[RFC patch 07/41] LTTng dynamic channels

[Mathieu Desnoyers]

Make channels dynamic (a channel can be added at module load time).
When a trace is setup, its channel array stays fixed even if the channels
change.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
---
 include/linux/ltt-channels.h |   94 +++++++++++
 ltt/ltt-channels.c           |  338 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 432 insertions(+)

Index: linux-2.6-lttng/ltt/ltt-channels.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/ltt/ltt-channels.c	2009-03-05 15:03:00.000000000 -0500
@@ -0,0 +1,338 @@
+/*
+ * ltt/ltt-channels.c
+ *
+ * (C) Copyright 2008 - Mathieu Desnoyers (mathieu.desnoyers@xxxxxxxxxx)
+ *
+ * LTTng channel management.
+ *
+ * Author:
+ *	Mathieu Desnoyers (mathieu.desnoyers@xxxxxxxxxx)
+ */
+
+#include <linux/module.h>
+#include <linux/ltt-channels.h>
+#include <linux/mutex.h>
+#include <linux/vmalloc.h>
+
+/*
+ * ltt_channel_mutex may be nested inside the LTT trace mutex.
+ * ltt_channel_mutex mutex may be nested inside markers mutex.
+ */
+static DEFINE_MUTEX(ltt_channel_mutex);
+static LIST_HEAD(ltt_channels);
+/*
+ * Index of next channel in array. Makes sure that as long as a trace channel is
+ * allocated, no array index will be re-used when a channel is freed and then
+ * another channel is allocated. This index is cleared and the array indexeds
+ * get reassigned when the index_kref goes back to 0, which indicates that no
+ * more trace channels are allocated.
+ */
+static unsigned int free_index;
+static struct kref index_kref;	/* Keeps track of allocated trace channels */
+
+static struct ltt_channel_setting *lookup_channel(const char *name)
+{
+	struct ltt_channel_setting *iter;
+
+	list_for_each_entry(iter, &ltt_channels, list)
+		if (strcmp(name, iter->name) == 0)
+			return iter;
+	return NULL;
+}
+
+/*
+ * Must be called when channel refcount falls to 0 _and_ also when the last
+ * trace is freed. This function is responsible for compacting the channel and
+ * event IDs when no users are active.
+ *
+ * Called with lock_markers() and channels mutex held.
+ */
+static void release_channel_setting(struct kref *kref)
+{
+	struct ltt_channel_setting *setting = container_of(kref,
+		struct ltt_channel_setting, kref);
+	struct ltt_channel_setting *iter;
+
+	if (atomic_read(&index_kref.refcount) == 0
+	    && atomic_read(&setting->kref.refcount) == 0) {
+		list_del(&setting->list);
+		kfree(setting);
+
+		free_index = 0;
+		list_for_each_entry(iter, &ltt_channels, list) {
+			iter->index = free_index++;
+			iter->free_event_id = 0;
+		}
+		markers_compact_event_ids();
+	}
+}
+
+/*
+ * Perform channel index compaction when the last trace channel is freed.
+ *
+ * Called with lock_markers() and channels mutex held.
+ */
+static void release_trace_channel(struct kref *kref)
+{
+	struct ltt_channel_setting *iter, *n;
+
+	list_for_each_entry_safe(iter, n, &ltt_channels, list)
+		release_channel_setting(&iter->kref);
+}
+
+/**
+ * ltt_channels_register - Register a trace channel.
+ * @name: channel name
+ *
+ * Uses refcounting.
