/*
   * Copyright (C) 2008 Oracle.  All rights reserved.
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public
   * License v2 as published by the Free Software Foundation.
   *
   * 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., 59 Temple Place - Suite 330,
   * Boston, MA 021110-1307, USA.
   */
  
  #include <linux/kernel.h>
  #include <linux/bio.h>
  #include <linux/buffer_head.h>
  #include <linux/file.h>
  #include <linux/fs.h>
  #include <linux/pagemap.h>
  #include <linux/highmem.h>
  #include <linux/time.h>
  #include <linux/init.h>
  #include <linux/string.h>

  #include <linux/backing-dev.h>
  #include <linux/mpage.h>
  #include <linux/swap.h>
  #include <linux/writeback.h>
  #include <linux/bit_spinlock.h>

  #include <linux/slab.h>

  #include "ctree.h"
  #include "disk-io.h"
  #include "transaction.h"
  #include "btrfs_inode.h"
  #include "volumes.h"
  #include "ordered-data.h"

  #include "compression.h"
  #include "extent_io.h"
  #include "extent_map.h"
  
  struct compressed_bio {
  	/* number of bios pending for this compressed extent */
  	atomic_t pending_bios;
  
  	/* the pages with the compressed data on them */
  	struct page **compressed_pages;
  
  	/* inode that owns this data */
  	struct inode *inode;
  
  	/* starting offset in the inode for our pages */
  	u64 start;
  
  	/* number of bytes in the inode we're working on */
  	unsigned long len;
  
  	/* number of bytes on disk */
  	unsigned long compressed_len;

  	/* the compression algorithm for this bio */
  	int compress_type;

  	/* number of compressed pages in the array */
  	unsigned long nr_pages;
  
  	/* IO errors */
  	int errors;

  	int mirror_num;

  
  	/* for reads, this is the bio we are copying the data into */
  	struct bio *orig_bio;

  
  	/*
  	 * the start of a variable length array of checksums only
  	 * used by reads
  	 */
  	u32 sums;

  };

  static int btrfs_decompress_biovec(int type, struct page **pages_in,
  				   u64 disk_start, struct bio_vec *bvec,
  				   int vcnt, size_t srclen);

  static inline int compressed_bio_size(struct btrfs_root *root,
  				      unsigned long disk_size)
  {

  	u16 csum_size = btrfs_super_csum_size(root->fs_info->super_copy);

  	return sizeof(struct compressed_bio) +
  		((disk_size + root->sectorsize - 1) / root->sectorsize) *
  		csum_size;
  }

  static struct bio *compressed_bio_alloc(struct block_device *bdev,
  					u64 first_byte, gfp_t gfp_flags)
  {

  	int nr_vecs;
  
  	nr_vecs = bio_get_nr_vecs(bdev);

  	return btrfs_bio_alloc(bdev, first_byte >> 9, nr_vecs, gfp_flags);

  }

  static int check_compressed_csum(struct inode *inode,
  				 struct compressed_bio *cb,
  				 u64 disk_start)
  {
  	int ret;

  	struct page *page;
  	unsigned long i;
  	char *kaddr;
  	u32 csum;
  	u32 *cb_sum = &cb->sums;

  	if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)

  		return 0;
  
  	for (i = 0; i < cb->nr_pages; i++) {
  		page = cb->compressed_pages[i];
  		csum = ~(u32)0;

  		kaddr = kmap_atomic(page);

  		csum = btrfs_csum_data(kaddr, csum, PAGE_CACHE_SIZE);

  		btrfs_csum_final(csum, (char *)&csum);

  		kunmap_atomic(kaddr);

  
  		if (csum != *cb_sum) {

  			btrfs_info(BTRFS_I(inode)->root->fs_info,
  			   "csum failed ino %llu extent %llu csum %u wanted %u mirror %d",
  			   btrfs_ino(inode), disk_start, csum, *cb_sum,
  			   cb->mirror_num);

  			ret = -EIO;
  			goto fail;
  		}
  		cb_sum++;
  
  	}
  	ret = 0;
  fail:
  	return ret;
  }

  /* when we finish reading compressed pages from the disk, we
   * decompress them and then run the bio end_io routines on the
   * decompressed pages (in the inode address space).
   *
   * This allows the checksumming and other IO error handling routines
   * to work normally
   *
   * The compressed pages are freed here, and it must be run
   * in process context
   */
  static void end_compressed_bio_read(struct bio *bio, int err)
  {

  	struct compressed_bio *cb = bio->bi_private;
  	struct inode *inode;
  	struct page *page;
  	unsigned long index;
  	int ret;
  
  	if (err)
  		cb->errors = 1;
  
