Date:	Fri, 24 Nov 2006 17:02:29 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tom Zanussi <zanussi@...ibm.com>,
	Karim Yaghmour <karim@...rsys.com>,
	Paul Mundt <lethal@...ux-sh.org>, Jes Sorensen <jes@....com>,
	Richard J Moore <richardj_moore@...ibm.com>,
	"Martin J. Bligh" <mbligh@...igh.org>,
	Michel Dagenais <michel.dagenais@...ymtl.ca>,
	Douglas Niehaus <niehaus@...s.ku.edu>, ltt-dev@...fik.org,
	systemtap@...rces.redhat.com
Subject: [PATCH 13/16] LTTng 0.6.36 for 2.6.18 : Relay transport

Transport through Relay and DebugFS.

patch13-2.6.18-lttng-core-0.6.36-transport.diff

Signed-off-by : Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>

--BEGIN--
--- /dev/null
+++ b/ltt/ltt-relay.c
@@ -0,0 +1,1274 @@
+/*
+ * ltt-relay.c
+ *
+ * (C) Copyright 2005-2006 - Mathieu Desnoyers (mathieu.desnoyers@...ymtl.ca)
+ *
+ * Contains the kernel code for the Linux Trace Toolkit.
+ *
+ * Author:
+ *	Mathieu Desnoyers (mathieu.desnoyers@...ymtl.ca)
+ *
+ * Inspired from LTT :
+ *	Karim Yaghmour (karim@...rsys.com)
+ *	Tom Zanussi (zanussi@...ibm.com)
+ *	Bob Wisniewski (bob@...son.ibm.com)
+ * And from K42 :
+ *  Bob Wisniewski (bob@...son.ibm.com)
+ *
+ * Changelog:
+ *  19/10/05, Complete lockless mechanism. (Mathieu Desnoyers)
+ *	27/05/05, Modular redesign and rewrite. (Mathieu Desnoyers)
+
+ * Comments :
+ * num_active_traces protects the functors. Changing the pointer is an atomic
+ * operation, but the functions can only be called when in tracing. It is then
+ * safe to unload a module in which sits a functor when no tracing is active.
+ *
+ * filter_control functor is protected by incrementing its module refcount.
+ *
+ */
+
+#include <linux/config.h>
+#include <linux/time.h>
+#include <ltt/ltt-tracer.h>
+#include <linux/relay.h>
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/ltt-facilities.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+#include <linux/bitops.h>
+#include <linux/fs.h>
+#include <linux/smp_lock.h>
+#include <linux/debugfs.h>
+#include <linux/stat.h>
+#include <linux/cpu.h>
+#include <asm/atomic.h>
+#include <asm/atomic-up.h>
+
+static struct dentry *ltt_root_dentry;
+static struct file_operations ltt_file_operations;
+
+/* How a force_switch must be done ?
+ *
+ * Is it 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 int ltt_relay_create_buffer(struct ltt_trace_struct *trace,
+	struct ltt_channel_struct *ltt_chan,
+	struct rchan_buf *buf,
+	unsigned int cpu,
+	unsigned n_subbufs);
+
+static void ltt_relay_destroy_buffer(struct ltt_channel_struct *ltt_chan,
+		unsigned int cpu);
+
+/* Trace callbacks */
+
+static void ltt_buffer_begin_callback(struct rchan_buf *buf,
+			u64 tsc, unsigned int subbuf_idx)
+{
+	struct ltt_channel_struct *channel =
+		(struct ltt_channel_struct*)buf->chan->private_data;
+	struct ltt_block_start_header *header =
+		(struct ltt_block_start_header*)
+			(buf->start + (subbuf_idx*buf->chan->subbuf_size));
+
+	header->begin.cycle_count = tsc;
+	header->begin.freq = ltt_frequency();
+	header->lost_size = 0xFFFFFFFF; // for debugging...
+	header->buf_size = buf->chan->subbuf_size;
+	ltt_write_trace_header(channel->trace, &header->trace);
+}
+
+static void ltt_buffer_end_callback(struct rchan_buf *buf,
+			u64 tsc, unsigned int offset, unsigned int subbuf_idx)
+{
+	struct ltt_block_start_header *header =
+		(struct ltt_block_start_header*)
+			(buf->start + (subbuf_idx*buf->chan->subbuf_size));
+
+	/* offset is assumed to never be 0 here : never deliver a completely
+	 * empty subbuffer.
