[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"

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


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;
        }

        /* On Linux, when some processors are offline
         * _SC_NPROCESSORS_CONF counts the offline
         * processors, whereas _SC_NPROCESSORS_ONLN
         * does not. If we used _SC_NPROCESSORS_ONLN,
         * getcpu() could return a value greater than
         * this sysconf, in which case the arrays
         * indexed by processor would overflow.
         */
        result = sysconf(_SC_NPROCESSORS_CONF);
        if(result == -1) {
                return -1;
        }

        n_cpus = result;

        return result;
}

/* _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));
}

static int ust_buffers_init_buffer(struct ust_trace *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;

        /* Check that the subbuffer size is larger than a page. */
        WARN_ON_ONCE(subbuf_size < PAGE_SIZE);

        /*
         * Make sure the number of subbuffers and subbuffer size are power of 2.
         */
        WARN_ON_ONCE(hweight32(subbuf_size) != 1);
        WARN_ON(hweight32(subbuf_cnt) != 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 = 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:
                do {} while(0);
        }

        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);
}

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

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(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 *)
                        ust_buffers_offset_address(buf,
                                subbuf_idx * buf->chan->subbuf_size);

        header->cycle_count_begin = tsc;
        header->data_size = 0xFFFFFFFF; /* for recognizing crashed buffers */
        header->sb_size = 0xFFFFFFFF; /* for recognizing crashed buffers */
        /* FIXME: add memory barrier? */
        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(struct ust_buffer *buf,
                u64 tsc, unsigned int offset, unsigned int subbuf_idx)
{
        struct ltt_subbuffer_header *header =
                (struct ltt_subbuffer_header *)
                        ust_buffers_offset_address(buf,
                                subbuf_idx * buf->chan->subbuf_size);
        u32 data_size = SUBBUF_OFFSET(offset - 1, buf->chan) + 1;

        header->data_size = data_size;
        header->sb_size = PAGE_ALIGN(data_size);
        header->cycle_count_end = tsc;
        header->events_lost = uatomic_read(&buf->events_lost);
        header->subbuf_corrupt = uatomic_read(&buf->corrupted_subbuffers);
        if(unlikely(header->events_lost > 0)) {
                DBG("Some events (%d) were lost in %s_%d", header->events_lost, buf->chan->channel_name, buf->cpu);
        }
}

/*
 * 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)
{
}

/*
 * Promote compiler barrier to a smp_mb().
 * For the specific LTTng case, this IPI call should be removed if the
 * architecture does not reorder writes.  This should eventually be provided by
 * a separate architecture-specific infrastructure.
 */
//ust// static void remote_mb(void *info)
//ust// {
//ust//         smp_mb();
//ust// }

int ust_buffers_get_subbuf(struct ust_buffer *buf, long *consumed)
{
        struct ust_channel *channel = buf->chan;
        long consumed_old, consumed_idx, commit_count, write_offset;
//ust// int retval;

        consumed_old = uatomic_read(&buf->consumed);
        consumed_idx = SUBBUF_INDEX(consumed_old, buf->chan);
        commit_count = uatomic_read(&buf->commit_count[consumed_idx].cc_sb);
        /*
         * 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_call_function_single can fail if the remote CPU is offline,
         * this is OK because then there is no wmb to execute there.
         * If our thread is executing on the same CPU as the on the buffers
         * belongs to, we don't have to synchronize it at all. If we are
         * migrated, the scheduler will take care of the memory barriers.
         * Normally, smp_call_function_single() should ensure program order when
         * executing the remote function, which implies that it surrounds the
         * function execution with :
         * smp_mb()
         * send IPI
         * csd_lock_wait
         *                recv IPI
         *                smp_mb()
         *                exec. function
         *                smp_mb()
         *                csd unlock
         * smp_mb()
         *
         * However, smp_call_function_single() does not seem to clearly execute
         * such barriers. It depends on spinlock semantic to provide the barrier
         * before executing the IPI and, when busy-looping, csd_lock_wait only
         * executes smp_mb() when it has to wait for the other CPU.
         *
         * I don't trust this code. Therefore, let's add the smp_mb() sequence
         * required ourself, even if duplicated. It has no performance impact
         * anyway.
         *
         * smp_mb() is needed because smp_rmb() and smp_wmb() only order read vs
         * read and write vs write. They do not ensure core synchronization. We
         * really have to ensure total order between the 3 barriers running on
         * the 2 CPUs.
         */
//ust// #ifdef LTT_NO_IPI_BARRIER
        /*
         * Local rmb to match the remote wmb to read the commit count before the
         * buffer data and the write offset.
         */
        smp_rmb();
//ust// #else
//ust//         if (raw_smp_processor_id() != buf->cpu) {
//ust//                 smp_mb();       /* Total order with IPI handler smp_mb() */
//ust//                 smp_call_function_single(buf->cpu, remote_mb, NULL, 1);
//ust//                 smp_mb();       /* Total order with IPI handler smp_mb() */
//ust//         }
//ust// #endif

        write_offset = uatomic_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;
        }

