/*
   * Public API and common code for kernel->userspace relay file support.
   *

   * See Documentation/filesystems/relay.txt for an overview.

   *
   * Copyright (C) 2002-2005 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
   * Copyright (C) 1999-2005 - Karim Yaghmour (karim@opersys.com)
   *
   * Moved to kernel/relay.c by Paul Mundt, 2006.

   * November 2006 - CPU hotplug support by Mathieu Desnoyers
   * 	(mathieu.desnoyers@polymtl.ca)

   *
   * This file is released under the GPL.
   */
  #include <linux/errno.h>
  #include <linux/stddef.h>
  #include <linux/slab.h>

  #include <linux/export.h>

  #include <linux/string.h>
  #include <linux/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);

  
  /*
   * close() vm_op implementation for relay file mapping.
   */
  static void relay_file_mmap_close(struct vm_area_struct *vma)
  {
  	struct rchan_buf *buf = vma->vm_private_data;
  	buf->chan->cb->buf_unmapped(buf, vma->vm_file);
  }
  
  /*

   * fault() vm_op implementation for relay file mapping.

   */

  static vm_fault_t relay_buf_fault(struct vm_fault *vmf)

  {
  	struct page *page;

  	struct rchan_buf *buf = vmf->vma->vm_private_data;

  	pgoff_t pgoff = vmf->pgoff;

  	if (!buf)

  		return VM_FAULT_OOM;

  	page = vmalloc_to_page(buf->start + (pgoff << PAGE_SHIFT));

  	if (!page)

  		return VM_FAULT_SIGBUS;

  	get_page(page);

  	vmf->page = page;

  	return 0;

  }
  
  /*
   * vm_ops for relay file mappings.
   */

  static const struct vm_operations_struct relay_file_mmap_ops = {

  	.fault = relay_buf_fault,

  	.close = relay_file_mmap_close,
  };

  /*
   * allocate an array of pointers of struct page
   */
  static struct page **relay_alloc_page_array(unsigned int n_pages)
  {

  	const size_t pa_size = n_pages * sizeof(struct page *);
  	if (pa_size > PAGE_SIZE)
  		return vzalloc(pa_size);
  	return kzalloc(pa_size, GFP_KERNEL);

  }
  
  /*
   * free an array of pointers of struct page
   */
  static void relay_free_page_array(struct page **array)
  {

  	kvfree(array);

  }

  /**
   *	relay_mmap_buf: - mmap channel buffer to process address space
   *	@buf: relay channel buffer
   *	@vma: vm_area_struct describing memory to be mapped
   *
   *	Returns 0 if ok, negative on error
   *
   *	Caller should already have grabbed mmap_sem.
   */

  static int relay_mmap_buf(struct rchan_buf *buf, struct vm_area_struct *vma)

  {
  	unsigned long length = vma->vm_end - vma->vm_start;
  	struct file *filp = vma->vm_file;
  
  	if (!buf)
  		return -EBADF;
  
  	if (length != (unsigned long)buf->chan->alloc_size)
  		return -EINVAL;
  
  	vma->vm_ops = &relay_file_mmap_ops;

  	vma->vm_flags |= VM_DONTEXPAND;

  	vma->vm_private_data = buf;
  	buf->chan->cb->buf_mapped(buf, filp);
  
  	return 0;
  }
  
  /**
   *	relay_alloc_buf - allocate a channel buffer
   *	@buf: the buffer struct
   *	@size: total size of the buffer
   *

   *	Returns a pointer to the resulting buffer, %NULL if unsuccessful. The

   *	passed in size will get page aligned, if it isn't already.

   */

  static void *relay_alloc_buf(struct rchan_buf *buf, size_t *size)

  {
  	void *mem;
  	unsigned int i, j, n_pages;

  	*size = PAGE_ALIGN(*size);
  	n_pages = *size >> PAGE_SHIFT;

  	buf->page_array = relay_alloc_page_array(n_pages);

  	if (!buf->page_array)
  		return NULL;
  
  	for (i = 0; i < n_pages; i++) {
  		buf->page_array[i] = alloc_page(GFP_KERNEL);
  		if (unlikely(!buf->page_array[i]))
  			goto depopulate;

  		set_page_private(buf->page_array[i], (unsigned long)buf);