+	 * The lost size is between 0 and subbuf_size-1 */
+	header->lost_size = SUBBUF_OFFSET((buf->chan->subbuf_size - offset),
+				buf->chan);
+	header->end.cycle_count = tsc;
+	header->end.freq = ltt_frequency();
+}
+
+static int ltt_subbuf_start_callback(struct rchan_buf *buf,
+				void *subbuf,
+				void *prev_subbuf,
+				size_t prev_padding)
+{
+	return 0;
+}
+
+
+
+static void ltt_deliver(struct rchan_buf *buf,
+		unsigned subbuf_idx,
+		void *subbuf)
+{
+	struct ltt_channel_struct *channel =
+		(struct ltt_channel_struct*)buf->chan->private_data;
+	struct ltt_channel_buf_struct *ltt_buf = &channel->buf[buf->cpu];
+
+	atomic_set(&ltt_buf->wakeup_readers, 1);
+}
+
+static void ltt_buf_mapped_callback(struct rchan_buf *buf,
+		struct file *filp)
+{
+}
+
+static void ltt_buf_unmapped_callback(struct rchan_buf *buf,
+		struct file *filp)
+{
+}
+
+static struct dentry *ltt_create_buf_file_callback(const char *filename,
+				  struct dentry *parent,
+				  int mode,
+				  struct rchan_buf *buf,
+				  int *is_global)
+{
+	struct ltt_channel_struct *ltt_chan;
+	int err;
+	struct dentry *dentry;
+
+	ltt_chan = buf->chan->private_data;
+	err = ltt_relay_create_buffer(ltt_chan->trace, ltt_chan,
+					buf, buf->cpu,
+					buf->chan->n_subbufs);
+	if(err)
+		return ERR_PTR(err);
+
+	dentry = debugfs_create_file(filename, mode, parent, buf,
+			&ltt_file_operations);
+	if(!dentry)
+		goto error;
+	return dentry;
+error:
+	ltt_relay_destroy_buffer(ltt_chan, buf->cpu);
+	return NULL;
+}
+
+static int ltt_remove_buf_file_callback(struct dentry *dentry)
+{
+	struct rchan_buf *buf = dentry->d_inode->u.generic_ip;
+	struct ltt_channel_struct *ltt_chan = buf->chan->private_data;
+
+	debugfs_remove(dentry);
+	ltt_relay_destroy_buffer(ltt_chan, buf->cpu);
+
+	return 0;
+}
+
+/* This function should not be called from NMI interrupt context */
+static void ltt_buf_unfull(struct rchan_buf *buf,
+		unsigned subbuf_idx,
+		void *subbuf)
+{
+	struct ltt_channel_struct *ltt_channel =
+		(struct ltt_channel_struct*)buf->chan->private_data;
+	struct ltt_channel_buf_struct *ltt_buf = &ltt_channel->buf[buf->cpu];
+	if (waitqueue_active(&ltt_buf->write_wait))
+		schedule_work(&ltt_buf->wake_writers);
+}
+
+
+/**
+ *	ltt_poll - poll file op for ltt files
+ *	@filp: the file
+ *	@wait: poll table
+ *
+ *	Poll implemention.
+ */
+static unsigned int ltt_poll(struct file *filp, poll_table *wait)
+{
+	unsigned int mask = 0;
+	struct inode *inode = filp->f_dentry->d_inode;
+	struct rchan_buf *buf = inode->u.generic_ip;
+	struct ltt_channel_struct *ltt_channel =
+		(struct ltt_channel_struct*)buf->chan->private_data;
+	struct ltt_channel_buf_struct *ltt_buf = &ltt_channel->buf[buf->cpu];
+
+	//printk(KERN_DEBUG "DEBUG : in LTT poll %p\n", filp);
+	if (filp->f_mode & FMODE_READ) {
+		poll_wait(filp, &buf->read_wait, wait);
+
+		if (atomic_read(&ltt_buf->active_readers) != 0) {
+			return 0;
+		} else {
+			if (SUBBUF_TRUNC(
+				atomic_read(&ltt_buf->offset), buf->chan)
+			- SUBBUF_TRUNC(
+				atomic_read(&ltt_buf->consumed), buf->chan)
+			== 0) {
+				if (buf->finalized) return POLLHUP;
+				else return 0;
+			} else {
+				struct rchan *rchan =
+					ltt_channel->trans_channel_data;
+				if (SUBBUF_TRUNC(atomic_read(&ltt_buf->offset),
+						buf->chan)
+				- SUBBUF_TRUNC(atomic_read(&ltt_buf->consumed),
+							buf->chan)
+				>= rchan->alloc_size)
+					return POLLPRI | POLLRDBAND;
+				else
+					return POLLIN | POLLRDNORM;
+			}
+		}
+	}
+	return mask;
+}
+
+
+/**
+ *	ltt_ioctl - ioctl control on the debugfs file
+ *
+ *	@inode: the inode
+ *	@filp: the file
+ *	@cmd: the command
+ *	@arg: command arg
+ *
+ *	This ioctl implements three commands necessary for a minimal
+ *	producer/consumer implementation :
+ *	RELAY_GET_SUBBUF
+ *		Get the next sub buffer that can be read. It never blocks.
+ *	RELAY_PUT_SUBBUF
+ *		Release the currently read sub-buffer. Parameter is the last
+ *		put subbuffer (returned by GET_SUBBUF).
+ *	RELAY_GET_N_BUBBUFS
+ *		returns the number of sub buffers in the per cpu channel.
+ *	RELAY_GET_SUBBUF_SIZE
+ *		returns the size of the sub buffers.
+ *
+ */
+static int ltt_ioctl(struct inode *inode, struct file *filp,
+		unsigned int cmd, unsigned long arg)
+{
+	struct rchan_buf *buf = inode->u.generic_ip;
+	struct ltt_channel_struct *ltt_channel =
+		(struct ltt_channel_struct*)buf->chan->private_data;
+	struct ltt_channel_buf_struct *ltt_buf = &ltt_channel->buf[buf->cpu];
+	u32 __user *argp = (u32 __user *)arg;
+
+	switch (cmd) {
+		case RELAY_GET_SUBBUF:
+		{
+			unsigned int consumed_old, consumed_idx;
+			atomic_inc(&ltt_buf->active_readers);
