Convert buffering system to per-cpu

[ust.git] / libust / buffers.c

/*
 * buffers.c
 * LTTng userspace tracer buffering system
 *
 * Copyright (C) 2009 - Pierre-Marc Fournier (pierre-marc dot fournier at polymtl dot ca)
 * Copyright (C) 2008 - Mathieu Desnoyers (mathieu.desnoyers@polymtl.ca)
 *
 * 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; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * 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 <unistd.h>
#include <sys/mman.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <fcntl.h>
#include <ust/kernelcompat.h>
#include <kcompat/kref.h>
#include "buffers.h"
#include "channels.h"
#include "tracer.h"
#include "tracercore.h"
#include "usterr.h"

static DEFINE_MUTEX(ust_buffers_channels_mutex);
static LIST_HEAD(ust_buffers_channels);

static int get_n_cpus(void)
{
        int result;
        static int n_cpus = 0;

        if(n_cpus) {
                return n_cpus;
        }

        result = sysconf(_SC_NPROCESSORS_ONLN);
        if(result == -1) {
                return -1;
        }

        n_cpus = result;

        return result;
}

static int ust_buffers_init_buffer(struct ltt_trace_struct *trace,
                struct ust_channel *ltt_chan,
                struct ust_buffer *buf,
                unsigned int n_subbufs);

static int ust_buffers_alloc_buf(struct ust_buffer *buf, size_t *size)
{
        void *ptr;
        int result;

        *size = PAGE_ALIGN(*size);

        result = buf->shmid = shmget(getpid(), *size, IPC_CREAT | IPC_EXCL | 0700);
        if(result == -1 && errno == EINVAL) {
                ERR("shmget() returned EINVAL; maybe /proc/sys/kernel/shmmax should be increased.");
                return -1;
        }
        else if(result == -1) {
                PERROR("shmget");
                return -1;
        }

        /* FIXME: should have matching call to shmdt */
        ptr = shmat(buf->shmid, NULL, 0);
        if(ptr == (void *) -1) {
                perror("shmat");
                goto destroy_shmem;
        }

        /* Already mark the shared memory for destruction. This will occur only
         * when all users have detached.
         */
        result = shmctl(buf->shmid, IPC_RMID, NULL);
        if(result == -1) {
                perror("shmctl");
                return -1;
        }

        buf->buf_data = ptr;
        buf->buf_size = *size;

        return 0;

        destroy_shmem:
        result = shmctl(buf->shmid, IPC_RMID, NULL);
        if(result == -1) {
                perror("shmctl");
        }

        return -1;
}

int ust_buffers_create_buf(struct ust_channel *channel, int cpu)
{
        int result;
        struct ust_buffer *buf = channel->buf[cpu];

        buf->cpu = cpu;
        result = ust_buffers_alloc_buf(buf, &channel->alloc_size);
        if(result)
                return -1;

        buf->chan = channel;
        kref_get(&channel->kref);
        return 0;
}

static void ust_buffers_destroy_channel(struct kref *kref)
{
        struct ust_channel *chan = container_of(kref, struct ust_channel, kref);
        free(chan);
}

static void ust_buffers_destroy_buf(struct ust_buffer *buf)
{
        struct ust_channel *chan = buf->chan;
        int result;

        result = munmap(buf->buf_data, buf->buf_size);
        if(result == -1) {
                PERROR("munmap");
        }

//ust// chan->buf[buf->cpu] = NULL;
        free(buf);
        kref_put(&chan->kref, ust_buffers_destroy_channel);
}

/* called from kref_put */
static void ust_buffers_remove_buf(struct kref *kref)
{
        struct ust_buffer *buf = container_of(kref, struct ust_buffer, kref);
        ust_buffers_destroy_buf(buf);
}

int ust_buffers_open_buf(struct ust_channel *chan, int cpu)
{
        int result;

        result = ust_buffers_create_buf(chan, cpu);
        if (result == -1)
                return -1;

        kref_init(&chan->buf[cpu]->kref);

        result = ust_buffers_init_buffer(chan->trace, chan, chan->buf[cpu], chan->subbuf_cnt);
        if(result == -1)
                return -1;

        return 0;

        /* FIXME: decrementally destroy on error? */
}

/**
 *      ust_buffers_close_buf - close a channel buffer
 *      @buf: buffer
 */
static void ust_buffers_close_buf(struct ust_buffer *buf)
{
        kref_put(&buf->kref, ust_buffers_remove_buf);
}

int ust_buffers_channel_open(struct ust_channel *chan, size_t subbuf_size, size_t subbuf_cnt)
{
        int i;
        int result;

        if(subbuf_size == 0 || subbuf_cnt == 0)
                return -1;

        chan->version = UST_CHANNEL_VERSION;
        chan->subbuf_cnt = subbuf_cnt;
        chan->subbuf_size = subbuf_size;
        chan->subbuf_size_order = get_count_order(subbuf_size);
        chan->alloc_size = FIX_SIZE(subbuf_size * subbuf_cnt);

        kref_init(&chan->kref);

        mutex_lock(&ust_buffers_channels_mutex);
        for(i=0; i<chan->n_cpus; i++) {
                result = ust_buffers_open_buf(chan, i);
                if (result == -1)
                        goto error;
        }
        list_add(&chan->list, &ust_buffers_channels);
        mutex_unlock(&ust_buffers_channels_mutex);

        return 0;

        /* Jump directly inside the loop to close the buffers that were already
         * opened. */
        for(; i>=0; i--) {
                ust_buffers_close_buf(chan->buf[i]);
error:
        }

        kref_put(&chan->kref, ust_buffers_destroy_channel);
        mutex_unlock(&ust_buffers_channels_mutex);
        return -1;
}

void ust_buffers_channel_close(struct ust_channel *chan)
{
        int i;
        if(!chan)
                return;

        mutex_lock(&ust_buffers_channels_mutex);
        for(i=0; i<chan->n_cpus; i++) {
        /* FIXME: if we make it here, then all buffers were necessarily allocated. Moreover, we don't
         * initialize to NULL so we cannot use this check. Should we? */
//ust//         if (chan->buf[i])
                        ust_buffers_close_buf(chan->buf[i]);
        }

        list_del(&chan->list);
        kref_put(&chan->kref, ust_buffers_destroy_channel);
        mutex_unlock(&ust_buffers_channels_mutex);
}

