SoW-2020-0003: Trace Hit Counters
[lttng-tools.git] / src / bin / lttng-sessiond / kernel.c
index 1f987ef7d365a2890146d5c5cccdc1f3cf72660a..25d744d1107ef11cf342f21990e0b4bffbac6fa3 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 <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 <common/tracker.h>
+#include <common/utils.h>
+#include <lttng/event.h>
+#include <lttng/lttng-error.h>
+#include <lttng/tracker.h>
 
+#include <lttng/userspace-probe.h>
+#include <lttng/userspace-probe-internal.h>
+#include <lttng/condition/on-event.h>
+#include <lttng/condition/on-event-internal.h>
+#include <lttng/event-rule/event-rule.h>
+#include <lttng/event-rule/event-rule-internal.h>
+#include <lttng/event-rule/userspace-probe-internal.h>
+#include <lttng/map/map.h>
+#include <lttng/map/map-internal.h>
+#include <lttng/map/map-query-internal.h>
+#include <lttng/map-key.h>
+#include <lttng/map-key-internal.h>
+
+#include "event-notifier-error-accounting.h"
 #include "lttng-sessiond.h"
 #include "lttng-syscall.h"
+#include "condition-internal.h"
 #include "consumer.h"
 #include "kernel.h"
 #include "kernel-consumer.h"
 #include "kern-modules.h"
+#include "map.h"
+#include "sessiond-config.h"
 #include "utils.h"
 #include "rotate.h"
 #include "modprobe.h"
+#include "tracker.h"
+#include "notification-thread-commands.h"
 
 /*
  * Key used to reference a channel between the sessiond and the consumer. This
@@ -49,9 +64,10 @@ 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_event_notifier_group_fd = -1;
+static int kernel_tracer_event_notifier_group_notification_fd = -1;
+static struct cds_lfht *kernel_token_to_event_notifier_rule_ht;
 
-#include <lttng/userspace-probe.h>
-#include <lttng/userspace-probe-internal.h>
 /*
  * Add context on a kernel channel.
  *
@@ -223,6 +239,51 @@ error:
        return -1;
 }
 
+/*
+ * Create a kernel event notifier group, register it to the kernel tracer and
+ * add it to the kernel session.
+ */
+static int kernel_create_event_notifier_group(int *event_notifier_group_fd)
+{
+       int ret;
+       int local_fd = -1;
+
+       assert(event_notifier_group_fd);
+
+       /* Kernel event notifier group creation. */
+       ret = kernctl_create_event_notifier_group(kernel_tracer_fd);
+       if (ret < 0) {
+               PERROR("Failed to create kernel event notifier group");
+               ret = -1;
+               goto error;
+       }
+
+       local_fd = ret;
+
+       /* Prevent fd duplication after execlp(). */
+       ret = fcntl(local_fd, F_SETFD, FD_CLOEXEC);
+       if (ret < 0) {
+               PERROR("Failed to set FD_CLOEXEC on kernel event notifier group file descriptor: fd = %d",
+                               local_fd);
+               goto error;
+       }
+
+       DBG("Created kernel event notifier group: fd = %d", local_fd);
+       *event_notifier_group_fd = local_fd;
+       local_fd = -1;
+       ret = 0;
+error:
+       if (local_fd >= 0) {
+               ret = close(local_fd);
+               if (ret) {
+                       PERROR("Failed to close kernel event notifier group file descriptor: fd = %d",
+                                       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.
@@ -234,7 +295,7 @@ error:
 static
 int extract_userspace_probe_offset_function_elf(
                const struct lttng_userspace_probe_location *probe_location,
-               struct ltt_kernel_session *session, uint64_t *offset)
+               uid_t uid, gid_t gid, uint64_t *offset)
 {
        int fd;
        int ret = 0;
@@ -271,8 +332,7 @@ int extract_userspace_probe_offset_function_elf(
                goto end;
        }
 
-       ret = run_as_extract_elf_symbol_offset(fd, symbol, session->uid,
-                       session->gid, offset);
+       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);
@@ -296,7 +356,7 @@ end:
 static
 int extract_userspace_probe_offset_tracepoint_sdt(
                const struct lttng_userspace_probe_location *probe_location,
-               struct ltt_kernel_session *session, uint64_t **offsets,
+               uid_t uid, gid_t gid, uint64_t **offsets,
                uint32_t *offsets_count)
 {
        enum lttng_userspace_probe_location_lookup_method_type lookup_method_type;
@@ -342,7 +402,7 @@ int extract_userspace_probe_offset_tracepoint_sdt(
        }
 
        ret = run_as_extract_sdt_probe_offsets(fd, provider_name, probe_name,
-                       session->uid, session->gid, offsets, offsets_count);
+                       uid, gid, offsets, offsets_count);
        if (ret < 0) {
                DBG("userspace probe offset calculation failed for sdt "
                                "probe %s:%s", provider_name, probe_name);
@@ -363,29 +423,16 @@ end:
        return ret;
 }
 
-/*
- * Extract the offsets of the instrumentation point for the different lookup
- * methods.
- */
 static
-int userspace_probe_add_callsites(struct lttng_event *ev,
-                       struct ltt_kernel_session *session, int fd)
+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;
-       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;
-       }
-       lookup_method =
-                       lttng_userspace_probe_location_get_lookup_method(location);
+       lookup_method = lttng_userspace_probe_location_get_lookup_method(location);
        if (!lookup_method) {
                ret = -1;
                goto end;
@@ -398,7 +445,8 @@ int userspace_probe_add_callsites(struct lttng_event *ev,
                struct lttng_kernel_event_callsite callsite;
                uint64_t offset;
 
-               ret = extract_userspace_probe_offset_function_elf(location, session, &offset);
+               ret = extract_userspace_probe_offset_function_elf(location,
+                               uid, gid, &offset);
                if (ret) {
                        ret = LTTNG_ERR_PROBE_LOCATION_INVAL;
                        goto end;
@@ -407,8 +455,7 @@ int userspace_probe_add_callsites(struct lttng_event *ev,
                callsite.u.uprobe.offset = offset;
                ret = kernctl_add_callsite(fd, &callsite);
                if (ret) {
-                       WARN("Adding callsite to userspace probe "
-                                       "event %s failed.", ev->name);
+                       WARN("Failed to add callsite to ELF userspace probe.");
                        ret = LTTNG_ERR_KERN_ENABLE_FAIL;
                        goto end;
                }
@@ -425,8 +472,8 @@ int userspace_probe_add_callsites(struct lttng_event *ev,
                 * This call allocates the offsets buffer. This buffer must be freed
                 * by the caller
                 */
-               ret = extract_userspace_probe_offset_tracepoint_sdt(location, session,
-                               &offsets, &offsets_count);
+               ret = extract_userspace_probe_offset_tracepoint_sdt(location,
+                               uid, gid, &offsets, &offsets_count);
                if (ret) {
                        ret = LTTNG_ERR_PROBE_LOCATION_INVAL;
                        goto end;
@@ -435,8 +482,7 @@ int userspace_probe_add_callsites(struct lttng_event *ev,
                        callsite.u.uprobe.offset = offsets[i];
                        ret = kernctl_add_callsite(fd, &callsite);
                        if (ret) {
-                               WARN("Adding callsite to userspace probe "
-                                               "event %s failed.", ev->name);
+                               WARN("Failed to add callsite to SDT userspace probe");
                                ret = LTTNG_ERR_KERN_ENABLE_FAIL;
                                free(offsets);
                                goto end;
@@ -453,6 +499,75 @@ 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)
+{
+       int ret;
+       const struct lttng_userspace_probe_location *location = NULL;
+
+       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("Failed to add callsite to userspace probe event '%s'",
+                               ev->name);
+       }
+
+end:
+       return ret;
+}
+
+/*
+ * Extract the offsets of the instrumentation point for the different look-up
+ * methods.
+ */
+static int userspace_probe_event_rule_add_callsites(
+               const struct lttng_event_rule *rule,
+               const struct lttng_credentials *creds,
+               int fd)
+{
+       int ret;
+       enum lttng_event_rule_status status;
+       enum lttng_event_rule_type event_rule_type;
+       const struct lttng_userspace_probe_location *location = NULL;
+
+       assert(rule);
+       assert(creds);
+
+       event_rule_type = lttng_event_rule_get_type(rule);
+       assert(event_rule_type == LTTNG_EVENT_RULE_TYPE_USERSPACE_PROBE);
+
+       status = lttng_event_rule_userspace_probe_get_location(rule, &location);
+       if (status != LTTNG_EVENT_RULE_STATUS_OK || !location) {
+               ret = -1;
+               goto end;
+       }
+
+       ret = userspace_probe_add_callsite(location,
+                       lttng_credentials_get_uid(creds),
+                       lttng_credentials_get_gid(creds), fd);
+       if (ret) {
+               WARN("Failed to add callsite to user space probe object: fd = %d",
+                               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.
@@ -461,7 +576,7 @@ end:
 int kernel_create_event(struct lttng_event *ev,
                struct ltt_kernel_channel *channel,
                char *filter_expression,
-               struct lttng_filter_bytecode *filter)
+               struct lttng_bytecode *filter)
 {
        int err, fd;
        enum lttng_error_code ret;
@@ -522,7 +637,8 @@ int kernel_create_event(struct lttng_event *ev,
        }
 
