN_KERNEL, session);
+                       DBG("Clear kernel channel %" PRIu64 ", session %s",
+                                       chan->key, session->name);
+                       ret = consumer_clear_channel(socket, chan->key);
                        if (ret < 0) {
-                               ret = LTTNG_ERR_KERN_CONSUMER_FAIL;
                                goto error;
                        }
+               }
 
-                       DBG("Rotate channel %" PRIu64 ", session %s", chan->key, session->name);
-                       ret = consumer_rotate_channel(socket, chan->key,
-                                       ksess->uid, ksess->gid, ksess->consumer,
-                                       ksess->consumer->subdir,
-                                       /* is_metadata_channel */ false,
-                                       session->current_archive_id,
-                                       &session->rotate_pending_relay);
-                       if (ret < 0) {
-                               ret = LTTNG_ERR_KERN_CONSUMER_FAIL;
-                               goto error;
-                       }
+               if (!ksess->metadata) {
+                       /*
+                        * Nothing to do for the metadata.
+                        * This is a snapshot session.
+                        * The metadata is genererated on the fly.
+                        */
+                       continue;
                }
 
                /*
-                * Rotate the metadata channel.
+                * Clear the metadata channel.
+                * Metadata channel is not cleared per se but we still need to
+                * perform a rotation operation on it behind the scene.
                 */
-               ret = consumer_rotate_channel(socket, ksess->metadata->key,
-                               ksess->uid, ksess->gid, ksess->consumer,
-                               ksess->consumer->subdir,
-                               /* is_metadata_channel */ true,
-                               session->current_archive_id,
-                               &session->rotate_pending_relay);
+               ret = consumer_clear_channel(socket, ksess->metadata->key);
                if (ret < 0) {
-                       ret = LTTNG_ERR_KERN_CONSUMER_FAIL;
                        goto error;
                }
        }
 
-       ret = LTTNG_OK;
+       goto end;
+error:
+       switch (-ret) {
+       case LTTCOMM_CONSUMERD_RELAYD_CLEAR_DISALLOWED:
+             status = LTTNG_ERR_CLEAR_RELAY_DISALLOWED;
+             break;
+       default:
+             status = LTTNG_ERR_CLEAR_FAIL_CONSUMER;
+             break;
+       }
+end:
+       rcu_read_unlock();
+       return status;
+}
+
+enum lttng_error_code kernel_create_trigger_group_notification_fd(
+               int *trigger_group_notification_fd)
+{
+       enum lttng_error_code ret = LTTNG_OK;
+       int local_fd = -1;
+
+       assert(trigger_group_notification_fd);
+
+       ret = kernctl_create_trigger_group_notification_fd(kernel_tracer_trigger_group_fd);
+       if (ret < 0) {
+               PERROR("ioctl kernel create trigger group");
+               ret = -1;
+               goto error;
+       }
+
+       /* Store locally */
+       local_fd = ret;
+
+       /* Prevent fd duplication after execlp() */
+       ret = fcntl(local_fd, F_SETFD, FD_CLOEXEC);
+       if (ret < 0) {
+               PERROR("fcntl session fd");
+       }
+
+       DBG("Kernel trigger group notification created (fd: %d)",
+                       local_fd);
+       ret = 0;
+
+error:
+       *trigger_group_notification_fd = local_fd;
+       return ret;
+}
+
+enum lttng_error_code kernel_destroy_trigger_group_notification_fd(
+               int trigger_group_notification_fd)
+{
+       enum lttng_error_code ret = LTTNG_OK;
+       DBG("Closing trigger group notification fd %d", trigger_group_notification_fd);
+       if (trigger_group_notification_fd >= 0) {
+               ret = close(trigger_group_notification_fd);
+               if (ret) {
+                       PERROR("close");
+               }
+       }
+       return ret;
+}
+
+static int kernel_create_token_event_rule(struct lttng_event_rule *rule,
+               const struct lttng_credentials *creds, uint64_t token)
+{
+       int err, fd;
+       enum lttng_error_code ret;
+       struct ltt_kernel_token_event_rule *event;
+       struct lttng_kernel_trigger trigger;
+
+       assert(rule);
+
+       ret = trace_kernel_create_token_event_rule(rule, token, &event);
+       if (ret != LTTNG_OK) {
+               goto error;
+       }
+       
+       trace_kernel_init_trigger_from_event_rule(event->event_rule, &trigger);
+       trigger.id = event->token;
+
+       fd = kernctl_create_trigger(kernel_tracer_trigger_group_fd, &trigger);
+       if (fd < 0) {
+               switch (-fd) {
+               case EEXIST:
+                       ret = LTTNG_ERR_KERN_EVENT_EXIST;
+                       break;
+               case ENOSYS:
+                       WARN("Trigger type not implemented");
+                       ret = LTTNG_ERR_KERN_EVENT_ENOSYS;
+                       break;
+               case ENOENT:
+                       WARN("Event %s not found!", trigger.name);
+                       ret = LTTNG_ERR_KERN_ENABLE_FAIL;
+                       break;
+               default:
+                       ret = LTTNG_ERR_KERN_ENABLE_FAIL;
+                       PERROR("create trigger ioctl");
+               }
+               goto free_event;
+       }
+
+       event->fd = fd;
+       /* Prevent fd duplication after execlp() */
+       err = fcntl(event->fd, F_SETFD, FD_CLOEXEC);
+       if (err < 0) {
+               PERROR("fcntl session fd");
+       }
 