  	}
  	mem = vmap(buf->page_array, n_pages, VM_MAP, PAGE_KERNEL);
  	if (!mem)
  		goto depopulate;

  	memset(mem, 0, *size);

  	buf->page_count = n_pages;
  	return mem;
  
  depopulate:
  	for (j = 0; j < i; j++)
  		__free_page(buf->page_array[j]);

  	relay_free_page_array(buf->page_array);

  	return NULL;
  }
  
  /**
   *	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)

  {

  	struct rchan_buf *buf;

  	if (chan->n_subbufs > KMALLOC_MAX_SIZE / sizeof(size_t *))

  		return NULL;

  	buf = kzalloc(sizeof(struct rchan_buf), GFP_KERNEL);
  	if (!buf)
  		return NULL;

  	buf->padding = kmalloc_array(chan->n_subbufs, sizeof(size_t *),
  				     GFP_KERNEL);

  	if (!buf->padding)
  		goto free_buf;

  	buf->start = relay_alloc_buf(buf, &chan->alloc_size);

  	if (!buf->start)
  		goto free_buf;
  
  	buf->chan = chan;
  	kref_get(&buf->chan->kref);
  	return buf;
  
  free_buf:
  	kfree(buf->padding);
  	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;
  	unsigned int i;
  
  	if (likely(buf->start)) {
  		vunmap(buf->start);
  		for (i = 0; i < buf->page_count; i++)
  			__free_page(buf->page_array[i]);

  		relay_free_page_array(buf->page_array);

  	}

  	*per_cpu_ptr(chan->buf, buf->cpu) = NULL;

  	kfree(buf->padding);
  	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 filesystem, 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);

  	relay_destroy_buf(buf);
  }
  
  /**
   *	relay_buf_empty - boolean, is the channel buffer empty?
   *	@buf: channel buffer
   *
   *	Returns 1 if the buffer is empty, 0 otherwise.
   */

  static int relay_buf_empty(struct rchan_buf *buf)

  {
  	return (buf->subbufs_produced - buf->subbufs_consumed) ? 0 : 1;
  }

  
  /**
   *	relay_buf_full - boolean, is the channel buffer full?
   *	@buf: channel buffer
   *
   *	Returns 1 if the buffer is full, 0 otherwise.
   */
  int relay_buf_full(struct rchan_buf *buf)
  {
  	size_t ready = buf->subbufs_produced - buf->subbufs_consumed;
  	return (ready >= buf->chan->n_subbufs) ? 1 : 0;
  }
  EXPORT_SYMBOL_GPL(relay_buf_full);
  
  /*
   * 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.
   */
  
  /*
   * subbuf_start() default callback.  Does nothing.
   */
  static int subbuf_start_default_callback (struct rchan_buf *buf,
  					  void *subbuf,
  					  void *prev_subbuf,
  					  size_t prev_padding)
  {
  	if (relay_buf_full(buf))
  		return 0;
  
  	return 1;
  }
  
  /*
   * buf_mapped() default callback.  Does nothing.
   */
  static void buf_mapped_default_callback(struct rchan_buf *buf,
  					struct file *filp)
  {
  }
  
  /*
   * buf_unmapped() default callback.  Does nothing.
   */
  static void buf_unmapped_default_callback(struct rchan_buf *buf,
  					  struct file *filp)
  {
  }
  
  /*
   * create_buf_file_create() default callback.  Does nothing.
   */
  static struct dentry *create_buf_file_default_callback(const char *filename,
  						       struct dentry *parent,

  						       umode_t mode,

  						       struct rchan_buf *buf,
  						       int *is_global)
  {
  	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 = {
  	.subbuf_start = subbuf_start_default_callback,
  	.buf_mapped = buf_mapped_default_callback,
  	.buf_unmapped = buf_unmapped_default_callback,
  	.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

   *	@work: contains the channel buffer

   *

   *	This is the function used to defer reader waking

   */

  static void wakeup_readers(struct irq_work *work)

  {

  	struct rchan_buf *buf;
  
  	buf = container_of(work, struct rchan_buf, wakeup_work);

  	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)