  	/* if there are more bios still pending for this compressed
  	 * extent, just exit
  	 */
  	if (!atomic_dec_and_test(&cb->pending_bios))
  		goto out;

  	inode = cb->inode;

  	ret = check_compressed_csum(inode, cb,
  				    (u64)bio->bi_iter.bi_sector << 9);

  	if (ret)
  		goto csum_failed;

  	/* ok, we're the last bio for this extent, lets start
  	 * the decompression.
  	 */

  	ret = btrfs_decompress_biovec(cb->compress_type,
  				      cb->compressed_pages,
  				      cb->start,
  				      cb->orig_bio->bi_io_vec,
  				      cb->orig_bio->bi_vcnt,
  				      cb->compressed_len);

  csum_failed:

  	if (ret)
  		cb->errors = 1;
  
  	/* release the compressed pages */
  	index = 0;
  	for (index = 0; index < cb->nr_pages; index++) {
  		page = cb->compressed_pages[index];
  		page->mapping = NULL;
  		page_cache_release(page);
  	}
  
  	/* do io completion on the original bio */

  	if (cb->errors) {

  		bio_io_error(cb->orig_bio);

  	} else {

  		int i;
  		struct bio_vec *bvec;

  
  		/*
  		 * we have verified the checksum already, set page
  		 * checked so the end_io handlers know about it
  		 */

  		bio_for_each_segment_all(bvec, cb->orig_bio, i)

  			SetPageChecked(bvec->bv_page);

  		bio_endio(cb->orig_bio, 0);

  	}

  
  	/* finally free the cb struct */
  	kfree(cb->compressed_pages);
  	kfree(cb);
  out:
  	bio_put(bio);
  }
  
  /*
   * Clear the writeback bits on all of the file
   * pages for a compressed write
   */

  static noinline void end_compressed_writeback(struct inode *inode, u64 start,
  					      unsigned long ram_size)

  {
  	unsigned long index = start >> PAGE_CACHE_SHIFT;
  	unsigned long end_index = (start + ram_size - 1) >> PAGE_CACHE_SHIFT;
  	struct page *pages[16];
  	unsigned long nr_pages = end_index - index + 1;
  	int i;
  	int ret;

  	while (nr_pages > 0) {

  		ret = find_get_pages_contig(inode->i_mapping, index,

  				     min_t(unsigned long,
  				     nr_pages, ARRAY_SIZE(pages)), pages);

  		if (ret == 0) {
  			nr_pages -= 1;
  			index += 1;
  			continue;
  		}
  		for (i = 0; i < ret; i++) {
  			end_page_writeback(pages[i]);
  			page_cache_release(pages[i]);
  		}
  		nr_pages -= ret;
  		index += ret;
  	}
  	/* the inode may be gone now */

  }
  
  /*
   * do the cleanup once all the compressed pages hit the disk.
   * This will clear writeback on the file pages and free the compressed
   * pages.
   *
   * This also calls the writeback end hooks for the file pages so that
   * metadata and checksums can be updated in the file.
   */
  static void end_compressed_bio_write(struct bio *bio, int err)
  {
  	struct extent_io_tree *tree;
  	struct compressed_bio *cb = bio->bi_private;
  	struct inode *inode;
  	struct page *page;
  	unsigned long index;
  
  	if (err)
  		cb->errors = 1;
  
  	/* if there are more bios still pending for this compressed
  	 * extent, just exit
  	 */
  	if (!atomic_dec_and_test(&cb->pending_bios))
  		goto out;
  
  	/* ok, we're the last bio for this extent, step one is to
  	 * call back into the FS and do all the end_io operations
  	 */
  	inode = cb->inode;
  	tree = &BTRFS_I(inode)->io_tree;

  	cb->compressed_pages[0]->mapping = cb->inode->i_mapping;

  	tree->ops->writepage_end_io_hook(cb->compressed_pages[0],
  					 cb->start,
  					 cb->start + cb->len - 1,
  					 NULL, 1);

  	cb->compressed_pages[0]->mapping = NULL;

  
  	end_compressed_writeback(inode, cb->start, cb->len);
  	/* note, our inode could be gone now */
  