/* _ust_buffers_write()
 *
 * @buf: destination buffer
 * @offset: offset in destination
 * @src: source buffer
 * @len: length of source
 * @cpy: already copied
 */

void _ust_buffers_write(struct ust_buffer *buf, size_t offset,
        const void *src, size_t len, ssize_t cpy)
{
        do {
                len -= cpy;
                src += cpy;
                offset += cpy;

                WARN_ON(offset >= buf->buf_size);

                cpy = min_t(size_t, len, buf->buf_size - offset);
                ust_buffers_do_copy(buf->buf_data + offset, src, cpy);
        } while (unlikely(len != cpy));
}

void *ltt_buffers_offset_address(struct ust_buffer *buf, size_t offset)
{
        return ((char *)buf->buf_data)+offset;
}

/*
 * -------
 */

/*
 * Last TSC comparison functions. Check if the current TSC overflows
 * LTT_TSC_BITS bits from the last TSC read. Reads and writes last_tsc
 * atomically.
 */

/* FIXME: does this test work properly? */
#if (BITS_PER_LONG == 32)
static inline void save_last_tsc(struct ust_buffer *ltt_buf,
                                        u64 tsc)
{
        ltt_buf->last_tsc = (unsigned long)(tsc >> LTT_TSC_BITS);
}

static inline int last_tsc_overflow(struct ust_buffer *ltt_buf,
                                        u64 tsc)
{
        unsigned long tsc_shifted = (unsigned long)(tsc >> LTT_TSC_BITS);

        if (unlikely((tsc_shifted - ltt_buf->last_tsc)))
                return 1;
        else
                return 0;
}
#else
static inline void save_last_tsc(struct ust_buffer *ltt_buf,
                                        u64 tsc)
{
        ltt_buf->last_tsc = (unsigned long)tsc;
}

static inline int last_tsc_overflow(struct ust_buffer *ltt_buf,
                                        u64 tsc)
{
        if (unlikely((tsc - ltt_buf->last_tsc) >> LTT_TSC_BITS))
                return 1;
        else
                return 0;
}
#endif

/*
 * A switch is done during tracing or as a final flush after tracing (so it
 * won't write in the new sub-buffer).
 */
enum force_switch_mode { FORCE_ACTIVE, FORCE_FLUSH };

static void ust_buffers_destroy_buffer(struct ust_channel *ltt_chan, int cpu);

static void ltt_force_switch(struct ust_buffer *buf,
                enum force_switch_mode mode);

/*
 * Trace callbacks
 */
static void ltt_buffer_begin_callback(struct ust_buffer *buf,
                        u64 tsc, unsigned int subbuf_idx)
{
        struct ust_channel *channel = buf->chan;
        struct ltt_subbuffer_header *header =
                (struct ltt_subbuffer_header *)
                        ltt_buffers_offset_address(buf,
                                subbuf_idx * buf->chan->subbuf_size);

        header->cycle_count_begin = tsc;
        header->lost_size = 0xFFFFFFFF; /* for debugging */
        header->buf_size = buf->chan->subbuf_size;
        ltt_write_trace_header(channel->trace, header);
}

/*
 * offset is assumed to never be 0 here : never deliver a completely empty
 * subbuffer. The lost size is between 0 and subbuf_size-1.
 */
static notrace void ltt_buffer_end_callback(struct ust_buffer *buf,
                u64 tsc, unsigned int offset, unsigned int subbuf_idx)
{
        struct ltt_subbuffer_header *header =
                (struct ltt_subbuffer_header *)
                        ltt_buffers_offset_address(buf,
                                subbuf_idx * buf->chan->subbuf_size);

        header->lost_size = SUBBUF_OFFSET((buf->chan->subbuf_size - offset),
                                buf->chan);
        header->cycle_count_end = tsc;
        header->events_lost = local_read(&buf->events_lost);
        header->subbuf_corrupt = local_read(&buf->corrupted_subbuffers);

}

void (*wake_consumer)(void *, int) = NULL;

void relay_set_wake_consumer(void (*wake)(void *, int))
{
        wake_consumer = wake;
}

void relay_wake_consumer(void *arg, int finished)
{
        if(wake_consumer)
                wake_consumer(arg, finished);
}

static notrace void ltt_deliver(struct ust_buffer *buf, unsigned int subbuf_idx,
                long commit_count)
{
        int result;

//ust// #ifdef CONFIG_LTT_VMCORE
        local_set(&buf->commit_seq[subbuf_idx], commit_count);
//ust// #endif

        /* wakeup consumer */
        result = write(buf->data_ready_fd_write, "1", 1);
        if(result == -1) {
                PERROR("write (in ltt_relay_buffer_flush)");
                ERR("this should never happen!");
        }
//ust// atomic_set(&ltt_buf->wakeup_readers, 1);
}

/*
 * This function should not be called from NMI interrupt context
 */
static notrace void ltt_buf_unfull(struct ust_buffer *buf,
                unsigned int subbuf_idx,
                long offset)
{
//ust// struct ltt_channel_struct *ltt_channel =
//ust//         (struct ltt_channel_struct *)buf->chan->private_data;
//ust// struct ltt_channel_buf_struct *ltt_buf = ltt_channel->buf;
//ust//
//ust// ltt_relay_wake_writers(ltt_buf);
}

int ust_buffers_do_get_subbuf(struct ust_buffer *buf, long *pconsumed_old)
{
        struct ust_channel *channel = buf->chan;
        long consumed_old, consumed_idx, commit_count, write_offset;
        consumed_old = atomic_long_read(&buf->consumed);
        consumed_idx = SUBBUF_INDEX(consumed_old, buf->chan);
        commit_count = local_read(&buf->commit_count[consumed_idx]);
        /*
         * Make sure we read the commit count before reading the buffer
         * data and the write offset. Correct consumed offset ordering
         * wrt commit count is insured by the use of cmpxchg to update
         * the consumed offset.
         */
        smp_rmb();
        write_offset = local_read(&buf->offset);
        /*
         * Check that the subbuffer we are trying to consume has been
         * already fully committed.
         */
        if (((commit_count - buf->chan->subbuf_size)
             & channel->commit_count_mask)
            - (BUFFER_TRUNC(consumed_old, buf->chan)
               >> channel->n_subbufs_order)
            != 0) {
                return -EAGAIN;
        }
        /*
         * Check that we are not about to read the same subbuffer in
         * which the writer head is.
         */
        if ((SUBBUF_TRUNC(write_offset, buf->chan)
           - SUBBUF_TRUNC(consumed_old, buf->chan))
           == 0) {
                return -EAGAIN;
        }

