Fix: don't perform extra flush on metadata channel

[lttng-modules.git] / lttng-events.c

/*
 * lttng-events.c
 *
 * Holds LTTng per-session event registry.
 *
 * Copyright (C) 2010-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; only
 * version 2.1 of the License.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/*
 * This page_alloc.h wrapper needs to be included before gfpflags.h because it
 * overrides a function with a define.
 */
#include "wrapper/page_alloc.h"

#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/jiffies.h>
#include <linux/utsname.h>
#include <linux/err.h>
#include <linux/seq_file.h>
#include <linux/file.h>
#include <linux/anon_inodes.h>
#include <wrapper/file.h>
#include <linux/jhash.h>
#include <linux/uaccess.h>
#include <linux/vmalloc.h>

#include <wrapper/uuid.h>
#include <wrapper/vmalloc.h>    /* for wrapper_vmalloc_sync_all() */
#include <wrapper/random.h>
#include <wrapper/tracepoint.h>
#include <wrapper/list.h>
#include <lttng-kernel-version.h>
#include <lttng-events.h>
#include <lttng-tracer.h>
#include <lttng-abi-old.h>
#include <lttng-endian.h>
#include <wrapper/vzalloc.h>
#include <wrapper/ringbuffer/backend.h>
#include <wrapper/ringbuffer/frontend.h>

#define METADATA_CACHE_DEFAULT_SIZE 4096

static LIST_HEAD(sessions);
static LIST_HEAD(lttng_transport_list);
/*
 * Protect the sessions and metadata caches.
 */
static DEFINE_MUTEX(sessions_mutex);
static struct kmem_cache *event_cache;

static void lttng_session_lazy_sync_enablers(struct lttng_session *session);
static void lttng_session_sync_enablers(struct lttng_session *session);
static void lttng_enabler_destroy(struct lttng_enabler *enabler);

static void _lttng_event_destroy(struct lttng_event *event);
static void _lttng_channel_destroy(struct lttng_channel *chan);
static int _lttng_event_unregister(struct lttng_event *event);
static
int _lttng_event_metadata_statedump(struct lttng_session *session,
                                  struct lttng_channel *chan,
                                  struct lttng_event *event);
static
int _lttng_session_metadata_statedump(struct lttng_session *session);
static
void _lttng_metadata_channel_hangup(struct lttng_metadata_stream *stream);

void synchronize_trace(void)
{
        synchronize_sched();
#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,4,0))
#ifdef CONFIG_PREEMPT_RT_FULL
        synchronize_rcu();
#endif
#else /* (LINUX_VERSION_CODE >= KERNEL_VERSION(3,4,0)) */
#ifdef CONFIG_PREEMPT_RT
        synchronize_rcu();
#endif
#endif /* (LINUX_VERSION_CODE >= KERNEL_VERSION(3,4,0)) */
}

void lttng_lock_sessions(void)
{
        mutex_lock(&sessions_mutex);
}

void lttng_unlock_sessions(void)
{
        mutex_unlock(&sessions_mutex);
}

/*
 * Called with sessions lock held.
 */
int lttng_session_active(void)
{
        struct lttng_session *iter;

        list_for_each_entry(iter, &sessions, list) {
                if (iter->active)
                        return 1;
        }
        return 0;
}

struct lttng_session *lttng_session_create(void)
{
        struct lttng_session *session;
        struct lttng_metadata_cache *metadata_cache;
        int i;

        mutex_lock(&sessions_mutex);
        session = kzalloc(sizeof(struct lttng_session), GFP_KERNEL);
        if (!session)
                goto err;
        INIT_LIST_HEAD(&session->chan);
        INIT_LIST_HEAD(&session->events);
        uuid_le_gen(&session->uuid);

        metadata_cache = kzalloc(sizeof(struct lttng_metadata_cache),
                        GFP_KERNEL);
        if (!metadata_cache)
                goto err_free_session;
        metadata_cache->data = lttng_vzalloc(METADATA_CACHE_DEFAULT_SIZE);
        if (!metadata_cache->data)
                goto err_free_cache;
        metadata_cache->cache_alloc = METADATA_CACHE_DEFAULT_SIZE;
        kref_init(&metadata_cache->refcount);
        mutex_init(&metadata_cache->lock);
        session->metadata_cache = metadata_cache;
        INIT_LIST_HEAD(&metadata_cache->metadata_stream);
        memcpy(&metadata_cache->uuid, &session->uuid,
                sizeof(metadata_cache->uuid));
        INIT_LIST_HEAD(&session->enablers_head);
        for (i = 0; i < LTTNG_EVENT_HT_SIZE; i++)
                INIT_HLIST_HEAD(&session->events_ht.table[i]);
        list_add(&session->list, &sessions);
        mutex_unlock(&sessions_mutex);
        return session;

err_free_cache:
        kfree(metadata_cache);
err_free_session:
        kfree(session);
err:
        mutex_unlock(&sessions_mutex);
        return NULL;
}

void metadata_cache_destroy(struct kref *kref)
{
        struct lttng_metadata_cache *cache =
                container_of(kref, struct lttng_metadata_cache, refcount);
        vfree(cache->data);
        kfree(cache);
}

void lttng_session_destroy(struct lttng_session *session)
{
        struct lttng_channel *chan, *tmpchan;
        struct lttng_event *event, *tmpevent;
        struct lttng_metadata_stream *metadata_stream;
        struct lttng_enabler *enabler, *tmpenabler;
        int ret;

        mutex_lock(&sessions_mutex);
        ACCESS_ONCE(session->active) = 0;
        list_for_each_entry(chan, &session->chan, list) {
                ret = lttng_syscalls_unregister(chan);
                WARN_ON(ret);
        }
        list_for_each_entry(event, &session->events, list) {
                ret = _lttng_event_unregister(event);
                WARN_ON(ret);
        }
        synchronize_trace();    /* Wait for in-flight events to complete */
        list_for_each_entry_safe(enabler, tmpenabler,
                        &session->enablers_head, node)
                lttng_enabler_destroy(enabler);
        list_for_each_entry_safe(event, tmpevent, &session->events, list)
                _lttng_event_destroy(event);
        list_for_each_entry_safe(chan, tmpchan, &session->chan, list) {
                BUG_ON(chan->channel_type == METADATA_CHANNEL);
                _lttng_channel_destroy(chan);
        }
        list_for_each_entry(metadata_stream, &session->metadata_cache->metadata_stream, list)
                _lttng_metadata_channel_hangup(metadata_stream);
        if (session->pid_tracker)
                lttng_pid_tracker_destroy(session->pid_tracker);
        kref_put(&session->metadata_cache->refcount, metadata_cache_destroy);
        list_del(&session->list);
        mutex_unlock(&sessions_mutex);
        kfree(session);
}

int lttng_session_enable(struct lttng_session *session)
{
        int ret = 0;
        struct lttng_channel *chan;

        mutex_lock(&sessions_mutex);
        if (session->active) {
                ret = -EBUSY;
                goto end;
        }

        /* Set transient enabler state to "enabled" */
        session->tstate = 1;

        /*
         * Snapshot the number of events per channel to know the type of header
         * we need to use.
         */
        list_for_each_entry(chan, &session->chan, list) {
                if (chan->header_type)
                        continue;               /* don't change it if session stop/restart */
                if (chan->free_event_id < 31)
                        chan->header_type = 1;  /* compact */
                else
                        chan->header_type = 2;  /* large */
        }

        /* We need to sync enablers with session before activation. */
        lttng_session_sync_enablers(session);

        /* Clear each stream's quiescent state. */
        list_for_each_entry(chan, &session->chan, list)
                lib_ring_buffer_clear_quiescent_channel(chan->chan);

        ACCESS_ONCE(session->active) = 1;
        ACCESS_ONCE(session->been_active) = 1;
        ret = _lttng_session_metadata_statedump(session);
        if (ret) {
                ACCESS_ONCE(session->active) = 0;
                goto end;
        }
        ret = lttng_statedump_start(session);
        if (ret)
                ACCESS_ONCE(session->active) = 0;
end:
        mutex_unlock(&sessions_mutex);
        return ret;
}

int lttng_session_disable(struct lttng_session *session)
{
        int ret = 0;
        struct lttng_channel *chan;

        mutex_lock(&sessions_mutex);
        if (!session->active) {
                ret = -EBUSY;
                goto end;
        }
        ACCESS_ONCE(session->active) = 0;

        /* Set transient enabler state to "disabled" */
        session->tstate = 0;
        lttng_session_sync_enablers(session);

