Fix: don't do 0 byte event reservation

[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
 */

#include <linux/module.h>
#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/jiffies.h>
#include <linux/utsname.h>
#include "wrapper/uuid.h"
#include "wrapper/vmalloc.h"    /* for wrapper_vmalloc_sync_all() */
#include "wrapper/random.h"
#include "wrapper/tracepoint.h"
#include "lttng-events.h"
#include "lttng-tracer.h"
#include "lttng-abi-old.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_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();
#ifdef CONFIG_PREEMPT_RT
        synchronize_rcu();
#endif
}

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

        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 = kzalloc(METADATA_CACHE_DEFAULT_SIZE,
                        GFP_KERNEL);
        if (!metadata_cache->data)
                goto err_free_cache;
        metadata_cache->cache_alloc = METADATA_CACHE_DEFAULT_SIZE;
        kref_init(&metadata_cache->refcount);
        session->metadata_cache = metadata_cache;
        INIT_LIST_HEAD(&metadata_cache->metadata_stream);
        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);
        kfree(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;
        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(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);
        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;
        }

        /*
         * 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 */
        }

        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;

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

int lttng_channel_enable(struct lttng_channel *channel)
{
        int old;

        if (channel->channel_type == METADATA_CHANNEL)
                return -EPERM;
        old = xchg(&channel->enabled, 1);
        if (old)
                return -EEXIST;
        return 0;
}

int lttng_channel_disable(struct lttng_channel *channel)
{
        int old;

        if (channel->channel_type == METADATA_CHANNEL)
                return -EPERM;
        old = xchg(&channel->enabled, 0);
        if (!old)
                return -EEXIST;
        return 0;
}

int lttng_event_enable(struct lttng_event *event)
{
        int old;

        if (event->chan->channel_type == METADATA_CHANNEL)
                return -EPERM;
        old = xchg(&event->enabled, 1);
        if (old)
                return -EEXIST;
        return 0;
}

int lttng_event_disable(struct lttng_event *event)
{
        int old;

        if (event->chan->channel_type == METADATA_CHANNEL)
                return -EPERM;
        old = xchg(&event->enabled, 0);
        if (!old)
                return -EEXIST;
        return 0;
}

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++;
        /*
         * 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->enabled = 1;
        chan->ops = &transport->ops;
        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.
 */
struct lttng_event *lttng_event_create(struct lttng_channel *chan,
                                   struct lttng_kernel_event *event_param,
                                   void *filter,
                                   const struct lttng_event_desc *internal_desc)
{
        struct lttng_event *event;
        int ret;

        mutex_lock(&sessions_mutex);
        if (chan->free_event_id == -1U)
                goto full;
        /*
         * This is O(n^2) (for each event, the loop is called at event
         * creation). Might require a hash if we have lots of events.
         */
        list_for_each_entry(event, &chan->session->events, list)
                if (!strcmp(event->desc->name, event_param->name))
                        goto exist;
        event = kmem_cache_zalloc(event_cache, GFP_KERNEL);
        if (!event)
                goto cache_error;
        event->chan = chan;
        event->filter = filter;
        event->id = chan->free_event_id++;
        event->enabled = 1;
        event->instrumentation = event_param->instrumentation;
        /* Populate lttng_event structure before tracepoint registration. */
        smp_wmb();
        switch (event_param->instrumentation) {
        case LTTNG_KERNEL_TRACEPOINT:
                event->desc = lttng_event_get(event_param->name);
                if (!event->desc)
                        goto register_error;
                ret = kabi_2635_tracepoint_probe_register(event_param->name,
                                event->desc->probe_callback,
                                event);
                if (ret)
                        goto register_error;
                break;
        case LTTNG_KERNEL_KPROBE:
                ret = lttng_kprobes_register(event_param->name,
                                event_param->u.kprobe.symbol_name,
                                event_param->u.kprobe.offset,
                                event_param->u.kprobe.addr,
                                event);
                if (ret)
                        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 */
                event_return =
                        kmem_cache_zalloc(event_cache, GFP_KERNEL);
                if (!event_return)
                        goto register_error;
                event_return->chan = chan;
                event_return->filter = filter;
                event_return->id = chan->free_event_id++;
                event_return->enabled = 1;
                event_return->instrumentation = event_param->instrumentation;
                /*
                 * Populate lttng_event structure before kretprobe registration.
                 */
                smp_wmb();
                ret = lttng_kretprobes_register(event_param->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);
                        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);
                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:
                ret = lttng_ftrace_register(event_param->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:
                event->desc = internal_desc;
                if (!event->desc)
                        goto register_error;
                break;
        default:
                WARN_ON_ONCE(1);
        }
        ret = _lttng_event_metadata_statedump(chan->session, chan, event);
        if (ret)
                goto statedump_error;
        list_add(&event->list, &chan->session->events);
        mutex_unlock(&sessions_mutex);
        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:
full:
        mutex_unlock(&sessions_mutex);
        return NULL;
}