+ */
+int ltt_channels_register(const char *name)
+{
+	struct ltt_channel_setting *setting;
+	int ret = 0;
+
+	mutex_lock(&ltt_channel_mutex);
+	setting = lookup_channel(name);
+	if (setting) {
+		if (atomic_read(&setting->kref.refcount) == 0)
+			goto init_kref;
+		else {
+			kref_get(&setting->kref);
+			goto end;
+		}
+	}
+	setting = kzalloc(sizeof(*setting), GFP_KERNEL);
+	if (!setting) {
+		ret = -ENOMEM;
+		goto end;
+	}
+	list_add(&setting->list, &ltt_channels);
+	strncpy(setting->name, name, PATH_MAX-1);
+	setting->index = free_index++;
+init_kref:
+	kref_init(&setting->kref);
+end:
+	mutex_unlock(&ltt_channel_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ltt_channels_register);
+
+/**
+ * ltt_channels_unregister - Unregister a trace channel.
+ * @name: channel name
+ *
+ * Must be called with markers mutex held.
+ */
+int ltt_channels_unregister(const char *name)
+{
+	struct ltt_channel_setting *setting;
+	int ret = 0;
+
+	mutex_lock(&ltt_channel_mutex);
+	setting = lookup_channel(name);
+	if (!setting || atomic_read(&setting->kref.refcount) == 0) {
+		ret = -ENOENT;
+		goto end;
+	}
+	kref_put(&setting->kref, release_channel_setting);
+end:
+	mutex_unlock(&ltt_channel_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ltt_channels_unregister);
+
+/**
+ * ltt_channels_set_default - Set channel default behavior.
+ * @name: default channel name
+ * @subbuf_size: size of the subbuffers
+ * @subbuf_cnt: number of subbuffers
+ */
+int ltt_channels_set_default(const char *name,
+			     unsigned int subbuf_size,
+			     unsigned int subbuf_cnt)
+{
+	struct ltt_channel_setting *setting;
+	int ret = 0;
+
+	mutex_lock(&ltt_channel_mutex);
+	setting = lookup_channel(name);
+	if (!setting || atomic_read(&setting->kref.refcount) == 0) {
+		ret = -ENOENT;
+		goto end;
+	}
+	setting->subbuf_size = subbuf_size;
+	setting->subbuf_cnt = subbuf_cnt;
+end:
+	mutex_unlock(&ltt_channel_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ltt_channels_set_default);
+
+/**
+ * ltt_channels_get_name_from_index - get channel name from channel index
+ * @index: channel index
+ *
+ * Allows to lookup the channel name given its index. Done to keep the name
+ * information outside of each trace channel instance.
+ */
+const char *ltt_channels_get_name_from_index(unsigned int index)
+{
+	struct ltt_channel_setting *iter;
+
+	list_for_each_entry(iter, &ltt_channels, list)
+		if (iter->index == index && atomic_read(&iter->kref.refcount))
+			return iter->name;
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(ltt_channels_get_name_from_index);
+
+static struct ltt_channel_setting *
+ltt_channels_get_setting_from_name(const char *name)
+{
+	struct ltt_channel_setting *iter;
+
+	list_for_each_entry(iter, &ltt_channels, list)
+		if (!strcmp(iter->name, name)
+		    && atomic_read(&iter->kref.refcount))
+			return iter;
+	return NULL;
+}
+
+/**
+ * ltt_channels_get_index_from_name - get channel index from channel name
+ * @name: channel name
+ *
+ * Allows to lookup the channel index given its name. Done to keep the name
+ * information outside of each trace channel instance.
+ * Returns -1 if not found.
+ */
+int ltt_channels_get_index_from_name(const char *name)
+{
+	struct ltt_channel_setting *setting;
+
+	setting = ltt_channels_get_setting_from_name(name);
+	if (setting)
+		return setting->index;
+	else
+		return -1;
+}
+EXPORT_SYMBOL_GPL(ltt_channels_get_index_from_name);
+
+/**
+ * ltt_channels_trace_alloc - Allocate channel structures for a trace
+ * @subbuf_size: subbuffer size. 0 uses default.
+ * @subbuf_cnt: number of subbuffers per per-cpu buffers. 0 uses default.
+ * @flags: Default channel flags
+ *
+ * Use the current channel list to allocate the channels for a trace.