        /* Set each stream's quiescent state. */
        list_for_each_entry(chan, &session->chan, list)
                lib_ring_buffer_set_quiescent_channel(chan->chan);
end:
        mutex_unlock(&sessions_mutex);
        return ret;
}

int lttng_session_metadata_regenerate(struct lttng_session *session)
{
        int ret = 0;
        struct lttng_channel *chan;
        struct lttng_event *event;
        struct lttng_metadata_cache *cache = session->metadata_cache;
        struct lttng_metadata_stream *stream;

        mutex_lock(&sessions_mutex);
        if (!session->active) {
                ret = -EBUSY;
                goto end;
        }

        mutex_lock(&cache->lock);
        memset(cache->data, 0, cache->cache_alloc);
        cache->metadata_written = 0;
        cache->version++;
        list_for_each_entry(stream, &session->metadata_cache->metadata_stream, list) {
                stream->metadata_out = 0;
                stream->metadata_in = 0;
        }
        mutex_unlock(&cache->lock);

        session->metadata_dumped = 0;
        list_for_each_entry(chan, &session->chan, list) {
                chan->metadata_dumped = 0;
        }

        list_for_each_entry(event, &session->events, list) {
                event->metadata_dumped = 0;
        }

        ret = _lttng_session_metadata_statedump(session);

end:
        mutex_unlock(&sessions_mutex);
        return ret;
}



int lttng_channel_enable(struct lttng_channel *channel)
{
        int ret = 0;

        mutex_lock(&sessions_mutex);
        if (channel->channel_type == METADATA_CHANNEL) {
                ret = -EPERM;
                goto end;
        }
        if (channel->enabled) {
                ret = -EEXIST;
                goto end;
        }
        /* Set transient enabler state to "enabled" */
        channel->tstate = 1;
        lttng_session_sync_enablers(channel->session);
        /* Set atomically the state to "enabled" */
        ACCESS_ONCE(channel->enabled) = 1;
end:
        mutex_unlock(&sessions_mutex);
        return ret;
}

int lttng_channel_disable(struct lttng_channel *channel)
{
        int ret = 0;

        mutex_lock(&sessions_mutex);
        if (channel->channel_type == METADATA_CHANNEL) {
                ret = -EPERM;
                goto end;
        }
        if (!channel->enabled) {
                ret = -EEXIST;
                goto end;
        }
        /* Set atomically the state to "disabled" */
        ACCESS_ONCE(channel->enabled) = 0;
        /* Set transient enabler state to "enabled" */
        channel->tstate = 0;
        lttng_session_sync_enablers(channel->session);
end:
        mutex_unlock(&sessions_mutex);
        return ret;
}

int lttng_event_enable(struct lttng_event *event)
{
        int ret = 0;

        mutex_lock(&sessions_mutex);
        if (event->chan->channel_type == METADATA_CHANNEL) {
                ret = -EPERM;
                goto end;
        }
        if (event->enabled) {
                ret = -EEXIST;
                goto end;
        }
        switch (event->instrumentation) {
        case LTTNG_KERNEL_TRACEPOINT:
        case LTTNG_KERNEL_SYSCALL:
                ret = -EINVAL;
                break;
        case LTTNG_KERNEL_KPROBE:
        case LTTNG_KERNEL_FUNCTION:
        case LTTNG_KERNEL_NOOP:
                ACCESS_ONCE(event->enabled) = 1;
                break;
        case LTTNG_KERNEL_KRETPROBE:
                ret = lttng_kretprobes_event_enable_state(event, 1);
                break;
        default:
                WARN_ON_ONCE(1);
                ret = -EINVAL;
        }
end:
        mutex_unlock(&sessions_mutex);
        return ret;
}

int lttng_event_disable(struct lttng_event *event)
{
        int ret = 0;

        mutex_lock(&sessions_mutex);
        if (event->chan->channel_type == METADATA_CHANNEL) {
                ret = -EPERM;
                goto end;
        }
        if (!event->enabled) {
                ret = -EEXIST;
                goto end;
        }
        switch (event->instrumentation) {
        case LTTNG_KERNEL_TRACEPOINT:
        case LTTNG_KERNEL_SYSCALL:
                ret = -EINVAL;
                break;
        case LTTNG_KERNEL_KPROBE:
        case LTTNG_KERNEL_FUNCTION:
        case LTTNG_KERNEL_NOOP:
                ACCESS_ONCE(event->enabled) = 0;
                break;
        case LTTNG_KERNEL_KRETPROBE:
                ret = lttng_kretprobes_event_enable_state(event, 0);
                break;
        default:
                WARN_ON_ONCE(1);
                ret = -EINVAL;
        }
end:
        mutex_unlock(&sessions_mutex);
        return ret;
}

static struct lttng_transport *lttng_transport_find(const char *name)
{
        struct lttng_transport *transport;

        list_for_each_entry(transport, &lttng_transport_list, node) {
                if (!strcmp(transport->name, name))
                        return transport;
        }
        return NULL;
}

struct lttng_channel *lttng_channel_create(struct lttng_session *session,
                                       const char *transport_name,
                                       void *buf_addr,
                                       size_t subbuf_size, size_t num_subbuf,
                                       unsigned int switch_timer_interval,
                                       unsigned int read_timer_interval,
                                       enum channel_type channel_type)
{
        struct lttng_channel *chan;
        struct lttng_transport *transport = NULL;

        mutex_lock(&sessions_mutex);
        if (session->been_active && channel_type != METADATA_CHANNEL)
                goto active;    /* Refuse to add channel to active session */
        transport = lttng_transport_find(transport_name);
        if (!transport) {
                printk(KERN_WARNING "LTTng transport %s not found\n",
                       transport_name);
                goto notransport;
        }
        if (!try_module_get(transport->owner)) {
                printk(KERN_WARNING "LTT : Can't lock transport module.\n");
                goto notransport;
        }
        chan = kzalloc(sizeof(struct lttng_channel), GFP_KERNEL);
        if (!chan)
                goto nomem;
        chan->session = session;
        chan->id = session->free_chan_id++;
        chan->ops = &transport->ops;
        /*
         * Note: the channel creation op already writes into the packet
         * headers. Therefore the "chan" information used as input
         * should be already accessible.
         */
        chan->chan = transport->ops.channel_create(transport_name,
                        chan, buf_addr, subbuf_size, num_subbuf,
                        switch_timer_interval, read_timer_interval);
        if (!chan->chan)
                goto create_error;
        chan->tstate = 1;
        chan->enabled = 1;
        chan->transport = transport;
        chan->channel_type = channel_type;
        list_add(&chan->list, &session->chan);
        mutex_unlock(&sessions_mutex);
        return chan;

create_error:
        kfree(chan);
nomem:
        if (transport)
                module_put(transport->owner);
notransport:
active:
        mutex_unlock(&sessions_mutex);
        return NULL;
}

/*
 * Only used internally at session destruction for per-cpu channels, and
 * when metadata channel is released.
 * Needs to be called with sessions mutex held.
 */
static
void _lttng_channel_destroy(struct lttng_channel *chan)
{
        chan->ops->channel_destroy(chan->chan);
        module_put(chan->transport->owner);
        list_del(&chan->list);
        lttng_destroy_context(chan->ctx);
        kfree(chan);
}

void lttng_metadata_channel_destroy(struct lttng_channel *chan)
{
        BUG_ON(chan->channel_type != METADATA_CHANNEL);

        /* Protect the metadata cache with the sessions_mutex. */
        mutex_lock(&sessions_mutex);
        _lttng_channel_destroy(chan);
        mutex_unlock(&sessions_mutex);
}
EXPORT_SYMBOL_GPL(lttng_metadata_channel_destroy);

static
void _lttng_metadata_channel_hangup(struct lttng_metadata_stream *stream)
{
        stream->finalized = 1;
        wake_up_interruptible(&stream->read_wait);
}

/*
 * Supports event creation while tracing session is active.
 * Needs to be called with sessions mutex held.
 */
struct lttng_event *_lttng_event_create(struct lttng_channel *chan,
                                struct lttng_kernel_event *event_param,
                                void *filter,
                                const struct lttng_event_desc *event_desc,
                                enum lttng_kernel_instrumentation itype)
{
        struct lttng_session *session = chan->session;
        struct lttng_event *event;
        const char *event_name;
        struct hlist_head *head;
        size_t name_len;
        uint32_t hash;
        int ret;

        if (chan->free_event_id == -1U) {
                ret = -EMFILE;
                goto full;
        }

        switch (itype) {
        case LTTNG_KERNEL_TRACEPOINT:
                event_name = event_desc->name;
                break;
        case LTTNG_KERNEL_KPROBE:
        case LTTNG_KERNEL_KRETPROBE:
        case LTTNG_KERNEL_FUNCTION:
        case LTTNG_KERNEL_NOOP:
        case LTTNG_KERNEL_SYSCALL:
                event_name = event_param->name;
                break;
        default:
                WARN_ON_ONCE(1);
                ret = -EINVAL;
                goto type_error;
        }
        name_len = strlen(event_name);
        hash = jhash(event_name, name_len, 0);
        head = &session->events_ht.table[hash & (LTTNG_EVENT_HT_SIZE - 1)];
        lttng_hlist_for_each_entry(event, head, hlist) {
                WARN_ON_ONCE(!event->desc);
                if (!strncmp(event->desc->name, event_name,
                                        LTTNG_KERNEL_SYM_NAME_LEN - 1)
                                && chan == event->chan) {
                        ret = -EEXIST;
                        goto exist;
                }
        }