+       if (event->filter) {
+               err = kernctl_filter(event->fd, event->filter);
+               if (err < 0) {
+                       switch (-err) {
+                       case ENOMEM:
+                               ret = LTTNG_ERR_FILTER_NOMEM;
+                               break;
+                       default:
+                               ret = LTTNG_ERR_FILTER_INVAL;
+                               break;
+                       }
+                       goto filter_error;
+               }
+       }
+
+       if (lttng_event_rule_get_type(event->event_rule) ==
+                       LTTNG_EVENT_RULE_TYPE_UPROBE) {
+               ret = userspace_probe_event_rule_add_callsites(
+                               rule, creds, event->fd);
+               if (ret) {
+                       goto add_callsite_error;
+               }
+       }
+
+       err = kernctl_enable(event->fd);
+       if (err < 0) {
+               switch (-err) {
+               case EEXIST:
+                       ret = LTTNG_ERR_KERN_EVENT_EXIST;
+                       break;
+               default:
+                       PERROR("enable kernel trigger");
+                       ret = LTTNG_ERR_KERN_ENABLE_FAIL;
+                       break;
+               }
+               goto enable_error;
+       }
+
+       /* Add event to event list */
+       cds_list_add(&event->list, &kernel_tracer_token_list.head);
+
+       DBG("Trigger %s created (fd: %d)", trigger.name, event->fd);
+
+       return 0;
+
+add_callsite_error:
+enable_error:
+filter_error:
+       {
+               int closeret;
+
+               closeret = close(event->fd);
+               if (closeret) {
+                       PERROR("close event fd");
+               }
+       }
+free_event:
+       free(event);
 error:
+       return ret;
+}
+
+enum lttng_error_code kernel_update_tokens(void)
+{
+       enum lttng_error_code ret = LTTNG_OK;
+       enum lttng_trigger_status t_status;
+       struct ltt_kernel_token_event_rule *token_event_rule_element;
+       struct lttng_triggers *triggers;
+       unsigned int count;
+       
+       /* TODO error handling */
+
+       /* Get list of token trigger from the notification thread here */
+       rcu_read_lock();
+       pthread_mutex_lock(&notification_trigger_tokens_ht_lock);
+       ret = notification_thread_command_get_tokens(notification_thread_handle, &triggers);
+       if (ret != LTTNG_OK) {
+               ret = -1;
+               goto end;
+       }
+
+       assert(triggers);
+
+       t_status = lttng_triggers_get_count(triggers, &count);
+       if (t_status != LTTNG_TRIGGER_STATUS_OK) {
+               ret = -1;
+               goto end;
+       }
+
+       for (unsigned int i = 0; i < count; i++) {
+               struct lttng_condition *condition;
+               struct lttng_event_rule *event_rule;
+               struct lttng_trigger *trigger;
+               struct ltt_kernel_token_event_rule *k_token;
+               const struct lttng_credentials *creds;
+               uint64_t token;
+
+               trigger = lttng_triggers_get_pointer_of_index(triggers, i);
+               assert(trigger);
+
+               /* TODO: error checking and type checking */
+               token = lttng_trigger_get_key(trigger);
+               condition = lttng_trigger_get_condition(trigger);
+               (void) lttng_condition_event_rule_get_rule_no_const(condition, &event_rule);
+
+               if (lttng_event_rule_get_domain_type(event_rule) != LTTNG_DOMAIN_KERNEL) {
+                       /* Skip ust related trigger */
+                       continue;
+               }
+
+               creds = lttng_trigger_get_credentials(trigger);
+               /* Iterate over all known token trigger */
+               k_token = trace_kernel_find_trigger_by_token(&kernel_tracer_token_list, token);
+               if (!k_token) {
+                       ret = kernel_create_token_event_rule(event_rule, creds, token);
+                       if (ret < 0) {
+                               goto end;
+                       }
+               }
+       }
+
+       /* Remove all unknown trigger from the app
+        * TODO find a way better way then this, do it on the unregister command
+        * and be specific on the token to remove instead of going over all
+        * trigger known to the app. This is sub optimal.
+        */
+       cds_list_for_each_entry (token_event_rule_element, &kernel_tracer_token_list.head,
+                       list) {
+               uint64_t token;
+               bool found = false;
+
+               token = token_event_rule_element->token;
+
+       /*
+                * Check if the app event trigger still exists on the
+                * notification side.
+                * TODO: might want to change the backing data struct of the
+                * lttng_triggers object to allow quick lookup?
+                * For kernel mostly all of this can be removed once we delete
+                * on a per trigger basis.
+                */
+
+               for (unsigned int i = 0; i < count; i++) {
+                       struct lttng_trigger *trigger;
+                       uint64_t inner_token;
+
+                       trigger = lttng_triggers_get_pointer_of_index(
+                                       triggers, i);
+                       assert(trigger);
+
+                       inner_token = lttng_trigger_get_key(trigger);
+
+                       if (inner_token == token) {
+                               found = true;
+                               break;
+                       }
+               }
+
+               if (found) {
+                       /* Still valid */
+                       continue;
+               }
+
+               kernel_disable_token_event_rule(token_event_rule_element);
+               trace_kernel_destroy_token_event_rule(token_event_rule_element);
+       }
+end:
        rcu_read_unlock();
+       pthread_mutex_unlock(&notification_trigger_tokens_ht_lock);
        return ret;
+
+}
+
+int kernel_get_notification_fd(void)
+{
+       return kernel_tracer_trigger_group_notification_fd;
 }
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