/*
   * Copyright (C) 2007 Jens Axboe <jens.axboe@oracle.com>
   *
   * Scatterlist handling helpers.
   *
   * This source code is licensed under the GNU General Public License,
   * Version 2. See the file COPYING for more details.
   */
  #include <linux/module.h>
  #include <linux/scatterlist.h>

  #include <linux/highmem.h>

  
  /**
   * sg_next - return the next scatterlist entry in a list
   * @sg:		The current sg entry
   *
   * Description:
   *   Usually the next entry will be @sg@ + 1, but if this sg element is part
   *   of a chained scatterlist, it could jump to the start of a new
   *   scatterlist array.
   *
   **/
  struct scatterlist *sg_next(struct scatterlist *sg)
  {
  #ifdef CONFIG_DEBUG_SG
  	BUG_ON(sg->sg_magic != SG_MAGIC);
  #endif
  	if (sg_is_last(sg))
  		return NULL;
  
  	sg++;
  	if (unlikely(sg_is_chain(sg)))
  		sg = sg_chain_ptr(sg);
  
  	return sg;
  }
  EXPORT_SYMBOL(sg_next);
  
  /**
   * sg_last - return the last scatterlist entry in a list
   * @sgl:	First entry in the scatterlist
   * @nents:	Number of entries in the scatterlist
   *
   * Description:
   *   Should only be used casually, it (currently) scans the entire list
   *   to get the last entry.
   *
   *   Note that the @sgl@ pointer passed in need not be the first one,
   *   the important bit is that @nents@ denotes the number of entries that
   *   exist from @sgl@.
   *
   **/
  struct scatterlist *sg_last(struct scatterlist *sgl, unsigned int nents)
  {
  #ifndef ARCH_HAS_SG_CHAIN
  	struct scatterlist *ret = &sgl[nents - 1];
  #else
  	struct scatterlist *sg, *ret = NULL;
  	unsigned int i;
  
  	for_each_sg(sgl, sg, nents, i)
  		ret = sg;
  
  #endif
  #ifdef CONFIG_DEBUG_SG
  	BUG_ON(sgl[0].sg_magic != SG_MAGIC);
  	BUG_ON(!sg_is_last(ret));
  #endif
  	return ret;
  }
  EXPORT_SYMBOL(sg_last);
  
  /**
   * sg_init_table - Initialize SG table
   * @sgl:	   The SG table
   * @nents:	   Number of entries in table
   *
   * Notes:
   *   If this is part of a chained sg table, sg_mark_end() should be
   *   used only on the last table part.
   *
   **/
  void sg_init_table(struct scatterlist *sgl, unsigned int nents)
  {
  	memset(sgl, 0, sizeof(*sgl) * nents);
  #ifdef CONFIG_DEBUG_SG
  	{
  		unsigned int i;
  		for (i = 0; i < nents; i++)
  			sgl[i].sg_magic = SG_MAGIC;
  	}
  #endif
  	sg_mark_end(&sgl[nents - 1]);
  }
  EXPORT_SYMBOL(sg_init_table);
  
  /**
   * sg_init_one - Initialize a single entry sg list
   * @sg:		 SG entry
   * @buf:	 Virtual address for IO
   * @buflen:	 IO length
   *
   **/
  void sg_init_one(struct scatterlist *sg, const void *buf, unsigned int buflen)
  {
  	sg_init_table(sg, 1);
  	sg_set_buf(sg, buf, buflen);
  }
  EXPORT_SYMBOL(sg_init_one);
  
  /*
   * The default behaviour of sg_alloc_table() is to use these kmalloc/kfree
   * helpers.
   */
  static struct scatterlist *sg_kmalloc(unsigned int nents, gfp_t gfp_mask)
  {
  	if (nents == SG_MAX_SINGLE_ALLOC)
  		return (struct scatterlist *) __get_free_page(gfp_mask);
  	else
  		return kmalloc(nents * sizeof(struct scatterlist), gfp_mask);
  }
  
  static void sg_kfree(struct scatterlist *sg, unsigned int nents)
  {
  	if (nents == SG_MAX_SINGLE_ALLOC)
  		free_page((unsigned long) sg);
  	else
  		kfree(sg);
  }
  
  /**
   * __sg_free_table - Free a previously mapped sg table
   * @table:	The sg table header to use

   * @max_ents:	The maximum number of entries per single scatterlist

   * @free_fn:	Free function
   *
   *  Description:

   *    Free an sg table previously allocated and setup with
   *    __sg_alloc_table().  The @max_ents value must be identical to
   *    that previously used with __sg_alloc_table().

