LTTng relay buffer allocation, read, write v2

Index: linux-2.6-lttng/ltt/ltt-relay-alloc.c
===================================================================
@@ -0,0 +1,462 @@
+/*
+ * Public API and common code for kernel->userspace relay file support.
+ *
+ * Copyright (C) 2002-2005 - Tom Zanussi ([email protected]), IBM Corp
+ * Copyright (C) 1999-2005 - Karim Yaghmour ([email protected])
+ * Copyright (C) 2008 - Mathieu Desnoyers ([email protected])
+ *
+ * Moved to kernel/relay.c by Paul Mundt, 2006.
+ * November 2006 - CPU hotplug support by Mathieu Desnoyers
+ * 	([email protected])
+ *
+ * This file is released under the GPL.
+ */
+#include <linux/errno.h>
+#include <linux/stddef.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/ltt-relay.h>
+#include <linux/vmalloc.h>
+#include <linux/mm.h>
+#include <linux/cpu.h>
+#include <linux/splice.h>
+
+/* list of open channels, for cpu hotplug */
+static DEFINE_MUTEX(relay_channels_mutex);
+static LIST_HEAD(relay_channels);
+
+/**
+ *	relay_alloc_buf - allocate a channel buffer
+ *	@buf: the buffer struct
+ *	@size: total size of the buffer
+ */
+static int relay_alloc_buf(struct rchan_buf *buf, size_t *size)
+{
+	unsigned int i, n_pages;
+	struct buf_page *buf_page, *n;
+
+	*size = PAGE_ALIGN(*size);
+	n_pages = *size >> PAGE_SHIFT;
+
+	INIT_LIST_HEAD(&buf->pages);
+
+	for (i = 0; i < n_pages; i++) {
+		buf_page = kmalloc(sizeof(struct buf_page), GFP_KERNEL);
+		if (unlikely(!buf_page))
+			goto depopulate;
+		buf_page->page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+		if (unlikely(!buf_page->page)) {
+			kfree(buf_page);
+			goto depopulate;
+		}
+		list_add_tail(&buf_page->list, &buf->pages);
+		buf_page->offset = (size_t)i << PAGE_SHIFT;
+		if (i == 0) {
+			buf->wpage = buf_page;
+			buf->hpage[0] = buf_page;
+			buf->hpage[1] = buf_page;
+			buf->rpage = buf_page;
+		}
+	}
+	buf->page_count = n_pages;
+	return 0;
+
+depopulate:
+	list_for_each_entry_safe(buf_page, n, &buf->pages, list) {
+		list_del_init(&buf_page->list);
+		__free_page(buf_page->page);
+		kfree(buf_page);
+	}
+	return -ENOMEM;
+}
+
+/**
+ *	relay_create_buf - allocate and initialize a channel buffer
+ *	@chan: the relay channel
+ *
+ *	Returns channel buffer if successful, %NULL otherwise.
+ */
+static struct rchan_buf *relay_create_buf(struct rchan *chan)
+{
+	int ret;
+	struct rchan_buf *buf = kzalloc(sizeof(struct rchan_buf), GFP_KERNEL);
+	if (!buf)
+		return NULL;
+
+	ret = relay_alloc_buf(buf, &chan->alloc_size);
+	if (ret)
+		goto free_buf;
+
+	buf->chan = chan;
+	kref_get(&buf->chan->kref);
+	return buf;
+
+free_buf:
+	kfree(buf);
+	return NULL;
+}
+
+/**
+ *	relay_destroy_channel - free the channel struct
+ *	@kref: target kernel reference that contains the relay channel
+ *
+ *	Should only be called from kref_put().
+ */
+static void relay_destroy_channel(struct kref *kref)
+{
+	struct rchan *chan = container_of(kref, struct rchan, kref);
+	kfree(chan);
+}
+
+/**
+ *	relay_destroy_buf - destroy an rchan_buf struct and associated buffer
+ *	@buf: the buffer struct
+ */
+static void relay_destroy_buf(struct rchan_buf *buf)
+{
+	struct rchan *chan = buf->chan;
+	struct buf_page *buf_page, *n;
+
+	list_for_each_entry_safe(buf_page, n, &buf->pages, list) {
+		list_del_init(&buf_page->list);
+		__free_page(buf_page->page);
+		kfree(buf_page);
+	}
+	chan->buf[buf->cpu] = NULL;
+	kfree(buf);
+	kref_put(&chan->kref, relay_destroy_channel);
+}
+
+/**
+ *	relay_remove_buf - remove a channel buffer
+ *	@kref: target kernel reference that contains the relay buffer
+ *
+ *	Removes the file from the fileystem, which also frees the
+ *	rchan_buf_struct and the channel buffer.  Should only be called from
+ *	kref_put().
+ */
+static void relay_remove_buf(struct kref *kref)
+{
+	struct rchan_buf *buf = container_of(kref, struct rchan_buf, kref);
+	buf->chan->cb->remove_buf_file(buf->dentry);
+	relay_destroy_buf(buf);
+}
+
+/*
+ * High-level relay kernel API and associated functions.