+			consumed_old = atomic_read(&ltt_buf->consumed);
+			consumed_idx = SUBBUF_INDEX(consumed_old, buf->chan);
+			if (SUBBUF_OFFSET(
+				atomic_read(
+					&ltt_buf->commit_count[consumed_idx]),
+				buf->chan) != 0) {
+				atomic_dec(&ltt_buf->active_readers);
+				return -EAGAIN;
+			}
+			if ((SUBBUF_TRUNC(
+				atomic_read(&ltt_buf->offset), buf->chan)
+			- SUBBUF_TRUNC(consumed_old, buf->chan))
+			== 0) {
+				atomic_dec(&ltt_buf->active_readers);
+				return -EAGAIN;
+			}
+			smp_rmb();
+			//printk(KERN_DEBUG "LTT ioctl get subbuf %d\n",
+			//		consumed_old);
+			return put_user((u32)consumed_old, argp);
+			break;
+		}
+		case RELAY_PUT_SUBBUF:
+		{
+			u32 consumed_old;
+			int ret;
+			unsigned int consumed_new;
+
+			ret = get_user(consumed_old, argp);
+			if (ret)
+				return ret; /* will return -EFAULT */
+
+			//printk(KERN_DEBUG "LTT ioctl put subbuf %d\n",
+			//		consumed_old);
+			consumed_new = SUBBUF_ALIGN(consumed_old, buf->chan);
+			spin_lock(&ltt_buf->full_lock);
+			if (atomic_cmpxchg(
+				&ltt_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. */
+				atomic_dec(&ltt_buf->active_readers);
+				spin_unlock(&ltt_buf->full_lock);
+				return -EIO;
+			} else {
+				/* tell the client that buffer is now unfull */
+				int index;
+				void *data;
+				index = SUBBUF_INDEX(consumed_old, buf->chan);
+				data = buf->start +
+					BUFFER_OFFSET(consumed_old, buf->chan);
+				ltt_buf_unfull(buf, index, data);
+				atomic_dec(&ltt_buf->active_readers);
+				spin_unlock(&ltt_buf->full_lock);
+			}
+			break;
+		}
+		case RELAY_GET_N_SUBBUFS:
+			//printk(KERN_DEBUG "LTT ioctl get n subbufs\n");
+			return put_user((u32)buf->chan->n_subbufs, argp);
+			break;
+		case RELAY_GET_SUBBUF_SIZE:
+			//printk(KERN_DEBUG "LTT ioctl get subbuf size\n");
+			return put_user((u32)buf->chan->subbuf_size, argp);
+			break;
+		default:
+			return -ENOIOCTLCMD;
+	}
+	return 0;
+}
+
+#ifdef CONFIG_COMPAT
+
+static long ltt_compat_ioctl(struct file *file, unsigned cmd, unsigned long arg)
+{
+	long ret = -ENOIOCTLCMD;
+
+	lock_kernel();
+	ret = ltt_ioctl(file->f_dentry->d_inode, file, cmd, arg);
+	unlock_kernel();
+
+	return ret;
+}
+
+#endif //CONFIG_COMPAT
+
+static void ltt_relay_print_subbuffer_errors(struct ltt_channel_struct *ltt_chan,
+		int cons_off, unsigned int i)
+{
+	struct rchan *rchan = ltt_chan->trans_channel_data;
+	int cons_idx;
+
+	printk(KERN_WARNING
+		"LTT : unread channel %s offset is %d "
+		"and cons_off : %d (cpu %u)\n",
+		ltt_chan->channel_name,
+		atomic_read(&ltt_chan->buf[i].offset), cons_off, i);
+	/* Check each sub-buffer for non zero commit count */
+	cons_idx = SUBBUF_INDEX(cons_off, rchan);
+	if (SUBBUF_OFFSET(atomic_read(&ltt_chan->buf[i].commit_count[cons_idx]),
+				rchan))
+		printk(KERN_ALERT
+			"LTT : %s : subbuffer %u has non zero "
+			"commit count.\n",
+			ltt_chan->channel_name, cons_idx);
+	printk(KERN_ALERT "LTT : %s : commit count : %u, subbuf size %zd\n",
+			ltt_chan->channel_name,
+			atomic_read(&ltt_chan->buf[i].commit_count[cons_idx]),
+			rchan->subbuf_size);
+}
+
+static void ltt_relay_print_errors(struct ltt_trace_struct *trace,
+		struct ltt_channel_struct *ltt_chan, int cpu)
+{
+	struct rchan *rchan = ltt_chan->trans_channel_data;
+	int cons_off;
+
+	for (cons_off = atomic_read(&ltt_chan->buf[cpu].consumed);
+		(SUBBUF_TRUNC(atomic_read(&ltt_chan->buf[cpu].offset),
+				rchan)
+			- cons_off) > 0;
+		cons_off = SUBBUF_ALIGN(cons_off, rchan)) {
+		ltt_relay_print_subbuffer_errors(ltt_chan, cons_off, cpu);
+	}
+}
+
+static void ltt_relay_print_buffer_errors(struct ltt_channel_struct *ltt_chan,
+			unsigned int cpu)
+{
+	struct ltt_trace_struct *trace = ltt_chan->trace;
+	
+	if (atomic_read(&ltt_chan->buf[cpu].events_lost))
+		printk(KERN_ALERT 
+			"LTT : %s : %d events lost "
+			"in %s channel (cpu %u).\n",
+			ltt_chan->channel_name,
+			atomic_read(&ltt_chan->buf[cpu].events_lost),
+			ltt_chan->channel_name, cpu);
+	if (atomic_read(&ltt_chan->buf[cpu].corrupted_subbuffers))
+		printk(KERN_ALERT 
+			"LTT : %s : %d corrupted subbuffers "
+			"in %s channel (cpu %u).\n",
+			ltt_chan->channel_name,
+			atomic_read(
+				&ltt_chan->buf[cpu].corrupted_subbuffers),
+			ltt_chan->channel_name, cpu);
+
+	ltt_relay_print_errors(trace, ltt_chan, cpu);
+}
+
+static void ltt_relay_remove_dirs(struct ltt_trace_struct *trace)
+{
+	debugfs_remove(trace->dentry.control_root);
+	debugfs_remove(trace->dentry.trace_root);
+}
+
+static void ltt_relay_release_channel(struct kref *kref)
+{
+	struct ltt_channel_struct *ltt_chan = container_of(kref,
+			struct ltt_channel_struct, kref);
+	kfree(ltt_chan);
+}
+
+/* Create ltt buffer.