   *
   **/

  void __sg_free_table(struct sg_table *table, unsigned int max_ents,
  		     sg_free_fn *free_fn)

  {
  	struct scatterlist *sgl, *next;
  
  	if (unlikely(!table->sgl))
  		return;
  
  	sgl = table->sgl;
  	while (table->orig_nents) {
  		unsigned int alloc_size = table->orig_nents;
  		unsigned int sg_size;
  
  		/*

  		 * If we have more than max_ents segments left,

  		 * then assign 'next' to the sg table after the current one.
  		 * sg_size is then one less than alloc size, since the last
  		 * element is the chain pointer.
  		 */

  		if (alloc_size > max_ents) {
  			next = sg_chain_ptr(&sgl[max_ents - 1]);
  			alloc_size = max_ents;

  			sg_size = alloc_size - 1;
  		} else {
  			sg_size = alloc_size;
  			next = NULL;
  		}
  
  		table->orig_nents -= sg_size;
  		free_fn(sgl, alloc_size);
  		sgl = next;
  	}
  
  	table->sgl = NULL;
  }
  EXPORT_SYMBOL(__sg_free_table);
  
  /**
   * sg_free_table - Free a previously allocated sg table
   * @table:	The mapped sg table header
   *
   **/
  void sg_free_table(struct sg_table *table)
  {

  	__sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);

  }
  EXPORT_SYMBOL(sg_free_table);
  
  /**
   * __sg_alloc_table - Allocate and initialize an sg table with given allocator
   * @table:	The sg table header to use
   * @nents:	Number of entries in sg list

   * @max_ents:	The maximum number of entries the allocator returns per call

   * @gfp_mask:	GFP allocation mask
   * @alloc_fn:	Allocator to use
   *

   * Description:
   *   This function returns a @table @nents long. The allocator is
   *   defined to return scatterlist chunks of maximum size @max_ents.
   *   Thus if @nents is bigger than @max_ents, the scatterlists will be
   *   chained in units of @max_ents.
   *

   * Notes:
   *   If this function returns non-0 (eg failure), the caller must call
   *   __sg_free_table() to cleanup any leftover allocations.
   *
   **/

  int __sg_alloc_table(struct sg_table *table, unsigned int nents,
  		     unsigned int max_ents, gfp_t gfp_mask,

  		     sg_alloc_fn *alloc_fn)
  {
  	struct scatterlist *sg, *prv;
  	unsigned int left;
  
  #ifndef ARCH_HAS_SG_CHAIN

  	BUG_ON(nents > max_ents);

  #endif
  
  	memset(table, 0, sizeof(*table));
  
  	left = nents;
  	prv = NULL;
  	do {
  		unsigned int sg_size, alloc_size = left;

  		if (alloc_size > max_ents) {
  			alloc_size = max_ents;

  			sg_size = alloc_size - 1;
  		} else
  			sg_size = alloc_size;
  
  		left -= sg_size;
  
  		sg = alloc_fn(alloc_size, gfp_mask);
  		if (unlikely(!sg))
  			return -ENOMEM;
  
  		sg_init_table(sg, alloc_size);
  		table->nents = table->orig_nents += sg_size;
  
  		/*
  		 * If this is the first mapping, assign the sg table header.
  		 * If this is not the first mapping, chain previous part.
  		 */
  		if (prv)

  			sg_chain(prv, max_ents, sg);

  		else
  			table->sgl = sg;
  
  		/*
  		 * If no more entries after this one, mark the end
  		 */
  		if (!left)
  			sg_mark_end(&sg[sg_size - 1]);
  