        event = kmem_cache_zalloc(event_cache, GFP_KERNEL);
        if (!event) {
                ret = -ENOMEM;
                goto cache_error;
        }
        event->chan = chan;
        event->filter = filter;
        event->id = chan->free_event_id++;
        event->instrumentation = itype;
        event->evtype = LTTNG_TYPE_EVENT;
        INIT_LIST_HEAD(&event->bytecode_runtime_head);
        INIT_LIST_HEAD(&event->enablers_ref_head);

        switch (itype) {
        case LTTNG_KERNEL_TRACEPOINT:
                /* Event will be enabled by enabler sync. */
                event->enabled = 0;
                event->registered = 0;
                event->desc = lttng_event_get(event_name);
                if (!event->desc) {
                        ret = -ENOENT;
                        goto register_error;
                }
                /* Populate lttng_event structure before event registration. */
                smp_wmb();
                break;
        case LTTNG_KERNEL_KPROBE:
                /*
                 * Needs to be explicitly enabled after creation, since
                 * we may want to apply filters.
                 */
                event->enabled = 0;
                event->registered = 1;
                /*
                 * Populate lttng_event structure before event
                 * registration.
                 */
                smp_wmb();
                ret = lttng_kprobes_register(event_name,
                                event_param->u.kprobe.symbol_name,
                                event_param->u.kprobe.offset,
                                event_param->u.kprobe.addr,
                                event);
                if (ret) {
                        ret = -EINVAL;
                        goto register_error;
                }
                ret = try_module_get(event->desc->owner);
                WARN_ON_ONCE(!ret);
                break;
        case LTTNG_KERNEL_KRETPROBE:
        {
                struct lttng_event *event_return;

                /* kretprobe defines 2 events */
                /*
                 * Needs to be explicitly enabled after creation, since
                 * we may want to apply filters.
                 */
                event->enabled = 0;
                event->registered = 1;
                event_return =
                        kmem_cache_zalloc(event_cache, GFP_KERNEL);
                if (!event_return) {
                        ret = -ENOMEM;
                        goto register_error;
                }
                event_return->chan = chan;
                event_return->filter = filter;
                event_return->id = chan->free_event_id++;
                event_return->enabled = 0;
                event_return->registered = 1;
                event_return->instrumentation = itype;
                /*
                 * Populate lttng_event structure before kretprobe registration.
                 */
                smp_wmb();
                ret = lttng_kretprobes_register(event_name,
                                event_param->u.kretprobe.symbol_name,
                                event_param->u.kretprobe.offset,
                                event_param->u.kretprobe.addr,
                                event, event_return);
                if (ret) {
                        kmem_cache_free(event_cache, event_return);
                        ret = -EINVAL;
                        goto register_error;
                }
                /* Take 2 refs on the module: one per event. */
                ret = try_module_get(event->desc->owner);
                WARN_ON_ONCE(!ret);
                ret = try_module_get(event->desc->owner);
                WARN_ON_ONCE(!ret);
                ret = _lttng_event_metadata_statedump(chan->session, chan,
                                                    event_return);
                WARN_ON_ONCE(ret > 0);
                if (ret) {
                        kmem_cache_free(event_cache, event_return);
                        module_put(event->desc->owner);
                        module_put(event->desc->owner);
                        goto statedump_error;
                }
                list_add(&event_return->list, &chan->session->events);
                break;
        }
        case LTTNG_KERNEL_FUNCTION:
                /*
                 * Needs to be explicitly enabled after creation, since
                 * we may want to apply filters.
                 */
                event->enabled = 0;
                event->registered = 1;
                /*
                 * Populate lttng_event structure before event
                 * registration.
                 */
                smp_wmb();
                ret = lttng_ftrace_register(event_name,
                                event_param->u.ftrace.symbol_name,
                                event);
                if (ret) {
                        goto register_error;
                }
                ret = try_module_get(event->desc->owner);
                WARN_ON_ONCE(!ret);
                break;
        case LTTNG_KERNEL_NOOP:
        case LTTNG_KERNEL_SYSCALL:
                /*
                 * Needs to be explicitly enabled after creation, since
                 * we may want to apply filters.
                 */
                event->enabled = 0;
                event->registered = 0;
                event->desc = event_desc;
                if (!event->desc) {
                        ret = -EINVAL;
                        goto register_error;
                }
                break;
        default:
                WARN_ON_ONCE(1);
                ret = -EINVAL;
                goto register_error;
        }
        ret = _lttng_event_metadata_statedump(chan->session, chan, event);
        WARN_ON_ONCE(ret > 0);
        if (ret) {
                goto statedump_error;
        }
        hlist_add_head(&event->hlist, head);
        list_add(&event->list, &chan->session->events);
        return event;

statedump_error:
        /* If a statedump error occurs, events will not be readable. */
register_error:
        kmem_cache_free(event_cache, event);
cache_error:
exist:
type_error:
full:
        return ERR_PTR(ret);
}

struct lttng_event *lttng_event_create(struct lttng_channel *chan,
                                struct lttng_kernel_event *event_param,
                                void *filter,
                                const struct lttng_event_desc *event_desc,
                                enum lttng_kernel_instrumentation itype)
{
        struct lttng_event *event;

        mutex_lock(&sessions_mutex);
        event = _lttng_event_create(chan, event_param, filter, event_desc,
                                itype);
        mutex_unlock(&sessions_mutex);
        return event;
}

/* Only used for tracepoints for now. */
static
void register_event(struct lttng_event *event)
{
        const struct lttng_event_desc *desc;
        int ret = -EINVAL;

        if (event->registered)
                return;

        desc = event->desc;
        switch (event->instrumentation) {
        case LTTNG_KERNEL_TRACEPOINT:
                ret = lttng_wrapper_tracepoint_probe_register(desc->kname,
                                                  desc->probe_callback,
                                                  event);
                break;
        case LTTNG_KERNEL_SYSCALL:
                ret = lttng_syscall_filter_enable(event->chan,
                        desc->name);
                break;
        case LTTNG_KERNEL_KPROBE:
        case LTTNG_KERNEL_KRETPROBE:
        case LTTNG_KERNEL_FUNCTION:
        case LTTNG_KERNEL_NOOP:
                ret = 0;
                break;
        default:
                WARN_ON_ONCE(1);
        }
        if (!ret)
                event->registered = 1;
}

/*
 * Only used internally at session destruction.
 */
int _lttng_event_unregister(struct lttng_event *event)
{
        const struct lttng_event_desc *desc;
        int ret = -EINVAL;

        if (!event->registered)
                return 0;

        desc = event->desc;
        switch (event->instrumentation) {
        case LTTNG_KERNEL_TRACEPOINT:
                ret = lttng_wrapper_tracepoint_probe_unregister(event->desc->kname,
                                                  event->desc->probe_callback,
                                                  event);
                break;
        case LTTNG_KERNEL_KPROBE:
                lttng_kprobes_unregister(event);
                ret = 0;
                break;
        case LTTNG_KERNEL_KRETPROBE:
                lttng_kretprobes_unregister(event);
                ret = 0;
                break;
        case LTTNG_KERNEL_FUNCTION:
                lttng_ftrace_unregister(event);
                ret = 0;
                break;
        case LTTNG_KERNEL_SYSCALL:
                ret = lttng_syscall_filter_disable(event->chan,
                        desc->name);
                break;
        case LTTNG_KERNEL_NOOP:
                ret = 0;
                break;
        default:
                WARN_ON_ONCE(1);
        }
        if (!ret)
                event->registered = 0;
        return ret;
}

/*
 * Only used internally at session destruction.
 */
static
void _lttng_event_destroy(struct lttng_event *event)
{
        switch (event->instrumentation) {
        case LTTNG_KERNEL_TRACEPOINT:
                lttng_event_put(event->desc);
                break;
        case LTTNG_KERNEL_KPROBE:
                module_put(event->desc->owner);
                lttng_kprobes_destroy_private(event);
                break;
        case LTTNG_KERNEL_KRETPROBE:
                module_put(event->desc->owner);
                lttng_kretprobes_destroy_private(event);
                break;
        case LTTNG_KERNEL_FUNCTION:
                module_put(event->desc->owner);
                lttng_ftrace_destroy_private(event);
                break;
        case LTTNG_KERNEL_NOOP:
        case LTTNG_KERNEL_SYSCALL:
                break;
        default:
                WARN_ON_ONCE(1);
        }
        list_del(&event->list);
        lttng_destroy_context(event->ctx);
        kmem_cache_free(event_cache, event);
}

int lttng_session_track_pid(struct lttng_session *session, int pid)
{
        int ret;

        if (pid < -1)
                return -EINVAL;
        mutex_lock(&sessions_mutex);
        if (pid == -1) {
                /* track all pids: destroy tracker. */
                if (session->pid_tracker) {
                        struct lttng_pid_tracker *lpf;