+ */
+static int ltt_relay_create_buffer(struct ltt_trace_struct *trace,
+	struct ltt_channel_struct *ltt_chan,
+	struct rchan_buf *buf,
+	unsigned int cpu,
+	unsigned n_subbufs)
+{
+	unsigned int j;
+
+	ltt_chan->buf[cpu].commit_count =
+		kmalloc(sizeof(atomic_t) * n_subbufs, GFP_KERNEL);
+	if (!ltt_chan->buf[cpu].commit_count)
+		return -ENOMEM;
+	kref_get(&trace->kref);
+	kref_get(&trace->ltt_transport_kref);
+	kref_get(&ltt_chan->kref);
+	atomic_set(&ltt_chan->buf[cpu].offset,
+		ltt_subbuf_header_len());
+	atomic_set(&ltt_chan->buf[cpu].consumed, 0);
+	atomic_set(&ltt_chan->buf[cpu].active_readers, 0);
+	for (j = 0; j < n_subbufs; j++)
+		atomic_set(&ltt_chan->buf[cpu].commit_count[j], 0);
+	init_waitqueue_head(&ltt_chan->buf[cpu].write_wait);
+	atomic_set(&ltt_chan->buf[cpu].wakeup_readers, 0);
+	INIT_WORK(&ltt_chan->buf[cpu].wake_writers,
+			ltt_wakeup_writers, &ltt_chan->buf[cpu]);
+	spin_lock_init(&ltt_chan->buf[cpu].full_lock);
+	
+	ltt_buffer_begin_callback(buf, trace->start_tsc, 0);
+	/* atomic_add made on atomic_up variable on data that belongs to
+	 * various CPUs : ok because tracing not started (for this cpu). */
+	atomic_add(ltt_subbuf_header_len(),
+		&ltt_chan->buf[cpu].commit_count[0]);
+
+	atomic_set(&ltt_chan->buf[cpu].events_lost, 0);
+	atomic_set(&ltt_chan->buf[cpu].corrupted_subbuffers, 0);
+
+	return 0;
+}
+
+static void ltt_relay_destroy_buffer(struct ltt_channel_struct *ltt_chan,
+					unsigned int cpu)
+{
+	struct ltt_trace_struct *trace = ltt_chan->trace;
+
+	kref_put(&ltt_chan->trace->ltt_transport_kref,
+		ltt_release_transport);
+	ltt_relay_print_buffer_errors(ltt_chan, cpu);
+	kfree(ltt_chan->buf[cpu].commit_count);
+	ltt_chan->buf[cpu].commit_count = NULL;
+	kref_put(&ltt_chan->kref, ltt_relay_release_channel);
+	kref_put(&trace->kref, ltt_release_trace);
+}
+
+/* Create channel.
+ */
+static int ltt_relay_create_channel(char *trace_name,
+		struct ltt_trace_struct *trace,
+		struct dentry *dir,
+		char *channel_name,
+		struct ltt_channel_struct **ltt_chan,
+		unsigned int subbuf_size, unsigned int n_subbufs,
+		int overwrite)
+{
+	char *tmpname;
+	int err = 0;
+
+	tmpname = kmalloc(PATH_MAX, GFP_KERNEL);
+	if (!tmpname)
+		return EPERM;
+	if (overwrite) {
+		strncpy(tmpname, LTT_FLIGHT_PREFIX, PATH_MAX-1);
+		strncat(tmpname, channel_name,
+			PATH_MAX-1-sizeof(LTT_FLIGHT_PREFIX));
+	} else {
+		strncpy(tmpname, channel_name, PATH_MAX-1);
+	}
+
+	*ltt_chan = kzalloc(sizeof(struct ltt_channel_struct), GFP_KERNEL);
+	if (!(*ltt_chan))
+		goto ltt_chan_alloc_error;
+	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)->trans_channel_data = relay_open(tmpname,
+			dir,
+			subbuf_size,
+			n_subbufs,
+			&trace->callbacks,
+			*ltt_chan);
+	
+	if ((*ltt_chan)->trans_channel_data == NULL) {
+		printk(KERN_ERR "LTT : Can't open %s channel for trace %s\n",
+				tmpname, trace_name);
+		goto relay_open_error;
+	}
+
+	strncpy((*ltt_chan)->channel_name, tmpname, PATH_MAX-1);
+
+	err = 0;
+	goto end;
+
+relay_open_error:
+	kfree(*ltt_chan);
+	*ltt_chan = NULL;
+ltt_chan_alloc_error:
+	err = EPERM;
+end:
+	kfree(tmpname);
+	return err;
+}
+
+static int ltt_relay_create_dirs(struct ltt_trace_struct *new_trace)
+{
+	new_trace->dentry.trace_root = debugfs_create_dir(new_trace->trace_name,
+			ltt_root_dentry);
+	if (new_trace->dentry.trace_root == NULL) {
+		printk(KERN_ERR "LTT : Trace directory name %s already taken\n",
+				new_trace->trace_name);
+		return EEXIST;
+	}
+
+	new_trace->dentry.control_root = debugfs_create_dir(LTT_CONTROL_ROOT,
+			new_trace->dentry.trace_root);
+	if (new_trace->dentry.control_root == NULL) {
+		printk(KERN_ERR "LTT : Trace control subdirectory name "\
+				"%s/%s already taken\n",
+				new_trace->trace_name, LTT_CONTROL_ROOT);
+		debugfs_remove(new_trace->dentry.trace_root);
+		return EEXIST;
+	}
+
+	new_trace->callbacks.subbuf_start = ltt_subbuf_start_callback;
+	new_trace->callbacks.buf_mapped = ltt_buf_mapped_callback;
+	new_trace->callbacks.buf_unmapped = ltt_buf_unmapped_callback;
+	new_trace->callbacks.create_buf_file = ltt_create_buf_file_callback;
+	new_trace->callbacks.remove_buf_file = ltt_remove_buf_file_callback;
+
+	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 an atomic_up_cmpxchg is used for some atomic
+ * operations, this function must be called from the CPU which owns the buffer
+ * for a ACTIVE flush.