  {
  	size_t i;
  
  	if (init) {
  		init_waitqueue_head(&buf->read_wait);
  		kref_init(&buf->kref);

  		init_irq_work(&buf->wakeup_work, wakeup_readers);
  	} else {
  		irq_work_sync(&buf->wakeup_work);
  	}

  
  	buf->subbufs_produced = 0;
  	buf->subbufs_consumed = 0;
  	buf->bytes_consumed = 0;
  	buf->finalized = 0;
  	buf->data = buf->start;
  	buf->offset = 0;
  
  	for (i = 0; i < buf->chan->n_subbufs; i++)
  		buf->padding[i] = 0;
  
  	buf->chan->cb->subbuf_start(buf, buf->data, NULL, 0);
  }
  
  /**
   *	relay_reset - reset the channel
   *	@chan: the channel
   *
   *	This has the effect of erasing all data from all channel buffers
   *	and restarting the channel in its initial state.  The buffers
   *	are not freed, so any mappings are still in effect.
   *

   *	NOTE. Care should be taken that the channel isn't actually

   *	being used by anything when this call is made.
   */
  void relay_reset(struct rchan *chan)
  {

  	struct rchan_buf *buf;

  	unsigned int i;

  
  	if (!chan)
  		return;

  	if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0))) {
  		__relay_reset(buf, 0);

  		return;

  	}

  
  	mutex_lock(&relay_channels_mutex);

  	for_each_possible_cpu(i)

  		if ((buf = *per_cpu_ptr(chan->buf, i)))
  			__relay_reset(buf, 0);

  	mutex_unlock(&relay_channels_mutex);

  }
  EXPORT_SYMBOL_GPL(relay_reset);

  static inline void relay_set_buf_dentry(struct rchan_buf *buf,
  					struct dentry *dentry)
  {
  	buf->dentry = dentry;

  	d_inode(buf->dentry)->i_size = buf->early_bytes;

  }
  
  static struct dentry *relay_create_buf_file(struct rchan *chan,
  					    struct rchan_buf *buf,
  					    unsigned int cpu)
  {
  	struct dentry *dentry;
  	char *tmpname;
  
  	tmpname = kzalloc(NAME_MAX + 1, GFP_KERNEL);
  	if (!tmpname)
  		return NULL;
  	snprintf(tmpname, NAME_MAX, "%s%d", chan->base_filename, cpu);
  
  	/* Create file in fs */
  	dentry = chan->cb->create_buf_file(tmpname, chan->parent,
  					   S_IRUSR, buf,
  					   &chan->is_global);

  	if (IS_ERR(dentry))
  		dentry = NULL;

  
  	kfree(tmpname);
  
  	return dentry;
  }

  /*

   *	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;

   	if (chan->is_global)

  		return *per_cpu_ptr(chan->buf, 0);

  
  	buf = relay_create_buf(chan);
  	if (!buf)

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

  	} else {
  		/* Only retrieve global info, nothing more, nothing less */
  		dentry = chan->cb->create_buf_file(NULL, NULL,
  						   S_IRUSR, buf,
  						   &chan->is_global);

  		if (IS_ERR_OR_NULL(dentry))

  			goto free_buf;

  	}

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

   	if(chan->is_global) {

  		*per_cpu_ptr(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;

  	irq_work_sync(&buf->wakeup_work);

  	buf->chan->cb->remove_buf_file(buf->dentry);

  	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;
  }

  int relay_prepare_cpu(unsigned int cpu)

  {

  	struct rchan *chan;

  	struct rchan_buf *buf;

  	mutex_lock(&relay_channels_mutex);
  	list_for_each_entry(chan, &relay_channels, list) {
  		if ((buf = *per_cpu_ptr(chan->buf, cpu)))
  			continue;
  		buf = relay_open_buf(chan, cpu);
  		if (!buf) {
  			pr_err("relay: cpu %d buffer creation failed
  ", cpu);
  			mutex_unlock(&relay_channels_mutex);
  			return -ENOMEM;

  		}

  		*per_cpu_ptr(chan->buf, cpu) = buf;

  	}

  	mutex_unlock(&relay_channels_mutex);
  	return 0;

  }
  
  /**

   *	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.

   *
   *	If opening a buffer (@parent = NULL) that you later wish to register
   *	in a filesystem, call relay_late_setup_files() once the @parent dentry
   *	is available.

