/*
   * A simple kernel FIFO implementation.
   *
   * Copyright (C) 2004 Stelian Pop <stelian@popies.net>
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
   *
   */
  
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/err.h>
  #include <linux/kfifo.h>

  #include <linux/log2.h>

  
  /**
   * kfifo_init - allocates a new FIFO using a preallocated buffer
   * @buffer: the preallocated buffer to be used.
   * @size: the size of the internal buffer, this have to be a power of 2.
   * @gfp_mask: get_free_pages mask, passed to kmalloc()
   * @lock: the lock to be used to protect the fifo buffer
   *

   * Do NOT pass the kfifo to kfifo_free() after use! Simply free the
   * &struct kfifo with kfree().

   */
  struct kfifo *kfifo_init(unsigned char *buffer, unsigned int size,

  			 gfp_t gfp_mask, spinlock_t *lock)

  {
  	struct kfifo *fifo;
  
  	/* size must be a power of 2 */

  	BUG_ON(!is_power_of_2(size));

  
  	fifo = kmalloc(sizeof(struct kfifo), gfp_mask);
  	if (!fifo)
  		return ERR_PTR(-ENOMEM);
  
  	fifo->buffer = buffer;
  	fifo->size = size;
  	fifo->in = fifo->out = 0;
  	fifo->lock = lock;
  
  	return fifo;
  }
  EXPORT_SYMBOL(kfifo_init);
  
  /**
   * kfifo_alloc - allocates a new FIFO and its internal buffer
   * @size: the size of the internal buffer to be allocated.
   * @gfp_mask: get_free_pages mask, passed to kmalloc()
   * @lock: the lock to be used to protect the fifo buffer
   *
   * The size will be rounded-up to a power of 2.
   */

  struct kfifo *kfifo_alloc(unsigned int size, gfp_t gfp_mask, spinlock_t *lock)

  {
  	unsigned char *buffer;
  	struct kfifo *ret;
  
  	/*
  	 * round up to the next power of 2, since our 'let the indices
  	 * wrap' tachnique works only in this case.
  	 */
  	if (size & (size - 1)) {
  		BUG_ON(size > 0x80000000);
  		size = roundup_pow_of_two(size);
  	}
  
  	buffer = kmalloc(size, gfp_mask);
  	if (!buffer)
  		return ERR_PTR(-ENOMEM);
  
  	ret = kfifo_init(buffer, size, gfp_mask, lock);
  
  	if (IS_ERR(ret))
  		kfree(buffer);
  
  	return ret;
  }
  EXPORT_SYMBOL(kfifo_alloc);
  
  /**
   * kfifo_free - frees the FIFO
   * @fifo: the fifo to be freed.
   */
  void kfifo_free(struct kfifo *fifo)
  {
  	kfree(fifo->buffer);
  	kfree(fifo);
  }
  EXPORT_SYMBOL(kfifo_free);
  
  /**
   * __kfifo_put - puts some data into the FIFO, no locking version
   * @fifo: the fifo to be used.
   * @buffer: the data to be added.
   * @len: the length of the data to be added.
   *

   * This function copies at most @len bytes from the @buffer into

   * the FIFO depending on the free space, and returns the number of
   * bytes copied.
   *
   * Note that with only one concurrent reader and one concurrent
   * writer, you don't need extra locking to use these functions.
   */
  unsigned int __kfifo_put(struct kfifo *fifo,
  			 unsigned char *buffer, unsigned int len)
  {
  	unsigned int l;
  
  	len = min(len, fifo->size - fifo->in + fifo->out);

  	/*
  	 * Ensure that we sample the fifo->out index -before- we
  	 * start putting bytes into the kfifo.
  	 */
  
  	smp_mb();

  	/* first put the data starting from fifo->in to buffer end */
  	l = min(len, fifo->size - (fifo->in & (fifo->size - 1)));
  	memcpy(fifo->buffer + (fifo->in & (fifo->size - 1)), buffer, l);
  
  	/* then put the rest (if any) at the beginning of the buffer */
  	memcpy(fifo->buffer, buffer + l, len - l);

  	/*
  	 * Ensure that we add the bytes to the kfifo -before-
  	 * we update the fifo->in index.
  	 */
  
  	smp_wmb();

  	fifo->in += len;
  
  	return len;
  }
  EXPORT_SYMBOL(__kfifo_put);
  
  /**
   * __kfifo_get - gets some data from the FIFO, no locking version
   * @fifo: the fifo to be used.
   * @buffer: where the data must be copied.
   * @len: the size of the destination buffer.
   *

   * This function copies at most @len bytes from the FIFO into the
   * @buffer and returns the number of copied bytes.

   *
   * Note that with only one concurrent reader and one concurrent
   * writer, you don't need extra locking to use these functions.
   */
  unsigned int __kfifo_get(struct kfifo *fifo,
  			 unsigned char *buffer, unsigned int len)
  {
  	unsigned int l;
  
  	len = min(len, fifo->in - fifo->out);

  	/*
  	 * Ensure that we sample the fifo->in index -before- we
  	 * start removing bytes from the kfifo.
  	 */
  
  	smp_rmb();

  	/* first get the data from fifo->out until the end of the buffer */
  	l = min(len, fifo->size - (fifo->out & (fifo->size - 1)));
  	memcpy(buffer, fifo->buffer + (fifo->out & (fifo->size - 1)), l);
  
  	/* then get the rest (if any) from the beginning of the buffer */
  	memcpy(buffer + l, fifo->buffer, len - l);

  	/*
  	 * Ensure that we remove the bytes from the kfifo -before-
  	 * we update the fifo->out index.
  	 */
  
  	smp_mb();

  	fifo->out += len;
  
  	return len;
  }
  EXPORT_SYMBOL(__kfifo_get);