+ */
+static void ltt_force_switch(struct rchan_buf *buf, enum force_switch_mode mode)
+{
+	struct ltt_channel_struct *ltt_channel =
+			(struct ltt_channel_struct*)buf->chan->private_data;
+	struct ltt_channel_buf_struct *ltt_buf = &ltt_channel->buf[buf->cpu];
+	struct rchan *rchan = ltt_channel->trans_channel_data;
+
+	u64 tsc;
+	int offset_begin, offset_end, offset_old;
+	int reserve_commit_diff;
+	int consumed_old, consumed_new;
+	int commit_count;
+	int end_switch_old;
+
+	do {
+		offset_old = atomic_read(&ltt_buf->offset);
+		offset_begin = offset_old;
+		end_switch_old = 0;
+
+		if (SUBBUF_OFFSET(offset_begin, buf->chan) != 0) {
+			offset_begin = SUBBUF_ALIGN(offset_begin, buf->chan);
+			end_switch_old = 1;
+		} else {
+			/* we do not have to switch : buffer is empty */
+			return;
+		}
+		if (mode == FORCE_ACTIVE)
+			offset_begin += ltt_subbuf_header_len();
+		/* Always begin_switch in FORCE_ACTIVE mode */
+		/* Test new buffer integrity */
+		reserve_commit_diff = SUBBUF_OFFSET(
+			buf->chan->subbuf_size
+			- atomic_read(
+			&ltt_buf->commit_count[SUBBUF_INDEX(offset_begin,
+						buf->chan)]), buf->chan);
+		if (reserve_commit_diff == 0) {
+			/* Next buffer not corrupted. */
+			if (mode == FORCE_ACTIVE && !ltt_channel->overwrite &&
+				(offset_begin - atomic_read(&ltt_buf->consumed))
+				>= rchan->alloc_size) {
+	  			/* We do not overwrite non consumed buffers
+				 * and we are full :
+				 * ignore switch while tracing is active. */
+				return;
+			}
+		} else {
+			/* Next subbuffer corrupted. Force pushing reader even
+			 * in normal mode */
+		}
+		offset_end = offset_begin;
+
+		tsc = ltt_get_timestamp64();
+		if (tsc == 0) {
+			/* Error in getting the timestamp : should not happen :
+			 * it would mean we are called from an NMI during a
+			 * write seqlock on xtime. */
+			return;
+		}
+	} while (atomic_up_cmpxchg(&ltt_buf->offset, offset_old, offset_end)
+							!= offset_old);
+
+	if (mode == FORCE_ACTIVE) {
+		/* Push the reader if necessary */
+		do {
+			consumed_old = atomic_read(&ltt_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 fartest 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 happen if a sub-buffer is corrupted */
+			if ((SUBBUF_TRUNC(offset_end-1, buf->chan)
+					- SUBBUF_TRUNC(consumed_old,
+						buf->chan))
+					>= rchan->alloc_size)
+				consumed_new =
+					SUBBUF_ALIGN(consumed_old, buf->chan);
+			else {
+				consumed_new = consumed_old;
+				break;
+			}
+		} while (atomic_cmpxchg(&ltt_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 who died between the reserve
+			 * and the commit. */
+			if (reserve_commit_diff) {
+				/* We have to alter the sub-buffer commit
+				 * count : a sub-buffer is corrupted */
+				atomic_up_add(reserve_commit_diff,
+					&ltt_buf->commit_count[SUBBUF_INDEX(
+						offset_begin, buf->chan)]);
+				atomic_up_inc(&ltt_buf->corrupted_subbuffers);
+			}
+		}
+	}
+
+	/* Always switch */
+	if (end_switch_old) {
+		/* 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
+		 * themself.
+		 * 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.
+		 * Offset old should never be 0. */
+		ltt_channel->buffer_end(buf, tsc, offset_old,
+				SUBBUF_INDEX((offset_old-1), buf->chan));
+		/* Must write buffer end before incrementing commit count */
+		smp_wmb();
+		commit_count =
+			atomic_up_add_return(buf->chan->subbuf_size
+				- (SUBBUF_OFFSET(offset_old-1, buf->chan) + 1),
+				&ltt_buf->commit_count[SUBBUF_INDEX(
+						offset_old-1, buf->chan)]);
+		if (SUBBUF_OFFSET(commit_count, buf->chan) == 0) {
+			ltt_deliver(buf,
+				SUBBUF_INDEX((offset_old-1), buf->chan), NULL);
+		}
+	}
+
+	if (mode == FORCE_ACTIVE) {
+		/* New sub-buffer */
+		/* 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 */
+		ltt_channel->buffer_begin(buf, tsc,
+				SUBBUF_INDEX(offset_begin, buf->chan));
+		/* Must write buffer begin before incrementing commit count */
+		smp_wmb();
+		commit_count =
+			atomic_up_add_return(ltt_subbuf_header_len(),
+			 &ltt_buf->commit_count[SUBBUF_INDEX(offset_begin,
+				 buf->chan)]);
+		/* Check if the written buffer has to be delivered */
+		if (SUBBUF_OFFSET(commit_count, buf->chan) == 0) {
+			ltt_deliver(buf,
+				SUBBUF_INDEX(offset_begin, buf->chan), NULL);
+		}
+	}
+}
+
+/* LTTng channel flush function.