        if (ev->type == LTTNG_EVENT_USERSPACE_PROBE) {
-               ret = userspace_probe_add_callsites(ev, channel->session, event->fd);
+               ret = userspace_probe_event_add_callsites(ev, channel->session,
+                               event->fd);
                if (ret) {
                        goto add_callsite_error;
                }
@@ -679,143 +795,429 @@ error:
        return ret;
 }
 
-
-int kernel_track_pid(struct ltt_kernel_session *session, int pid)
+/*
+ * Disable a kernel event notifier.
+ */
+static
+int kernel_disable_event_notifier_rule(struct ltt_kernel_event_notifier_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;
+       assert(event);
+
+       rcu_read_lock();
+       cds_lfht_del(kernel_token_to_event_notifier_rule_ht, &event->ht_node);
+       rcu_read_unlock();
+
+       ret = kernctl_disable(event->fd);
+       if (ret < 0) {
+               switch (-ret) {
+               case EEXIST:
+                       ret = LTTNG_ERR_KERN_EVENT_EXIST;
+                       break;
+               default:
+                       PERROR("Failed to disable kernel event notifier: fd = %d, token = %" PRIu64,
+                                       event->fd, event->token);
+                       break;
+               }
+               goto error;
        }
-       switch (-ret) {
-       case EINVAL:
-               return LTTNG_ERR_INVALID;
-       case ENOMEM:
-               return LTTNG_ERR_NOMEM;
-       case EEXIST:
-               return LTTNG_ERR_PID_TRACKED;
+
+       event->enabled = 0;
+       DBG("Disabled kernel event notifier: fd = %d, token = %" PRIu64,
+                       event->fd, event->token);
+
+error:
+       return ret;
+}
+
+static
+struct process_attr_tracker *_kernel_get_process_attr_tracker(
+               struct ltt_kernel_session *session,
+               enum lttng_process_attr process_attr)
+{
+       switch (process_attr) {
+       case LTTNG_PROCESS_ATTR_PROCESS_ID:
+               return session->tracker_pid;
+       case LTTNG_PROCESS_ATTR_VIRTUAL_PROCESS_ID:
+               return session->tracker_vpid;
+       case LTTNG_PROCESS_ATTR_USER_ID:
+               return session->tracker_uid;
+       case LTTNG_PROCESS_ATTR_VIRTUAL_USER_ID:
+               return session->tracker_vuid;
+       case LTTNG_PROCESS_ATTR_GROUP_ID:
+               return session->tracker_gid;
+       case LTTNG_PROCESS_ATTR_VIRTUAL_GROUP_ID:
+               return session->tracker_vgid;
        default:
-               return LTTNG_ERR_UNK;
+               return NULL;
        }
 }
 
-int kernel_untrack_pid(struct ltt_kernel_session *session, int pid)
+const struct process_attr_tracker *kernel_get_process_attr_tracker(
+               struct ltt_kernel_session *session,
+               enum lttng_process_attr process_attr)
+{
+       return (const struct process_attr_tracker *)
+                       _kernel_get_process_attr_tracker(session, process_attr);
+}
+
+enum lttng_error_code kernel_process_attr_tracker_set_tracking_policy(
+               struct ltt_kernel_session *session,
+               enum lttng_process_attr process_attr,
+               enum lttng_tracking_policy policy)
 {
        int ret;
+       enum lttng_error_code ret_code = LTTNG_OK;
+       struct process_attr_tracker *tracker =
+                       _kernel_get_process_attr_tracker(session, process_attr);
+       enum lttng_tracking_policy previous_policy;
+
+       if (!tracker) {
+               ret_code = LTTNG_ERR_INVALID;
+               goto end;
+       }
 
-       DBG("Kernel untrack PID %d for session id %" PRIu64 ".",
-                       pid, session->id);
-       ret = kernctl_untrack_pid(session->fd, pid);
-       if (!ret) {
-               return LTTNG_OK;
+       previous_policy = process_attr_tracker_get_tracking_policy(tracker);
+       ret = process_attr_tracker_set_tracking_policy(tracker, policy);
+       if (ret) {
+               ret_code = LTTNG_ERR_UNK;
+               goto end;
+       }
+
+       if (previous_policy == policy) {
+               goto end;
+       }
+
+       switch (policy) {
+       case LTTNG_TRACKING_POLICY_INCLUDE_ALL:
+               if (process_attr == LTTNG_PROCESS_ATTR_PROCESS_ID) {
+                       /*
+                        * Maintain a special case for the process ID process
+                        * attribute tracker as it was the only supported
+                        * attribute prior to 2.12.
+                        */
+                       ret = kernctl_track_pid(session->fd, -1);
+               } else {
+                       ret = kernctl_track_id(session->fd, process_attr, -1);
+               }
+               break;
+       case LTTNG_TRACKING_POLICY_EXCLUDE_ALL:
+       case LTTNG_TRACKING_POLICY_INCLUDE_SET:
+               /* fall-through. */
+               if (process_attr == LTTNG_PROCESS_ATTR_PROCESS_ID) {
+                       /*
+                        * Maintain a special case for the process ID process
+                        * attribute tracker as it was the only supported
+                        * attribute prior to 2.12.
+                        */
+                       ret = kernctl_untrack_pid(session->fd, -1);
+               } else {
+                       ret = kernctl_untrack_id(session->fd, process_attr, -1);
+               }
+               break;
+       default:
+               abort();
        }
+       /* kern-ctl error handling */
        switch (-ret) {
+       case 0:
+               ret_code = LTTNG_OK;
+               break;
        case EINVAL:
-               return LTTNG_ERR_INVALID;
+               ret_code = LTTNG_ERR_INVALID;
+               break;
        case ENOMEM:
-               return LTTNG_ERR_NOMEM;
-       case ENOENT:
-               return LTTNG_ERR_PID_NOT_TRACKED;
+               ret_code = LTTNG_ERR_NOMEM;
+               break;
+       case EEXIST:
+               ret_code = LTTNG_ERR_PROCESS_ATTR_EXISTS;
+               break;
        default:
-               return LTTNG_ERR_UNK;
+               ret_code = LTTNG_ERR_UNK;
+               break;
        }
+end:
+       return ret_code;
 }
 
-ssize_t kernel_list_tracker_pids(struct ltt_kernel_session *session,
-               int **_pids)
+enum lttng_error_code kernel_process_attr_tracker_inclusion_set_add_value(
+               struct ltt_kernel_session *session,
+               enum lttng_process_attr process_attr,
+               const struct process_attr_value *value)
 {
-       int fd, ret;
-       int pid;
-       ssize_t nbmem, count = 0;
-       FILE *fp;
-       int *pids;
+       int ret, integral_value;
+       enum lttng_error_code ret_code;
+       struct process_attr_tracker *tracker;
+       enum process_attr_tracker_status status;
 
