relay.c

Kernel code of linux kernel

	if (chan->has_base_filename) {
		dentry = relay_create_buf_file(chan, buf, cpu);
		if (!dentry)
			goto free_buf;
		relay_set_buf_dentry(buf, dentry);
	}

 	buf->cpu = cpu;
 	__relay_reset(buf, 1);

 	if(chan->is_global) {
 		chan->buf[0] = buf;
 		buf->cpu = 0;
  	}

	return buf;

free_buf:
 	relay_destroy_buf(buf);
	return NULL;
}

/**
 *	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)
{
	buf->finalized = 1;
	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->subbuf_start)
		cb->subbuf_start = subbuf_start_default_callback;
	if (!cb->buf_mapped)
		cb->buf_mapped = buf_mapped_default_callback;
	if (!cb->buf_unmapped)
		cb->buf_unmapped = buf_unmapped_default_callback;
	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;
}

/**
 *	relay_open - create a new relay channel
 *	@base_filename: base name of files to create, %NULL for buffering only
 *	@parent: dentry of parent directory, %NULL for root directory or buffer
 *	@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 *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 (!(subbuf_size && n_subbufs))
		return NULL;

	chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);
	if (!chan)
		return NULL;

	chan->version = RELAYFS_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;
	if (base_filename) {
		chan->has_base_filename = 1;
		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(relay_open);

struct rchan_percpu_buf_dispatcher {
	struct rchan_buf *buf;
	struct dentry *dentry;
};

/* Called in atomic context. */
static void __relay_set_buf_dentry(void *info)
{
	struct rchan_percpu_buf_dispatcher *p = info;

	relay_set_buf_dentry(p->buf, p->dentry);
}

/**
 *	relay_late_setup_files - triggers file creation
 *	@chan: channel to operate on
 *	@base_filename: base name of files to create
 *	@parent: dentry of parent directory, %NULL for root directory
 *
 *	Returns 0 if successful, non-zero otherwise.
 *
 *	Use to setup files for a previously buffer-only channel.
 *	Useful to do early tracing in kernel, before VFS is up, for example.
 */
int relay_late_setup_files(struct rchan *chan,
			   const char *base_filename,
			   struct dentry *parent)
{
	int err = 0;
	unsigned int i, curr_cpu;
	unsigned long flags;
	struct dentry *dentry;
	struct rchan_percpu_buf_dispatcher disp;

	if (!chan || !base_filename)
		return -EINVAL;

	strlcpy(chan->base_filename, base_filename, NAME_MAX);

	mutex_lock(&relay_channels_mutex);
	/* Is chan already set up? */
	if (unlikely(chan->has_base_filename))
		return -EEXIST;
	chan->has_base_filename = 1;
	chan->parent = parent;
	curr_cpu = get_cpu();
	/*
	 * The CPU hotplug notifier ran before us and created buffers with
	 * no files associated. So it's safe to call relay_setup_buf_file()
	 * on all currently online CPUs.
	 */
	for_each_online_cpu(i) {
		if (unlikely(!chan->buf[i])) {
			printk(KERN_ERR "relay_late_setup_files: CPU %u "
					"has no buffer, it must have!\n", i);
			BUG();
			err = -EINVAL;
			break;
		}

		dentry = relay_create_buf_file(chan, chan->buf[i], i);
		if (unlikely(!dentry)) {
			err = -EINVAL;
			break;
		}

		if (curr_cpu == i) {
			local_irq_save(flags);
			relay_set_buf_dentry(chan->buf[i], dentry);
			local_irq_restore(flags);
		} else {
			disp.buf = chan->buf[i];
			disp.dentry = dentry;
			smp_mb();
			/* relay_channels_mutex must be held, so wait. */
			err = smp_call_function_single(i,
						       __relay_set_buf_dentry,
						       &disp, 1);
		}
		if (unlikely(err))
			break;
	}
	put_cpu();
	mutex_unlock(&relay_channels_mutex);

	return err;
}

/**
 *	relay_switch_subbuf - switch to a new sub-buffer
 *	@buf: channel buffer
 *	@length: size of current event
 *
 *	Returns either the length passed in or 0 if full.
 *
 *	Performs sub-buffer-switch tasks such as invoking callbacks,
 *	updating padding counts, waking up readers, etc.
 */
size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
{
	void *old, *new;
	size_t old_subbuf, new_subbuf;

	if (unlikely(length > buf->chan->subbuf_size))
		goto toobig;