+ *
+ * Must be called when no tracing is active in the channel, because of
+ * accesses across CPUs. */
+static void ltt_relay_buffer_flush(struct rchan_buf *buf)
+{
+	buf->finalized = 1;
+	ltt_force_switch(buf, FORCE_FLUSH);
+}
+
+static void ltt_relay_async_wakeup_chan(struct ltt_channel_struct *ltt_channel)
+{
+	unsigned int i;
+	struct rchan *rchan = ltt_channel->trans_channel_data;
+
+	for_each_possible_cpu(i) {
+		if (atomic_read(&ltt_channel->buf[i].wakeup_readers) == 1) {
+			atomic_set(&ltt_channel->buf[i].wakeup_readers, 0);
+			wake_up_interruptible(&rchan->buf[i]->read_wait);
+		}
+	}
+}
+
+/* Wake writers :
+ *
+ * This must be done after the trace is removed from the RCU list so that there
+ * are no stalled writers. */
+static void ltt_relay_wake_writers(struct ltt_channel_buf_struct *ltt_buf)
+{
+
+	if (waitqueue_active(&ltt_buf->write_wait))
+		schedule_work(&ltt_buf->wake_writers);
+}
+
+static void ltt_relay_finish_buffer(struct ltt_channel_struct *ltt_channel,
+	unsigned int cpu)
+{
+	struct rchan *rchan = ltt_channel->trans_channel_data;
+	struct ltt_channel_buf_struct *ltt_buf;
+
+	printk("finish for cpu %d , %p\n", cpu, rchan->buf[cpu]);
+	if (rchan->buf[cpu]) {
+		ltt_buf = &ltt_channel->buf[cpu];;
+		ltt_relay_buffer_flush(rchan->buf[cpu]);
+		ltt_relay_wake_writers(ltt_buf);
+	}
+}
+
+
+static void ltt_relay_finish_channel(struct ltt_channel_struct *ltt_channel)
+{
+	unsigned int i;
+
+	for_each_possible_cpu(i) {
+		ltt_relay_finish_buffer(ltt_channel, i);
+	}
+}
+
+static void ltt_relay_remove_channel(struct ltt_channel_struct *channel)
+{
+	struct rchan *rchan = channel->trans_channel_data;
+
+	relay_close(rchan);
+	kref_put(&channel->kref, ltt_relay_release_channel);
+}
+
+/* ltt_relay_reserve_slot
+ *
+ * Atomic slot reservation in a LTTng buffer. It will take care of
+ * sub-buffer switching.
+ *
+ * Parameters:
+ *
+ * @trace : the trace structure to log to.
+ * @buf : the buffer to reserve space into.
+ * @data_size : size of the variable length data to log.
+ * @slot_size : pointer to total size of the slot (out)
+ * @tsc : pointer to the tsc at the slot reservation (out)
+ * @before_hdr_pad : dynamic padding before the event header.
+ * @after_hdr_pad : dynamic padding after the event header.
+ *
+ * Return : NULL if not enough space, else returns the pointer
+ * 					to the beginning of the reserved slot. */
+static void *ltt_relay_reserve_slot(
+		struct ltt_trace_struct *trace,
+		struct ltt_channel_struct *ltt_channel,
+		void **transport_data,
+		size_t data_size,
+		size_t *slot_size,
+		u64 *tsc,
+		size_t *before_hdr_pad,
+		size_t *after_hdr_pad,
+		size_t *header_size)
+{
+	struct rchan *rchan = ltt_channel->trans_channel_data;
+	struct rchan_buf *buf = *transport_data = rchan->buf[smp_processor_id()];
+	struct ltt_channel_buf_struct *ltt_buf = &ltt_channel->buf[buf->cpu];
+	int offset_begin, offset_end, offset_old;
+	int begin_switch, end_switch_current, end_switch_old;
+	int reserve_commit_diff = 0;
+	size_t size = 0;
+	int consumed_old, consumed_new;
+	int commit_count;
+
+	if (ltt_nesting[smp_processor_id()] > 4) {
+		atomic_up_inc(&ltt_buf->events_lost);
+		return NULL;
+	}
+
+	do {
+		offset_old = atomic_read(&ltt_buf->offset);
+		offset_begin = offset_old;
+		begin_switch = 0;
+		end_switch_current = 0;
+		end_switch_old = 0;
+
+		if (SUBBUF_OFFSET(offset_begin, buf->chan) == 0) {
+			begin_switch = 1; /* For offset_begin */
+		} else {
+			size = ltt_get_header_size(trace,
+					buf->start + offset_begin,
+					before_hdr_pad, after_hdr_pad,
+					header_size) + data_size;
+			if ((SUBBUF_OFFSET(offset_begin, buf->chan)+size)
+					> buf->chan->subbuf_size) {
+				end_switch_old = 1;	/* For offset_old */
+				begin_switch = 1;	/* For offset_begin */
+			}
+		}
+		if (begin_switch) {
+			if (end_switch_old) {
+				offset_begin =
+					SUBBUF_ALIGN(offset_begin, buf->chan);
+			}
+			offset_begin = offset_begin +
+				ltt_subbuf_header_len();
+			/* Test new buffer integrity */
+			reserve_commit_diff = SUBBUF_OFFSET(
+				buf->chan->subbuf_size - atomic_read(
+				&ltt_buf->commit_count[
+						SUBBUF_INDEX(offset_begin,
+						buf->chan)]), buf->chan);
+			if (reserve_commit_diff == 0) {
+				/* Next buffer not corrupted. */
+				if (!ltt_channel->overwrite &&
+					(SUBBUF_TRUNC(offset_begin, buf->chan)
+					- SUBBUF_TRUNC(
+						atomic_read(&ltt_buf->consumed),
+						buf->chan))
+					>= rchan->alloc_size) {
+					/* We do not overwrite non consumed
+					 * buffers and we are full : event
+					 * is lost. */
+					atomic_up_inc(&ltt_buf->events_lost);
+					return NULL;
+				} 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. */
+			}
+			size = ltt_get_header_size(trace,
+					buf->start + offset_begin,
+					before_hdr_pad, after_hdr_pad,
+					header_size) + data_size;
+			if ((SUBBUF_OFFSET(offset_begin,buf->chan) + size)
+					> buf->chan->subbuf_size) {
+				/* Event too big for subbuffers, report error,
+				 * don't complete the sub-buffer switch. */
+				atomic_up_inc(&ltt_buf->events_lost);
+				return NULL;