        /* FIXME: is this ok to disable the reading feature? */
//ust// retval = update_read_sb_index(buf, consumed_idx);
//ust// if (retval)
//ust//         return retval;

        *consumed = consumed_old;

        return 0;
}

int ust_buffers_put_subbuf(struct ust_buffer *buf, unsigned long uconsumed_old)
{
        long consumed_new, consumed_old;

        consumed_old = uatomic_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 (uatomic_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;
}

//ust// static void switch_buffer(unsigned long data)
//ust// {
//ust//         struct ltt_channel_buf_struct *ltt_buf =
//ust//                 (struct ltt_channel_buf_struct *)data;
//ust//         struct rchan_buf *buf = ltt_buf->rbuf;
//ust//
//ust//         if (buf)
//ust//                 ltt_force_switch(buf, FORCE_ACTIVE);
//ust//
//ust//         ltt_buf->switch_timer.expires += ltt_buf->switch_timer_interval;
//ust//         add_timer_on(&ltt_buf->switch_timer, smp_processor_id());
//ust// }
//ust//
//ust// static void start_switch_timer(struct ltt_channel_struct *ltt_channel)
//ust// {
//ust//         struct rchan *rchan = ltt_channel->trans_channel_data;
//ust//         int cpu;
//ust//
//ust//         if (!ltt_channel->switch_timer_interval)
//ust//                 return;
//ust//
//ust//         // TODO : hotplug
//ust//         for_each_online_cpu(cpu) {
//ust//                 struct ltt_channel_buf_struct *ltt_buf;
//ust//                 struct rchan_buf *buf;
//ust//
//ust//                 buf = rchan->buf[cpu];
//ust//                 ltt_buf = buf->chan_private;
//ust//                 buf->random_access = 1;
//ust//                 ltt_buf->switch_timer_interval =
//ust//                         ltt_channel->switch_timer_interval;
//ust//                 init_timer(&ltt_buf->switch_timer);
//ust//                 ltt_buf->switch_timer.function = switch_buffer;
//ust//                 ltt_buf->switch_timer.expires = jiffies +
//ust//                                         ltt_buf->switch_timer_interval;
//ust//                 ltt_buf->switch_timer.data = (unsigned long)ltt_buf;
//ust//                 add_timer_on(&ltt_buf->switch_timer, cpu);
//ust//         }
//ust// }
//ust//
//ust// /*
//ust//  * Cannot use del_timer_sync with add_timer_on, so use an IPI to locally
//ust//  * delete the timer.
//ust//  */
//ust// static void stop_switch_timer_ipi(void *info)
//ust// {
//ust//         struct ltt_channel_buf_struct *ltt_buf =
//ust//                 (struct ltt_channel_buf_struct *)info;
//ust//
//ust//         del_timer(&ltt_buf->switch_timer);
//ust// }
//ust//
//ust// static void stop_switch_timer(struct ltt_channel_struct *ltt_channel)
//ust// {
//ust//         struct rchan *rchan = ltt_channel->trans_channel_data;
//ust//         int cpu;
//ust//
//ust//         if (!ltt_channel->switch_timer_interval)
//ust//                 return;
//ust//
//ust//         // TODO : hotplug
//ust//         for_each_online_cpu(cpu) {
//ust//                 struct ltt_channel_buf_struct *ltt_buf;
//ust//                 struct rchan_buf *buf;
//ust//
//ust//                 buf = rchan->buf[cpu];
//ust//                 ltt_buf = buf->chan_private;
//ust//                 smp_call_function(stop_switch_timer_ipi, ltt_buf, 1);
//ust//                 buf->random_access = 0;
//ust//         }
//ust// }

//ust// static void ust_buffers_print_written(struct ust_channel *chan,
//ust//                 long cons_off, unsigned int cpu)
//ust// {
//ust//         struct ust_buffer *buf = chan->buf[cpu];
//ust//         long cons_idx, events_count;
//ust//
//ust//         cons_idx = SUBBUF_INDEX(cons_off, chan);
//ust//         events_count = uatomic_read(&buf->commit_count[cons_idx].events);
//ust//
//ust//         if (events_count)
//ust//                 printk(KERN_INFO
//ust//                         "channel %s: %lu events written (cpu %u, index %lu)\n",
//ust//                         chan->channel_name, events_count, cpu, cons_idx);
//ust// }

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, commit_count_sb, write_offset;

        cons_idx = SUBBUF_INDEX(cons_off, channel);
        commit_count = uatomic_read(&ltt_buf->commit_count[cons_idx].cc);
        commit_count_sb = uatomic_read(&ltt_buf->commit_count[cons_idx].cc_sb);

        /*
         * 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 = uatomic_read(&ltt_buf->offset);
        WARN( "LTT : unread channel %s offset is %ld "
                "and cons_off : %ld (cpu %d)\n",
                channel->channel_name, write_offset, cons_off, cpu);
        /* 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 [cc, cc_sb] [%lu,%lu].\n",
                        channel->channel_name, cons_idx, commit_count, commit_count_sb);
        }
        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 ust_trace *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;