+ */
+
+/*
+ * rchan_callback implementations defining default channel behavior.  Used
+ * in place of corresponding NULL values in client callback struct.
+ */
+
+/*
+ * create_buf_file_create() default callback.  Does nothing.
+ */
+static struct dentry *create_buf_file_default_callback(const char *filename,
+						       struct dentry *parent,
+						       int mode,
+						       struct rchan_buf *buf)
+{
+	return NULL;
+}
+
+/*
+ * remove_buf_file() default callback.  Does nothing.
+ */
+static int remove_buf_file_default_callback(struct dentry *dentry)
+{
+	return -EINVAL;
+}
+
+/* relay channel default callbacks */
+static struct rchan_callbacks default_channel_callbacks = {
+	.create_buf_file = create_buf_file_default_callback,
+	.remove_buf_file = remove_buf_file_default_callback,
+};
+
+/**
+ *	wakeup_readers - wake up readers waiting on a channel
+ *	@data: contains the channel buffer
+ *
+ *	This is the timer function used to defer reader waking.
+ */
+static void wakeup_readers(unsigned long data)
+{
+	struct rchan_buf *buf = (struct rchan_buf *)data;
+	wake_up_interruptible(&buf->read_wait);
+}
+
+/**
+ *	__relay_reset - reset a channel buffer
+ *	@buf: the channel buffer
+ *	@init: 1 if this is a first-time initialization
+ *
+ *	See relay_reset() for description of effect.
+ */
+static void __relay_reset(struct rchan_buf *buf, unsigned int init)
+{
+	if (init) {
+		init_waitqueue_head(&buf->read_wait);
+		kref_init(&buf->kref);
+		setup_timer(&buf->timer, wakeup_readers, (unsigned long)buf);
+	} else
+		del_timer_sync(&buf->timer);
+
+	buf->finalized = 0;
+}
+
+/*
+ *	relay_open_buf - create a new relay channel buffer
+ *
+ *	used by relay_open() and CPU hotplug.
+ */
+static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
+{
+ 	struct rchan_buf *buf = NULL;
+	struct dentry *dentry;
+ 	char *tmpname;
+
+	tmpname = kzalloc(NAME_MAX + 1, GFP_KERNEL);
+ 	if (!tmpname)
+ 		goto end;
+ 	snprintf(tmpname, NAME_MAX, "%s%d", chan->base_filename, cpu);
+
+	buf = relay_create_buf(chan);
+	if (!buf)
+ 		goto free_name;
+
+ 	buf->cpu = cpu;
+ 	__relay_reset(buf, 1);
+
+	/* Create file in fs */
+ 	dentry = chan->cb->create_buf_file(tmpname, chan->parent, S_IRUSR,
+ 					   buf);
+ 	if (!dentry)
+ 		goto free_buf;
+
+	buf->dentry = dentry;
+
+ 	goto free_name;
+
+free_buf:
+ 	relay_destroy_buf(buf);
+ 	buf = NULL;
+free_name:
+ 	kfree(tmpname);
+end:
+	return buf;
+}
+
+/**
+ *	relay_close_buf - close a channel buffer
+ *	@buf: channel buffer
+ *
+ *	Marks the buffer finalized and restores the default callbacks.
+ *	The channel buffer and channel buffer data structure are then freed
+ *	automatically when the last reference is given up.
+ */
+static void relay_close_buf(struct rchan_buf *buf)
+{
+	del_timer_sync(&buf->timer);
+	kref_put(&buf->kref, relay_remove_buf);
+}
+
+static void setup_callbacks(struct rchan *chan,
+				   struct rchan_callbacks *cb)
+{
+	if (!cb) {
+		chan->cb = &default_channel_callbacks;
+		return;
+	}
+
+	if (!cb->create_buf_file)
+		cb->create_buf_file = create_buf_file_default_callback;
+	if (!cb->remove_buf_file)
+		cb->remove_buf_file = remove_buf_file_default_callback;
+	chan->cb = cb;
+}
+
+/**
+ * 	relay_hotcpu_callback - CPU hotplug callback
+ * 	@nb: notifier block
+ * 	@action: hotplug action to take
+ * 	@hcpu: CPU number
+ *
+ * 	Returns the success/failure of the operation. (%NOTIFY_OK, %NOTIFY_BAD)
+ */
+static int __cpuinit relay_hotcpu_callback(struct notifier_block *nb,
+				unsigned long action,
+				void *hcpu)
+{
+	unsigned int hotcpu = (unsigned long)hcpu;
+	struct rchan *chan;
+
+	switch(action) {
+	case CPU_UP_PREPARE:
+	case CPU_UP_PREPARE_FROZEN:
+		mutex_lock(&relay_channels_mutex);
+		list_for_each_entry(chan, &relay_channels, list) {
+			if (chan->buf[hotcpu])
+				continue;
+			chan->buf[hotcpu] = relay_open_buf(chan, hotcpu);
+			if(!chan->buf[hotcpu]) {
+				printk(KERN_ERR
+					"relay_hotcpu_callback: cpu %d buffer "
+					"creation failed\n", hotcpu);
+				mutex_unlock(&relay_channels_mutex);
+				return NOTIFY_BAD;
+			}
+		}
+		mutex_unlock(&relay_channels_mutex);
+		break;
+	case CPU_DEAD:
+	case CPU_DEAD_FROZEN:
+		/* No need to flush the cpu : will be flushed upon
+		 * final relay_flush() call. */
+		break;
+	}
+	return NOTIFY_OK;
+}
+
+/**
+ *	ltt_relay_open - create a new relay channel
+ *	@base_filename: base name of files to create
+ *	@parent: dentry of parent directory, %NULL for root directory
+ *	@subbuf_size: size of sub-buffers
+ *	@n_subbufs: number of sub-buffers
+ *	@cb: client callback functions
+ *	@private_data: user-defined data
+ *
+ *	Returns channel pointer if successful, %NULL otherwise.