-       fd = kernctl_list_tracker_pids(session->fd);
-       if (fd < 0) {
-               PERROR("kernel tracker pids list");
-               goto error;
+       /*
+        * Convert process attribute tracker value to the integral
+        * representation required by the kern-ctl API.
+        */
+       switch (process_attr) {
+       case LTTNG_PROCESS_ATTR_PROCESS_ID:
+       case LTTNG_PROCESS_ATTR_VIRTUAL_PROCESS_ID:
+               integral_value = (int) value->value.pid;
+               break;
+       case LTTNG_PROCESS_ATTR_USER_ID:
+       case LTTNG_PROCESS_ATTR_VIRTUAL_USER_ID:
+               if (value->type == LTTNG_PROCESS_ATTR_VALUE_TYPE_USER_NAME) {
+                       uid_t uid;
+
+                       ret_code = utils_user_id_from_name(
+                                       value->value.user_name, &uid);
+                       if (ret_code != LTTNG_OK) {
+                               goto end;
+                       }
+                       integral_value = (int) uid;
+               } else {
+                       integral_value = (int) value->value.uid;
+               }
+               break;
+       case LTTNG_PROCESS_ATTR_GROUP_ID:
+       case LTTNG_PROCESS_ATTR_VIRTUAL_GROUP_ID:
+               if (value->type == LTTNG_PROCESS_ATTR_VALUE_TYPE_GROUP_NAME) {
+                       gid_t gid;
+
+                       ret_code = utils_group_id_from_name(
+                                       value->value.group_name, &gid);
+                       if (ret_code != LTTNG_OK) {
+                               goto end;
+                       }
+                       integral_value = (int) gid;
+               } else {
+                       integral_value = (int) value->value.gid;
+               }
+               break;
+       default:
+               ret_code = LTTNG_ERR_INVALID;
+               goto end;
        }
 
-       fp = fdopen(fd, "r");
-       if (fp == NULL) {
-               PERROR("kernel tracker pids list fdopen");
-               goto error_fp;
+       tracker = _kernel_get_process_attr_tracker(session, process_attr);
+       if (!tracker) {
+               ret_code = LTTNG_ERR_INVALID;
+               goto end;
        }
 
-       nbmem = KERNEL_TRACKER_PIDS_INIT_LIST_SIZE;
-       pids = zmalloc(sizeof(*pids) * nbmem);
-       if (pids == NULL) {
-               PERROR("alloc list pids");
-               count = -ENOMEM;
+       status = process_attr_tracker_inclusion_set_add_value(tracker, value);
+       if (status != PROCESS_ATTR_TRACKER_STATUS_OK) {
+               switch (status) {
+               case PROCESS_ATTR_TRACKER_STATUS_EXISTS:
+                       ret_code = LTTNG_ERR_PROCESS_ATTR_EXISTS;
+                       break;
+               case PROCESS_ATTR_TRACKER_STATUS_INVALID_TRACKING_POLICY:
+                       ret_code = LTTNG_ERR_PROCESS_ATTR_TRACKER_INVALID_TRACKING_POLICY;
+                       break;
+               case PROCESS_ATTR_TRACKER_STATUS_ERROR:
+               default:
+                       ret_code = LTTNG_ERR_UNK;
+                       break;
+               }
                goto end;
        }
 
-       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;
+       DBG("Kernel track %s %d for session id %" PRIu64,
+                       lttng_process_attr_to_string(process_attr),
+                       integral_value, session->id);
+       if (process_attr == LTTNG_PROCESS_ATTR_PROCESS_ID) {
+               /*
+                * Maintain a special case for the process ID process attribute
+                * tracker as it was the only supported attribute prior to 2.12.
+                */
+               ret = kernctl_track_pid(session->fd, integral_value);
+       } else {
+               ret = kernctl_track_id(
+                               session->fd, process_attr, integral_value);
+       }
+       if (ret == 0) {
+               ret_code = LTTNG_OK;
+               goto end;
        }
 
-       *_pids = pids;
-       DBG("Kernel list tracker pids done (%zd pids)", count);
-end:
-       ret = fclose(fp);       /* closes both fp and fd */
-       if (ret) {
-               PERROR("fclose");
+       kernel_wait_quiescent();
+
+       /* kern-ctl error handling */
+       switch (-ret) {
+       case 0:
+               ret_code = LTTNG_OK;
+               break;
+       case EINVAL:
+               ret_code = LTTNG_ERR_INVALID;
+               break;
+       case ENOMEM:
+               ret_code = LTTNG_ERR_NOMEM;
+               break;
+       case EEXIST:
+               ret_code = LTTNG_ERR_PROCESS_ATTR_EXISTS;
+               break;
+       default:
+               ret_code = LTTNG_ERR_UNK;
+               break;
        }
-       return count;
 
-error_fp:
-       ret = close(fd);
-       if (ret) {
-               PERROR("close");
+       /* Attempt to remove the value from the tracker. */
+       status = process_attr_tracker_inclusion_set_remove_value(
+                       tracker, value);
+       if (status != PROCESS_ATTR_TRACKER_STATUS_OK) {
+               ERR("Failed to roll-back the tracking of kernel %s process attribute %d while handling a kern-ctl error",
+                               lttng_process_attr_to_string(process_attr),
+                               integral_value);
        }
-error:
-       return -1;
+end:
+       return ret_code;
 }
 
-/*
- * Create kernel metadata, open from the kernel tracer and add it to the
- * kernel session.
- */
-int kernel_open_metadata(struct ltt_kernel_session *session)
+enum lttng_error_code kernel_process_attr_tracker_inclusion_set_remove_value(
+               struct ltt_kernel_session *session,
+               enum lttng_process_attr process_attr,
+               const struct process_attr_value *value)
 {
-       int ret;
-       struct ltt_kernel_metadata *lkm = NULL;
+       int ret, integral_value;
+       enum lttng_error_code ret_code;
+       struct process_attr_tracker *tracker;
+       enum process_attr_tracker_status status;
 
-       assert(session);
+       /*
+        * Convert process attribute tracker value to the integral
+        * representation required by the kern-ctl API.
+        */
+       switch (process_attr) {
+       case LTTNG_PROCESS_ATTR_PROCESS_ID:
+       case LTTNG_PROCESS_ATTR_VIRTUAL_PROCESS_ID:
+               integral_value = (int) value->value.pid;
+               break;
+       case LTTNG_PROCESS_ATTR_USER_ID:
+       case LTTNG_PROCESS_ATTR_VIRTUAL_USER_ID:
+               if (value->type == LTTNG_PROCESS_ATTR_VALUE_TYPE_USER_NAME) {
+                       uid_t uid;
+
+                       ret_code = utils_user_id_from_name(
+                                       value->value.user_name, &uid);
+                       if (ret_code != LTTNG_OK) {
+                               goto end;
+                       }
+                       integral_value = (int) uid;
+               } else {
+                       integral_value = (int) value->value.uid;
+               }
+               break;
+       case LTTNG_PROCESS_ATTR_GROUP_ID:
+       case LTTNG_PROCESS_ATTR_VIRTUAL_GROUP_ID:
+               if (value->type == LTTNG_PROCESS_ATTR_VALUE_TYPE_GROUP_NAME) {
+                       gid_t gid;
+
+                       ret_code = utils_group_id_from_name(
+                                       value->value.group_name, &gid);
+                       if (ret_code != LTTNG_OK) {
+                               goto end;
+                       }
+                       integral_value = (int) gid;
+               } else {
+                       integral_value = (int) value->value.gid;
+               }
+               break;
+       default:
+               ret_code = LTTNG_ERR_INVALID;
+               goto end;
+       }
 
-       /* Allocate kernel metadata */
-       lkm = trace_kernel_create_metadata();
-       if (lkm == NULL) {
-               goto error;
+       tracker = _kernel_get_process_attr_tracker(session, process_attr);
+       if (!tracker) {
+               ret_code = LTTNG_ERR_INVALID;
+               goto end;
        }
 