  		/*
  		 * only really needed for mempool backed sg allocations (like
  		 * SCSI), a possible improvement here would be to pass the
  		 * table pointer into the allocator and let that clear these
  		 * flags
  		 */
  		gfp_mask &= ~__GFP_WAIT;
  		gfp_mask |= __GFP_HIGH;
  		prv = sg;
  	} while (left);
  
  	return 0;
  }
  EXPORT_SYMBOL(__sg_alloc_table);
  
  /**
   * sg_alloc_table - Allocate and initialize an sg table
   * @table:	The sg table header to use
   * @nents:	Number of entries in sg list
   * @gfp_mask:	GFP allocation mask
   *
   *  Description:
   *    Allocate and initialize an sg table. If @nents@ is larger than
   *    SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
   *
   **/
  int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
  {
  	int ret;

  	ret = __sg_alloc_table(table, nents, SG_MAX_SINGLE_ALLOC,
  			       gfp_mask, sg_kmalloc);

  	if (unlikely(ret))

  		__sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);

  
  	return ret;
  }
  EXPORT_SYMBOL(sg_alloc_table);

  
  /**
   * sg_copy_buffer - Copy data between a linear buffer and an SG list
   * @sgl:		 The SG list
   * @nents:		 Number of SG entries
   * @buf:		 Where to copy from
   * @buflen:		 The number of bytes to copy
   * @to_buffer: 		 transfer direction (non zero == from an sg list to a
   * 			 buffer, 0 == from a buffer to an sg list
   *
   * Returns the number of copied bytes.
   *
   **/
  static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
  			     void *buf, size_t buflen, int to_buffer)
  {
  	struct scatterlist *sg;
  	size_t buf_off = 0;
  	int i;
  
  	WARN_ON(!irqs_disabled());
  
  	for_each_sg(sgl, sg, nents, i) {
  		struct page *page;
  		int n = 0;
  		unsigned int sg_off = sg->offset;
  		unsigned int sg_copy = sg->length;
  
  		if (sg_copy > buflen)
  			sg_copy = buflen;
  		buflen -= sg_copy;
  
  		while (sg_copy > 0) {
  			unsigned int page_copy;
  			void *p;
  
  			page_copy = PAGE_SIZE - sg_off;
  			if (page_copy > sg_copy)
  				page_copy = sg_copy;
  
  			page = nth_page(sg_page(sg), n);
  			p = kmap_atomic(page, KM_BIO_SRC_IRQ);
  
  			if (to_buffer)
  				memcpy(buf + buf_off, p + sg_off, page_copy);
  			else {
  				memcpy(p + sg_off, buf + buf_off, page_copy);
  				flush_kernel_dcache_page(page);
  			}
  
  			kunmap_atomic(p, KM_BIO_SRC_IRQ);
  
  			buf_off += page_copy;
  			sg_off += page_copy;
  			if (sg_off == PAGE_SIZE) {
  				sg_off = 0;
  				n++;
  			}
  			sg_copy -= page_copy;
  		}
  
  		if (!buflen)
  			break;
  	}
  
  	return buf_off;
  }
  
  /**
   * sg_copy_from_buffer - Copy from a linear buffer to an SG list
   * @sgl:		 The SG list
   * @nents:		 Number of SG entries
   * @buf:		 Where to copy from
   * @buflen:		 The number of bytes to copy
   *
   * Returns the number of copied bytes.
   *
   **/
  size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
  			   void *buf, size_t buflen)
  {
  	return sg_copy_buffer(sgl, nents, buf, buflen, 0);
  }
  EXPORT_SYMBOL(sg_copy_from_buffer);
  
  /**
   * sg_copy_to_buffer - Copy from an SG list to a linear buffer
   * @sgl:		 The SG list
   * @nents:		 Number of SG entries
   * @buf:		 Where to copy to
   * @buflen:		 The number of bytes to copy
   *
   * Returns the number of copied bytes.
   *
   **/
  size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
  			 void *buf, size_t buflen)
  {
  	return sg_copy_buffer(sgl, nents, buf, buflen, 1);
  }
  EXPORT_SYMBOL(sg_copy_to_buffer);