+ *
+ *	Creates a channel buffer for each cpu using the sizes and
+ *	attributes specified.  The created channel buffer files
+ *	will be named base_filename0...base_filenameN-1.  File
+ *	permissions will be %S_IRUSR.
+ */
+struct rchan *ltt_relay_open(const char *base_filename,
+			 struct dentry *parent,
+			 size_t subbuf_size,
+			 size_t n_subbufs,
+			 struct rchan_callbacks *cb,
+			 void *private_data)
+{
+	unsigned int i;
+	struct rchan *chan;
+	if (!base_filename)
+		return NULL;
+
+	if (!(subbuf_size && n_subbufs))
+		return NULL;
+
+	chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);
+	if (!chan)
+		return NULL;
+
+	chan->version = LTT_RELAY_CHANNEL_VERSION;
+	chan->n_subbufs = n_subbufs;
+	chan->subbuf_size = subbuf_size;
+	chan->alloc_size = FIX_SIZE(subbuf_size * n_subbufs);
+	chan->parent = parent;
+	chan->private_data = private_data;
+	strlcpy(chan->base_filename, base_filename, NAME_MAX);
+	setup_callbacks(chan, cb);
+	kref_init(&chan->kref);
+
+	mutex_lock(&relay_channels_mutex);
+	for_each_online_cpu(i) {
+		chan->buf[i] = relay_open_buf(chan, i);
+		if (!chan->buf[i])
+			goto free_bufs;
+	}
+	list_add(&chan->list, &relay_channels);
+	mutex_unlock(&relay_channels_mutex);
+
+	return chan;
+
+free_bufs:
+	for_each_online_cpu(i) {
+		if (!chan->buf[i])
+			break;
+		relay_close_buf(chan->buf[i]);
+	}
+
+	kref_put(&chan->kref, relay_destroy_channel);
+	mutex_unlock(&relay_channels_mutex);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(ltt_relay_open);
+
+/**
+ *	ltt_relay_close - close the channel
+ *	@chan: the channel
+ *
+ *	Closes all channel buffers and frees the channel.
+ */
+void ltt_relay_close(struct rchan *chan)
+{
+	unsigned int i;
+
+	if (!chan)
+		return;
+
+	mutex_lock(&relay_channels_mutex);
+	for_each_possible_cpu(i)
+		if (chan->buf[i])
+			relay_close_buf(chan->buf[i]);
+
+	list_del(&chan->list);
+	kref_put(&chan->kref, relay_destroy_channel);
+	mutex_unlock(&relay_channels_mutex);
+}
+EXPORT_SYMBOL_GPL(ltt_relay_close);
+
+/**
+ *	relay_file_open - open file op for relay files
+ *	@inode: the inode
+ *	@filp: the file
+ *
+ *	Increments the channel buffer refcount.
+ */
+static int relay_file_open(struct inode *inode, struct file *filp)
+{
+	struct rchan_buf *buf = inode->i_private;
+	kref_get(&buf->kref);
+	filp->private_data = buf;
+
+	return nonseekable_open(inode, filp);
+}
+
+/**
+ *	relay_file_release - release file op for relay files
+ *	@inode: the inode
+ *	@filp: the file
+ *
+ *	Decrements the channel refcount, as the filesystem is
+ *	no longer using it.
+ */
+static int relay_file_release(struct inode *inode, struct file *filp)
+{
+	struct rchan_buf *buf = filp->private_data;
+	kref_put(&buf->kref, relay_remove_buf);
+
+	return 0;
+}
+
+const struct file_operations ltt_relay_file_operations = {
+	.open		= relay_file_open,
+	.llseek		= no_llseek,
+	.release	= relay_file_release,
+};
+EXPORT_SYMBOL_GPL(ltt_relay_file_operations);
+
+static __init int relay_init(void)
+{
+	hotcpu_notifier(relay_hotcpu_callback, 5);
+	return 0;
+}
+
+module_init(relay_init);

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