-       /* Kernel tracer metadata creation */
-       ret = kernctl_open_metadata(session->fd, &lkm->conf->attr);
-       if (ret < 0) {
-               goto error_open;
+       status = process_attr_tracker_inclusion_set_remove_value(
+                       tracker, value);
+       if (status != PROCESS_ATTR_TRACKER_STATUS_OK) {
+               switch (status) {
+               case PROCESS_ATTR_TRACKER_STATUS_MISSING:
+                       ret_code = LTTNG_ERR_PROCESS_ATTR_MISSING;
+                       break;
+               case PROCESS_ATTR_TRACKER_STATUS_INVALID_TRACKING_POLICY:
+                       ret_code = LTTNG_ERR_PROCESS_ATTR_TRACKER_INVALID_TRACKING_POLICY;
+                       break;
+               case PROCESS_ATTR_TRACKER_STATUS_ERROR:
+               default:
+                       ret_code = LTTNG_ERR_UNK;
+                       break;
+               }
+               goto end;
+       }
+
+       DBG("Kernel track %s %d for session id %" PRIu64,
+                       lttng_process_attr_to_string(process_attr),
+                       integral_value, session->id);
+       if (process_attr == LTTNG_PROCESS_ATTR_PROCESS_ID) {
+               /*
+                * Maintain a special case for the process ID process attribute
+                * tracker as it was the only supported attribute prior to 2.12.
+                */
+               ret = kernctl_untrack_pid(session->fd, integral_value);
+       } else {
+               ret = kernctl_untrack_id(
+                               session->fd, process_attr, integral_value);
+       }
+       if (ret == 0) {
+               ret_code = LTTNG_OK;
+               goto end;
+       }
+       kernel_wait_quiescent();
+
+       /* kern-ctl error handling */
+       switch (-ret) {
+       case 0:
+               ret_code = LTTNG_OK;
+               break;
+       case EINVAL:
+               ret_code = LTTNG_ERR_INVALID;
+               break;
+       case ENOMEM:
+               ret_code = LTTNG_ERR_NOMEM;
+               break;
+       case ENOENT:
+               ret_code = LTTNG_ERR_PROCESS_ATTR_MISSING;
+               break;
+       default:
+               ret_code = LTTNG_ERR_UNK;
+               break;
+       }
+
+       /* Attempt to add the value to the tracker. */
+       status = process_attr_tracker_inclusion_set_add_value(
+                       tracker, value);
+       if (status != PROCESS_ATTR_TRACKER_STATUS_OK) {
+               ERR("Failed to roll-back the tracking of kernel %s process attribute %d while handling a kern-ctl error",
+                               lttng_process_attr_to_string(process_attr),
+                               integral_value);
+       }
+end:
+       return ret_code;
+}
+
+/*
+ * Create kernel metadata, open from the kernel tracer and add it to the
+ * kernel session.
+ */
+int kernel_open_metadata(struct ltt_kernel_session *session)
+{
+       int ret;
+       struct ltt_kernel_metadata *lkm = NULL;
+
+       assert(session);
+
+       /* Allocate kernel metadata */
+       lkm = trace_kernel_create_metadata();
+       if (lkm == NULL) {
+               goto error;
+       }
+
+       /* Kernel tracer metadata creation */
+       ret = kernctl_open_metadata(session->fd, &lkm->conf->attr);
+       if (ret < 0) {
+               goto error_open;
        }
 
        lkm->fd = ret;
@@ -1395,16 +1797,10 @@ int kernel_syscall_mask(int chan_fd, char **syscall_mask, uint32_t *nr_bits)
        return kernctl_syscall_mask(chan_fd, syscall_mask, nr_bits);
 }
 
-/*
- * Check for the support of the RING_BUFFER_SNAPSHOT_SAMPLE_POSITIONS 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_snapshot_sample_positions(void)
+static
+int kernel_tracer_abi_greater_or_equal(unsigned int major, unsigned int minor)
 {
-       int ret = 0; // Not supported by default
+       int ret;
        struct lttng_kernel_tracer_abi_version abi;
 
        ret = kernctl_tracer_abi_version(kernel_tracer_fd, &abi);
@@ -1413,18 +1809,24 @@ int kernel_supports_ring_buffer_snapshot_sample_positions(void)
                goto error;
        }
 
+       ret = abi.major > major || (abi.major == major && abi.minor >= minor);
+error:
+       return ret;
+}
+
+/*
+ * Check for the support of the RING_BUFFER_SNAPSHOT_SAMPLE_POSITIONS 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_snapshot_sample_positions(void)
+{
        /*
         * RING_BUFFER_SNAPSHOT_SAMPLE_POSITIONS was introduced in 2.3
         */
-       if (abi.major >= 2 && abi.minor >= 3) {
-               /* Supported */
-               ret = 1;
-       } else {
-               /* Not supported */
-               ret = 0;
-       }
-error:
-       return ret;
+       return kernel_tracer_abi_greater_or_equal(2, 3);
 }
 
 /*
@@ -1435,27 +1837,25 @@ error:
  */
 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.
+        */
+       return kernel_tracer_abi_greater_or_equal(2, 1);
+}
 
+/*
+ * Check for the support of event notifiers via abi version number.
+ *
+ * Return 1 on success, 0 when feature is not supported, negative value in case
+ * of errors.
+ */
+int kernel_supports_event_notifiers(void)
+{
        /*
-        * Packet sequence number was introduced in 2.8
+        * Event notifiers were introduced in LTTng 2.13, lttng-modules ABI 2.6.
         */
-       if (abi.major >= 2 && abi.minor >= 8) {
-               /* Supported */
-               ret = 1;
-       } else {
-               /* Not supported */
-               ret = 0;
-       }
-error:
-       return ret;
+       return kernel_tracer_abi_greater_or_equal(2, 6);
 }
 
 /*
@@ -1487,7 +1887,7 @@ enum lttng_error_code kernel_rotate_session(struct ltt_session *session)
                        socket, node.node) {
                struct ltt_kernel_channel *chan;
 
-                /* For each channel, ask the consumer to rotate it. */
+               /* 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);
@@ -1495,7 +1895,7 @@ enum lttng_error_code kernel_rotate_session(struct ltt_session *session)
                                        ksess->uid, ksess->gid, ksess->consumer,
                                        /* is_metadata_channel */ false);
                        if (ret < 0) {
-                               status = LTTNG_ERR_KERN_CONSUMER_FAIL;
+                               status = LTTNG_ERR_ROTATION_FAIL_CONSUMER;
                                goto error;
                        }
                }
@@ -1507,7 +1907,7 @@ enum lttng_error_code kernel_rotate_session(struct ltt_session *session)
                                ksess->uid, ksess->gid, ksess->consumer,
                                /* is_metadata_channel */ true);
                if (ret < 0) {
-                       status = LTTNG_ERR_KERN_CONSUMER_FAIL;
+                       status = LTTNG_ERR_ROTATION_FAIL_CONSUMER;
                        goto error;
                }
        }
@@ -1580,35 +1980,90 @@ int init_kernel_tracer(void)
        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).");
        }
 
-       DBG("Kernel tracer fd %d", kernel_tracer_fd);
+       ret = kernel_supports_event_notifiers();
+       if (ret < 0) {
+               ERR("Failed to check for kernel tracer event notifier support");
+               goto error_modules;
+       }
+       ret = kernel_create_event_notifier_group(&kernel_tracer_event_notifier_group_fd);
+       if (ret < 0) {
+               /* This is not fatal. */
+               WARN("Failed to create kernel event notifier group");
+               kernel_tracer_event_notifier_group_fd = -1;
+       } else {
+               enum event_notifier_error_accounting_status error_accounting_status;
+               enum lttng_error_code error_code_ret =
+                               kernel_create_event_notifier_group_notification_fd(
+                                               &kernel_tracer_event_notifier_group_notification_fd);
+
+               if (error_code_ret != LTTNG_OK) {
+                       goto error_modules;
+               }
+
+               error_accounting_status = event_notifier_error_accounting_register_kernel(
+                               kernel_tracer_event_notifier_group_fd);
+               if (error_accounting_status != EVENT_NOTIFIER_ERROR_ACCOUNTING_STATUS_OK) {
+                       ERR("Error initializing event notifier error accounting for kernel tracer.");
+                       error_code_ret = LTTNG_ERR_EVENT_NOTIFIER_ERROR_ACCOUNTING;
+                       goto error_modules;
+               }
+
+               kernel_token_to_event_notifier_rule_ht = cds_lfht_new(
+                               DEFAULT_HT_SIZE, 1, 0,
+                               CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING,
+                               NULL);
+               if (!kernel_token_to_event_notifier_rule_ht) {
+                       goto error_token_ht;
+               }
+       }
+
+       DBG("Kernel tracer initialized: kernel tracer fd = %d, event notifier group fd = %d, event notifier group notification fd = %d",
+                       kernel_tracer_fd, kernel_tracer_event_notifier_group_fd,
+                       kernel_tracer_event_notifier_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");
+               PERROR("Failed to close kernel tracer file descriptor: fd = %d",
+                               kernel_tracer_fd);
        }
        kernel_tracer_fd = -1;
        return LTTNG_ERR_KERN_VERSION;
 