                        lpf = session->pid_tracker;
                        rcu_assign_pointer(session->pid_tracker, NULL);
                        synchronize_trace();
                        lttng_pid_tracker_destroy(lpf);
                }
                ret = 0;
        } else {
                if (!session->pid_tracker) {
                        struct lttng_pid_tracker *lpf;

                        lpf = lttng_pid_tracker_create();
                        if (!lpf) {
                                ret = -ENOMEM;
                                goto unlock;
                        }
                        ret = lttng_pid_tracker_add(lpf, pid);
                        rcu_assign_pointer(session->pid_tracker, lpf);
                } else {
                        ret = lttng_pid_tracker_add(session->pid_tracker, pid);
                }
        }
unlock:
        mutex_unlock(&sessions_mutex);
        return ret;
}

int lttng_session_untrack_pid(struct lttng_session *session, int pid)
{
        int ret;

        if (pid < -1)
                return -EINVAL;
        mutex_lock(&sessions_mutex);
        if (pid == -1) {
                /* untrack all pids: replace by empty tracker. */
                struct lttng_pid_tracker *old_lpf = session->pid_tracker;
                struct lttng_pid_tracker *lpf;

                lpf = lttng_pid_tracker_create();
                if (!lpf) {
                        ret = -ENOMEM;
                        goto unlock;
                }
                rcu_assign_pointer(session->pid_tracker, lpf);
                synchronize_trace();
                if (old_lpf)
                        lttng_pid_tracker_destroy(old_lpf);
                ret = 0;
        } else {
                if (!session->pid_tracker) {
                        ret = -ENOENT;
                        goto unlock;
                }
                ret = lttng_pid_tracker_del(session->pid_tracker, pid);
        }
unlock:
        mutex_unlock(&sessions_mutex);
        return ret;
}

static
void *pid_list_start(struct seq_file *m, loff_t *pos)
{
        struct lttng_session *session = m->private;
        struct lttng_pid_tracker *lpf;
        struct lttng_pid_hash_node *e;
        int iter = 0, i;

        mutex_lock(&sessions_mutex);
        lpf = session->pid_tracker;
        if (lpf) {
                for (i = 0; i < LTTNG_PID_TABLE_SIZE; i++) {
                        struct hlist_head *head = &lpf->pid_hash[i];

                        lttng_hlist_for_each_entry(e, head, hlist) {
                                if (iter++ >= *pos)
                                        return e;
                        }
                }
        } else {
                /* PID tracker disabled. */
                if (iter >= *pos && iter == 0) {
                        return session; /* empty tracker */
                }
                iter++;
        }
        /* End of list */
        return NULL;
}

/* Called with sessions_mutex held. */
static
void *pid_list_next(struct seq_file *m, void *p, loff_t *ppos)
{
        struct lttng_session *session = m->private;
        struct lttng_pid_tracker *lpf;
        struct lttng_pid_hash_node *e;
        int iter = 0, i;

        (*ppos)++;
        lpf = session->pid_tracker;
        if (lpf) {
                for (i = 0; i < LTTNG_PID_TABLE_SIZE; i++) {
                        struct hlist_head *head = &lpf->pid_hash[i];

                        lttng_hlist_for_each_entry(e, head, hlist) {
                                if (iter++ >= *ppos)
                                        return e;
                        }
                }
        } else {
                /* PID tracker disabled. */
                if (iter >= *ppos && iter == 0)
                        return session; /* empty tracker */
                iter++;
        }

        /* End of list */
        return NULL;
}

static
void pid_list_stop(struct seq_file *m, void *p)
{
        mutex_unlock(&sessions_mutex);
}

static
int pid_list_show(struct seq_file *m, void *p)
{
        int pid;

        if (p == m->private) {
                /* Tracker disabled. */
                pid = -1;
        } else {
                const struct lttng_pid_hash_node *e = p;

                pid = lttng_pid_tracker_get_node_pid(e);
        }
        seq_printf(m,   "process { pid = %d; };\n", pid);
        return 0;
}

static
const struct seq_operations lttng_tracker_pids_list_seq_ops = {
        .start = pid_list_start,
        .next = pid_list_next,
        .stop = pid_list_stop,
        .show = pid_list_show,
};

static
int lttng_tracker_pids_list_open(struct inode *inode, struct file *file)
{
        return seq_open(file, &lttng_tracker_pids_list_seq_ops);
}

static
int lttng_tracker_pids_list_release(struct inode *inode, struct file *file)
{
        struct seq_file *m = file->private_data;
        struct lttng_session *session = m->private;
        int ret;

        WARN_ON_ONCE(!session);
        ret = seq_release(inode, file);
        if (!ret && session)
                fput(session->file);
        return ret;
}

const struct file_operations lttng_tracker_pids_list_fops = {
        .owner = THIS_MODULE,
        .open = lttng_tracker_pids_list_open,
        .read = seq_read,
        .llseek = seq_lseek,
        .release = lttng_tracker_pids_list_release,
};

int lttng_session_list_tracker_pids(struct lttng_session *session)
{
        struct file *tracker_pids_list_file;
        struct seq_file *m;
        int file_fd, ret;

        file_fd = lttng_get_unused_fd();
        if (file_fd < 0) {
                ret = file_fd;
                goto fd_error;
        }

        tracker_pids_list_file = anon_inode_getfile("[lttng_tracker_pids_list]",
                                          &lttng_tracker_pids_list_fops,
                                          NULL, O_RDWR);
        if (IS_ERR(tracker_pids_list_file)) {
                ret = PTR_ERR(tracker_pids_list_file);
                goto file_error;
        }
        if (atomic_long_add_unless(&session->file->f_count,
                1, INT_MAX) == INT_MAX) {
                goto refcount_error;
        }
        ret = lttng_tracker_pids_list_fops.open(NULL, tracker_pids_list_file);
        if (ret < 0)
                goto open_error;
        m = tracker_pids_list_file->private_data;
        m->private = session;
        fd_install(file_fd, tracker_pids_list_file);

        return file_fd;

open_error:
        atomic_long_dec(&session->file->f_count);
refcount_error:
        fput(tracker_pids_list_file);
file_error:
        put_unused_fd(file_fd);
fd_error:
        return ret;
}

/*
 * Enabler management.
 */
static
int lttng_match_enabler_wildcard(const char *desc_name,
                const char *name)
{
        /* Compare excluding final '*' */
        if (strncmp(desc_name, name, strlen(name) - 1))
                return 0;
        return 1;
}

static
int lttng_match_enabler_name(const char *desc_name,
                const char *name)
{
        if (strcmp(desc_name, name))
                return 0;
        return 1;
}

static
int lttng_desc_match_enabler(const struct lttng_event_desc *desc,
                struct lttng_enabler *enabler)
{
        const char *desc_name, *enabler_name;

        enabler_name = enabler->event_param.name;
        switch (enabler->event_param.instrumentation) {
        case LTTNG_KERNEL_TRACEPOINT:
                desc_name = desc->name;
                break;
        case LTTNG_KERNEL_SYSCALL:
                desc_name = desc->name;
                if (!strncmp(desc_name, "compat_", strlen("compat_")))
                        desc_name += strlen("compat_");
                if (!strncmp(desc_name, "syscall_exit_",
                                strlen("syscall_exit_"))) {
                        desc_name += strlen("syscall_exit_");
                } else if (!strncmp(desc_name, "syscall_entry_",
                                strlen("syscall_entry_"))) {
                        desc_name += strlen("syscall_entry_");
                } else {
                        WARN_ON_ONCE(1);
                        return -EINVAL;
                }
                break;
        default:
                WARN_ON_ONCE(1);
                return -EINVAL;
        }
        switch (enabler->type) {
        case LTTNG_ENABLER_WILDCARD:
                return lttng_match_enabler_wildcard(desc_name, enabler_name);
        case LTTNG_ENABLER_NAME:
                return lttng_match_enabler_name(desc_name, enabler_name);
        default:
                return -EINVAL;
        }
}

static
int lttng_event_match_enabler(struct lttng_event *event,
                struct lttng_enabler *enabler)
{
        if (enabler->event_param.instrumentation != event->instrumentation)
                return 0;
        if (lttng_desc_match_enabler(event->desc, enabler)
                        && event->chan == enabler->chan)
                return 1;
        else
                return 0;
}

static
struct lttng_enabler_ref *lttng_event_enabler_ref(struct lttng_event *event,
                struct lttng_enabler *enabler)
{
        struct lttng_enabler_ref *enabler_ref;

        list_for_each_entry(enabler_ref,
                        &event->enablers_ref_head, node) {
                if (enabler_ref->ref == enabler)
                        return enabler_ref;
        }
        return NULL;
}

static
void lttng_create_tracepoint_if_missing(struct lttng_enabler *enabler)
{
        struct lttng_session *session = enabler->chan->session;
        struct lttng_probe_desc *probe_desc;
        const struct lttng_event_desc *desc;
        int i;
        struct list_head *probe_list;

        probe_list = lttng_get_probe_list_head();
        /*
         * For each probe event, if we find that a probe event matches
         * our enabler, create an associated lttng_event if not
         * already present.
         */
        list_for_each_entry(probe_desc, probe_list, head) {
                for (i = 0; i < probe_desc->nr_events; i++) {
                        int found = 0;
                        struct hlist_head *head;
                        const char *event_name;
                        size_t name_len;
                        uint32_t hash;
                        struct lttng_event *event;