+			} 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 */
+		}
+		offset_end = offset_begin + size;
+
+		if ((SUBBUF_OFFSET(offset_end, buf->chan)) == 0) {
+			/* The offset_end will fall at the very beginning of
+			 * the next subbuffer. */
+			end_switch_current = 1;	/* For offset_begin */
+		}
+#ifdef CONFIG_LTT_HEARTBEAT_EVENT
+		if (begin_switch || end_switch_old || end_switch_current)
+			*tsc = ltt_get_timestamp64();
+		else
+			*tsc = ltt_get_timestamp32();
+#else
+		*tsc = ltt_get_timestamp64();
+#endif //CONFIG_LTT_HEARTBEAT_EVENT
+		if (*tsc == 0) {
+			/* Error in getting the timestamp, event lost */
+			atomic_up_inc(&ltt_buf->events_lost);
+			return NULL;
+		}
+
+	} while (atomic_up_cmpxchg(&ltt_buf->offset, offset_old, offset_end)
+							!= offset_old);
+
+
+	/* Push the reader if necessary */
+	do {
+		consumed_old = atomic_read(&ltt_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 fartest
+		 * 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 happen if a sub-buffer is corrupted */
+		if ((SUBBUF_TRUNC(offset_end-1, buf->chan)
+					- SUBBUF_TRUNC(consumed_old, buf->chan))
+					>= rchan->alloc_size)
+			consumed_new = SUBBUF_ALIGN(consumed_old, buf->chan);
+		else {
+			consumed_new = consumed_old;
+			break;
+		}
+	} while (atomic_cmpxchg(&ltt_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
+		 * who died between the reserve and the commit. */
+		if (reserve_commit_diff) {
+			/* We have to alter the sub-buffer commit count : a
+			 * sub-buffer is corrupted. We do not deliver it. */
+			atomic_up_add(
+				reserve_commit_diff,
+				&ltt_buf->commit_count[
+					SUBBUF_INDEX(offset_begin, buf->chan)]);
+			atomic_up_inc(&ltt_buf->corrupted_subbuffers);
+		}
+	}
+
+	if (end_switch_old) {
+		/* 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 themself.
+		 * 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.*/
+		ltt_channel->buffer_end(buf, *tsc, offset_old,
+			SUBBUF_INDEX((offset_old-1), buf->chan));
+		/* Must write buffer end before incrementing commit count */
+		smp_wmb();
+		commit_count =
+			atomic_up_add_return(buf->chan->subbuf_size
+				- (SUBBUF_OFFSET(offset_old-1, buf->chan)+1),
+				&ltt_buf->commit_count[SUBBUF_INDEX(
+						offset_old-1, buf->chan)]);
+		if (SUBBUF_OFFSET(commit_count, buf->chan) == 0) {
+			ltt_deliver(buf, SUBBUF_INDEX((offset_old-1),
+						buf->chan), NULL);
+		}
+	}
+
+	if (begin_switch) {
+		/* New sub-buffer */
+		/* 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 */
+		ltt_channel->buffer_begin(buf, *tsc, SUBBUF_INDEX(offset_begin,
+					buf->chan));
+		commit_count = atomic_up_add_return(
+				ltt_subbuf_header_len(),
+				&ltt_buf->commit_count[
+					SUBBUF_INDEX(offset_begin, buf->chan)]);
+		/* Check if the written buffer has to be delivered */
+		if (SUBBUF_OFFSET(commit_count, buf->chan) == 0) {
+			ltt_deliver(buf,
+				SUBBUF_INDEX(offset_begin, buf->chan), NULL);
+		}
+	}
+
+	if (end_switch_current) {
+		/* 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 themself.
+		 * 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. */
+		ltt_channel->buffer_end(buf, *tsc, offset_end,
+			SUBBUF_INDEX((offset_end-1), buf->chan));
+		/* Must write buffer begin before incrementing commit count */
+		smp_wmb();
+		commit_count =
+			atomic_up_add_return(buf->chan->subbuf_size
+				- (SUBBUF_OFFSET(offset_end-1, buf->chan)+1),
+				&ltt_buf->commit_count[SUBBUF_INDEX(
+						offset_end-1, buf->chan)]);
+		if (SUBBUF_OFFSET(commit_count, buf->chan) == 0) {
+			ltt_deliver(buf,
+				SUBBUF_INDEX((offset_end-1), buf->chan), NULL);
+		}
+	}
+
+	*slot_size = size;
+
+	//BUG_ON(*slot_size != (data_size + *before_hdr_pad + *after_hdr_pad + *header_size));
+	//BUG_ON(*slot_size != (offset_end - offset_begin));
+
+	return buf->start + BUFFER_OFFSET(offset_begin, buf->chan);
+}
+
+
+/* ltt_relay_commit_slot
+ *
+ * Atomic unordered slot commit. Increments the commit count in the
+ * specified sub-buffer, and delivers it if necessary.
+ *
+ * Parameters:
+ *
+ * @buf : the buffer to commit to.
+ * @reserved : address of the beginnig of the reserved slot.
+ * @slot_size : size of the reserved slot.
+ *
+ */
+static void ltt_relay_commit_slot(
+		struct ltt_channel_struct *ltt_channel,
+		void **transport_data,
+		void *reserved,
+		size_t slot_size)
+{
+	struct rchan_buf *buf = *transport_data;
+	struct ltt_channel_buf_struct *ltt_buf = &ltt_channel->buf[buf->cpu];
+	unsigned int offset_begin = reserved - buf->start;
+	int commit_count;
+
+	/* Must write slot data before incrementing commit count */
+	smp_wmb();
+	commit_count = atomic_up_add_return(slot_size,
+		&ltt_buf->commit_count[SUBBUF_INDEX(offset_begin, buf->chan)]);
+	/* Check if all commits have been done */
+	if (SUBBUF_OFFSET(commit_count, buf->chan) == 0)
+		ltt_deliver(buf, SUBBUF_INDEX(offset_begin, buf->chan), NULL);
+}
+
+/* This is called with preemption disabled when user space has requested
+ * blocking mode.  If one of the active traces has free space below a
+ * specific threshold value, we reenable preemption and block.