        *pconsumed_old = consumed_old;
        return 0;
}

int ust_buffers_do_put_subbuf(struct ust_buffer *buf, u32 uconsumed_old)
{
        long consumed_new, consumed_old;

        consumed_old = atomic_long_read(&buf->consumed);
        consumed_old = consumed_old & (~0xFFFFFFFFL);
        consumed_old = consumed_old | uconsumed_old;
        consumed_new = SUBBUF_ALIGN(consumed_old, buf->chan);

//ust// spin_lock(&ltt_buf->full_lock);
        if (atomic_long_cmpxchg(&buf->consumed, consumed_old,
                                consumed_new)
            != consumed_old) {
                /* We have been pushed by the writer : the last
                 * buffer read _is_ corrupted! It can also
                 * happen if this is a buffer we never got. */
//ust//         spin_unlock(&ltt_buf->full_lock);
                return -EIO;
        } else {
                /* tell the client that buffer is now unfull */
                int index;
                long data;
                index = SUBBUF_INDEX(consumed_old, buf->chan);
                data = BUFFER_OFFSET(consumed_old, buf->chan);
                ltt_buf_unfull(buf, index, data);
//ust//         spin_unlock(&ltt_buf->full_lock);
        }
        return 0;
}

static void ltt_relay_print_subbuffer_errors(
                struct ust_channel *channel,
                long cons_off, int cpu)
{
        struct ust_buffer *ltt_buf = channel->buf[cpu];
        long cons_idx, commit_count, write_offset;

        cons_idx = SUBBUF_INDEX(cons_off, channel);
        commit_count = local_read(&ltt_buf->commit_count[cons_idx]);
        /*
         * No need to order commit_count and write_offset reads because we
         * execute after trace is stopped when there are no readers left.
         */
        write_offset = local_read(&ltt_buf->offset);
        WARN( "LTT : unread channel %s offset is %ld "
                "and cons_off : %ld\n",
                channel->channel_name, write_offset, cons_off);
        /* Check each sub-buffer for non filled commit count */
        if (((commit_count - channel->subbuf_size) & channel->commit_count_mask)
            - (BUFFER_TRUNC(cons_off, channel) >> channel->n_subbufs_order) != 0) {
                ERR("LTT : %s : subbuffer %lu has non filled "
                        "commit count %lu.\n",
                        channel->channel_name, cons_idx, commit_count);
        }
        ERR("LTT : %s : commit count : %lu, subbuf size %zd\n",
                        channel->channel_name, commit_count,
                        channel->subbuf_size);
}

static void ltt_relay_print_errors(struct ltt_trace_struct *trace,
                struct ust_channel *channel, int cpu)
{
        struct ust_buffer *ltt_buf = channel->buf[cpu];
        long cons_off;

        /*
         * Can be called in the error path of allocation when
         * trans_channel_data is not yet set.
         */
        if (!channel)
                return;

        for (cons_off = atomic_long_read(&ltt_buf->consumed);
                        (SUBBUF_TRUNC(local_read(&ltt_buf->offset),
                                      channel)
                         - cons_off) > 0;
                        cons_off = SUBBUF_ALIGN(cons_off, channel))
                ltt_relay_print_subbuffer_errors(channel, cons_off, cpu);
}

static void ltt_relay_print_buffer_errors(struct ust_channel *channel, int cpu)
{
        struct ltt_trace_struct *trace = channel->trace;
        struct ust_buffer *ltt_buf = channel->buf[cpu];

        if (local_read(&ltt_buf->events_lost))
                ERR("channel %s: %ld events lost",
                        channel->channel_name,
                        local_read(&ltt_buf->events_lost));
        if (local_read(&ltt_buf->corrupted_subbuffers))
                ERR("channel %s : %ld corrupted subbuffers",
                        channel->channel_name,
                        local_read(&ltt_buf->corrupted_subbuffers));

        ltt_relay_print_errors(trace, channel, cpu);
}

static void ltt_relay_release_channel(struct kref *kref)
{
        struct ust_channel *ltt_chan = container_of(kref,
                        struct ust_channel, kref);
        free(ltt_chan->buf);
}

/*
 * Create ltt buffer.
 */
//ust// static int ltt_relay_create_buffer(struct ltt_trace_struct *trace,
//ust//                 struct ltt_channel_struct *ltt_chan, struct rchan_buf *buf,
//ust//                 unsigned int cpu, unsigned int n_subbufs)
//ust// {
//ust//         struct ltt_channel_buf_struct *ltt_buf =
//ust//                 percpu_ptr(ltt_chan->buf, cpu);
//ust//         unsigned int j;
//ust// 
//ust//         ltt_buf->commit_count =
//ust//                 kzalloc_node(sizeof(ltt_buf->commit_count) * n_subbufs,
//ust//                         GFP_KERNEL, cpu_to_node(cpu));
//ust//         if (!ltt_buf->commit_count)
//ust//                 return -ENOMEM;
//ust//         kref_get(&trace->kref);
//ust//         kref_get(&trace->ltt_transport_kref);
//ust//         kref_get(&ltt_chan->kref);
//ust//         local_set(&ltt_buf->offset, ltt_subbuffer_header_size());
//ust//         atomic_long_set(&ltt_buf->consumed, 0);
//ust//         atomic_long_set(&ltt_buf->active_readers, 0);
//ust//         for (j = 0; j < n_subbufs; j++)
//ust//                 local_set(&ltt_buf->commit_count[j], 0);
//ust//         init_waitqueue_head(&ltt_buf->write_wait);
//ust//         atomic_set(&ltt_buf->wakeup_readers, 0);
//ust//         spin_lock_init(&ltt_buf->full_lock);
//ust// 
//ust//         ltt_buffer_begin_callback(buf, trace->start_tsc, 0);
//ust//         /* atomic_add made on local variable on data that belongs to
//ust//          * various CPUs : ok because tracing not started (for this cpu). */
//ust//         local_add(ltt_subbuffer_header_size(), &ltt_buf->commit_count[0]);
//ust// 
//ust//         local_set(&ltt_buf->events_lost, 0);
//ust//         local_set(&ltt_buf->corrupted_subbuffers, 0);
//ust// 
//ust//         return 0;
//ust// }