+ * Called with trace lock held. Does not perform the trace buffer allocation,
+ * because we must let the user overwrite specific channel sizes.
+ */
+struct ltt_channel_struct *ltt_channels_trace_alloc(unsigned int *nr_channels,
+						    int overwrite,
+						    int active)
+{
+	struct ltt_channel_struct *channel = NULL;
+	struct ltt_channel_setting *iter;
+
+	mutex_lock(&ltt_channel_mutex);
+	if (!free_index)
+		goto end;
+	if (!atomic_read(&index_kref.refcount))
+		kref_init(&index_kref);
+	else
+		kref_get(&index_kref);
+	*nr_channels = free_index;
+	channel = kzalloc(sizeof(struct ltt_channel_struct) * free_index,
+			  GFP_KERNEL);
+	if (!channel)
+		goto end;
+	list_for_each_entry(iter, &ltt_channels, list) {
+		if (!atomic_read(&iter->kref.refcount))
+			continue;
+		channel[iter->index].subbuf_size = iter->subbuf_size;
+		channel[iter->index].subbuf_cnt = iter->subbuf_cnt;
+		channel[iter->index].overwrite = overwrite;
+		channel[iter->index].active = active;
+		channel[iter->index].channel_name = iter->name;
+	}
+end:
+	mutex_unlock(&ltt_channel_mutex);
+	return channel;
+}
+EXPORT_SYMBOL_GPL(ltt_channels_trace_alloc);
+
+/**
+ * ltt_channels_trace_free - Free one trace's channels
+ * @channels: channels to free
+ *
+ * Called with trace lock held. The actual channel buffers must be freed before
+ * this function is called.
+ */
+void ltt_channels_trace_free(struct ltt_channel_struct *channels)
+{
+	lock_markers();
+	mutex_lock(&ltt_channel_mutex);
+	kfree(channels);
+	kref_put(&index_kref, release_trace_channel);
+	mutex_unlock(&ltt_channel_mutex);
+	unlock_markers();
+}
+EXPORT_SYMBOL_GPL(ltt_channels_trace_free);
+
+/**
+ * _ltt_channels_get_event_id - get next event ID for a marker
+ * @channel: channel name
+ * @name: event name
+ *
+ * Returns a unique event ID (for this channel) or < 0 on error.
+ * Must be called with channels mutex held.
+ */
+int _ltt_channels_get_event_id(const char *channel, const char *name)
+{
+	struct ltt_channel_setting *setting;
+	int ret;
+
+	setting = ltt_channels_get_setting_from_name(channel);
+	if (!setting) {
+		ret = -ENOENT;
+		goto end;
+	}
+	if (strcmp(channel, "metadata") == 0) {
+		if (strcmp(name, "core_marker_id") == 0)
+			ret = 0;
+		else if (strcmp(name, "core_marker_format") == 0)
+			ret = 1;
+		else
+			ret = -ENOENT;
+		goto end;
+	}
+	if (setting->free_event_id == EVENTS_PER_CHANNEL - 1) {
+		ret = -ENOSPC;
+		goto end;
+	}
+	ret = setting->free_event_id++;
+end:
+	return ret;
+}
+
+/**
+ * ltt_channels_get_event_id - get next event ID for a marker
+ * @channel: channel name
+ * @name: event name
+ *
+ * Returns a unique event ID (for this channel) or < 0 on error.
+ */
+int ltt_channels_get_event_id(const char *channel, const char *name)
+{
+	int ret;
+
+	mutex_lock(&ltt_channel_mutex);
+	ret = _ltt_channels_get_event_id(channel, name);
+	mutex_unlock(&ltt_channel_mutex);
+	return ret;
+}
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Mathieu Desnoyers");
+MODULE_DESCRIPTION("Linux Trace Toolkit Next Generation Channel Management");
Index: linux-2.6-lttng/include/linux/ltt-channels.h
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/include/linux/ltt-channels.h	2009-03-05 15:03:13.000000000 -0500
@@ -0,0 +1,94 @@
+#ifndef _LTT_CHANNELS_H
+#define _LTT_CHANNELS_H
+
+/*
+ * Copyright (C) 2008 Mathieu Desnoyers (mathieu.desnoyers@xxxxxxxxxx)
+ *
+ * Dynamic tracer channel allocation.