+
+error_token_ht:
+       ret = close(kernel_tracer_event_notifier_group_notification_fd);
+       if (ret) {
+               PERROR("Failed to close kernel tracer event notifier group notification file descriptor: fd = %d",
+                               kernel_tracer_event_notifier_group_notification_fd);
+       }
+
 error_modules:
+       ret = close(kernel_tracer_event_notifier_group_fd);
+       if (ret) {
+               PERROR("Failed to close kernel tracer event notifier group file descriptor: fd = %d",
+                               kernel_tracer_event_notifier_group_fd);
+       }
+
        ret = close(kernel_tracer_fd);
        if (ret) {
-               PERROR("close");
+               PERROR("Failed to close kernel tracer file descriptor: fd = %d",
+                               kernel_tracer_fd);
        }
 
 error_open:
@@ -1627,18 +2082,54 @@ error:
 LTTNG_HIDDEN
 void cleanup_kernel_tracer(void)
 {
-       int ret;
+       DBG2("Closing kernel event notifier group notification file descriptor");
+       if (kernel_tracer_event_notifier_group_notification_fd >= 0) {
+               int ret = notification_thread_command_remove_tracer_event_source(
+                               notification_thread_handle,
+                               kernel_tracer_event_notifier_group_notification_fd);
+               if (ret != LTTNG_OK) {
+                       ERR("Failed to remove kernel event notifier notification from notification thread");
+               }
+
+               ret = close(kernel_tracer_event_notifier_group_notification_fd);
+               if (ret) {
+                       PERROR("Failed to close kernel event notifier group notification file descriptor: fd = %d",
+                                       kernel_tracer_event_notifier_group_notification_fd);
+               }
+
+               kernel_tracer_event_notifier_group_notification_fd = -1;
+       }
+
+       if (kernel_token_to_event_notifier_rule_ht) {
+               const int ret = cds_lfht_destroy(
+                               kernel_token_to_event_notifier_rule_ht, NULL);
+               assert(ret == 0);
+       }
+
+       DBG2("Closing kernel event notifier group file descriptor");
+       if (kernel_tracer_event_notifier_group_fd >= 0) {
+               const int ret = close(kernel_tracer_event_notifier_group_fd);
+
+               if (ret) {
+                       PERROR("Failed to close kernel event notifier group file descriptor: fd = %d",
+                                       kernel_tracer_event_notifier_group_fd);
+               }
+
+               kernel_tracer_event_notifier_group_fd = -1;
+       }
 
        DBG2("Closing kernel fd");
        if (kernel_tracer_fd >= 0) {
-               ret = close(kernel_tracer_fd);
+               const int ret = close(kernel_tracer_fd);
+
                if (ret) {
-                       PERROR("close");
+                       PERROR("Failed to close kernel tracer file descriptor: fd = %d",
+                                       kernel_tracer_fd);
                }
+
                kernel_tracer_fd = -1;
        }
-       DBG("Unloading kernel modules");
-       modprobe_remove_lttng_all();
+
        free(syscall_table);
 }
 
@@ -1647,13 +2138,8 @@ 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)
+static
+enum lttng_error_code  kernel_clear_session_channels(struct ltt_session *session)
 {
        int ret;
        enum lttng_error_code status = LTTNG_OK;
@@ -1664,9 +2150,6 @@ enum lttng_error_code kernel_clear_session(struct ltt_session *session)
        assert(ksess);
        assert(ksess->consumer);
 
-       DBG("Clear kernel session %s (session %" PRIu64 ")",
-                       session->name, session->id);
-
        rcu_read_lock();
 
        if (ksess->active) {
@@ -1713,6 +2196,7 @@ enum lttng_error_code kernel_clear_session(struct ltt_session *session)
                }
        }
 