                        desc = probe_desc->event_desc[i];
                        if (!lttng_desc_match_enabler(desc, enabler))
                                continue;
                        event_name = desc->name;
                        name_len = strlen(event_name);

                        /*
                         * Check if already created.
                         */
                        hash = jhash(event_name, name_len, 0);
                        head = &session->events_ht.table[hash & (LTTNG_EVENT_HT_SIZE - 1)];
                        lttng_hlist_for_each_entry(event, head, hlist) {
                                if (event->desc == desc
                                                && event->chan == enabler->chan)
                                        found = 1;
                        }
                        if (found)
                                continue;

                        /*
                         * We need to create an event for this
                         * event probe.
                         */
                        event = _lttng_event_create(enabler->chan,
                                        NULL, NULL, desc,
                                        LTTNG_KERNEL_TRACEPOINT);
                        if (!event) {
                                printk(KERN_INFO "Unable to create event %s\n",
                                        probe_desc->event_desc[i]->name);
                        }
                }
        }
}

static
void lttng_create_syscall_if_missing(struct lttng_enabler *enabler)
{
        int ret;

        ret = lttng_syscalls_register(enabler->chan, NULL);
        WARN_ON_ONCE(ret);
}

/*
 * Create struct lttng_event if it is missing and present in the list of
 * tracepoint probes.
 * Should be called with sessions mutex held.
 */
static
void lttng_create_event_if_missing(struct lttng_enabler *enabler)
{
        switch (enabler->event_param.instrumentation) {
        case LTTNG_KERNEL_TRACEPOINT:
                lttng_create_tracepoint_if_missing(enabler);
                break;
        case LTTNG_KERNEL_SYSCALL:
                lttng_create_syscall_if_missing(enabler);
                break;
        default:
                WARN_ON_ONCE(1);
                break;
        }
}

/*
 * Create events associated with an enabler (if not already present),
 * and add backward reference from the event to the enabler.
 * Should be called with sessions mutex held.
 */
static
int lttng_enabler_ref_events(struct lttng_enabler *enabler)
{
        struct lttng_session *session = enabler->chan->session;
        struct lttng_event *event;

        /* First ensure that probe events are created for this enabler. */
        lttng_create_event_if_missing(enabler);

        /* For each event matching enabler in session event list. */
        list_for_each_entry(event, &session->events, list) {
                struct lttng_enabler_ref *enabler_ref;

                if (!lttng_event_match_enabler(event, enabler))
                        continue;
                enabler_ref = lttng_event_enabler_ref(event, enabler);
                if (!enabler_ref) {
                        /*
                         * If no backward ref, create it.
                         * Add backward ref from event to enabler.
                         */
                        enabler_ref = kzalloc(sizeof(*enabler_ref), GFP_KERNEL);
                        if (!enabler_ref)
                                return -ENOMEM;
                        enabler_ref->ref = enabler;
                        list_add(&enabler_ref->node,
                                &event->enablers_ref_head);
                }

                /*
                 * Link filter bytecodes if not linked yet.
                 */
                lttng_enabler_event_link_bytecode(event, enabler);

                /* TODO: merge event context. */
        }
        return 0;
}

/*
 * Called at module load: connect the probe on all enablers matching
 * this event.
 * Called with sessions lock held.
 */
int lttng_fix_pending_events(void)
{
        struct lttng_session *session;

        list_for_each_entry(session, &sessions, list)
                lttng_session_lazy_sync_enablers(session);
        return 0;
}

struct lttng_enabler *lttng_enabler_create(enum lttng_enabler_type type,
                struct lttng_kernel_event *event_param,
                struct lttng_channel *chan)
{
        struct lttng_enabler *enabler;

        enabler = kzalloc(sizeof(*enabler), GFP_KERNEL);
        if (!enabler)
                return NULL;
        enabler->type = type;
        INIT_LIST_HEAD(&enabler->filter_bytecode_head);
        memcpy(&enabler->event_param, event_param,
                sizeof(enabler->event_param));
        enabler->chan = chan;
        /* ctx left NULL */
        enabler->enabled = 0;
        enabler->evtype = LTTNG_TYPE_ENABLER;
        mutex_lock(&sessions_mutex);
        list_add(&enabler->node, &enabler->chan->session->enablers_head);
        lttng_session_lazy_sync_enablers(enabler->chan->session);
        mutex_unlock(&sessions_mutex);
        return enabler;
}

int lttng_enabler_enable(struct lttng_enabler *enabler)
{
        mutex_lock(&sessions_mutex);
        enabler->enabled = 1;
        lttng_session_lazy_sync_enablers(enabler->chan->session);
        mutex_unlock(&sessions_mutex);
        return 0;
}

int lttng_enabler_disable(struct lttng_enabler *enabler)
{
        mutex_lock(&sessions_mutex);
        enabler->enabled = 0;
        lttng_session_lazy_sync_enablers(enabler->chan->session);
        mutex_unlock(&sessions_mutex);
        return 0;
}

int lttng_enabler_attach_bytecode(struct lttng_enabler *enabler,
                struct lttng_kernel_filter_bytecode __user *bytecode)
{
        struct lttng_filter_bytecode_node *bytecode_node;
        uint32_t bytecode_len;
        int ret;

        ret = get_user(bytecode_len, &bytecode->len);
        if (ret)
                return ret;
        bytecode_node = kzalloc(sizeof(*bytecode_node) + bytecode_len,
                        GFP_KERNEL);
        if (!bytecode_node)
                return -ENOMEM;
        ret = copy_from_user(&bytecode_node->bc, bytecode,
                sizeof(*bytecode) + bytecode_len);
        if (ret)
                goto error_free;
        bytecode_node->enabler = enabler;
        /* Enforce length based on allocated size */
        bytecode_node->bc.len = bytecode_len;
        list_add_tail(&bytecode_node->node, &enabler->filter_bytecode_head);
        lttng_session_lazy_sync_enablers(enabler->chan->session);
        return 0;

error_free:
        kfree(bytecode_node);
        return ret;
}

int lttng_enabler_attach_context(struct lttng_enabler *enabler,
                struct lttng_kernel_context *context_param)
{
        return -ENOSYS;
}

static
void lttng_enabler_destroy(struct lttng_enabler *enabler)
{
        struct lttng_filter_bytecode_node *filter_node, *tmp_filter_node;

        /* Destroy filter bytecode */
        list_for_each_entry_safe(filter_node, tmp_filter_node,
                        &enabler->filter_bytecode_head, node) {
                kfree(filter_node);
        }

        /* Destroy contexts */
        lttng_destroy_context(enabler->ctx);

        list_del(&enabler->node);
        kfree(enabler);
}

/*
 * lttng_session_sync_enablers should be called just before starting a
 * session.
 * Should be called with sessions mutex held.
 */
static
void lttng_session_sync_enablers(struct lttng_session *session)
{
        struct lttng_enabler *enabler;
        struct lttng_event *event;

        list_for_each_entry(enabler, &session->enablers_head, node)
                lttng_enabler_ref_events(enabler);
        /*
         * For each event, if at least one of its enablers is enabled,
         * and its channel and session transient states are enabled, we
         * enable the event, else we disable it.
         */
        list_for_each_entry(event, &session->events, list) {
                struct lttng_enabler_ref *enabler_ref;
                struct lttng_bytecode_runtime *runtime;
                int enabled = 0, has_enablers_without_bytecode = 0;

                switch (event->instrumentation) {
                case LTTNG_KERNEL_TRACEPOINT:
                case LTTNG_KERNEL_SYSCALL:
                        /* Enable events */
                        list_for_each_entry(enabler_ref,
                                        &event->enablers_ref_head, node) {
                                if (enabler_ref->ref->enabled) {
                                        enabled = 1;
                                        break;
                                }
                        }
                        break;
                default:
                        /* Not handled with lazy sync. */
                        continue;
                }
                /*
                 * Enabled state is based on union of enablers, with
                 * intesection of session and channel transient enable
                 * states.
                 */
                enabled = enabled && session->tstate && event->chan->tstate;

                ACCESS_ONCE(event->enabled) = enabled;
                /*
                 * Sync tracepoint registration with event enabled
                 * state.
                 */
                if (enabled) {
                        register_event(event);
                } else {
                        _lttng_event_unregister(event);
                }