//ust// for (cons_off = 0; cons_off < rchan->alloc_size;
//ust//      cons_off = SUBBUF_ALIGN(cons_off, rchan))
//ust//         ust_buffers_print_written(ltt_chan, cons_off, cpu);
        for (cons_off = uatomic_read(&ltt_buf->consumed);
                        (SUBBUF_TRUNC(uatomic_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 ust_trace *trace = channel->trace;
        struct ust_buffer *ltt_buf = channel->buf[cpu];

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

        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 ust_trace *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//         uatomic_set(&ltt_buf->offset, ltt_subbuffer_header_size());
//ust//         uatomic_set(&ltt_buf->consumed, 0);
//ust//         uatomic_set(&ltt_buf->active_readers, 0);
//ust//         for (j = 0; j < n_subbufs; j++)
//ust//                 uatomic_set(&ltt_buf->commit_count[j], 0);
//ust//         init_waitqueue_head(&ltt_buf->write_wait);
//ust//         uatomic_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//         uatomic_add(&ltt_buf->commit_count[0], ltt_subbuffer_header_size());
//ust//
//ust//         uatomic_set(&ltt_buf->events_lost, 0);
//ust//         uatomic_set(&ltt_buf->corrupted_subbuffers, 0);
//ust//
//ust//         return 0;
//ust// }

static int ust_buffers_init_buffer(struct ust_trace *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);
        uatomic_set(&buf->offset, ltt_subbuffer_header_size());
        uatomic_set(&buf->consumed, 0);
        uatomic_set(&buf->active_readers, 0);
        for (j = 0; j < n_subbufs; j++) {
                uatomic_set(&buf->commit_count[j].cc, 0);
                uatomic_set(&buf->commit_count[j].cc_sb, 0);
        }
//ust// init_waitqueue_head(&buf->write_wait);
//ust// uatomic_set(&buf->wakeup_readers, 0);
//ust// spin_lock_init(&buf->full_lock);

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

        uatomic_add(&buf->commit_count[0].cc, ltt_subbuffer_header_size());

        uatomic_set(&buf->events_lost, 0);
        uatomic_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// }
        memset(buf->commit_seq, 0, sizeof(buf->commit_seq[0]) * n_subbufs);

        /* 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 ust_trace *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 ust_trace *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->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 (uatomic_read(&ltt_buf->wakeup_readers) == 1) {
//ust//                 uatomic_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);
}