  	/*
  	 * release the compressed pages, these came from alloc_page and
  	 * are not attached to the inode at all
  	 */
  	index = 0;
  	for (index = 0; index < cb->nr_pages; index++) {
  		page = cb->compressed_pages[index];
  		page->mapping = NULL;
  		page_cache_release(page);
  	}
  
  	/* finally free the cb struct */
  	kfree(cb->compressed_pages);
  	kfree(cb);
  out:
  	bio_put(bio);
  }
  
  /*
   * worker function to build and submit bios for previously compressed pages.
   * The corresponding pages in the inode should be marked for writeback
   * and the compressed pages should have a reference on them for dropping
   * when the IO is complete.
   *
   * This also checksums the file bytes and gets things ready for
   * the end io hooks.
   */
  int btrfs_submit_compressed_write(struct inode *inode, u64 start,
  				 unsigned long len, u64 disk_start,
  				 unsigned long compressed_len,
  				 struct page **compressed_pages,
  				 unsigned long nr_pages)
  {
  	struct bio *bio = NULL;
  	struct btrfs_root *root = BTRFS_I(inode)->root;
  	struct compressed_bio *cb;
  	unsigned long bytes_left;
  	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;

  	int pg_index = 0;

  	struct page *page;
  	u64 first_byte = disk_start;
  	struct block_device *bdev;
  	int ret;

  	int skip_sum = BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM;

  
  	WARN_ON(start & ((u64)PAGE_CACHE_SIZE - 1));

  	cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);

  	if (!cb)
  		return -ENOMEM;

  	atomic_set(&cb->pending_bios, 0);
  	cb->errors = 0;
  	cb->inode = inode;
  	cb->start = start;
  	cb->len = len;

  	cb->mirror_num = 0;

  	cb->compressed_pages = compressed_pages;
  	cb->compressed_len = compressed_len;
  	cb->orig_bio = NULL;
  	cb->nr_pages = nr_pages;
  
  	bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;

  	bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);

  	if (!bio) {

  		kfree(cb);
  		return -ENOMEM;
  	}

  	bio->bi_private = cb;
  	bio->bi_end_io = end_compressed_bio_write;
  	atomic_inc(&cb->pending_bios);
  
  	/* create and submit bios for the compressed pages */
  	bytes_left = compressed_len;

  	for (pg_index = 0; pg_index < cb->nr_pages; pg_index++) {
  		page = compressed_pages[pg_index];

  		page->mapping = inode->i_mapping;

  		if (bio->bi_iter.bi_size)

  			ret = io_tree->ops->merge_bio_hook(WRITE, page, 0,

  							   PAGE_CACHE_SIZE,
  							   bio, 0);
  		else
  			ret = 0;

  		page->mapping = NULL;

  		if (ret || bio_add_page(bio, page, PAGE_CACHE_SIZE, 0) <
  		    PAGE_CACHE_SIZE) {
  			bio_get(bio);

  			/*
  			 * inc the count before we submit the bio so
  			 * we know the end IO handler won't happen before
  			 * we inc the count.  Otherwise, the cb might get
  			 * freed before we're done setting it up
  			 */
  			atomic_inc(&cb->pending_bios);

  			ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);

  			BUG_ON(ret); /* -ENOMEM */

  			if (!skip_sum) {
  				ret = btrfs_csum_one_bio(root, inode, bio,
  							 start, 1);

  				BUG_ON(ret); /* -ENOMEM */

  			}

  			ret = btrfs_map_bio(root, WRITE, bio, 0, 1);

  			BUG_ON(ret); /* -ENOMEM */

  
  			bio_put(bio);
  
  			bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);

  			BUG_ON(!bio);

  			bio->bi_private = cb;
  			bio->bi_end_io = end_compressed_bio_write;
  			bio_add_page(bio, page, PAGE_CACHE_SIZE, 0);
  		}

  		if (bytes_left < PAGE_CACHE_SIZE) {

  			btrfs_info(BTRFS_I(inode)->root->fs_info,
  					"bytes left %lu compress len %lu nr %lu",

  			       bytes_left, cb->compressed_len, cb->nr_pages);
  		}

  		bytes_left -= PAGE_CACHE_SIZE;
  		first_byte += PAGE_CACHE_SIZE;

  		cond_resched();

  	}
  	bio_get(bio);
  
  	ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);

  	BUG_ON(ret); /* -ENOMEM */

  	if (!skip_sum) {
  		ret = btrfs_csum_one_bio(root, inode, bio, start, 1);