static int ust_buffers_init_buffer(struct ltt_trace_struct *trace,
                struct ust_channel *ltt_chan, struct ust_buffer *buf,
                unsigned int n_subbufs)
{
        unsigned int j;
        int fds[2];
        int result;

        buf->commit_count =
                zmalloc(sizeof(buf->commit_count) * n_subbufs);
        if (!buf->commit_count)
                return -ENOMEM;
        kref_get(&trace->kref);
        kref_get(&trace->ltt_transport_kref);
        kref_get(&ltt_chan->kref);
        local_set(&buf->offset, ltt_subbuffer_header_size());
        atomic_long_set(&buf->consumed, 0);
        atomic_long_set(&buf->active_readers, 0);
        for (j = 0; j < n_subbufs; j++)
                local_set(&buf->commit_count[j], 0);
//ust// init_waitqueue_head(&buf->write_wait);
//ust// atomic_set(&buf->wakeup_readers, 0);
//ust// spin_lock_init(&buf->full_lock);

        ltt_buffer_begin_callback(buf, trace->start_tsc, 0);

        local_add(ltt_subbuffer_header_size(), &buf->commit_count[0]);

        local_set(&buf->events_lost, 0);
        local_set(&buf->corrupted_subbuffers, 0);

        result = pipe(fds);
        if(result == -1) {
                PERROR("pipe");
                return -1;
        }
        buf->data_ready_fd_read = fds[0];
        buf->data_ready_fd_write = fds[1];

        /* FIXME: do we actually need this? */
        result = fcntl(fds[0], F_SETFL, O_NONBLOCK);
        if(result == -1) {
                PERROR("fcntl");
        }

//ust// buf->commit_seq = malloc(sizeof(buf->commit_seq) * n_subbufs);
//ust// if(!ltt_buf->commit_seq) {
//ust//         return -1;
//ust// }

        /* FIXME: decrementally destroy on error */

        return 0;
}

/* FIXME: use this function */
static void ust_buffers_destroy_buffer(struct ust_channel *ltt_chan, int cpu)
{
        struct ltt_trace_struct *trace = ltt_chan->trace;
        struct ust_buffer *ltt_buf = ltt_chan->buf[cpu];

        kref_put(&ltt_chan->trace->ltt_transport_kref,
                ltt_release_transport);
        ltt_relay_print_buffer_errors(ltt_chan, cpu);
//ust// free(ltt_buf->commit_seq);
        kfree(ltt_buf->commit_count);
        ltt_buf->commit_count = NULL;
        kref_put(&ltt_chan->kref, ltt_relay_release_channel);
        kref_put(&trace->kref, ltt_release_trace);
//ust// wake_up_interruptible(&trace->kref_wq);
}

static int ust_buffers_alloc_channel_buf_structs(struct ust_channel *chan)
{
        void *ptr;
        int result;
        size_t size;
        int i;

        size = PAGE_ALIGN(1);

        for(i=0; i<chan->n_cpus; i++) {

                result = chan->buf_struct_shmids[i] = shmget(getpid(), size, IPC_CREAT | IPC_EXCL | 0700);
                if(result == -1) {
                        PERROR("shmget");
                        goto destroy_previous;
                }

                /* FIXME: should have matching call to shmdt */
                ptr = shmat(chan->buf_struct_shmids[i], NULL, 0);
                if(ptr == (void *) -1) {
                        perror("shmat");
                        goto destroy_shm;
                }

                /* Already mark the shared memory for destruction. This will occur only
                 * when all users have detached.
                 */
                result = shmctl(chan->buf_struct_shmids[i], IPC_RMID, NULL);
                if(result == -1) {
                        perror("shmctl");
                        goto destroy_previous;
                }

                chan->buf[i] = ptr;
        }

        return 0;

        /* Jumping inside this loop occurs from within the other loop above with i as
         * counter, so it unallocates the structures for the cpu = current_i down to
         * zero. */
        for(; i>=0; i--) {
                destroy_shm:
                result = shmctl(chan->buf_struct_shmids[i], IPC_RMID, NULL);
                if(result == -1) {
                        perror("shmctl");
                }

                destroy_previous:
                continue;
        }

        return -1;
}

/*
 * Create channel.
 */
static int ust_buffers_create_channel(const char *trace_name, struct ltt_trace_struct *trace,
        const char *channel_name, struct ust_channel *ltt_chan,
        unsigned int subbuf_size, unsigned int n_subbufs, int overwrite)
{
        int result;

        kref_init(&ltt_chan->kref);

        ltt_chan->trace = trace;
        ltt_chan->buffer_begin = ltt_buffer_begin_callback;
        ltt_chan->buffer_end = ltt_buffer_end_callback;
        ltt_chan->overwrite = overwrite;
        ltt_chan->n_subbufs_order = get_count_order(n_subbufs);
        ltt_chan->commit_count_mask = (~0UL >> ltt_chan->n_subbufs_order);
        ltt_chan->n_cpus = get_n_cpus();
//ust// ltt_chan->buf = percpu_alloc_mask(sizeof(struct ltt_channel_buf_struct), GFP_KERNEL, cpu_possible_map);
        ltt_chan->buf = (void *) malloc(ltt_chan->n_cpus * sizeof(void *));
        if(ltt_chan->buf == NULL) {
                goto error;
        }
        ltt_chan->buf_struct_shmids = (int *) malloc(ltt_chan->n_cpus * sizeof(int));
        if(ltt_chan->buf_struct_shmids == NULL)
                goto free_buf;

        result = ust_buffers_alloc_channel_buf_structs(ltt_chan);
        if(result != 0) {
                goto free_buf_struct_shmids;
        }

        result = ust_buffers_channel_open(ltt_chan, subbuf_size, n_subbufs);
        if (result != 0) {
                ERR("Cannot open channel for trace %s", trace_name);
                goto unalloc_buf_structs;
        }

        return 0;

unalloc_buf_structs:
        /* FIXME: put a call here to unalloc the buf structs! */

free_buf_struct_shmids:
        free(ltt_chan->buf_struct_shmids);

free_buf:
        free(ltt_chan->buf);

error:
        return -1;
}

/*
 * LTTng channel flush function.
 *
 * Must be called when no tracing is active in the channel, because of
 * accesses across CPUs.
 */
static notrace void ltt_relay_buffer_flush(struct ust_buffer *buf)
{
        int result;