+
        goto end;
 error:
        switch (-ret) {
@@ -1727,3 +2211,834 @@ end:
        rcu_read_unlock();
        return status;
 }
+
+static
+enum lttng_error_code kernel_map_clear_all(struct ltt_kernel_map *map)
+{
+       enum lttng_error_code status;
+       uint64_t descr_count, i;
+       int ret;
+
+       assert(map);
+
+       ret = kernctl_counter_map_descriptor_count(map->fd, &descr_count);
+       if (ret) {
+               ERR("Error getting map descriptor count");
+               status = LTTNG_ERR_MAP_VALUES_LIST_FAIL;
+               goto end;
+       }
+
+       for(i = 0; i < descr_count; i++) {
+               struct lttng_kernel_counter_map_descriptor descriptor = {0};
+               struct lttng_kernel_counter_clear counter_clear = {0};
+
+               descriptor.descriptor_index = i;
+
+               ret = kernctl_counter_map_descriptor(map->fd, &descriptor);
+               if (ret) {
+                       ERR("Error getting map descriptor %"PRIu64, i);
+                       status = LTTNG_ERR_MAP_VALUES_LIST_FAIL;
+                       goto end;
+               }
+
+               counter_clear.index.number_dimensions = 1;
+               counter_clear.index.dimension_indexes[0] = descriptor.array_index;
+
+               ret = kernctl_counter_clear(map->fd, &counter_clear);
+               if (ret) {
+                       ERR("Error clearing value of map descriptor %"PRIu64, i);
+                       status = LTTNG_ERR_MAP_VALUES_LIST_FAIL;
+                       goto end;
+               }
+       }
+
+       status = LTTNG_OK;
+end:
+       return status;
+}
+
+static
+enum lttng_error_code kernel_clear_session_maps(struct ltt_session *session)
+{
+       enum lttng_error_code status = LTTNG_OK;
+       struct ltt_kernel_map *map;
+       struct ltt_kernel_session *ksess = session->kernel_session;
+
+       assert(ksess);
+
+       cds_list_for_each_entry(map, &ksess->map_list.head, list) {
+               DBG("Clear kernel map %" PRIu64 ", session %s",
+                               map->key, session->name);
+               status = kernel_map_clear_all(map);
+               if (status != LTTNG_OK) {
+                       ERR("Clearing all values of map");
+                       goto end;
+               }
+       }
+
+end:
+       return status;
+}
+
+/*
+ *  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)
+{
+       enum lttng_error_code status = LTTNG_OK;
+       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;
+       }
+
+       status = kernel_clear_session_channels(session);
+       if (status != LTTNG_OK) {
+               goto end;
+       }
+       /*
+        * Iterate and clear all kernel maps.
+        */
+       status = kernel_clear_session_maps(session);
+       if (status != LTTNG_OK) {
+               goto end;
+       }
+
+
+end:
+       rcu_read_unlock();
+       return status;
+}
+
+enum lttng_error_code kernel_create_event_notifier_group_notification_fd(
+               int *event_notifier_group_notification_fd)
+{
+       int local_fd = -1, ret;
+       enum lttng_error_code error_code_ret;
+
+       assert(event_notifier_group_notification_fd);
+
+       ret = kernctl_create_event_notifier_group_notification_fd(
+                       kernel_tracer_event_notifier_group_fd);
+       if (ret < 0) {
+               PERROR("Failed to create kernel event notifier group notification file descriptor");
+               error_code_ret = LTTNG_ERR_EVENT_NOTIFIER_GROUP_NOTIFICATION_FD;
+               goto error;
+       }
+
+       local_fd = ret;
+
+       /* Prevent fd duplication after execlp(). */
+       ret = fcntl(local_fd, F_SETFD, FD_CLOEXEC);
+       if (ret < 0) {
+               PERROR("Failed to set FD_CLOEXEC on kernel event notifier group notification file descriptor: fd = %d",
+                               local_fd);
+               error_code_ret = LTTNG_ERR_EVENT_NOTIFIER_GROUP_NOTIFICATION_FD;
+               goto error;
+       }
+
+       DBG("Created kernel notifier group notification file descriptor: fd = %d",
+                       local_fd);
+       error_code_ret = LTTNG_OK;
+       *event_notifier_group_notification_fd = local_fd;
+       local_fd = -1;
+
+error:
+       if (local_fd >= 0) {
+               ret = close(local_fd);
+               if (ret) {
+                       PERROR("Failed to close kernel event notifier group notification file descriptor: fd = %d",
+                                       local_fd);
+               }
+       }
+
+       return error_code_ret;
+}
+
+enum lttng_error_code kernel_destroy_event_notifier_group_notification_fd(
+               int event_notifier_group_notification_fd)
+{
+       enum lttng_error_code ret_code = LTTNG_OK;
+
+       DBG("Closing event notifier group notification file descriptor: fd = %d",
+                       event_notifier_group_notification_fd);
+       if (event_notifier_group_notification_fd >= 0) {
+               const int ret = close(event_notifier_group_notification_fd);
+               if (ret) {
+                       PERROR("Failed to close event notifier group notification file descriptor: fd = %d",
+                                       event_notifier_group_notification_fd);
+               }
+       }
+
+       return ret_code;
+}
+
+static
+unsigned long hash_trigger(const struct lttng_trigger *trigger)
+{
+       const struct lttng_condition *condition =
+                       lttng_trigger_get_const_condition(trigger);
+
+       return lttng_condition_hash(condition);
+}
+
+static
+int match_trigger(struct cds_lfht_node *node, const void *key)
+{
+       const struct ltt_kernel_event_notifier_rule *event_notifier_rule;
+       const struct lttng_trigger *trigger = key;
+
+       event_notifier_rule = caa_container_of(node,
+                       const struct ltt_kernel_event_notifier_rule, ht_node);
+
+       return lttng_trigger_is_equal(trigger, event_notifier_rule->trigger);
+}
+
+static
+int add_key_token(struct lttng_kernel_key_token *kernel_key_token,
+               const struct lttng_map_key_token *key_token)
+{
+       int ret;
+       switch (key_token->type) {
+       case LTTNG_MAP_KEY_TOKEN_TYPE_STRING:
+       {
+               const struct lttng_map_key_token_string *str_token;
+               str_token = (typeof(str_token)) key_token;
+
+               kernel_key_token->type = LTTNG_KERNEL_KEY_TOKEN_STRING;
+               kernel_key_token->arg.string_ptr = (uint64_t) str_token->string;
+
+               break;
+       }
+       case LTTNG_MAP_KEY_TOKEN_TYPE_VARIABLE:
+       {
+               const struct lttng_map_key_token_variable *var_token;
+               var_token = (typeof(var_token)) key_token;
+               switch (var_token->type) {
+               case LTTNG_MAP_KEY_TOKEN_VARIABLE_TYPE_EVENT_NAME:
+                       kernel_key_token->type = LTTNG_KERNEL_KEY_TOKEN_EVENT_NAME;
+                       break;
+               case LTTNG_MAP_KEY_TOKEN_VARIABLE_TYPE_PROVIDER_NAME:
+                       /* The kernel events don't have providers */
+                       ERR("Provider variable token type not supported for kernel tracer");
+                       ret = -1;
+                       goto end;
+               default:
+                       abort();
+               }
+
+               break;
+       }
+       default:
+               abort();
+       }
+       ret = 0;
+end:
+       return ret;
+}
+
+enum lttng_error_code kernel_create_event_counter(
+               struct ltt_kernel_map *kmap,
+               const struct lttng_credentials *creds,
+               uint64_t action_tracer_token,
+               const struct lttng_event_rule *event_rule,
+               struct lttng_map_key *key)
+{
+       int err, fd, ret = 0;
+       unsigned int i, key_token_count;
+       enum lttng_error_code error_code_ret;
+       enum lttng_map_key_status status;
+       struct ltt_kernel_event_counter *event_counter;
+       struct lttng_kernel_counter_event k_counter_event = {};
+
+
+       event_counter = zmalloc(sizeof(*event_counter));
+       if (!event_counter) {
+               error_code_ret = LTTNG_ERR_NOMEM;
+               goto error;
+       }
+
+       trace_kernel_init_event_counter_from_event_rule(event_rule,
+                       &k_counter_event);
+       event_counter->fd = -1;
+       event_counter->enabled = 1;
+       event_counter->action_tracer_token = action_tracer_token;
+       event_counter->filter = lttng_event_rule_get_filter_bytecode(event_rule);
+
+       k_counter_event.event.token = action_tracer_token;
+
+       /* Set the key pattern for this event counter. */
+       k_counter_event.key.nr_dimensions = 1;
+
+       status = lttng_map_key_get_token_count(key, &key_token_count);
+       if (status != LTTNG_MAP_KEY_STATUS_OK) {
+               error_code_ret = LTTNG_ERR_UNK;
+               goto error;
+       }
+
+       assert(key_token_count > 0);
+
+       k_counter_event.key.key_dimensions[0].nr_key_tokens = key_token_count;
+
+       for (i = 0; i < key_token_count; i++) {
+               const struct lttng_map_key_token *token =
+                               lttng_map_key_get_token_at_index(key, i);
+
+               ret = add_key_token(&k_counter_event.key.key_dimensions[0].key_tokens[i],
+                               token);
+               if (ret) {
+                       ERR("Error appending map key token");
+                       error_code_ret = LTTNG_ERR_INVALID;
+                       goto error;
+               }
+       }
+
+       fd = kernctl_create_counter_event(kmap->fd, &k_counter_event);
+       if (fd < 0) {
+               switch (-fd) {
+               case EEXIST:
+                       error_code_ret = LTTNG_ERR_KERN_EVENT_EXIST;
+                       break;
+               case ENOSYS:
+                       WARN("Event counter type not implemented");
+                       error_code_ret = LTTNG_ERR_KERN_EVENT_ENOSYS;
+                       break;
+               case ENOENT:
+                       WARN("Event counter %s not found!", k_counter_event.event.name);