//ust// /*
//ust//  * Returns :
//ust//  * 0 if ok
//ust//  * !0 if execution must be aborted.
//ust//  */
//ust// static inline int ltt_relay_try_reserve(
//ust//                 struct ust_channel *channel, struct ust_buffer *buf,
//ust//                 struct ltt_reserve_switch_offsets *offsets, size_t data_size,
//ust//                 u64 *tsc, unsigned int *rflags, int largest_align)
//ust// {
//ust//         offsets->begin = uatomic_read(&buf->offset);
//ust//         offsets->old = offsets->begin;
//ust//         offsets->begin_switch = 0;
//ust//         offsets->end_switch_current = 0;
//ust//         offsets->end_switch_old = 0;
//ust//
//ust//         *tsc = trace_clock_read64();
//ust//         if (last_tsc_overflow(buf, *tsc))
//ust//                 *rflags = LTT_RFLAG_ID_SIZE_TSC;
//ust//
//ust//         if (SUBBUF_OFFSET(offsets->begin, buf->chan) == 0) {
//ust//                 offsets->begin_switch = 1;              /* For offsets->begin */
//ust//         } else {
//ust//                 offsets->size = ust_get_header_size(channel,
//ust//                                         offsets->begin, data_size,
//ust//                                         &offsets->before_hdr_pad, *rflags);
//ust//                 offsets->size += ltt_align(offsets->begin + offsets->size,
//ust//                                            largest_align)
//ust//                                  + data_size;
//ust//                 if ((SUBBUF_OFFSET(offsets->begin, buf->chan) + offsets->size)
//ust//                                 > buf->chan->subbuf_size) {
//ust//                         offsets->end_switch_old = 1;    /* For offsets->old */
//ust//                         offsets->begin_switch = 1;      /* For offsets->begin */
//ust//                 }
//ust//         }
//ust//         if (offsets->begin_switch) {
//ust//                 long subbuf_index;
//ust//
//ust//                 if (offsets->end_switch_old)
//ust//                         offsets->begin = SUBBUF_ALIGN(offsets->begin,
//ust//                                                       buf->chan);
//ust//                 offsets->begin = offsets->begin + ltt_subbuffer_header_size();
//ust//                 /* Test new buffer integrity */
//ust//                 subbuf_index = SUBBUF_INDEX(offsets->begin, buf->chan);
//ust//                 offsets->reserve_commit_diff =
//ust//                         (BUFFER_TRUNC(offsets->begin, buf->chan)
//ust//                          >> channel->n_subbufs_order)
//ust//                         - (uatomic_read(&buf->commit_count[subbuf_index])
//ust//                                 & channel->commit_count_mask);
//ust//                 if (offsets->reserve_commit_diff == 0) {
//ust//                         long consumed;
//ust//
//ust//                         consumed = uatomic_read(&buf->consumed);
//ust//
//ust//                         /* Next buffer not corrupted. */
//ust//                         if (!channel->overwrite &&
//ust//                                 (SUBBUF_TRUNC(offsets->begin, buf->chan)
//ust//                                  - SUBBUF_TRUNC(consumed, buf->chan))
//ust//                                 >= channel->alloc_size) {
//ust//
//ust//                                 long consumed_idx = SUBBUF_INDEX(consumed, buf->chan);
//ust//                                 long commit_count = uatomic_read(&buf->commit_count[consumed_idx]);
//ust//                                 if(((commit_count - buf->chan->subbuf_size) & channel->commit_count_mask) - (BUFFER_TRUNC(consumed, buf->chan) >> channel->n_subbufs_order) != 0) {
//ust//                                         WARN("Event dropped. Caused by non-committed event.");
//ust//                                 }
//ust//                                 else {
//ust//                                         WARN("Event dropped. Caused by non-consumed buffer.");
//ust//                                 }
//ust//                                 /*
//ust//                                  * We do not overwrite non consumed buffers
//ust//                                  * and we are full : event is lost.
//ust//                                  */
//ust//                                 uatomic_inc(&buf->events_lost);
//ust//                                 return -1;
//ust//                         } else {
//ust//                                 /*
//ust//                                  * next buffer not corrupted, we are either in
//ust//                                  * overwrite mode or the buffer is not full.
//ust//                                  * It's safe to write in this new subbuffer.
//ust//                                  */
//ust//                         }
//ust//                 } else {
//ust//                         /*
//ust//                          * Next subbuffer corrupted. Force pushing reader even
//ust//                          * in normal mode. It's safe to write in this new
//ust//                          * subbuffer.
//ust//                          */
//ust//                 }
//ust//                 offsets->size = ust_get_header_size(channel,
//ust//                                         offsets->begin, data_size,
//ust//                                         &offsets->before_hdr_pad, *rflags);
//ust//                 offsets->size += ltt_align(offsets->begin + offsets->size,
//ust//                                            largest_align)
//ust//                                  + data_size;
//ust//                 if ((SUBBUF_OFFSET(offsets->begin, buf->chan) + offsets->size)
//ust//                                 > buf->chan->subbuf_size) {
//ust//                         /*
//ust//                          * Event too big for subbuffers, report error, don't
//ust//                          * complete the sub-buffer switch.
//ust//                          */
//ust//                         uatomic_inc(&buf->events_lost);
//ust//                         return -1;
//ust//                 } else {
//ust//                         /*
//ust//                          * We just made a successful buffer switch and the event
//ust//                          * fits in the new subbuffer. Let's write.
//ust//                          */
//ust//                 }