   */
  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;

  	struct rchan_buf *buf;

  
  	if (!(subbuf_size && n_subbufs))
  		return NULL;

  	if (subbuf_size > UINT_MAX / n_subbufs)
  		return NULL;

  	chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);

  	if (!chan)
  		return NULL;

  	chan->buf = alloc_percpu(struct rchan_buf *);

  	chan->version = RELAYFS_CHANNEL_VERSION;
  	chan->n_subbufs = n_subbufs;
  	chan->subbuf_size = subbuf_size;

  	chan->alloc_size = PAGE_ALIGN(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) {

  		buf = relay_open_buf(chan, i);
  		if (!buf)

  			goto free_bufs;

  		*per_cpu_ptr(chan->buf, i) = buf;

  	}

  	list_add(&chan->list, &relay_channels);
  	mutex_unlock(&relay_channels_mutex);

  	return chan;
  
  free_bufs:

  	for_each_possible_cpu(i) {

  		if ((buf = *per_cpu_ptr(chan->buf, i)))
  			relay_close_buf(buf);

  	}

  	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 created
   *	by relay_open() with a NULL parent dentry.
   *
   *	For example, this is useful for perfomring early tracing in kernel,
   *	before VFS is up and then exposing the early results once the dentry
   *	is available.

   */
  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_buf *buf;

  	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)) {
  		mutex_unlock(&relay_channels_mutex);

  		return -EEXIST;

  	}

  	chan->has_base_filename = 1;
  	chan->parent = parent;

  
  	if (chan->is_global) {
  		err = -EINVAL;

  		buf = *per_cpu_ptr(chan->buf, 0);
  		if (!WARN_ON_ONCE(!buf)) {
  			dentry = relay_create_buf_file(chan, buf, 0);

  			if (dentry && !WARN_ON_ONCE(!chan->is_global)) {

  				relay_set_buf_dentry(buf, dentry);

  				err = 0;
  			}
  		}
  		mutex_unlock(&relay_channels_mutex);
  		return err;
  	}

  	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) {

  		buf = *per_cpu_ptr(chan->buf, i);
  		if (unlikely(!buf)) {

  			WARN_ONCE(1, KERN_ERR "CPU has no buffer!
  ");

  			err = -EINVAL;
  			break;
  		}

  		dentry = relay_create_buf_file(chan, buf, i);

  		if (unlikely(!dentry)) {
  			err = -EINVAL;
  			break;
  		}
  
  		if (curr_cpu == i) {
  			local_irq_save(flags);

  			relay_set_buf_dentry(buf, dentry);

  			local_irq_restore(flags);
  		} else {

  			disp.buf = buf;

  			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;
  }

  EXPORT_SYMBOL_GPL(relay_late_setup_files);

  /**
   *	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)

  			d_inode(buf->dentry)->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.
  			 */

  			irq_work_queue(&buf->wakeup_work);
  		}

  	}
  
  	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 || cpu >= NR_CPUS)

  		return;

  	buf = *per_cpu_ptr(chan->buf, cpu);

  	if (!buf || subbufs_consumed > chan->n_subbufs)

  		return;

  	if (subbufs_consumed > buf->subbufs_produced - buf->subbufs_consumed)

  		buf->subbufs_consumed = buf->subbufs_produced;

  	else
  		buf->subbufs_consumed += subbufs_consumed;

  }
  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)
  {

  	struct rchan_buf *buf;

  	unsigned int i;

  
  	if (!chan)
  		return;

  	mutex_lock(&relay_channels_mutex);

  	if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0)))
  		relay_close_buf(buf);

  	else
  		for_each_possible_cpu(i)

  			if ((buf = *per_cpu_ptr(chan->buf, i)))
  				relay_close_buf(buf);

  
  	if (chan->last_toobig)
  		printk(KERN_WARNING "relay: one or more items not logged "

  		       "[item size (%zd) > sub-buffer size (%zd)]
  ",

  		       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)
  {

  	struct rchan_buf *buf;

  	unsigned int i;

  
  	if (!chan)
  		return;

  	if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0))) {
  		relay_switch_subbuf(buf, 0);

  		return;

  	}

  
  	mutex_lock(&relay_channels_mutex);
  	for_each_possible_cpu(i)

  		if ((buf = *per_cpu_ptr(chan->buf, i)))
  			relay_switch_subbuf(buf, 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 __poll_t relay_file_poll(struct file *filp, poll_table *wait)