//ust// buf->finalized = 1;
        ltt_force_switch(buf, FORCE_FLUSH);

        result = write(buf->data_ready_fd_write, "1", 1);
        if(result == -1) {
                PERROR("write (in ltt_relay_buffer_flush)");
                ERR("this should never happen!");
        }
}

static void ltt_relay_async_wakeup_chan(struct ust_channel *ltt_channel)
{
//ust// unsigned int i;
//ust// struct rchan *rchan = ltt_channel->trans_channel_data;
//ust//
//ust// for_each_possible_cpu(i) {
//ust//         struct ltt_channel_buf_struct *ltt_buf =
//ust//                 percpu_ptr(ltt_channel->buf, i);
//ust//
//ust//         if (atomic_read(&ltt_buf->wakeup_readers) == 1) {
//ust//                 atomic_set(&ltt_buf->wakeup_readers, 0);
//ust//                 wake_up_interruptible(&rchan->buf[i]->read_wait);
//ust//         }
//ust// }
}

static void ltt_relay_finish_buffer(struct ust_channel *channel, unsigned int cpu)
{
//      int result;

        if (channel->buf[cpu]) {
                struct ust_buffer *buf = channel->buf[cpu];
                ltt_relay_buffer_flush(buf);
//ust//         ltt_relay_wake_writers(ltt_buf);
                /* closing the pipe tells the consumer the buffer is finished */
                
                //result = write(ltt_buf->data_ready_fd_write, "D", 1);
                //if(result == -1) {
                //      PERROR("write (in ltt_relay_finish_buffer)");
                //      ERR("this should never happen!");
                //}
                close(buf->data_ready_fd_write);
        }
}


static void ltt_relay_finish_channel(struct ust_channel *channel)
{
        unsigned int i;

        for(i=0; i<channel->n_cpus; i++) {
                ltt_relay_finish_buffer(channel, i);
        }
}

static void ltt_relay_remove_channel(struct ust_channel *channel)
{
        ust_buffers_channel_close(channel);
        kref_put(&channel->kref, ltt_relay_release_channel);
}

struct ltt_reserve_switch_offsets {
        long begin, end, old;
        long begin_switch, end_switch_current, end_switch_old;
        long commit_count, reserve_commit_diff;
        size_t before_hdr_pad, size;
};

/*
 * Returns :
 * 0 if ok
 * !0 if execution must be aborted.
 */
static inline int ltt_relay_try_reserve(
                struct ust_channel *channel, struct ust_buffer *buf,
                struct ltt_reserve_switch_offsets *offsets, size_t data_size,
                u64 *tsc, unsigned int *rflags, int largest_align)
{
        offsets->begin = local_read(&buf->offset);
        offsets->old = offsets->begin;
        offsets->begin_switch = 0;
        offsets->end_switch_current = 0;
        offsets->end_switch_old = 0;

        *tsc = trace_clock_read64();
        if (last_tsc_overflow(buf, *tsc))
                *rflags = LTT_RFLAG_ID_SIZE_TSC;

        if (SUBBUF_OFFSET(offsets->begin, buf->chan) == 0) {
                offsets->begin_switch = 1;              /* For offsets->begin */
        } else {
                offsets->size = ust_get_header_size(channel,
                                        offsets->begin, data_size,
                                        &offsets->before_hdr_pad, *rflags);
                offsets->size += ltt_align(offsets->begin + offsets->size,
                                           largest_align)
                                 + data_size;
                if ((SUBBUF_OFFSET(offsets->begin, buf->chan) + offsets->size)
                                > buf->chan->subbuf_size) {
                        offsets->end_switch_old = 1;    /* For offsets->old */
                        offsets->begin_switch = 1;      /* For offsets->begin */
                }
        }
        if (offsets->begin_switch) {
                long subbuf_index;

                if (offsets->end_switch_old)
                        offsets->begin = SUBBUF_ALIGN(offsets->begin,
                                                      buf->chan);
                offsets->begin = offsets->begin + ltt_subbuffer_header_size();
                /* Test new buffer integrity */
                subbuf_index = SUBBUF_INDEX(offsets->begin, buf->chan);
                offsets->reserve_commit_diff =
                        (BUFFER_TRUNC(offsets->begin, buf->chan)
                         >> channel->n_subbufs_order)
                        - (local_read(&buf->commit_count[subbuf_index])
                                & channel->commit_count_mask);
                if (offsets->reserve_commit_diff == 0) {
                        long consumed;

                        consumed = atomic_long_read(&buf->consumed);

                        /* Next buffer not corrupted. */
                        if (!channel->overwrite &&
                                (SUBBUF_TRUNC(offsets->begin, buf->chan)
                                 - SUBBUF_TRUNC(consumed, buf->chan))
                                >= channel->alloc_size) {