//ust//         } else {
//ust//                 /*
//ust//                  * Event fits in the current buffer and we are not on a switch
//ust//                  * boundary. It's safe to write.
//ust//                  */
//ust//         }
//ust//         offsets->end = offsets->begin + offsets->size;
//ust//
//ust//         if ((SUBBUF_OFFSET(offsets->end, buf->chan)) == 0) {
//ust//                 /*
//ust//                  * The offset_end will fall at the very beginning of the next
//ust//                  * subbuffer.
//ust//                  */
//ust//                 offsets->end_switch_current = 1;        /* For offsets->begin */
//ust//         }
//ust//         return 0;
//ust// }
//ust//
//ust// /*
//ust//  * Returns :
//ust//  * 0 if ok
//ust//  * !0 if execution must be aborted.
//ust//  */
//ust// static inline int ltt_relay_try_switch(
//ust//                 enum force_switch_mode mode,
//ust//                 struct ust_channel *channel,
//ust//                 struct ust_buffer *buf,
//ust//                 struct ltt_reserve_switch_offsets *offsets,
//ust//                 u64 *tsc)
//ust// {
//ust//         long subbuf_index;
//ust//
//ust//         offsets->begin = uatomic_read(&buf->offset);
//ust//         offsets->old = offsets->begin;
//ust//         offsets->begin_switch = 0;
//ust//         offsets->end_switch_old = 0;
//ust//
//ust//         *tsc = trace_clock_read64();
//ust//
//ust//         if (SUBBUF_OFFSET(offsets->begin, buf->chan) != 0) {
//ust//                 offsets->begin = SUBBUF_ALIGN(offsets->begin, buf->chan);
//ust//                 offsets->end_switch_old = 1;
//ust//         } else {
//ust//                 /* we do not have to switch : buffer is empty */
//ust//                 return -1;
//ust//         }
//ust//         if (mode == FORCE_ACTIVE)
//ust//                 offsets->begin += ltt_subbuffer_header_size();
//ust//         /*
//ust//          * Always begin_switch in FORCE_ACTIVE mode.
//ust//          * Test new buffer integrity
//ust//          */
//ust//         subbuf_index = SUBBUF_INDEX(offsets->begin, buf->chan);
//ust//         offsets->reserve_commit_diff =
//ust//                 (BUFFER_TRUNC(offsets->begin, buf->chan)
//ust//                  >> channel->n_subbufs_order)
//ust//                 - (uatomic_read(&buf->commit_count[subbuf_index])
//ust//                         & channel->commit_count_mask);
//ust//         if (offsets->reserve_commit_diff == 0) {
//ust//                 /* Next buffer not corrupted. */
//ust//                 if (mode == FORCE_ACTIVE
//ust//                     && !channel->overwrite
//ust//                     && offsets->begin - uatomic_read(&buf->consumed)
//ust//                        >= channel->alloc_size) {
//ust//                         /*
//ust//                          * We do not overwrite non consumed buffers and we are
//ust//                          * full : ignore switch while tracing is active.
//ust//                          */
//ust//                         return -1;
//ust//                 }
//ust//         } else {
//ust//                 /*
//ust//                  * Next subbuffer corrupted. Force pushing reader even in normal
//ust//                  * mode
//ust//                  */
//ust//         }
//ust//         offsets->end = offsets->begin;
//ust//         return 0;
//ust// }
//ust//
//ust// static inline void ltt_reserve_push_reader(
//ust//                 struct ust_channel *channel,
//ust//                 struct ust_buffer *buf,
//ust//                 struct ltt_reserve_switch_offsets *offsets)
//ust// {
//ust//         long consumed_old, consumed_new;
//ust//
//ust//         do {
//ust//                 consumed_old = uatomic_read(&buf->consumed);
//ust//                 /*
//ust//                  * If buffer is in overwrite mode, push the reader consumed
//ust//                  * count if the write position has reached it and we are not
//ust//                  * at the first iteration (don't push the reader farther than
//ust//                  * the writer). This operation can be done concurrently by many
//ust//                  * writers in the same buffer, the writer being at the farthest
//ust//                  * write position sub-buffer index in the buffer being the one
//ust//                  * which will win this loop.
//ust//                  * If the buffer is not in overwrite mode, pushing the reader
//ust//                  * only happens if a sub-buffer is corrupted.
//ust//                  */
//ust//                 if ((SUBBUF_TRUNC(offsets->end-1, buf->chan)
//ust//                    - SUBBUF_TRUNC(consumed_old, buf->chan))
//ust//                    >= channel->alloc_size)
//ust//                         consumed_new = SUBBUF_ALIGN(consumed_old, buf->chan);
//ust//                 else {
//ust//                         consumed_new = consumed_old;
//ust//                         break;
//ust//                 }
//ust//         } while (uatomic_cmpxchg(&buf->consumed, consumed_old,
//ust//                         consumed_new) != consumed_old);
//ust//
//ust//         if (consumed_old != consumed_new) {
//ust//                 /*
//ust//                  * Reader pushed : we are the winner of the push, we can
//ust//                  * therefore reequilibrate reserve and commit. Atomic increment
//ust//                  * of the commit count permits other writers to play around
//ust//                  * with this variable before us. We keep track of
//ust//                  * corrupted_subbuffers even in overwrite mode :
//ust//                  * we never want to write over a non completely committed
//ust//                  * sub-buffer : possible causes : the buffer size is too low
//ust//                  * compared to the unordered data input, or there is a writer
//ust//                  * that died between the reserve and the commit.
//ust//                  */
//ust//                 if (offsets->reserve_commit_diff) {
//ust//                         /*
//ust//                          * We have to alter the sub-buffer commit count.
//ust//                          * We do not deliver the previous subbuffer, given it
//ust//                          * was either corrupted or not consumed (overwrite