+                       error_code_ret = LTTNG_ERR_KERN_ENABLE_FAIL;
+                       break;
+               default:
+                       error_code_ret = LTTNG_ERR_KERN_ENABLE_FAIL;
+                       PERROR("create event counter ioctl");
+               }
+       }
+
+       event_counter->fd = fd;
+       event_counter->enabled = true;
+
+       /* Prevent fd duplication after execlp() */
+       err = fcntl(fd, F_SETFD, FD_CLOEXEC);
+       if (err < 0) {
+               PERROR("fcntl session fd");
+       }
+
+       if (event_counter->filter) {
+               err = kernctl_filter(event_counter->fd, event_counter->filter);
+               if (err < 0) {
+                       switch (-err) {
+                       case ENOMEM:
+                               error_code_ret = LTTNG_ERR_FILTER_NOMEM;
+                               break;
+                       default:
+                               error_code_ret = LTTNG_ERR_FILTER_INVAL;
+                               break;
+                       }
+                       goto filter_error;
+               }
+       }
+       if (lttng_event_rule_get_type(event_rule) ==
+                       LTTNG_EVENT_RULE_TYPE_USERSPACE_PROBE) {
+               ret = userspace_probe_event_rule_add_callsites(
+                               event_rule, creds, event_counter->fd);
+               if (ret) {
+                       error_code_ret = LTTNG_ERR_KERN_ENABLE_FAIL;
+                       goto add_callsite_error;
+               }
+       }
+
+       err = kernctl_enable(event_counter->fd);
+       if (err < 0) {
+               switch (-err) {
+               case EEXIST:
+                       error_code_ret = LTTNG_ERR_KERN_EVENT_EXIST;
+                       break;
+               default:
+                       PERROR("enable kernel counter event");
+                       error_code_ret = LTTNG_ERR_KERN_ENABLE_FAIL;
+                       break;
+               }
+               goto enable_error;
+       }
+
+       /* Add event to event list */
+       rcu_read_lock();
+       lttng_ht_node_init_u64(&event_counter->ht_node,
+                       event_counter->action_tracer_token);
+       lttng_ht_add_unique_u64(kmap->event_counters_ht,
+                       &event_counter->ht_node);
+       rcu_read_unlock();
+       kmap->event_count++;
+
+       DBG("Kernel event counter %s created (fd: %d)",
+                       event_counter->event->name,
+                       event_counter->fd);
+       error_code_ret = LTTNG_OK;
+
+add_callsite_error:
+filter_error:
+enable_error:
+error:
+       return error_code_ret;
+}
+
+static enum lttng_error_code kernel_create_event_notifier_rule(
+               struct lttng_trigger *trigger,
+               const struct lttng_credentials *creds, uint64_t token)
+{
+       int err, fd, ret = 0;
+       enum lttng_error_code error_code_ret;
+       enum lttng_condition_status condition_status;
+       enum lttng_condition_type condition_type;
+       enum lttng_event_rule_type event_rule_type;
+       struct ltt_kernel_event_notifier_rule *event_notifier_rule;
+       struct lttng_kernel_event_notifier kernel_event_notifier = {};
+       unsigned int capture_bytecode_count = 0, i;
+       const struct lttng_condition *condition = NULL;
+       const struct lttng_event_rule *event_rule = NULL;
+       enum lttng_condition_status cond_status;
+
+       assert(trigger);
+
+       condition = lttng_trigger_get_const_condition(trigger);
+       assert(condition);
+
+       condition_type = lttng_condition_get_type(condition);
+       assert(condition_type == LTTNG_CONDITION_TYPE_ON_EVENT);
+
+       /* Does not acquire a reference. */
+       condition_status = lttng_condition_on_event_get_rule(
+                       condition, &event_rule);
+       assert(condition_status == LTTNG_CONDITION_STATUS_OK);
+       assert(event_rule);
+
+       event_rule_type = lttng_event_rule_get_type(event_rule);
+       assert(event_rule_type != LTTNG_EVENT_RULE_TYPE_UNKNOWN);
+
+       error_code_ret = trace_kernel_create_event_notifier_rule(trigger, token,
+                       lttng_condition_on_event_get_error_counter_index(condition),
+                       &event_notifier_rule);
+       if (error_code_ret != LTTNG_OK) {
+               goto error;
+       }
+
+       error_code_ret = trace_kernel_init_event_notifier_from_event_rule(
+                       event_rule, &kernel_event_notifier);
+       if (error_code_ret != LTTNG_OK) {
+               goto free_event;
+       }
+
+       kernel_event_notifier.event.token = event_notifier_rule->token;
+       kernel_event_notifier.error_counter_idx =
+                       lttng_condition_on_event_get_error_counter_index(condition);
+
+       fd = kernctl_create_event_notifier(
+                       kernel_tracer_event_notifier_group_fd,
+                       &kernel_event_notifier);
+       if (fd < 0) {
+               switch (-fd) {
+               case EEXIST:
+                       error_code_ret = LTTNG_ERR_KERN_EVENT_EXIST;
+                       break;
+               case ENOSYS:
+                       WARN("Failed to create kernel event notifier: not notifier type not implemented");
+                       error_code_ret = LTTNG_ERR_KERN_EVENT_ENOSYS;
+                       break;
+               case ENOENT:
+                       WARN("Failed to create kernel event notifier: not found: name = '%s'",
+                                       kernel_event_notifier.event.name);
+                       error_code_ret = LTTNG_ERR_KERN_ENABLE_FAIL;
+                       break;
+               default:
+                       PERROR("Failed to create kernel event notifier: error code = %d, name = '%s'",
+                                       fd, kernel_event_notifier.event.name);
+                       error_code_ret = LTTNG_ERR_KERN_ENABLE_FAIL;
+               }
+               goto free_event;
+       }
+
+       event_notifier_rule->fd = fd;
+       /* Prevent fd duplication after execlp(). */
+       err = fcntl(event_notifier_rule->fd, F_SETFD, FD_CLOEXEC);
+       if (err < 0) {
+               PERROR("Failed to set FD_CLOEXEC on kernel event notifier file descriptor: fd = %d",
+                               fd);
+               error_code_ret = LTTNG_ERR_FATAL;
+               goto set_cloexec_error;
+       }
+
+       if (event_notifier_rule->filter) {
+               err = kernctl_filter(event_notifier_rule->fd, event_notifier_rule->filter);
+               if (err < 0) {
+                       switch (-err) {
+                       case ENOMEM:
+                               error_code_ret = LTTNG_ERR_FILTER_NOMEM;
+                               break;
+                       default:
+                               error_code_ret = LTTNG_ERR_FILTER_INVAL;
+                               break;
+                       }
+                       goto filter_error;
+               }
+       }
+
+       if (lttng_event_rule_get_type(event_rule) ==
+                       LTTNG_EVENT_RULE_TYPE_USERSPACE_PROBE) {
+               ret = userspace_probe_event_rule_add_callsites(
+                               event_rule, creds, event_notifier_rule->fd);
+               if (ret) {
+                       error_code_ret = LTTNG_ERR_KERN_ENABLE_FAIL;
+                       goto add_callsite_error;
+               }
+       }
+
+       /* Set the capture bytecode if any */
+       cond_status = lttng_condition_on_event_get_capture_descriptor_count(condition, &capture_bytecode_count);
+       assert(cond_status == LTTNG_CONDITION_STATUS_OK);
+       for (i = 0; i < capture_bytecode_count; i++) {
+               const struct lttng_bytecode *capture_bytecode =
+                               lttng_condition_on_event_get_capture_bytecode_at_index(
+                                               condition, i);
+               if (capture_bytecode == NULL) {
+                       error_code_ret = LTTNG_ERR_KERN_ENABLE_FAIL;
+                       goto error;
+               }
+
+               ret = kernctl_capture(event_notifier_rule->fd, capture_bytecode);
+               if (ret < 0) {
+                       error_code_ret = LTTNG_ERR_KERN_ENABLE_FAIL;
+                       goto error;
+               }
+       }
+
+       err = kernctl_enable(event_notifier_rule->fd);
+       if (err < 0) {
+               switch (-err) {
+               case EEXIST:
+                       error_code_ret = LTTNG_ERR_KERN_EVENT_EXIST;
+                       break;
+               default:
+                       PERROR("enable kernel event notifier");
+                       error_code_ret = LTTNG_ERR_KERN_ENABLE_FAIL;
+                       break;
+               }
+               goto enable_error;
+       }
+
+       /* Add trigger to kernel token mapping in the hash table. */
+       rcu_read_lock();
+       cds_lfht_add(kernel_token_to_event_notifier_rule_ht, hash_trigger(trigger),
+                       &event_notifier_rule->ht_node);
+       rcu_read_unlock();
+
+       DBG("Created kernel event notifier: name = '%s', fd = %d",
+                       kernel_event_notifier.event.name,
+                       event_notifier_rule->fd);
+
+       return LTTNG_OK;
+
+add_callsite_error:
+enable_error:
+set_cloexec_error:
+filter_error:
+       {
+               const int close_ret = close(event_notifier_rule->fd);
+
+               if (close_ret) {
+                       PERROR("Failed to close kernel event notifier file descriptor: fd = %d",
+                                       event_notifier_rule->fd);
+               }
+       }
+free_event:
+       free(event_notifier_rule);
+error:
+       return error_code_ret;
+}
+
+enum lttng_error_code kernel_register_event_notifier(
+               struct lttng_trigger *trigger,
+               const struct lttng_credentials *cmd_creds)
+{
+       enum lttng_error_code ret;
+       enum lttng_condition_status status;
+       enum lttng_domain_type domain_type;
+       const struct lttng_event_rule *event_rule;
+       const struct lttng_condition *const condition =