  {

  	__poll_t mask = 0;

  	struct rchan_buf *buf = filp->private_data;
  
  	if (buf->finalized)

  		return EPOLLERR;

  
  	if (filp->f_mode & FMODE_READ) {
  		poll_wait(filp, &buf->read_wait, wait);
  		if (!relay_buf_empty(buf))

  			mask |= EPOLLIN | EPOLLRDNORM;

  	}
  
  	return mask;
  }
  
  /**
   *	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;
  }

  /*

   *	relay_file_read_consume - update the consumed count for the buffer
   */
  static void relay_file_read_consume(struct rchan_buf *buf,
  				    size_t read_pos,
  				    size_t bytes_consumed)
  {
  	size_t subbuf_size = buf->chan->subbuf_size;
  	size_t n_subbufs = buf->chan->n_subbufs;
  	size_t read_subbuf;

  	if (buf->subbufs_produced == buf->subbufs_consumed &&
  	    buf->offset == buf->bytes_consumed)
  		return;

  	if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
  		relay_subbufs_consumed(buf->chan, buf->cpu, 1);
  		buf->bytes_consumed = 0;
  	}
  
  	buf->bytes_consumed += bytes_consumed;

  	if (!read_pos)
  		read_subbuf = buf->subbufs_consumed % n_subbufs;
  	else
  		read_subbuf = read_pos / buf->chan->subbuf_size;

  	if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
  		if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
  		    (buf->offset == subbuf_size))
  			return;
  		relay_subbufs_consumed(buf->chan, buf->cpu, 1);
  		buf->bytes_consumed = 0;
  	}
  }

  /*

   *	relay_file_read_avail - boolean, are there unconsumed bytes available?
   */
  static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
  {

  	size_t subbuf_size = buf->chan->subbuf_size;
  	size_t n_subbufs = buf->chan->n_subbufs;

  	size_t produced = buf->subbufs_produced;
  	size_t consumed = buf->subbufs_consumed;

  	relay_file_read_consume(buf, read_pos, 0);

  	consumed = buf->subbufs_consumed;

  	if (unlikely(buf->offset > subbuf_size)) {
  		if (produced == consumed)
  			return 0;
  		return 1;

  	}

  	if (unlikely(produced - consumed >= n_subbufs)) {

  		consumed = produced - n_subbufs + 1;

  		buf->subbufs_consumed = consumed;

  		buf->bytes_consumed = 0;

  	}

  	produced = (produced % n_subbufs) * subbuf_size + buf->offset;
  	consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
  
  	if (consumed > produced)
  		produced += n_subbufs * subbuf_size;

  	if (consumed == produced) {
  		if (buf->offset == subbuf_size &&
  		    buf->subbufs_produced > buf->subbufs_consumed)
  			return 1;

  		return 0;

  	}

  	return 1;
  }
  
  /**
   *	relay_file_read_subbuf_avail - return bytes available in sub-buffer

   *	@read_pos: file read position
   *	@buf: relay channel buffer

   */
  static size_t relay_file_read_subbuf_avail(size_t read_pos,
  					   struct rchan_buf *buf)
  {
  	size_t padding, avail = 0;
  	size_t read_subbuf, read_offset, write_subbuf, write_offset;
  	size_t subbuf_size = buf->chan->subbuf_size;
  
  	write_subbuf = (buf->data - buf->start) / subbuf_size;
  	write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
  	read_subbuf = read_pos / subbuf_size;
  	read_offset = read_pos % subbuf_size;
  	padding = buf->padding[read_subbuf];
  
  	if (read_subbuf == write_subbuf) {
  		if (read_offset + padding < write_offset)
  			avail = write_offset - (read_offset + padding);
  	} else
  		avail = (subbuf_size - padding) - read_offset;
  
  	return avail;
  }
  
  /**
   *	relay_file_read_start_pos - find the first available byte to read

   *	@read_pos: file read position
   *	@buf: relay channel buffer

   *

   *	If the @read_pos is in the middle of padding, return the

   *	position of the first actually available byte, otherwise
   *	return the original value.
   */
  static size_t relay_file_read_start_pos(size_t read_pos,
  					struct rchan_buf *buf)
  {
  	size_t read_subbuf, padding, padding_start, padding_end;
  	size_t subbuf_size = buf->chan->subbuf_size;
  	size_t n_subbufs = buf->chan->n_subbufs;

  	size_t consumed = buf->subbufs_consumed % n_subbufs;