                /* Check if has enablers without bytecode enabled */
                list_for_each_entry(enabler_ref,
                                &event->enablers_ref_head, node) {
                        if (enabler_ref->ref->enabled
                                        && list_empty(&enabler_ref->ref->filter_bytecode_head)) {
                                has_enablers_without_bytecode = 1;
                                break;
                        }
                }
                event->has_enablers_without_bytecode =
                        has_enablers_without_bytecode;

                /* Enable filters */
                list_for_each_entry(runtime,
                                &event->bytecode_runtime_head, node)
                        lttng_filter_sync_state(runtime);
        }
}

/*
 * Apply enablers to session events, adding events to session if need
 * be. It is required after each modification applied to an active
 * session, and right before session "start".
 * "lazy" sync means we only sync if required.
 * Should be called with sessions mutex held.
 */
static
void lttng_session_lazy_sync_enablers(struct lttng_session *session)
{
        /* We can skip if session is not active */
        if (!session->active)
                return;
        lttng_session_sync_enablers(session);
}

/*
 * Serialize at most one packet worth of metadata into a metadata
 * channel.
 * We grab the metadata cache mutex to get exclusive access to our metadata
 * buffer and to the metadata cache. Exclusive access to the metadata buffer
 * allows us to do racy operations such as looking for remaining space left in
 * packet and write, since mutual exclusion protects us from concurrent writes.
 * Mutual exclusion on the metadata cache allow us to read the cache content
 * without racing against reallocation of the cache by updates.
 * Returns the number of bytes written in the channel, 0 if no data
 * was written and a negative value on error.
 */
int lttng_metadata_output_channel(struct lttng_metadata_stream *stream,
                struct channel *chan)
{
        struct lib_ring_buffer_ctx ctx;
        int ret = 0;
        size_t len, reserve_len;

        /*
         * Ensure we support mutiple get_next / put sequences followed by
         * put_next. The metadata cache lock protects reading the metadata
         * cache. It can indeed be read concurrently by "get_next_subbuf" and
         * "flush" operations on the buffer invoked by different processes.
         * Moreover, since the metadata cache memory can be reallocated, we
         * need to have exclusive access against updates even though we only
         * read it.
         */
        mutex_lock(&stream->metadata_cache->lock);
        WARN_ON(stream->metadata_in < stream->metadata_out);
        if (stream->metadata_in != stream->metadata_out)
                goto end;

        /* Metadata regenerated, change the version. */
        if (stream->metadata_cache->version != stream->version)
                stream->version = stream->metadata_cache->version;

        len = stream->metadata_cache->metadata_written -
                stream->metadata_in;
        if (!len)
                goto end;
        reserve_len = min_t(size_t,
                        stream->transport->ops.packet_avail_size(chan),
                        len);
        lib_ring_buffer_ctx_init(&ctx, chan, NULL, reserve_len,
                        sizeof(char), -1);
        /*
         * If reservation failed, return an error to the caller.
         */
        ret = stream->transport->ops.event_reserve(&ctx, 0);
        if (ret != 0) {
                printk(KERN_WARNING "LTTng: Metadata event reservation failed\n");
                goto end;
        }
        stream->transport->ops.event_write(&ctx,
                        stream->metadata_cache->data + stream->metadata_in,
                        reserve_len);
        stream->transport->ops.event_commit(&ctx);
        stream->metadata_in += reserve_len;
        ret = reserve_len;

end:
        mutex_unlock(&stream->metadata_cache->lock);
        return ret;
}

/*
 * Write the metadata to the metadata cache.
 * Must be called with sessions_mutex held.
 * The metadata cache lock protects us from concurrent read access from
 * thread outputting metadata content to ring buffer.
 */
int lttng_metadata_printf(struct lttng_session *session,
                          const char *fmt, ...)
{
        char *str;
        size_t len;
        va_list ap;
        struct lttng_metadata_stream *stream;

        WARN_ON_ONCE(!ACCESS_ONCE(session->active));

        va_start(ap, fmt);
        str = kvasprintf(GFP_KERNEL, fmt, ap);
        va_end(ap);
        if (!str)
                return -ENOMEM;

        len = strlen(str);
        mutex_lock(&session->metadata_cache->lock);
        if (session->metadata_cache->metadata_written + len >
                        session->metadata_cache->cache_alloc) {
                char *tmp_cache_realloc;
                unsigned int tmp_cache_alloc_size;

                tmp_cache_alloc_size = max_t(unsigned int,
                                session->metadata_cache->cache_alloc + len,
                                session->metadata_cache->cache_alloc << 1);
                tmp_cache_realloc = lttng_vzalloc(tmp_cache_alloc_size);
                if (!tmp_cache_realloc)
                        goto err;
                if (session->metadata_cache->data) {
                        memcpy(tmp_cache_realloc,
                                session->metadata_cache->data,
                                session->metadata_cache->cache_alloc);
                        vfree(session->metadata_cache->data);
                }

                session->metadata_cache->cache_alloc = tmp_cache_alloc_size;
                session->metadata_cache->data = tmp_cache_realloc;
        }
        memcpy(session->metadata_cache->data +
                        session->metadata_cache->metadata_written,
                        str, len);
        session->metadata_cache->metadata_written += len;
        mutex_unlock(&session->metadata_cache->lock);
        kfree(str);

        list_for_each_entry(stream, &session->metadata_cache->metadata_stream, list)
                wake_up_interruptible(&stream->read_wait);

        return 0;

err:
        mutex_unlock(&session->metadata_cache->lock);
        kfree(str);
        return -ENOMEM;
}

/*
 * Must be called with sessions_mutex held.
 */
static
int _lttng_field_statedump(struct lttng_session *session,
                         const struct lttng_event_field *field)
{
        int ret = 0;

        switch (field->type.atype) {
        case atype_integer:
                ret = lttng_metadata_printf(session,
                        "               integer { size = %u; align = %u; signed = %u; encoding = %s; base = %u;%s } _%s;\n",
                        field->type.u.basic.integer.size,
                        field->type.u.basic.integer.alignment,
                        field->type.u.basic.integer.signedness,
                        (field->type.u.basic.integer.encoding == lttng_encode_none)
                                ? "none"
                                : (field->type.u.basic.integer.encoding == lttng_encode_UTF8)
                                        ? "UTF8"
                                        : "ASCII",
                        field->type.u.basic.integer.base,
#if __BYTE_ORDER == __BIG_ENDIAN
                        field->type.u.basic.integer.reverse_byte_order ? " byte_order = le;" : "",
#else
                        field->type.u.basic.integer.reverse_byte_order ? " byte_order = be;" : "",
#endif
                        field->name);
                break;
        case atype_enum:
                ret = lttng_metadata_printf(session,
                        "               %s _%s;\n",
                        field->type.u.basic.enumeration.name,
                        field->name);
                break;
        case atype_array:
        {
                const struct lttng_basic_type *elem_type;

                elem_type = &field->type.u.array.elem_type;
                if (field->type.u.array.elem_alignment) {
                        ret = lttng_metadata_printf(session,
                        "               struct { } align(%u) _%s_padding;\n",
                                        field->type.u.array.elem_alignment * CHAR_BIT,
                                        field->name);
                        if (ret)
                                return ret;
                }
                ret = lttng_metadata_printf(session,
                        "               integer { size = %u; align = %u; signed = %u; encoding = %s; base = %u;%s } _%s[%u];\n",
                        elem_type->u.basic.integer.size,
                        elem_type->u.basic.integer.alignment,
                        elem_type->u.basic.integer.signedness,
                        (elem_type->u.basic.integer.encoding == lttng_encode_none)
                                ? "none"
                                : (elem_type->u.basic.integer.encoding == lttng_encode_UTF8)
                                        ? "UTF8"
                                        : "ASCII",
                        elem_type->u.basic.integer.base,
#if __BYTE_ORDER == __BIG_ENDIAN
                        elem_type->u.basic.integer.reverse_byte_order ? " byte_order = le;" : "",
#else
                        elem_type->u.basic.integer.reverse_byte_order ? " byte_order = be;" : "",
#endif
                        field->name, field->type.u.array.length);
                break;
        }
        case atype_sequence:
        {
                const struct lttng_basic_type *elem_type;
                const struct lttng_basic_type *length_type;

                elem_type = &field->type.u.sequence.elem_type;
                length_type = &field->type.u.sequence.length_type;
                ret = lttng_metadata_printf(session,
                        "               integer { size = %u; align = %u; signed = %u; encoding = %s; base = %u;%s } __%s_length;\n",
                        length_type->u.basic.integer.size,
                        (unsigned int) length_type->u.basic.integer.alignment,
                        length_type->u.basic.integer.signedness,
                        (length_type->u.basic.integer.encoding == lttng_encode_none)
                                ? "none"
                                : ((length_type->u.basic.integer.encoding == lttng_encode_UTF8)
                                        ? "UTF8"
                                        : "ASCII"),
                        length_type->u.basic.integer.base,
#if __BYTE_ORDER == __BIG_ENDIAN
                        length_type->u.basic.integer.reverse_byte_order ? " byte_order = le;" : "",
#else
                        length_type->u.basic.integer.reverse_byte_order ? " byte_order = be;" : "",
#endif
                        field->name);
                if (ret)
                        return ret;