//ust//                          * mode).
//ust//                          */
//ust//                         uatomic_add(&buf->commit_count[SUBBUF_INDEX(offsets->begin, buf->chan)],
//ust//                                 offsets->reserve_commit_diff);
//ust//                         if (!channel->overwrite
//ust//                             || offsets->reserve_commit_diff
//ust//                                != channel->subbuf_size) {
//ust//                                 /*
//ust//                                  * The reserve commit diff was not subbuf_size :
//ust//                                  * it means the subbuffer was partly written to
//ust//                                  * and is therefore corrupted. If it is multiple
//ust//                                  * of subbuffer size and we are in flight
//ust//                                  * recorder mode, we are skipping over a whole
//ust//                                  * subbuffer.
//ust//                                  */
//ust//                                 uatomic_inc(&buf->corrupted_subbuffers);
//ust//                         }
//ust//                 }
//ust//         }
//ust// }
//ust//
//ust// /**
//ust//  * ltt_relay_reserve_slot - Atomic slot reservation in a LTTng buffer.
//ust//  * @trace: the trace structure to log to.
//ust//  * @ltt_channel: channel structure
//ust//  * @transport_data: data structure specific to ltt relay
//ust//  * @data_size: size of the variable length data to log.
//ust//  * @slot_size: pointer to total size of the slot (out)
//ust//  * @buf_offset : pointer to reserved buffer offset (out)
//ust//  * @tsc: pointer to the tsc at the slot reservation (out)
//ust//  * @cpu: cpuid
//ust//  *
//ust//  * Return : -ENOSPC if not enough space, else returns 0.
//ust//  * It will take care of sub-buffer switching.
//ust//  */
//ust// static notrace int ltt_relay_reserve_slot(struct ust_trace *trace,
//ust//                 struct ust_channel *channel, void **transport_data,
//ust//                 size_t data_size, size_t *slot_size, long *buf_offset, u64 *tsc,
//ust//                 unsigned int *rflags, int largest_align, int cpu)
//ust// {
//ust//         struct ust_buffer *buf = *transport_data = channel->buf[cpu];
//ust//         struct ltt_reserve_switch_offsets offsets;
//ust//
//ust//         offsets.reserve_commit_diff = 0;
//ust//         offsets.size = 0;
//ust//
//ust//         /*
//ust//          * Perform retryable operations.
//ust//          */
//ust//         if (ltt_nesting > 4) {
//ust//                 uatomic_inc(&buf->events_lost);
//ust//                 return -EPERM;
//ust//         }
//ust//         do {
//ust//                 if (ltt_relay_try_reserve(channel, buf, &offsets, data_size, tsc, rflags,
//ust//                                 largest_align))
//ust//                         return -ENOSPC;
//ust//         } while (uatomic_cmpxchg(&buf->offset, offsets.old,
//ust//                         offsets.end) != offsets.old);
//ust//
//ust//         /*
//ust//          * Atomically update last_tsc. This update races against concurrent
//ust//          * atomic updates, but the race will always cause supplementary full TSC
//ust//          * events, never the opposite (missing a full TSC event when it would be
//ust//          * needed).
//ust//          */
//ust//         save_last_tsc(buf, *tsc);
//ust//
//ust//         /*
//ust//          * Push the reader if necessary
//ust//          */
//ust//         ltt_reserve_push_reader(channel, buf, &offsets);
//ust//
//ust//         /*
//ust//          * Switch old subbuffer if needed.
//ust//          */
//ust//         if (offsets.end_switch_old)
//ust//                 ltt_reserve_switch_old_subbuf(channel, buf, &offsets, tsc);
//ust//
//ust//         /*
//ust//          * Populate new subbuffer.
//ust//          */
//ust//         if (offsets.begin_switch)
//ust//                 ltt_reserve_switch_new_subbuf(channel, buf, &offsets, tsc);
//ust//
//ust//         if (offsets.end_switch_current)
//ust//                 ltt_reserve_end_switch_current(channel, buf, &offsets, tsc);
//ust//
//ust//         *slot_size = offsets.size;
//ust//         *buf_offset = offsets.begin + offsets.before_hdr_pad;
//ust//         return 0;
//ust// }
//ust//
//ust// /*
//ust//  * Force a sub-buffer switch for a per-cpu buffer. This operation is
//ust//  * completely reentrant : can be called while tracing is active with
//ust//  * absolutely no lock held.
//ust//  */
//ust// static notrace void ltt_force_switch(struct ust_buffer *buf,
//ust//                 enum force_switch_mode mode)
//ust// {
//ust//         struct ust_channel *channel = buf->chan;
//ust//         struct ltt_reserve_switch_offsets offsets;
//ust//         u64 tsc;
//ust//
//ust//         offsets.reserve_commit_diff = 0;
//ust//         offsets.size = 0;
//ust//
//ust//         /*
//ust//          * Perform retryable operations.
//ust//          */
//ust//         do {
//ust//                 if (ltt_relay_try_switch(mode, channel, buf, &offsets, &tsc))
//ust//                         return;
//ust//         } while (uatomic_cmpxchg(&buf->offset, offsets.old,
//ust//                         offsets.end) != offsets.old);
//ust//
//ust//         /*
//ust//          * Atomically update last_tsc. This update races against concurrent
//ust//          * atomic updates, but the race will always cause supplementary full TSC
//ust//          * events, never the opposite (missing a full TSC event when it would be
//ust//          * needed).
//ust//          */
//ust//         save_last_tsc(buf, tsc);
//ust//
//ust//         /*
//ust//          * Push the reader if necessary
//ust//          */
//ust//         if (mode == FORCE_ACTIVE)
//ust//                 ltt_reserve_push_reader(channel, buf, &offsets);
//ust//
//ust//         /*
//ust//          * Switch old subbuffer if needed.
//ust//          */
//ust//         if (offsets.end_switch_old)
//ust//                 ltt_reserve_switch_old_subbuf(channel, buf, &offsets, &tsc);
//ust//
//ust//         /*
//ust//          * Populate new subbuffer.
//ust//          */
//ust//         if (mode == FORCE_ACTIVE)
//ust//                 ltt_reserve_switch_new_subbuf(channel, buf, &offsets, &tsc);
//ust// }