  	if (!read_pos)
  		read_pos = consumed * subbuf_size + buf->bytes_consumed;

  	read_subbuf = read_pos / subbuf_size;
  	padding = buf->padding[read_subbuf];
  	padding_start = (read_subbuf + 1) * subbuf_size - padding;
  	padding_end = (read_subbuf + 1) * subbuf_size;
  	if (read_pos >= padding_start && read_pos < padding_end) {
  		read_subbuf = (read_subbuf + 1) % n_subbufs;
  		read_pos = read_subbuf * subbuf_size;
  	}
  
  	return read_pos;
  }
  
  /**
   *	relay_file_read_end_pos - return the new read position

   *	@read_pos: file read position
   *	@buf: relay channel buffer
   *	@count: number of bytes to be read

   */
  static size_t relay_file_read_end_pos(struct rchan_buf *buf,
  				      size_t read_pos,
  				      size_t count)
  {
  	size_t read_subbuf, padding, end_pos;
  	size_t subbuf_size = buf->chan->subbuf_size;
  	size_t n_subbufs = buf->chan->n_subbufs;
  
  	read_subbuf = read_pos / subbuf_size;
  	padding = buf->padding[read_subbuf];
  	if (read_pos % subbuf_size + count + padding == subbuf_size)
  		end_pos = (read_subbuf + 1) * subbuf_size;
  	else
  		end_pos = read_pos + count;
  	if (end_pos >= subbuf_size * n_subbufs)
  		end_pos = 0;
  
  	return end_pos;
  }

  static ssize_t relay_file_read(struct file *filp,
  			       char __user *buffer,
  			       size_t count,
  			       loff_t *ppos)

  {

  	struct rchan_buf *buf = filp->private_data;
  	size_t read_start, avail;

  	size_t written = 0;

  	int ret;

  	if (!count)

  		return 0;

  	inode_lock(file_inode(filp));

  	do {

  		void *from;

  		if (!relay_file_read_avail(buf, *ppos))
  			break;
  
  		read_start = relay_file_read_start_pos(*ppos, buf);
  		avail = relay_file_read_subbuf_avail(read_start, buf);
  		if (!avail)

  			break;

  		avail = min(count, avail);
  		from = buf->start + read_start;
  		ret = avail;
  		if (copy_to_user(buffer, from, avail))

  			break;

  		buffer += ret;
  		written += ret;
  		count -= ret;

  		relay_file_read_consume(buf, read_start, ret);
  		*ppos = relay_file_read_end_pos(buf, read_start, ret);
  	} while (count);
  	inode_unlock(file_inode(filp));

  	return written;

  }

  static void relay_consume_bytes(struct rchan_buf *rbuf, int bytes_consumed)
  {
  	rbuf->bytes_consumed += bytes_consumed;
  
  	if (rbuf->bytes_consumed >= rbuf->chan->subbuf_size) {
  		relay_subbufs_consumed(rbuf->chan, rbuf->cpu, 1);
  		rbuf->bytes_consumed %= rbuf->chan->subbuf_size;
  	}
  }

  static void relay_pipe_buf_release(struct pipe_inode_info *pipe,
  				   struct pipe_buffer *buf)

  {

  	struct rchan_buf *rbuf;
  
  	rbuf = (struct rchan_buf *)page_private(buf->page);

  	relay_consume_bytes(rbuf, buf->private);

  }

  static const struct pipe_buf_operations relay_pipe_buf_ops = {

  	.confirm = generic_pipe_buf_confirm,

  	.release = relay_pipe_buf_release,
  	.steal = generic_pipe_buf_steal,
  	.get = generic_pipe_buf_get,
  };

  static void relay_page_release(struct splice_pipe_desc *spd, unsigned int i)
  {
  }