                if (field->type.u.sequence.elem_alignment) {
                        ret = lttng_metadata_printf(session,
                        "               struct { } align(%u) _%s_padding;\n",
                                        field->type.u.sequence.elem_alignment * CHAR_BIT,
                                        field->name);
                        if (ret)
                                return ret;
                }
                ret = lttng_metadata_printf(session,
                        "               integer { size = %u; align = %u; signed = %u; encoding = %s; base = %u;%s } _%s[ __%s_length ];\n",
                        elem_type->u.basic.integer.size,
                        (unsigned int) elem_type->u.basic.integer.alignment,
                        elem_type->u.basic.integer.signedness,
                        (elem_type->u.basic.integer.encoding == lttng_encode_none)
                                ? "none"
                                : ((elem_type->u.basic.integer.encoding == lttng_encode_UTF8)
                                        ? "UTF8"
                                        : "ASCII"),
                        elem_type->u.basic.integer.base,
#if __BYTE_ORDER == __BIG_ENDIAN
                        elem_type->u.basic.integer.reverse_byte_order ? " byte_order = le;" : "",
#else
                        elem_type->u.basic.integer.reverse_byte_order ? " byte_order = be;" : "",
#endif
                        field->name,
                        field->name);
                break;
        }

        case atype_string:
                /* Default encoding is UTF8 */
                ret = lttng_metadata_printf(session,
                        "               string%s _%s;\n",
                        field->type.u.basic.string.encoding == lttng_encode_ASCII ?
                                " { encoding = ASCII; }" : "",
                        field->name);
                break;
        default:
                WARN_ON_ONCE(1);
                return -EINVAL;
        }
        return ret;
}

static
int _lttng_context_metadata_statedump(struct lttng_session *session,
                                    struct lttng_ctx *ctx)
{
        int ret = 0;
        int i;

        if (!ctx)
                return 0;
        for (i = 0; i < ctx->nr_fields; i++) {
                const struct lttng_ctx_field *field = &ctx->fields[i];

                ret = _lttng_field_statedump(session, &field->event_field);
                if (ret)
                        return ret;
        }
        return ret;
}

static
int _lttng_fields_metadata_statedump(struct lttng_session *session,
                                   struct lttng_event *event)
{
        const struct lttng_event_desc *desc = event->desc;
        int ret = 0;
        int i;

        for (i = 0; i < desc->nr_fields; i++) {
                const struct lttng_event_field *field = &desc->fields[i];

                ret = _lttng_field_statedump(session, field);
                if (ret)
                        return ret;
        }
        return ret;
}

/*
 * Must be called with sessions_mutex held.
 */
static
int _lttng_event_metadata_statedump(struct lttng_session *session,
                                  struct lttng_channel *chan,
                                  struct lttng_event *event)
{
        int ret = 0;

        if (event->metadata_dumped || !ACCESS_ONCE(session->active))
                return 0;
        if (chan->channel_type == METADATA_CHANNEL)
                return 0;

        ret = lttng_metadata_printf(session,
                "event {\n"
                "       name = \"%s\";\n"
                "       id = %u;\n"
                "       stream_id = %u;\n",
                event->desc->name,
                event->id,
                event->chan->id);
        if (ret)
                goto end;

        if (event->ctx) {
                ret = lttng_metadata_printf(session,
                        "       context := struct {\n");
                if (ret)
                        goto end;
        }
        ret = _lttng_context_metadata_statedump(session, event->ctx);
        if (ret)
                goto end;
        if (event->ctx) {
                ret = lttng_metadata_printf(session,
                        "       };\n");
                if (ret)
                        goto end;
        }

        ret = lttng_metadata_printf(session,
                "       fields := struct {\n"
                );
        if (ret)
                goto end;

        ret = _lttng_fields_metadata_statedump(session, event);
        if (ret)
                goto end;

        /*
         * LTTng space reservation can only reserve multiples of the
         * byte size.
         */
        ret = lttng_metadata_printf(session,
                "       };\n"
                "};\n\n");
        if (ret)
                goto end;

        event->metadata_dumped = 1;
end:
        return ret;

}

/*
 * Must be called with sessions_mutex held.
 */
static
int _lttng_channel_metadata_statedump(struct lttng_session *session,
                                    struct lttng_channel *chan)
{
        int ret = 0;

        if (chan->metadata_dumped || !ACCESS_ONCE(session->active))
                return 0;

        if (chan->channel_type == METADATA_CHANNEL)
                return 0;

        WARN_ON_ONCE(!chan->header_type);
        ret = lttng_metadata_printf(session,
                "stream {\n"
                "       id = %u;\n"
                "       event.header := %s;\n"
                "       packet.context := struct packet_context;\n",
                chan->id,
                chan->header_type == 1 ? "struct event_header_compact" :
                        "struct event_header_large");
        if (ret)
                goto end;

        if (chan->ctx) {
                ret = lttng_metadata_printf(session,
                        "       event.context := struct {\n");
                if (ret)
                        goto end;
        }
        ret = _lttng_context_metadata_statedump(session, chan->ctx);
        if (ret)
                goto end;
        if (chan->ctx) {
                ret = lttng_metadata_printf(session,
                        "       };\n");
                if (ret)
                        goto end;
        }

        ret = lttng_metadata_printf(session,
                "};\n\n");

        chan->metadata_dumped = 1;
end:
        return ret;
}

/*
 * Must be called with sessions_mutex held.
 */
static
int _lttng_stream_packet_context_declare(struct lttng_session *session)
{
        return lttng_metadata_printf(session,
                "struct packet_context {\n"
                "       uint64_clock_monotonic_t timestamp_begin;\n"
                "       uint64_clock_monotonic_t timestamp_end;\n"
                "       uint64_t content_size;\n"
                "       uint64_t packet_size;\n"
                "       uint64_t packet_seq_num;\n"
                "       unsigned long events_discarded;\n"
                "       uint32_t cpu_id;\n"
                "};\n\n"
                );
}

/*
 * Compact header:
 * id: range: 0 - 30.
 * id 31 is reserved to indicate an extended header.
 *
 * Large header:
 * id: range: 0 - 65534.
 * id 65535 is reserved to indicate an extended header.
 *
 * Must be called with sessions_mutex held.
 */
static
int _lttng_event_header_declare(struct lttng_session *session)
{
        return lttng_metadata_printf(session,
        "struct event_header_compact {\n"
        "       enum : uint5_t { compact = 0 ... 30, extended = 31 } id;\n"
        "       variant <id> {\n"
        "               struct {\n"
        "                       uint27_clock_monotonic_t timestamp;\n"
        "               } compact;\n"
        "               struct {\n"
        "                       uint32_t id;\n"
        "                       uint64_clock_monotonic_t timestamp;\n"
        "               } extended;\n"
        "       } v;\n"
        "} align(%u);\n"
        "\n"
        "struct event_header_large {\n"
        "       enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;\n"
        "       variant <id> {\n"
        "               struct {\n"
        "                       uint32_clock_monotonic_t timestamp;\n"
        "               } compact;\n"
        "               struct {\n"
        "                       uint32_t id;\n"
        "                       uint64_clock_monotonic_t timestamp;\n"
        "               } extended;\n"
        "       } v;\n"
        "} align(%u);\n\n",
        lttng_alignof(uint32_t) * CHAR_BIT,
        lttng_alignof(uint16_t) * CHAR_BIT
        );
}

 /*
 * Approximation of NTP time of day to clock monotonic correlation,
 * taken at start of trace.
 * Yes, this is only an approximation. Yes, we can (and will) do better
 * in future versions.
 * This function may return a negative offset. It may happen if the
 * system sets the REALTIME clock to 0 after boot.
 */
static
int64_t measure_clock_offset(void)
{
        uint64_t monotonic_avg, monotonic[2], realtime;
        uint64_t tcf = trace_clock_freq();
        int64_t offset;
        struct timespec rts = { 0, 0 };
        unsigned long flags;

        /* Disable interrupts to increase correlation precision. */
        local_irq_save(flags);
        monotonic[0] = trace_clock_read64();
        getnstimeofday(&rts);      
        monotonic[1] = trace_clock_read64();
        local_irq_restore(flags);

        monotonic_avg = (monotonic[0] + monotonic[1]) >> 1;
        realtime = (uint64_t) rts.tv_sec * tcf;
        if (tcf == NSEC_PER_SEC) {
                realtime += rts.tv_nsec;
        } else {
                uint64_t n = rts.tv_nsec * tcf;

                do_div(n, NSEC_PER_SEC);
                realtime += n;
        }
        offset = (int64_t) realtime - monotonic_avg;
        return offset;
}