/*
 * 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 void ltt_reserve_switch_old_subbuf(
                struct ust_channel *chan, struct ust_buffer *buf,
                struct ltt_reserve_switch_offsets *offsets, u64 *tsc)
{
        long oldidx = SUBBUF_INDEX(offsets->old - 1, chan);
        long commit_count, padding_size;

        padding_size = chan->subbuf_size
                        - (SUBBUF_OFFSET(offsets->old - 1, chan) + 1);
        ltt_buffer_end(buf, *tsc, offsets->old, oldidx);

        /*
         * Must write slot data before incrementing commit count.
         * This compiler barrier is upgraded into a smp_wmb() by the IPI
         * sent by get_subbuf() when it does its smp_rmb().
         */
        barrier();
        uatomic_add(&buf->commit_count[oldidx].cc, padding_size);
        commit_count = uatomic_read(&buf->commit_count[oldidx].cc);
        ltt_check_deliver(chan, buf, offsets->old - 1, commit_count, oldidx);
        ltt_write_commit_counter(chan, buf, oldidx,
                offsets->old, commit_count, padding_size);
}

/*
 * 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 void ltt_reserve_switch_new_subbuf(
                struct ust_channel *chan, struct ust_buffer *buf,
                struct ltt_reserve_switch_offsets *offsets, u64 *tsc)
{
        long beginidx = SUBBUF_INDEX(offsets->begin, chan);
        long commit_count;

        ltt_buffer_begin(buf, *tsc, beginidx);

        /*
         * Must write slot data before incrementing commit count.
         * This compiler barrier is upgraded into a smp_wmb() by the IPI
         * sent by get_subbuf() when it does its smp_rmb().
         */
        barrier();
        uatomic_add(&buf->commit_count[beginidx].cc, ltt_subbuffer_header_size());
        commit_count = uatomic_read(&buf->commit_count[beginidx].cc);
        /* Check if the written buffer has to be delivered */
        ltt_check_deliver(chan, buf, offsets->begin, commit_count, beginidx);
        ltt_write_commit_counter(chan, buf, beginidx,
                offsets->begin, commit_count, ltt_subbuffer_header_size());
}

/*
 * 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 void ltt_reserve_end_switch_current(
                struct ust_channel *chan,
                struct ust_buffer *buf,
                struct ltt_reserve_switch_offsets *offsets, u64 *tsc)
{
        long endidx = SUBBUF_INDEX(offsets->end - 1, chan);
        long commit_count, padding_size;

        padding_size = chan->subbuf_size
                        - (SUBBUF_OFFSET(offsets->end - 1, chan) + 1);

        ltt_buffer_end(buf, *tsc, offsets->end, endidx);

        /*
         * Must write slot data before incrementing commit count.
         * This compiler barrier is upgraded into a smp_wmb() by the IPI
         * sent by get_subbuf() when it does its smp_rmb().
         */
        barrier();
        uatomic_add(&buf->commit_count[endidx].cc, padding_size);
        commit_count = uatomic_read(&buf->commit_count[endidx].cc);
        ltt_check_deliver(chan, buf,
                offsets->end - 1, commit_count, endidx);
        ltt_write_commit_counter(chan, buf, endidx,
                offsets->end, commit_count, padding_size);
}

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

        offsets->begin = uatomic_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);
        reserve_commit_diff =
                (BUFFER_TRUNC(offsets->begin, buf->chan)
                 >> chan->n_subbufs_order)
                - (uatomic_read(&buf->commit_count[subbuf_index].cc_sb)
                        & chan->commit_count_mask);
        if (reserve_commit_diff == 0) {
                /* Next buffer not corrupted. */
                if (mode == FORCE_ACTIVE
                    && !chan->overwrite
                    && offsets->begin - uatomic_read(&buf->consumed)
                       >= chan->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;
}

/*
 * 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.
 */
void ltt_force_switch_lockless_slow(struct ust_buffer *buf,
                enum force_switch_mode mode)
{
        struct ust_channel *chan = buf->chan;
        struct ltt_reserve_switch_offsets offsets;
        u64 tsc;

        offsets.size = 0;

        DBG("Switching (forced) %s_%d", chan->channel_name, buf->cpu);
        /*
         * Perform retryable operations.
         */
        do {
                if (ltt_relay_try_switch_slow(mode, chan, buf,
                                &offsets, &tsc))
                        return;
        } while (uatomic_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(chan, buf, offsets.end - 1);
//ust//         ltt_clear_noref_flag(chan, buf, SUBBUF_INDEX(offsets.end - 1, chan));
        }

        /*
         * Switch old subbuffer if needed.
         */
        if (offsets.end_switch_old) {
//ust//         ltt_clear_noref_flag(rchan, buf, SUBBUF_INDEX(offsets.old - 1, rchan));
                ltt_reserve_switch_old_subbuf(chan, buf, &offsets, &tsc);
        }

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

/*
 * Returns :
 * 0 if ok
 * !0 if execution must be aborted.
 */
static int ltt_relay_try_reserve_slow(struct ust_channel *chan, struct ust_buffer *buf,
                struct ltt_reserve_switch_offsets *offsets, size_t data_size,
                u64 *tsc, unsigned int *rflags, int largest_align)
{
        long reserve_commit_diff;