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

        switch (event->instrumentation) {
        case LTTNG_KERNEL_TRACEPOINT:
                ret = kabi_2635_tracepoint_probe_unregister(event->desc->name,
                                                  event->desc->probe_callback,
                                                  event);
                if (ret)
                        return ret;
                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_NOOP:
                ret = 0;
                break;
        default:
                WARN_ON_ONCE(1);
        }
        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:
                break;
        default:
                WARN_ON_ONCE(1);
        }
        list_del(&event->list);
        lttng_destroy_context(event->ctx);
        kmem_cache_free(event_cache, event);
}

/*
 * Serialize at most one packet worth of metadata into a metadata
 * channel.
 * We have exclusive access to our metadata buffer (protected by the
 * sessions_mutex), so we can do racy operations such as looking for
 * remaining space left in packet and write, since mutual exclusion
 * protects us from concurrent writes.
 */
int lttng_metadata_output_channel(struct lttng_channel *chan,
                struct lttng_metadata_stream *stream)
{
        struct lib_ring_buffer_ctx ctx;
        int ret = 0;
        size_t len, reserve_len;

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

end:
        return ret;
}

/*
 * Write the metadata to the metadata cache.
 * Must be called with sessions_mutex held.
 */
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);
        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 = krealloc(session->metadata_cache->data,
                                tmp_cache_alloc_size, GFP_KERNEL);
                if (!tmp_cache_realloc)
                        goto err;
                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;
        kfree(str);

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

        return 0;

err:
        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,
#ifdef __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;
                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,
#ifdef __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,
#ifdef __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;

                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,
#ifdef __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"
                "       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.
 */
static
uint64_t measure_clock_offset(void)
{
        uint64_t offset, monotonic[2], realtime;
        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);

        offset = (monotonic[0] + monotonic[1]) >> 1;
        realtime = (uint64_t) rts.tv_sec * NSEC_PER_SEC;
        realtime += rts.tv_nsec;
        offset = realtime - offset;
        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"
                "       };\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,
#ifdef __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",
                "monotonic"
                );
        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 = \"Monotonic Clock\";\n"
                "       freq = %llu; /* Frequency, in Hz */\n"
                "       /* clock value offset from Epoch is: offset * (1/freq) */\n"
                "       offset = %llu;\n"
                "};\n\n",
                (unsigned long long) trace_clock_freq(),
                (unsigned 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.monotonic.value;\n"
                "} := uint27_clock_monotonic_t;\n"
                "\n"
                "typealias integer {\n"
                "       size = 32; align = %u; signed = false;\n"
                "       map = clock.monotonic.value;\n"
                "} := uint32_clock_monotonic_t;\n"
                "\n"
                "typealias integer {\n"
                "       size = 64; align = %u; signed = false;\n"
                "       map = clock.monotonic.value;\n"
                "} := uint64_clock_monotonic_t;\n\n",
                lttng_alignof(uint32_t) * CHAR_BIT,
                lttng_alignof(uint64_t) * CHAR_BIT
                );
        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;

        event_cache = KMEM_CACHE(lttng_event, 0);
        if (!event_cache)
                return -ENOMEM;
        ret = lttng_abi_init();
        if (ret)
                goto error_abi;
        return 0;
error_abi:
        kmem_cache_destroy(event_cache);
        return ret;
}

module_init(lttng_events_init);

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

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

module_exit(lttng_events_exit);

MODULE_LICENSE("GPL and additional rights");
MODULE_AUTHOR("Mathieu Desnoyers <mathieu.desnoyers@efficios.com>");
MODULE_DESCRIPTION("LTTng Events");