+                       lttng_trigger_get_const_condition(trigger);
+       const uint64_t token = lttng_trigger_get_tracer_token(trigger);
+
+       assert(condition);
+
+       /* Does not acquire a reference to the event rule. */
+       status = lttng_condition_on_event_get_rule(
+                       condition, &event_rule);
+       assert(status == LTTNG_CONDITION_STATUS_OK);
+
+       domain_type = lttng_event_rule_get_domain_type(event_rule);
+       assert(domain_type == LTTNG_DOMAIN_KERNEL);
+
+       ret = kernel_create_event_notifier_rule(trigger, cmd_creds, token);
+       if (ret != LTTNG_OK) {
+               ERR("Failed to create kernel event notifier rule");
+       }
+
+       return ret;
+}
+
+enum lttng_error_code kernel_unregister_event_notifier(
+               const struct lttng_trigger *trigger)
+{
+       struct ltt_kernel_event_notifier_rule *token_event_rule_element;
+       struct cds_lfht_node *node;
+       struct cds_lfht_iter iter;
+       enum lttng_error_code error_code_ret;
+       int ret;
+
+       rcu_read_lock();
+
+       cds_lfht_lookup(kernel_token_to_event_notifier_rule_ht,
+                       hash_trigger(trigger), match_trigger, trigger, &iter);
+
+       node = cds_lfht_iter_get_node(&iter);
+       if (!node) {
+               error_code_ret = LTTNG_ERR_TRIGGER_NOT_FOUND;
+               goto error;
+       }
+
+       token_event_rule_element = caa_container_of(node,
+                       struct ltt_kernel_event_notifier_rule, ht_node);
+
+       ret = kernel_disable_event_notifier_rule(token_event_rule_element);
+       if (ret) {
+               error_code_ret = LTTNG_ERR_FATAL;
+               goto error;
+       }
+
+       trace_kernel_destroy_event_notifier_rule(token_event_rule_element);
+       error_code_ret = LTTNG_OK;
+
+error:
+       rcu_read_unlock();
+
+       return error_code_ret;
+}
+
+struct key_ht_entry {
+       char *key;
+       struct lttng_ht_node_str node;
+};
+
+enum lttng_error_code kernel_list_map_values(const struct ltt_kernel_map *map,
+               const struct lttng_map_query *query,
+               struct lttng_map_content **map_content)
+{
+       enum lttng_map_status map_status;
+       enum lttng_error_code ret_code;
+       const char *map_name = NULL;
+       uint64_t descr_count, descr_idx, cpu_idx;
+       struct lttng_map_content *local_map_content;
+       struct lttng_ht *key_ht;
+       struct lttng_ht *values = NULL;
+       struct lttng_ht_node_str *node;
+       struct key_ht_entry *ht_entry;
+       struct lttng_ht_iter iter;
+       enum lttng_map_query_status map_query_status;
+       const char *key_filter;
+       bool sum_cpus = lttng_map_query_get_config_sum_by_cpu(query);
+       enum lttng_map_query_config_cpu config_cpu;
+       int ret;
+       int selected_cpu;
+
+
+       local_map_content = lttng_map_content_create(LTTNG_BUFFER_GLOBAL);
+       if (!local_map_content) {
+               ERR("Error creating map content");
+               ret_code = LTTNG_ERR_NOMEM;
+               goto end;
+       }
+
+       map_query_status = lttng_map_query_get_key_filter(query, &key_filter);
+       if (map_query_status == LTTNG_MAP_QUERY_STATUS_NONE) {
+               key_filter = NULL;
+       } else if (map_query_status != LTTNG_MAP_QUERY_STATUS_OK) {
+               ret_code = LTTNG_ERR_INVALID;
+               goto end;
+       }
+
+       config_cpu = lttng_map_query_get_config_cpu(query);
+       if (config_cpu == LTTNG_MAP_QUERY_CONFIG_CPU_SUBSET) {
+               unsigned int count;
+               map_query_status = lttng_map_query_get_cpu_count(query, &count);
+               assert(map_query_status == LTTNG_MAP_QUERY_STATUS_OK);
+               assert(count == 1);
+
+               map_query_status = lttng_map_query_get_cpu_at_index(query, 0,
+                               &selected_cpu);
+               assert(map_query_status == LTTNG_MAP_QUERY_STATUS_OK);
+       }
+
+       map_status = lttng_map_get_name(map->map, &map_name);
+       assert(map_status == LTTNG_MAP_STATUS_OK);
+
+       DBG("Listing kernel map values: map-name = '%s'", map_name);
+
+       ret = kernctl_counter_map_descriptor_count(map->fd, &descr_count);
+       if (ret) {
+               ERR("Error getting map descriptor count");
+               ret_code = LTTNG_ERR_MAP_VALUES_LIST_FAIL;
+               goto end;
+       }
+
+       /*
+        * The kernel tracer sends us descriptors that may be identical aside
+        * from their user token field. This ABI was design this way to cover a
+        * potential use case where the user wants to know what enabler might
+        * have contributed to a specific bucket.
+        *
+        * We use this hashtable to de-duplicate keys.
+        */
+       if (sum_cpus) {
+               values = lttng_ht_new(0, LTTNG_HT_TYPE_STRING);
+               if (!values) {
+                       ret_code = LTTNG_ERR_NOMEM;
+                       goto end;
+               }
+       }
+
+       DBG("Querying kernel for all map values: "
+                       "map-name = '%s', key-value count = %"PRIu64,
+                       map_name, descr_count);
+       for (cpu_idx = 0; cpu_idx < utils_get_number_of_possible_cpus(); cpu_idx++) {
+               struct lttng_kernel_counter_read value = {0};
+
+               if (config_cpu == LTTNG_MAP_QUERY_CONFIG_CPU_SUBSET) {
+                       if (selected_cpu != cpu_idx) {
+                               continue;
+                       }
+               }
+
+               if (!sum_cpus) {
+                       values = lttng_ht_new(0, LTTNG_HT_TYPE_STRING);
+                       assert(values);
+               }
+
+               key_ht = lttng_ht_new(0, LTTNG_HT_TYPE_STRING);
+               if (!key_ht) {
+                       ret_code = LTTNG_ERR_NOMEM;
+                       goto end;
+               }
+
+               for(descr_idx = 0; descr_idx < descr_count; descr_idx++) {
+                       struct lttng_kernel_counter_map_descriptor descriptor = {0};
+
+                       DBG("Querying kernel for map key-value descriptor: "
+                                       "map-name = '%s', descriptor = %"PRIu64,
+                                       map_name, descr_idx);
+                       descriptor.descriptor_index = descr_idx;
+
+                       ret = kernctl_counter_map_descriptor(map->fd, &descriptor);
+                       if (ret) {
+                               ERR("Error getting map descriptor %"PRIu64, descr_idx);
+                               ret_code = LTTNG_ERR_MAP_VALUES_LIST_FAIL;
+                               goto end;
+                       }
+
+                       if (key_filter && strcmp(key_filter, descriptor.key) != 0) {
+                               continue;
+                       }
+
+                       lttng_ht_lookup(key_ht, descriptor.key, &iter);
+                       node = lttng_ht_iter_get_node_str(&iter);
+                       if (node) {
+                               /* This key was already appended to the list. */
+                               continue;
+                       }
+
+
+                       value.index.number_dimensions = 1;
+                       value.index.dimension_indexes[0] = descriptor.array_index;
+                       value.cpu = cpu_idx;
+
+                       DBG("Querying kernel for map descriptor value: "
+                                       "map-name = '%s', counter-index = %"PRIu64,
+                                       map_name, descriptor.array_index);
+                       ret = kernctl_counter_read_value(map->fd, &value);
+                       if (ret) {
+                               ERR("Error getting value of map descriptor %"PRIu64, descr_idx);
+                               ret_code = LTTNG_ERR_MAP_VALUES_LIST_FAIL;
+                               goto end;
+                       }
+
+                       map_add_or_increment_map_values(values, descriptor.key,
+                                       value.value.value, value.value.underflow,
+                                       value.value.overflow);
+
+                       ht_entry = zmalloc(sizeof(*ht_entry));
+                       assert(ht_entry);
+                       ht_entry->key = strdup(descriptor.key);
+                       lttng_ht_node_init_str(&ht_entry->node, ht_entry->key);
+                       lttng_ht_add_unique_str(key_ht, &ht_entry->node);
+               }
+
+               if (!sum_cpus) {
+                       ret = map_new_content_section(local_map_content,
+                                       LTTNG_MAP_KEY_VALUE_PAIR_LIST_TYPE_KERNEL,
+                                       sum_cpus, 0,
+                                       cpu_idx, values);
+                       if (ret) {
+                               abort();
+                       }
+
+                       lttng_ht_destroy(values);
+               }
+
+               /*
+                * Remove all the keys before destroying the hashtable.
+                */
+               cds_lfht_for_each_entry(key_ht->ht, &iter.iter, ht_entry, node.node) {
+                       struct lttng_ht_iter entry_iter;
+
+                       entry_iter.iter.node = &ht_entry->node.node;
+                       lttng_ht_del(key_ht, &entry_iter);
+
+                       free(ht_entry);
+               }
+
+               lttng_ht_destroy(key_ht);
+       }
+
+       if (sum_cpus) {
+               ret = map_new_content_section(local_map_content,
+                               LTTNG_MAP_KEY_VALUE_PAIR_LIST_TYPE_KERNEL,
+                               sum_cpus, 0, 0, values);
+               if (ret) {
+                       abort();
+               }
+               lttng_ht_destroy(values);
+       }
+
+
+       *map_content = local_map_content;
+       local_map_content = NULL;
+       ret_code = LTTNG_OK;
+
+end:
+       lttng_map_content_destroy(local_map_content);
+       return ret_code;
+}
+
+int kernel_get_notification_fd(void)
+{
+       return kernel_tracer_event_notifier_group_notification_fd;
+}
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