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

                /*
                 * We are typically not filling the previous buffer completely.
                 */
                if (likely(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);
                reserve_commit_diff =
                  (BUFFER_TRUNC(offsets->begin, buf->chan)
                   >> chan->n_subbufs_order)
                  - (uatomic_read(&buf->commit_count[subbuf_index].cc_sb)
                                & chan->commit_count_mask);
                if (likely(reserve_commit_diff == 0)) {
                        /* Next buffer not corrupted. */
                        if (unlikely(!chan->overwrite &&
                                (SUBBUF_TRUNC(offsets->begin, buf->chan)
                                 - SUBBUF_TRUNC(uatomic_read(
                                                        &buf->consumed),
                                                buf->chan))
                                >= chan->alloc_size)) {
                                /*
                                 * We do not overwrite non consumed buffers
                                 * and we are full : event is lost.
                                 */
                                uatomic_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. Drop event in normal and
                         * overwrite mode. Caused by either a writer OOPS or
                         * too many nested writes over a reserve/commit pair.
                         */
                        uatomic_inc(&buf->events_lost);
                        return -1;
                }
                offsets->size = ust_get_header_size(chan,
                                        offsets->begin, data_size,
                                        &offsets->before_hdr_pad, *rflags);
                offsets->size += ltt_align(offsets->begin + offsets->size,
                                           largest_align)
                                 + data_size;
                if (unlikely((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.
                         */
                        uatomic_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 (unlikely((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;
}

/**
 * ltt_relay_reserve_slot_lockless_slow - Atomic slot reservation in a 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.
 */
int ltt_reserve_slot_lockless_slow(struct ust_trace *trace,
                struct ust_channel *chan, 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 = chan->buf[cpu];
        struct ltt_reserve_switch_offsets offsets;

        offsets.size = 0;

        do {
                if (unlikely(ltt_relay_try_reserve_slow(chan, buf, &offsets,
                                data_size, tsc, rflags, largest_align)))
                        return -ENOSPC;
        } while (unlikely(uatomic_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(chan, buf, offsets.end - 1);

        /*
         * Clear noref flag for this subbuffer.
         */
//ust// ltt_clear_noref_flag(chan, buf, SUBBUF_INDEX(offsets.end - 1, chan));

        /*
         * Switch old subbuffer if needed.
         */
        if (unlikely(offsets.end_switch_old)) {
//ust//         ltt_clear_noref_flag(chan, buf, SUBBUF_INDEX(offsets.old - 1, chan));
                ltt_reserve_switch_old_subbuf(chan, buf, &offsets, tsc);
                DBG("Switching %s_%d", chan->channel_name, cpu);
        }

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

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

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

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,
        },
};

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)) ust_buffers_exit(void)
{
        ltt_transport_unregister(&ust_relay_transport);
}

size_t ltt_write_event_header_slow(struct ust_trace *trace,
                struct ust_channel *channel,
                struct ust_buffer *buf, long buf_offset,
                u16 eID, u32 event_size,
                u64 tsc, unsigned int rflags)
{
        struct ltt_event_header header;
        u16 small_size;

        switch (rflags) {
        case LTT_RFLAG_ID_SIZE_TSC:
                header.id_time = 29 << LTT_TSC_BITS;
                break;
        case LTT_RFLAG_ID_SIZE:
                header.id_time = 30 << LTT_TSC_BITS;
                break;
        case LTT_RFLAG_ID:
                header.id_time = 31 << LTT_TSC_BITS;
                break;
        }

        header.id_time |= (u32)tsc & LTT_TSC_MASK;
        ust_buffers_write(buf, buf_offset, &header, sizeof(header));
        buf_offset += sizeof(header);

        switch (rflags) {
        case LTT_RFLAG_ID_SIZE_TSC:
                small_size = (u16)min_t(u32, event_size, LTT_MAX_SMALL_SIZE);
                ust_buffers_write(buf, buf_offset,
                        &eID, sizeof(u16));
                buf_offset += sizeof(u16);
                ust_buffers_write(buf, buf_offset,
                        &small_size, sizeof(u16));
                buf_offset += sizeof(u16);
                if (small_size == LTT_MAX_SMALL_SIZE) {
                        ust_buffers_write(buf, buf_offset,
                                &event_size, sizeof(u32));
                        buf_offset += sizeof(u32);
                }
                buf_offset += ltt_align(buf_offset, sizeof(u64));
                ust_buffers_write(buf, buf_offset,
                        &tsc, sizeof(u64));
                buf_offset += sizeof(u64);
                break;
        case LTT_RFLAG_ID_SIZE:
                small_size = (u16)min_t(u32, event_size, LTT_MAX_SMALL_SIZE);
                ust_buffers_write(buf, buf_offset,
                        &eID, sizeof(u16));
                buf_offset += sizeof(u16);
                ust_buffers_write(buf, buf_offset,
                        &small_size, sizeof(u16));
                buf_offset += sizeof(u16);
                if (small_size == LTT_MAX_SMALL_SIZE) {
                        ust_buffers_write(buf, buf_offset,
                                &event_size, sizeof(u32));
                        buf_offset += sizeof(u32);
                }
                break;
        case LTT_RFLAG_ID:
                ust_buffers_write(buf, buf_offset,
                        &eID, sizeof(u16));
                buf_offset += sizeof(u16);
                break;
        }

        return buf_offset;
}