+ */
+
+#include <linux/limits.h>
+#include <linux/kref.h>
+#include <linux/list.h>
+
+#define EVENTS_PER_CHANNEL	65536
+
+struct ltt_trace_struct;
+struct rchan_buf;
+
+struct ltt_channel_struct {
+	/* First 32 bytes cache-hot cacheline */
+	struct ltt_trace_struct	*trace;
+	void *buf;
+	void *trans_channel_data;
+	int overwrite:1;
+	int active:1;
+	unsigned int n_subbufs_order;
+	unsigned long commit_count_mask;	/*
+						 * Commit count mask, removing
+						 * the MSBs corresponding to
+						 * bits used to represent the
+						 * subbuffer index.
+						 */
+	/* End of first 32 bytes cacheline */
+
+	/*
+	 * buffer_begin - called on buffer-switch to a new sub-buffer
+	 * @buf: the channel buffer containing the new sub-buffer
+	 */
+	void (*buffer_begin) (struct rchan_buf *buf,
+			u64 tsc, unsigned int subbuf_idx);
+	/*
+	 * buffer_end - called on buffer-switch to a new sub-buffer
+	 * @buf: the channel buffer containing the previous sub-buffer
+	 */
+	void (*buffer_end) (struct rchan_buf *buf,
+			u64 tsc, unsigned int offset, unsigned int subbuf_idx);
+	struct kref kref;	/* Channel transport reference count */
+	struct ltt_channel_buf_access_ops *buf_access_ops;
+	unsigned int subbuf_size;
+	unsigned int subbuf_cnt;
+	const char *channel_name;
+} ____cacheline_aligned;
+
+/*
+ * ops for accessing struct channel data.
+ * Only meant to be used in slow-path code (ascii formatter code,
+ * buffer read-side access through a system call).
+ */
+struct ltt_channel_buf_access_ops {
+	unsigned long (*get_offset)(struct rchan_buf *buf);
+	unsigned long (*get_consumed)(struct rchan_buf *buf);
+	int (*open)(struct rchan_buf *buf);
+	int (*release)(struct rchan_buf *buf);
+	int (*get_subbuf)(struct rchan_buf *buf, unsigned long *consumed);
+	int (*put_subbuf)(struct rchan_buf *buf, unsigned long consumed);
+	unsigned long (*get_n_subbufs)(struct rchan_buf *buf);
+	unsigned long (*get_subbuf_size)(struct rchan_buf *buf);
+};
+
+struct ltt_channel_setting {
+	unsigned int subbuf_size;
+	unsigned int subbuf_cnt;
+	struct kref kref;	/* Number of references to structure content */
+	struct list_head list;
+	unsigned int index;	/* index of channel in trace channel array */
+	u16 free_event_id;	/* Next event ID to allocate */
+	char name[PATH_MAX];
+};
+
+int ltt_channels_register(const char *name);
+int ltt_channels_unregister(const char *name);
+int ltt_channels_set_default(const char *name,
+			     unsigned int subbuf_size,
+			     unsigned int subbuf_cnt);
+const char *ltt_channels_get_name_from_index(unsigned int index);
+int ltt_channels_get_index_from_name(const char *name);
+struct ltt_channel_struct *ltt_channels_trace_alloc(unsigned int *nr_channels,
+						    int overwrite,
+						    int active);
+void ltt_channels_trace_free(struct ltt_channel_struct *channels);
+int _ltt_channels_get_event_id(const char *channel, const char *name);
+int ltt_channels_get_event_id(const char *channel, const char *name);
+
+#endif /* _LTT_CHANNELS_H */

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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