/*
 * Output metadata into this session's metadata buffers.
 * Must be called with sessions_mutex held.
 */
static
int _lttng_session_metadata_statedump(struct lttng_session *session)
{
        unsigned char *uuid_c = session->uuid.b;
        unsigned char uuid_s[37], clock_uuid_s[BOOT_ID_LEN];
        struct lttng_channel *chan;
        struct lttng_event *event;
        int ret = 0;

        if (!ACCESS_ONCE(session->active))
                return 0;
        if (session->metadata_dumped)
                goto skip_session;

        snprintf(uuid_s, sizeof(uuid_s),
                "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x",
                uuid_c[0], uuid_c[1], uuid_c[2], uuid_c[3],
                uuid_c[4], uuid_c[5], uuid_c[6], uuid_c[7],
                uuid_c[8], uuid_c[9], uuid_c[10], uuid_c[11],
                uuid_c[12], uuid_c[13], uuid_c[14], uuid_c[15]);

        ret = lttng_metadata_printf(session,
                "typealias integer { size = 8; align = %u; signed = false; } := uint8_t;\n"
                "typealias integer { size = 16; align = %u; signed = false; } := uint16_t;\n"
                "typealias integer { size = 32; align = %u; signed = false; } := uint32_t;\n"
                "typealias integer { size = 64; align = %u; signed = false; } := uint64_t;\n"
                "typealias integer { size = %u; align = %u; signed = false; } := unsigned long;\n"
                "typealias integer { size = 5; align = 1; signed = false; } := uint5_t;\n"
                "typealias integer { size = 27; align = 1; signed = false; } := uint27_t;\n"
                "\n"
                "trace {\n"
                "       major = %u;\n"
                "       minor = %u;\n"
                "       uuid = \"%s\";\n"
                "       byte_order = %s;\n"
                "       packet.header := struct {\n"
                "               uint32_t magic;\n"
                "               uint8_t  uuid[16];\n"
                "               uint32_t stream_id;\n"
                "               uint64_t stream_instance_id;\n"
                "       };\n"
                "};\n\n",
                lttng_alignof(uint8_t) * CHAR_BIT,
                lttng_alignof(uint16_t) * CHAR_BIT,
                lttng_alignof(uint32_t) * CHAR_BIT,
                lttng_alignof(uint64_t) * CHAR_BIT,
                sizeof(unsigned long) * CHAR_BIT,
                lttng_alignof(unsigned long) * CHAR_BIT,
                CTF_SPEC_MAJOR,
                CTF_SPEC_MINOR,
                uuid_s,
#if __BYTE_ORDER == __BIG_ENDIAN
                "be"
#else
                "le"
#endif
                );
        if (ret)
                goto end;

        ret = lttng_metadata_printf(session,
                "env {\n"
                "       hostname = \"%s\";\n"
                "       domain = \"kernel\";\n"
                "       sysname = \"%s\";\n"
                "       kernel_release = \"%s\";\n"
                "       kernel_version = \"%s\";\n"
                "       tracer_name = \"lttng-modules\";\n"
                "       tracer_major = %d;\n"
                "       tracer_minor = %d;\n"
                "       tracer_patchlevel = %d;\n"
                "};\n\n",
                current->nsproxy->uts_ns->name.nodename,
                utsname()->sysname,
                utsname()->release,
                utsname()->version,
                LTTNG_MODULES_MAJOR_VERSION,
                LTTNG_MODULES_MINOR_VERSION,
                LTTNG_MODULES_PATCHLEVEL_VERSION
                );
        if (ret)
                goto end;

        ret = lttng_metadata_printf(session,
                "clock {\n"
                "       name = \"%s\";\n",
                trace_clock_name()
                );
        if (ret)
                goto end;

        if (!trace_clock_uuid(clock_uuid_s)) {
                ret = lttng_metadata_printf(session,
                        "       uuid = \"%s\";\n",
                        clock_uuid_s
                        );
                if (ret)
                        goto end;
        }

        ret = lttng_metadata_printf(session,
                "       description = \"%s\";\n"
                "       freq = %llu; /* Frequency, in Hz */\n"
                "       /* clock value offset from Epoch is: offset * (1/freq) */\n"
                "       offset = %lld;\n"
                "};\n\n",
                trace_clock_description(),
                (unsigned long long) trace_clock_freq(),
                (long long) measure_clock_offset()
                );
        if (ret)
                goto end;

        ret = lttng_metadata_printf(session,
                "typealias integer {\n"
                "       size = 27; align = 1; signed = false;\n"
                "       map = clock.%s.value;\n"
                "} := uint27_clock_monotonic_t;\n"
                "\n"
                "typealias integer {\n"
                "       size = 32; align = %u; signed = false;\n"
                "       map = clock.%s.value;\n"
                "} := uint32_clock_monotonic_t;\n"
                "\n"
                "typealias integer {\n"
                "       size = 64; align = %u; signed = false;\n"
                "       map = clock.%s.value;\n"
                "} := uint64_clock_monotonic_t;\n\n",
                trace_clock_name(),
                lttng_alignof(uint32_t) * CHAR_BIT,
                trace_clock_name(),
                lttng_alignof(uint64_t) * CHAR_BIT,
                trace_clock_name()
                );
        if (ret)
                goto end;

        ret = _lttng_stream_packet_context_declare(session);
        if (ret)
                goto end;

        ret = _lttng_event_header_declare(session);
        if (ret)
                goto end;

skip_session:
        list_for_each_entry(chan, &session->chan, list) {
                ret = _lttng_channel_metadata_statedump(session, chan);
                if (ret)
                        goto end;
        }

        list_for_each_entry(event, &session->events, list) {
                ret = _lttng_event_metadata_statedump(session, event->chan, event);
                if (ret)
                        goto end;
        }
        session->metadata_dumped = 1;
end:
        return ret;
}

/**
 * lttng_transport_register - LTT transport registration
 * @transport: transport structure
 *
 * Registers a transport which can be used as output to extract the data out of
 * LTTng. The module calling this registration function must ensure that no
 * trap-inducing code will be executed by the transport functions. E.g.
 * vmalloc_sync_all() must be called between a vmalloc and the moment the memory
 * is made visible to the transport function. This registration acts as a
 * vmalloc_sync_all. Therefore, only if the module allocates virtual memory
 * after its registration must it synchronize the TLBs.
 */
void lttng_transport_register(struct lttng_transport *transport)
{
        /*
         * Make sure no page fault can be triggered by the module about to be
         * registered. We deal with this here so we don't have to call
         * vmalloc_sync_all() in each module's init.
         */
        wrapper_vmalloc_sync_all();

        mutex_lock(&sessions_mutex);
        list_add_tail(&transport->node, &lttng_transport_list);
        mutex_unlock(&sessions_mutex);
}
EXPORT_SYMBOL_GPL(lttng_transport_register);

/**
 * lttng_transport_unregister - LTT transport unregistration
 * @transport: transport structure
 */
void lttng_transport_unregister(struct lttng_transport *transport)
{
        mutex_lock(&sessions_mutex);
        list_del(&transport->node);
        mutex_unlock(&sessions_mutex);
}
EXPORT_SYMBOL_GPL(lttng_transport_unregister);

static int __init lttng_events_init(void)
{
        int ret;

        ret = wrapper_lttng_fixup_sig(THIS_MODULE);
        if (ret)
                return ret;
        ret = wrapper_get_pfnblock_flags_mask_init();
        if (ret)
                return ret;
        ret = wrapper_get_pageblock_flags_mask_init();
        if (ret)
                return ret;
        ret = lttng_context_init();
        if (ret)
                return ret;
        ret = lttng_tracepoint_init();
        if (ret)
                goto error_tp;
        event_cache = KMEM_CACHE(lttng_event, 0);
        if (!event_cache) {
                ret = -ENOMEM;
                goto error_kmem;
        }
        ret = lttng_abi_init();
        if (ret)
                goto error_abi;
        ret = lttng_logger_init();
        if (ret)
                goto error_logger;
        return 0;

error_logger:
        lttng_abi_exit();
error_abi:
        kmem_cache_destroy(event_cache);
error_kmem:
        lttng_tracepoint_exit();
error_tp:
        lttng_context_exit();
        return ret;
}

module_init(lttng_events_init);

static void __exit lttng_events_exit(void)
{
        struct lttng_session *session, *tmpsession;

        lttng_logger_exit();
        lttng_abi_exit();
        list_for_each_entry_safe(session, tmpsession, &sessions, list)
                lttng_session_destroy(session);
        kmem_cache_destroy(event_cache);
        lttng_tracepoint_exit();
        lttng_context_exit();
}

module_exit(lttng_events_exit);

MODULE_LICENSE("GPL and additional rights");
MODULE_AUTHOR("Mathieu Desnoyers <mathieu.desnoyers@efficios.com>");
MODULE_DESCRIPTION("LTTng Events");
MODULE_VERSION(__stringify(LTTNG_MODULES_MAJOR_VERSION) "."
        __stringify(LTTNG_MODULES_MINOR_VERSION) "."
        __stringify(LTTNG_MODULES_PATCHLEVEL_VERSION)
        LTTNG_MODULES_EXTRAVERSION);