                                long consumed_idx = SUBBUF_INDEX(consumed, buf->chan);
                                long commit_count = local_read(&buf->commit_count[consumed_idx]);
                                if(((commit_count - buf->chan->subbuf_size) & channel->commit_count_mask) - (BUFFER_TRUNC(consumed, buf->chan) >> channel->n_subbufs_order) != 0) {
                                        WARN("Event dropped. Caused by non-committed event.");
                                }
                                else {
                                        WARN("Event dropped. Caused by non-consumed buffer.");
                                }
                                /*
                                 * We do not overwrite non consumed buffers
                                 * and we are full : event is lost.
                                 */
                                local_inc(&buf->events_lost);
                                return -1;
                        } else {
                                /*
                                 * next buffer not corrupted, we are either in
                                 * overwrite mode or the buffer is not full.
                                 * It's safe to write in this new subbuffer.
                                 */
                        }
                } else {
                        /*
                         * Next subbuffer corrupted. Force pushing reader even
                         * in normal mode. It's safe to write in this new
                         * subbuffer.
                         */
                }
                offsets->size = ust_get_header_size(channel,
                                        offsets->begin, data_size,
                                        &offsets->before_hdr_pad, *rflags);
                offsets->size += ltt_align(offsets->begin + offsets->size,
                                           largest_align)
                                 + data_size;
                if ((SUBBUF_OFFSET(offsets->begin, buf->chan) + offsets->size)
                                > buf->chan->subbuf_size) {
                        /*
                         * Event too big for subbuffers, report error, don't
                         * complete the sub-buffer switch.
                         */
                        local_inc(&buf->events_lost);
                        return -1;
                } else {
                        /*
                         * We just made a successful buffer switch and the event
                         * fits in the new subbuffer. Let's write.
                         */
                }
        } else {
                /*
                 * Event fits in the current buffer and we are not on a switch
                 * boundary. It's safe to write.
                 */
        }
        offsets->end = offsets->begin + offsets->size;

        if ((SUBBUF_OFFSET(offsets->end, buf->chan)) == 0) {
                /*
                 * The offset_end will fall at the very beginning of the next
                 * subbuffer.
                 */
                offsets->end_switch_current = 1;        /* For offsets->begin */
        }
        return 0;
}

/*
 * Returns :
 * 0 if ok
 * !0 if execution must be aborted.
 */
static inline int ltt_relay_try_switch(
                enum force_switch_mode mode,
                struct ust_channel *channel,
                struct ust_buffer *buf,
                struct ltt_reserve_switch_offsets *offsets,
                u64 *tsc)
{
        long subbuf_index;

        offsets->begin = local_read(&buf->offset);
        offsets->old = offsets->begin;
        offsets->begin_switch = 0;
        offsets->end_switch_old = 0;

        *tsc = trace_clock_read64();

        if (SUBBUF_OFFSET(offsets->begin, buf->chan) != 0) {
                offsets->begin = SUBBUF_ALIGN(offsets->begin, buf->chan);
                offsets->end_switch_old = 1;
        } else {
                /* we do not have to switch : buffer is empty */
                return -1;
        }
        if (mode == FORCE_ACTIVE)
                offsets->begin += ltt_subbuffer_header_size();
        /*
         * Always begin_switch in FORCE_ACTIVE mode.
         * Test new buffer integrity
         */
        subbuf_index = SUBBUF_INDEX(offsets->begin, buf->chan);
        offsets->reserve_commit_diff =
                (BUFFER_TRUNC(offsets->begin, buf->chan)
                 >> channel->n_subbufs_order)
                - (local_read(&buf->commit_count[subbuf_index])
                        & channel->commit_count_mask);
        if (offsets->reserve_commit_diff == 0) {
                /* Next buffer not corrupted. */
                if (mode == FORCE_ACTIVE
                    && !channel->overwrite
                    && offsets->begin - atomic_long_read(&buf->consumed)
                       >= channel->alloc_size) {
                        /*
                         * We do not overwrite non consumed buffers and we are
                         * full : ignore switch while tracing is active.
                         */
                        return -1;
                }
        } else {
                /*
                 * Next subbuffer corrupted. Force pushing reader even in normal
                 * mode
                 */
        }
        offsets->end = offsets->begin;
        return 0;
}

static inline void ltt_reserve_push_reader(
                struct ust_channel *channel,
                struct ust_buffer *buf,
                struct ltt_reserve_switch_offsets *offsets)
{
        long consumed_old, consumed_new;

        do {
                consumed_old = atomic_long_read(&buf->consumed);
                /*
                 * If buffer is in overwrite mode, push the reader consumed
                 * count if the write position has reached it and we are not
                 * at the first iteration (don't push the reader farther than
                 * the writer). This operation can be done concurrently by many
                 * writers in the same buffer, the writer being at the farthest
                 * write position sub-buffer index in the buffer being the one
                 * which will win this loop.
                 * If the buffer is not in overwrite mode, pushing the reader
                 * only happens if a sub-buffer is corrupted.
                 */
                if ((SUBBUF_TRUNC(offsets->end-1, buf->chan)
                   - SUBBUF_TRUNC(consumed_old, buf->chan))
                   >= channel->alloc_size)
                        consumed_new = SUBBUF_ALIGN(consumed_old, buf->chan);
                else {
                        consumed_new = consumed_old;
                        break;
                }
        } while (atomic_long_cmpxchg(&buf->consumed, consumed_old,
                        consumed_new) != consumed_old);

        if (consumed_old != consumed_new) {
                /*
                 * Reader pushed : we are the winner of the push, we can
                 * therefore reequilibrate reserve and commit. Atomic increment
                 * of the commit count permits other writers to play around
                 * with this variable before us. We keep track of
                 * corrupted_subbuffers even in overwrite mode :
                 * we never want to write over a non completely committed
                 * sub-buffer : possible causes : the buffer size is too low
                 * compared to the unordered data input, or there is a writer
                 * that died between the reserve and the commit.
                 */
                if (offsets->reserve_commit_diff) {
                        /*
                         * We have to alter the sub-buffer commit count.
                         * We do not deliver the previous subbuffer, given it
                         * was either corrupted or not consumed (overwrite
                         * mode).
                         */
                        local_add(offsets->reserve_commit_diff,
                                  &buf->commit_count[
                                        SUBBUF_INDEX(offsets->begin,
                                                     buf->chan)]);
                        if (!channel->overwrite
                            || offsets->reserve_commit_diff
                               != channel->subbuf_size) {
                                /*
                                 * The reserve commit diff was not subbuf_size :
                                 * it means the subbuffer was partly written to
                                 * and is therefore corrupted. If it is multiple
                                 * of subbuffer size and we are in flight
                                 * recorder mode, we are skipping over a whole
                                 * subbuffer.
                                 */
                                local_inc(&buf->corrupted_subbuffers);
                        }
                }
        }
}