+ */
+static int ltt_relay_user_blocking(struct ltt_trace_struct *trace,
+		unsigned int index, size_t data_size, struct user_dbg_data *dbg)
+{
+	struct rchan *rchan;
+	struct ltt_channel_buf_struct *ltt_buf;
+	struct ltt_channel_struct *channel;
+	struct rchan_buf *relay_buf;
+	DECLARE_WAITQUEUE(wait, current);
+
+	channel = ltt_get_channel_from_index(trace, index);
+	rchan = channel->trans_channel_data;
+	relay_buf = rchan->buf[smp_processor_id()];
+	ltt_buf = &channel->buf[smp_processor_id()];
+	/* Check if data is too big for the channel : do not
+	 * block for it */
+	if (LTT_RESERVE_CRITICAL + data_size > relay_buf->chan->subbuf_size)
+		return 0;
+
+	/* If free space too low, we block. We restart from the
+	 * beginning after we resume (cpu id may have changed
+	 * while preemption is active).
+	 */
+	spin_lock(&ltt_buf->full_lock);
+	if (!channel->overwrite &&
+		(dbg->avail_size = (dbg->write = atomic_read(
+			&channel->buf[relay_buf->cpu].offset))
+		+ LTT_RESERVE_CRITICAL + data_size
+		 - SUBBUF_TRUNC((dbg->read = atomic_read(
+		&channel->buf[relay_buf->cpu].consumed)),
+			 		relay_buf->chan))
+			>= rchan->alloc_size) {
+		__set_current_state(TASK_INTERRUPTIBLE);
+		add_wait_queue(&ltt_buf->write_wait, &wait);
+		spin_unlock(&ltt_buf->full_lock);
+		preempt_enable();
+		schedule();
+		__set_current_state(TASK_RUNNING);
+		remove_wait_queue(&ltt_buf->write_wait, &wait);
+		if (signal_pending(current))
+			return -ERESTARTSYS;
+		preempt_disable();
+		return 1;
+	}
+	spin_unlock(&ltt_buf->full_lock);
+	return 0;
+}
+
+static void ltt_relay_print_user_errors(struct ltt_trace_struct *trace,
+		unsigned int index, size_t data_size, struct user_dbg_data *dbg)
+{
+	struct rchan *rchan;
+	struct ltt_channel_buf_struct *ltt_buf;
+	struct ltt_channel_struct *channel;
+	struct rchan_buf *relay_buf;
+
+	channel = ltt_get_channel_from_index(trace, index);
+	rchan = channel->trans_channel_data;
+	relay_buf = rchan->buf[smp_processor_id()];
+	ltt_buf = &channel->buf[smp_processor_id()];
+	printk(KERN_ERR "Error in LTT usertrace : "
+	"buffer full : event lost in blocking "
+	"mode. Increase LTT_RESERVE_CRITICAL.\n");
+	printk(KERN_ERR "LTT nesting level is %u.\n",
+		ltt_nesting[smp_processor_id()]);
+	printk(KERN_ERR "LTT avail size %lu.\n",
+		dbg->avail_size);
+	printk(KERN_ERR "avai write : %lu, read : %lu\n",
+			dbg->write, dbg->read);
+	printk(KERN_ERR "LTT cur size %lu.\n",
+		(dbg->write = atomic_read(
+		&channel->buf[relay_buf->cpu].offset))
+	+ LTT_RESERVE_CRITICAL + data_size
+	 - SUBBUF_TRUNC((dbg->read = atomic_read(
+	&channel->buf[relay_buf->cpu].consumed)),
+				relay_buf->chan));
+	printk(KERN_ERR "cur write : %lu, read : %lu\n",
+			dbg->write, dbg->read);
+}
+
+static struct ltt_transport ltt_relay_transport = {
+	.name = "relay",
+	.owner = THIS_MODULE,
+	.ops = {
+		.create_dirs = ltt_relay_create_dirs,
+		.remove_dirs = ltt_relay_remove_dirs,
+		.create_channel = ltt_relay_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,
+		.user_blocking = ltt_relay_user_blocking,
+		.user_errors = ltt_relay_print_user_errors,
+	},
+};
+
+static int __init ltt_relay_init(void)
+{
+	printk(KERN_INFO "LTT : ltt-relay init\n");
+	ltt_root_dentry = debugfs_create_dir(LTT_RELAY_ROOT, NULL);
+	if (ltt_root_dentry == NULL)
+		return -EEXIST;
+
+	ltt_file_operations = relay_file_operations;
+	ltt_file_operations.owner = THIS_MODULE;
+	ltt_file_operations.poll = ltt_poll;
+	ltt_file_operations.ioctl = ltt_ioctl;
+#ifdef CONFIG_COMPAT
+	ltt_file_operations.compat_ioctl = ltt_compat_ioctl;
+#endif //CONFIG_COMPAT
+
+	ltt_transport_register(&ltt_relay_transport);
+
+	return 0;
+}
+
+static void __exit ltt_relay_exit(void)
+{
+	printk(KERN_INFO "LTT : ltt-relay exit\n");
+
+	ltt_transport_unregister(&ltt_relay_transport);
+
+	debugfs_remove(ltt_root_dentry);
+}
+
+module_init(ltt_relay_init);
+module_exit(ltt_relay_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Mathieu Desnoyers");
+MODULE_DESCRIPTION("Linux Trace Toolkit Next Generation Tracer");
+
--- a/Documentation/ioctl-number.txt
+++ b/Documentation/ioctl-number.txt
@@ -191,3 +191,6 @@ Code	Seq#	Include File		Comments
 					<mailto:aherrman@...ibm.com>
 0xF3	00-3F	video/sisfb.h		sisfb (in development)
 					<mailto:thomas@...ischhofer.net>
+0xF4	00-3F	linux/relayfs_fs.h RelayFS
+					<mailto:mathieu.desnoyers@...ymtl.ca>
+
--END--

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