  /*

   *	subbuf_splice_actor - splice up to one subbuf's worth of data
   */

  static ssize_t subbuf_splice_actor(struct file *in,

  			       loff_t *ppos,
  			       struct pipe_inode_info *pipe,
  			       size_t len,
  			       unsigned int flags,
  			       int *nonpad_ret)
  {

  	unsigned int pidx, poff, total_len, subbuf_pages, nr_pages;

  	struct rchan_buf *rbuf = in->private_data;
  	unsigned int subbuf_size = rbuf->chan->subbuf_size;

  	uint64_t pos = (uint64_t) *ppos;
  	uint32_t alloc_size = (uint32_t) rbuf->chan->alloc_size;
  	size_t read_start = (size_t) do_div(pos, alloc_size);

  	size_t read_subbuf = read_start / subbuf_size;
  	size_t padding = rbuf->padding[read_subbuf];
  	size_t nonpad_end = read_subbuf * subbuf_size + subbuf_size - padding;

  	struct page *pages[PIPE_DEF_BUFFERS];
  	struct partial_page partial[PIPE_DEF_BUFFERS];

  	struct splice_pipe_desc spd = {
  		.pages = pages,
  		.nr_pages = 0,

  		.nr_pages_max = PIPE_DEF_BUFFERS,

  		.partial = partial,

  		.ops = &relay_pipe_buf_ops,

  		.spd_release = relay_page_release,

  	};

  	ssize_t ret;

  
  	if (rbuf->subbufs_produced == rbuf->subbufs_consumed)
  		return 0;

  	if (splice_grow_spd(pipe, &spd))
  		return -ENOMEM;

  	/*
  	 * Adjust read len, if longer than what is available
  	 */
  	if (len > (subbuf_size - read_start % subbuf_size))
  		len = subbuf_size - read_start % subbuf_size;

  
  	subbuf_pages = rbuf->chan->alloc_size >> PAGE_SHIFT;
  	pidx = (read_start / PAGE_SIZE) % subbuf_pages;
  	poff = read_start & ~PAGE_MASK;

  	nr_pages = min_t(unsigned int, subbuf_pages, spd.nr_pages_max);

  	for (total_len = 0; spd.nr_pages < nr_pages; spd.nr_pages++) {

  		unsigned int this_len, this_end, private;
  		unsigned int cur_pos = read_start + total_len;

  		if (!len)

  			break;

  		this_len = min_t(unsigned long, len, PAGE_SIZE - poff);
  		private = this_len;

  		spd.pages[spd.nr_pages] = rbuf->page_array[pidx];
  		spd.partial[spd.nr_pages].offset = poff;

  		this_end = cur_pos + this_len;
  		if (this_end >= nonpad_end) {
  			this_len = nonpad_end - cur_pos;
  			private = this_len + padding;

  		}

  		spd.partial[spd.nr_pages].len = this_len;
  		spd.partial[spd.nr_pages].private = private;

  		len -= this_len;
  		total_len += this_len;
  		poff = 0;
  		pidx = (pidx + 1) % subbuf_pages;

  		if (this_end >= nonpad_end) {
  			spd.nr_pages++;

  			break;
  		}

  	}

  	ret = 0;

  	if (!spd.nr_pages)

  		goto out;

  	ret = *nonpad_ret = splice_to_pipe(pipe, &spd);
  	if (ret < 0 || ret < total_len)

  		goto out;

          if (read_start + ret == nonpad_end)
                  ret += padding;

  out:

  	splice_shrink_spd(&spd);
  	return ret;

  }
  
  static ssize_t relay_file_splice_read(struct file *in,
  				      loff_t *ppos,
  				      struct pipe_inode_info *pipe,
  				      size_t len,
  				      unsigned int flags)
  {
  	ssize_t spliced;
  	int ret;
  	int nonpad_ret = 0;
  
  	ret = 0;
  	spliced = 0;

  	while (len && !spliced) {

  		ret = subbuf_splice_actor(in, ppos, pipe, len, flags, &nonpad_ret);
  		if (ret < 0)
  			break;
  		else if (!ret) {

  			if (flags & SPLICE_F_NONBLOCK)

  				ret = -EAGAIN;

  			break;

  		}
  
  		*ppos += ret;
  		if (ret > len)
  			len = 0;
  		else
  			len -= ret;
  		spliced += nonpad_ret;
  		nonpad_ret = 0;
  	}
  
  	if (spliced)
  		return spliced;
  
  	return ret;

  }

  const struct file_operations relay_file_operations = {

  	.open		= relay_file_open,
  	.poll		= relay_file_poll,
  	.mmap		= relay_file_mmap,
  	.read		= relay_file_read,
  	.llseek		= no_llseek,
  	.release	= relay_file_release,

  	.splice_read	= relay_file_splice_read,

  };
  EXPORT_SYMBOL_GPL(relay_file_operations);