/*
 * ltt_reserve_switch_old_subbuf: switch old subbuffer
 *
 * Concurrency safe because we are the last and only thread to alter this
 * sub-buffer. As long as it is not delivered and read, no other thread can
 * alter the offset, alter the reserve_count or call the
 * client_buffer_end_callback on this sub-buffer.
 *
 * The only remaining threads could be the ones with pending commits. They will
 * have to do the deliver themselves.  Not concurrency safe in overwrite mode.
 * We detect corrupted subbuffers with commit and reserve counts. We keep a
 * corrupted sub-buffers count and push the readers across these sub-buffers.
 *
 * Not concurrency safe if a writer is stalled in a subbuffer and another writer
 * switches in, finding out it's corrupted.  The result will be than the old
 * (uncommited) subbuffer will be declared corrupted, and that the new subbuffer
 * will be declared corrupted too because of the commit count adjustment.
 *
 * Note : offset_old should never be 0 here.
 */
static inline void ltt_reserve_switch_old_subbuf(
                struct ust_channel *channel,
                struct ust_buffer *buf,
                struct ltt_reserve_switch_offsets *offsets, u64 *tsc)
{
        long oldidx = SUBBUF_INDEX(offsets->old - 1, channel);

        channel->buffer_end(buf, *tsc, offsets->old, oldidx);
        /* Must write buffer end before incrementing commit count */
        smp_wmb();
        offsets->commit_count =
                local_add_return(channel->subbuf_size
                                 - (SUBBUF_OFFSET(offsets->old - 1, channel)
                                 + 1),
                                 &buf->commit_count[oldidx]);
        if ((BUFFER_TRUNC(offsets->old - 1, channel)
                        >> channel->n_subbufs_order)
                        - ((offsets->commit_count - channel->subbuf_size)
                                & channel->commit_count_mask) == 0)
                ltt_deliver(buf, oldidx, offsets->commit_count);
}

/*
 * ltt_reserve_switch_new_subbuf: Populate new subbuffer.
 *
 * This code can be executed unordered : writers may already have written to the
 * sub-buffer before this code gets executed, caution.  The commit makes sure
 * that this code is executed before the deliver of this sub-buffer.
 */
static /*inline*/ void ltt_reserve_switch_new_subbuf(
                struct ust_channel *channel,
                struct ust_buffer *buf,
                struct ltt_reserve_switch_offsets *offsets, u64 *tsc)
{
        long beginidx = SUBBUF_INDEX(offsets->begin, channel);

        channel->buffer_begin(buf, *tsc, beginidx);
        /* Must write buffer end before incrementing commit count */
        smp_wmb();
        offsets->commit_count = local_add_return(ltt_subbuffer_header_size(),
                        &buf->commit_count[beginidx]);
        /* Check if the written buffer has to be delivered */
        if ((BUFFER_TRUNC(offsets->begin, channel)
                        >> channel->n_subbufs_order)
                        - ((offsets->commit_count - channel->subbuf_size)
                                & channel->commit_count_mask) == 0)
                ltt_deliver(buf, beginidx, offsets->commit_count);
}


/*
 * ltt_reserve_end_switch_current: finish switching current subbuffer
 *
 * Concurrency safe because we are the last and only thread to alter this
 * sub-buffer. As long as it is not delivered and read, no other thread can
 * alter the offset, alter the reserve_count or call the
 * client_buffer_end_callback on this sub-buffer.
 *
 * The only remaining threads could be the ones with pending commits. They will
 * have to do the deliver themselves.  Not concurrency safe in overwrite mode.
 * We detect corrupted subbuffers with commit and reserve counts. We keep a
 * corrupted sub-buffers count and push the readers across these sub-buffers.
 *
 * Not concurrency safe if a writer is stalled in a subbuffer and another writer
 * switches in, finding out it's corrupted.  The result will be than the old
 * (uncommited) subbuffer will be declared corrupted, and that the new subbuffer
 * will be declared corrupted too because of the commit count adjustment.
 */
static inline void ltt_reserve_end_switch_current(
                struct ust_channel *channel,
                struct ust_buffer *buf,
                struct ltt_reserve_switch_offsets *offsets, u64 *tsc)
{
        long endidx = SUBBUF_INDEX(offsets->end - 1, channel);

        channel->buffer_end(buf, *tsc, offsets->end, endidx);
        /* Must write buffer begin before incrementing commit count */
        smp_wmb();
        offsets->commit_count =
                local_add_return(channel->subbuf_size
                                 - (SUBBUF_OFFSET(offsets->end - 1, channel)
                                 + 1),
                                 &buf->commit_count[endidx]);
        if ((BUFFER_TRUNC(offsets->end - 1, channel)
                        >> channel->n_subbufs_order)
                        - ((offsets->commit_count - channel->subbuf_size)
                                & channel->commit_count_mask) == 0)
                ltt_deliver(buf, endidx, offsets->commit_count);
}

/**
 * ltt_relay_reserve_slot - Atomic slot reservation in a LTTng buffer.
 * @trace: the trace structure to log to.
 * @ltt_channel: channel structure
 * @transport_data: data structure specific to ltt relay
 * @data_size: size of the variable length data to log.
 * @slot_size: pointer to total size of the slot (out)
 * @buf_offset : pointer to reserved buffer offset (out)
 * @tsc: pointer to the tsc at the slot reservation (out)
 * @cpu: cpuid
 *
 * Return : -ENOSPC if not enough space, else returns 0.
 * It will take care of sub-buffer switching.
 */
static notrace int ltt_relay_reserve_slot(struct ltt_trace_struct *trace,
                struct ust_channel *channel, void **transport_data,
                size_t data_size, size_t *slot_size, long *buf_offset, u64 *tsc,
                unsigned int *rflags, int largest_align, int cpu)
{
        struct ust_buffer *buf = *transport_data = channel->buf[cpu];
        struct ltt_reserve_switch_offsets offsets;

        offsets.reserve_commit_diff = 0;
        offsets.size = 0;

        /*
         * Perform retryable operations.
         */
        if (ltt_nesting > 4) {
                local_inc(&buf->events_lost);
                return -EPERM;
        }
        do {
                if (ltt_relay_try_reserve(channel, buf, &offsets, data_size, tsc, rflags,
                                largest_align))
                        return -ENOSPC;
        } while (local_cmpxchg(&buf->offset, offsets.old,
                        offsets.end) != offsets.old);