	if (buf->offset != buf->chan->subbuf_size + 1) {
		buf->prev_padding = buf->chan->subbuf_size - buf->offset;
		old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
		buf->padding[old_subbuf] = buf->prev_padding;
		buf->subbufs_produced++;
		if (buf->dentry)
			buf->dentry->d_inode->i_size +=
				buf->chan->subbuf_size -
				buf->padding[old_subbuf];
		else
			buf->early_bytes += buf->chan->subbuf_size -
					    buf->padding[old_subbuf];
		smp_mb();
		if (waitqueue_active(&buf->read_wait))
			/*
			 * Calling wake_up_interruptible() from here
			 * will deadlock if we happen to be logging
			 * from the scheduler (trying to re-grab
			 * rq->lock), so defer it.
			 */
			__mod_timer(&buf->timer, jiffies + 1);
	}

	old = buf->data;
	new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
	new = buf->start + new_subbuf * buf->chan->subbuf_size;
	buf->offset = 0;
	if (!buf->chan->cb->subbuf_start(buf, new, old, buf->prev_padding)) {
		buf->offset = buf->chan->subbuf_size + 1;
		return 0;
	}
	buf->data = new;
	buf->padding[new_subbuf] = 0;

	if (unlikely(length + buf->offset > buf->chan->subbuf_size))
		goto toobig;

	return length;

toobig:
	buf->chan->last_toobig = length;
	return 0;
}
EXPORT_SYMBOL_GPL(relay_switch_subbuf);

/**
 *	relay_subbufs_consumed - update the buffer's sub-buffers-consumed count
 *	@chan: the channel
 *	@cpu: the cpu associated with the channel buffer to update
 *	@subbufs_consumed: number of sub-buffers to add to current buf's count
 *
 *	Adds to the channel buffer's consumed sub-buffer count.
 *	subbufs_consumed should be the number of sub-buffers newly consumed,
 *	not the total consumed.
 *
 *	NOTE. Kernel clients don't need to call this function if the channel
 *	mode is 'overwrite'.
 */
void relay_subbufs_consumed(struct rchan *chan,
			    unsigned int cpu,
			    size_t subbufs_consumed)
{
	struct rchan_buf *buf;

	if (!chan)
		return;

	if (cpu >= NR_CPUS || !chan->buf[cpu])
		return;

	buf = chan->buf[cpu];
	buf->subbufs_consumed += subbufs_consumed;
	if (buf->subbufs_consumed > buf->subbufs_produced)
		buf->subbufs_consumed = buf->subbufs_produced;
}
EXPORT_SYMBOL_GPL(relay_subbufs_consumed);

/**
 *	relay_close - close the channel
 *	@chan: the channel
 *
 *	Closes all channel buffers and frees the channel.
 */
void relay_close(struct rchan *chan)
{
	unsigned int i;

	if (!chan)
		return;

	mutex_lock(&relay_channels_mutex);
	if (chan->is_global && chan->buf[0])
		relay_close_buf(chan->buf[0]);
	else
		for_each_possible_cpu(i)
			if (chan->buf[i])
				relay_close_buf(chan->buf[i]);

	if (chan->last_toobig)
		printk(KERN_WARNING "relay: one or more items not logged "
		       "[item size (%Zd) > sub-buffer size (%Zd)]\n",
		       chan->last_toobig, chan->subbuf_size);

	list_del(&chan->list);
	kref_put(&chan->kref, relay_destroy_channel);
	mutex_unlock(&relay_channels_mutex);
}
EXPORT_SYMBOL_GPL(relay_close);

/**
 *	relay_flush - close the channel
 *	@chan: the channel
 *
 *	Flushes all channel buffers, i.e. forces buffer switch.
 */
void relay_flush(struct rchan *chan)
{
	unsigned int i;

	if (!chan)
		return;

	if (chan->is_global && chan->buf[0]) {
		relay_switch_subbuf(chan->buf[0], 0);
		return;
	}

	mutex_lock(&relay_channels_mutex);
	for_each_possible_cpu(i)
		if (chan->buf[i])
			relay_switch_subbuf(chan->buf[i], 0);
	mutex_unlock(&relay_channels_mutex);
}
EXPORT_SYMBOL_GPL(relay_flush);

/**
 *	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_mmap - mmap file op for relay files
 *	@filp: the file
 *	@vma: the vma describing what to map
 *
 *	Calls upon relay_mmap_buf() to map the file into user space.
 */
static int relay_file_mmap(struct file *filp, struct vm_area_struct *vma)
{
	struct rchan_buf *buf = filp->private_data;
	return relay_mmap_buf(buf, vma);
}

/**
 *	relay_file_poll - poll file op for relay files
 *	@filp: the file
 *	@wait: poll table
 *
 *	Poll implemention.
 */
static unsigned int relay_file_poll(struct file *filp, poll_table *wait)
{
	unsigned int mask = 0;
	struct rchan_buf *buf = filp->private_data;

	if (buf->finalized)
		return POLLERR;