        /*
         * Atomically update last_tsc. This update races against concurrent
         * atomic updates, but the race will always cause supplementary full TSC
         * events, never the opposite (missing a full TSC event when it would be
         * needed).
         */
        save_last_tsc(buf, *tsc);

        /*
         * Push the reader if necessary
         */
        ltt_reserve_push_reader(channel, buf, &offsets);

        /*
         * Switch old subbuffer if needed.
         */
        if (offsets.end_switch_old)
                ltt_reserve_switch_old_subbuf(channel, buf, &offsets, tsc);

        /*
         * Populate new subbuffer.
         */
        if (offsets.begin_switch)
                ltt_reserve_switch_new_subbuf(channel, buf, &offsets, tsc);

        if (offsets.end_switch_current)
                ltt_reserve_end_switch_current(channel, buf, &offsets, tsc);

        *slot_size = offsets.size;
        *buf_offset = offsets.begin + offsets.before_hdr_pad;
        return 0;
}

/*
 * Force a sub-buffer switch for a per-cpu buffer. This operation is
 * completely reentrant : can be called while tracing is active with
 * absolutely no lock held.
 *
 * Note, however, that as a local_cmpxchg is used for some atomic
 * operations, this function must be called from the CPU which owns the buffer
 * for a ACTIVE flush.
 */
static notrace void ltt_force_switch(struct ust_buffer *buf,
                enum force_switch_mode mode)
{
        struct ust_channel *channel = buf->chan;
        struct ltt_reserve_switch_offsets offsets;
        u64 tsc;

        offsets.reserve_commit_diff = 0;
        offsets.size = 0;

        /*
         * Perform retryable operations.
         */
        do {
                if (ltt_relay_try_switch(mode, channel, buf, &offsets, &tsc))
                        return;
        } while (local_cmpxchg(&buf->offset, offsets.old,
                        offsets.end) != offsets.old);

        /*
         * Atomically update last_tsc. This update races against concurrent
         * atomic updates, but the race will always cause supplementary full TSC
         * events, never the opposite (missing a full TSC event when it would be
         * needed).
         */
        save_last_tsc(buf, tsc);

        /*
         * Push the reader if necessary
         */
        if (mode == FORCE_ACTIVE)
                ltt_reserve_push_reader(channel, buf, &offsets);

        /*
         * Switch old subbuffer if needed.
         */
        if (offsets.end_switch_old)
                ltt_reserve_switch_old_subbuf(channel, buf, &offsets, &tsc);

        /*
         * Populate new subbuffer.
         */
        if (mode == FORCE_ACTIVE)
                ltt_reserve_switch_new_subbuf(channel, buf, &offsets, &tsc);
}

static struct ltt_transport ust_relay_transport = {
        .name = "ustrelay",
        .ops = {
                .create_channel = ust_buffers_create_channel,
                .finish_channel = ltt_relay_finish_channel,
                .remove_channel = ltt_relay_remove_channel,
                .wakeup_channel = ltt_relay_async_wakeup_chan,
//              .commit_slot = ltt_relay_commit_slot,
                .reserve_slot = ltt_relay_reserve_slot,
        },
};

/*
 * for flight recording. must be called after relay_commit.
 * This function decrements de subbuffer's lost_size each time the commit count
 * reaches back the reserve offset (module subbuffer size). It is useful for
 * crash dump.
 */
static /* inline */ void ltt_write_commit_counter(struct ust_buffer *buf,
                struct ust_buffer *ltt_buf,
                long idx, long buf_offset, long commit_count, size_t data_size)
{
        long offset;
        long commit_seq_old;

        offset = buf_offset + data_size;

        /*
         * SUBBUF_OFFSET includes commit_count_mask. We can simply
         * compare the offsets within the subbuffer without caring about
         * buffer full/empty mismatch because offset is never zero here
         * (subbuffer header and event headers have non-zero length).
         */
        if (unlikely(SUBBUF_OFFSET(offset - commit_count, buf->chan)))
                return;

        commit_seq_old = local_read(&ltt_buf->commit_seq[idx]);
        while (commit_seq_old < commit_count)
                commit_seq_old = local_cmpxchg(&ltt_buf->commit_seq[idx],
                                         commit_seq_old, commit_count);
}

/*
 * Atomic unordered slot commit. Increments the commit count in the
 * specified sub-buffer, and delivers it if necessary.
 *
 * Parameters:
 *
 * @ltt_channel : channel structure
 * @transport_data: transport-specific data
 * @buf_offset : offset following the event header.
 * @data_size : size of the event data.
 * @slot_size : size of the reserved slot.
 */
/* FIXME: make this function static inline in the .h! */
/*static*/ /* inline */ notrace void ltt_commit_slot(
                struct ust_channel *channel,
                void **transport_data, long buf_offset,
                size_t data_size, size_t slot_size)
{
        struct ust_buffer *buf = *transport_data;
        long offset_end = buf_offset;
        long endidx = SUBBUF_INDEX(offset_end - 1, channel);
        long commit_count;

        /* Must write slot data before incrementing commit count */
        smp_wmb();
        commit_count = local_add_return(slot_size,
                &buf->commit_count[endidx]);
        /* Check if all commits have been done */
        if ((BUFFER_TRUNC(offset_end - 1, channel)
                        >> channel->n_subbufs_order)
                        - ((commit_count - channel->subbuf_size)
                           & channel->commit_count_mask) == 0)
                ltt_deliver(buf, endidx, commit_count);
        /*
         * Update lost_size for each commit. It's needed only for extracting
         * ltt buffers from vmcore, after crash.
         */
        ltt_write_commit_counter(buf, buf, endidx,
                                 buf_offset, commit_count, data_size);
}


static char initialized = 0;

void __attribute__((constructor)) init_ustrelay_transport(void)
{
        if(!initialized) {
                ltt_transport_register(&ust_relay_transport);
                initialized = 1;
        }
}

static void __attribute__((destructor)) ltt_relay_exit(void)
{
        ltt_transport_unregister(&ust_relay_transport);
}