  		BUG_ON(ret); /* -ENOMEM */

  	}

  	ret = btrfs_map_bio(root, WRITE, bio, 0, 1);

  	BUG_ON(ret); /* -ENOMEM */

  
  	bio_put(bio);
  	return 0;
  }

  static noinline int add_ra_bio_pages(struct inode *inode,
  				     u64 compressed_end,
  				     struct compressed_bio *cb)
  {
  	unsigned long end_index;

  	unsigned long pg_index;

  	u64 last_offset;
  	u64 isize = i_size_read(inode);
  	int ret;
  	struct page *page;
  	unsigned long nr_pages = 0;
  	struct extent_map *em;
  	struct address_space *mapping = inode->i_mapping;

  	struct extent_map_tree *em_tree;
  	struct extent_io_tree *tree;
  	u64 end;
  	int misses = 0;
  
  	page = cb->orig_bio->bi_io_vec[cb->orig_bio->bi_vcnt - 1].bv_page;
  	last_offset = (page_offset(page) + PAGE_CACHE_SIZE);
  	em_tree = &BTRFS_I(inode)->extent_tree;
  	tree = &BTRFS_I(inode)->io_tree;
  
  	if (isize == 0)
  		return 0;
  
  	end_index = (i_size_read(inode) - 1) >> PAGE_CACHE_SHIFT;

  	while (last_offset < compressed_end) {

  		pg_index = last_offset >> PAGE_CACHE_SHIFT;

  		if (pg_index > end_index)

  			break;
  
  		rcu_read_lock();

  		page = radix_tree_lookup(&mapping->page_tree, pg_index);

  		rcu_read_unlock();

  		if (page && !radix_tree_exceptional_entry(page)) {

  			misses++;
  			if (misses > 4)
  				break;
  			goto next;
  		}

  		page = __page_cache_alloc(mapping_gfp_mask(mapping) &
  								~__GFP_FS);

  		if (!page)
  			break;

  		if (add_to_page_cache_lru(page, mapping, pg_index,

  								GFP_NOFS)) {

  			page_cache_release(page);
  			goto next;
  		}

  		end = last_offset + PAGE_CACHE_SIZE - 1;
  		/*
  		 * at this point, we have a locked page in the page cache
  		 * for these bytes in the file.  But, we have to make
  		 * sure they map to this compressed extent on disk.
  		 */
  		set_page_extent_mapped(page);

  		lock_extent(tree, last_offset, end);

  		read_lock(&em_tree->lock);

  		em = lookup_extent_mapping(em_tree, last_offset,
  					   PAGE_CACHE_SIZE);

  		read_unlock(&em_tree->lock);

  
  		if (!em || last_offset < em->start ||
  		    (last_offset + PAGE_CACHE_SIZE > extent_map_end(em)) ||

  		    (em->block_start >> 9) != cb->orig_bio->bi_iter.bi_sector) {

  			free_extent_map(em);

  			unlock_extent(tree, last_offset, end);

  			unlock_page(page);
  			page_cache_release(page);
  			break;
  		}
  		free_extent_map(em);
  
  		if (page->index == end_index) {
  			char *userpage;
  			size_t zero_offset = isize & (PAGE_CACHE_SIZE - 1);
  
  			if (zero_offset) {
  				int zeros;
  				zeros = PAGE_CACHE_SIZE - zero_offset;

  				userpage = kmap_atomic(page);

  				memset(userpage + zero_offset, 0, zeros);
  				flush_dcache_page(page);

  				kunmap_atomic(userpage);

  			}
  		}
  
  		ret = bio_add_page(cb->orig_bio, page,
  				   PAGE_CACHE_SIZE, 0);
  
  		if (ret == PAGE_CACHE_SIZE) {
  			nr_pages++;
  			page_cache_release(page);
  		} else {

  			unlock_extent(tree, last_offset, end);

  			unlock_page(page);
  			page_cache_release(page);
  			break;
  		}
  next:
  		last_offset += PAGE_CACHE_SIZE;
  	}

  	return 0;
  }

  /*
   * for a compressed read, the bio we get passed has all the inode pages
   * in it.  We don't actually do IO on those pages but allocate new ones
   * to hold the compressed pages on disk.
   *

   * bio->bi_iter.bi_sector points to the compressed extent on disk

   * bio->bi_io_vec points to all of the inode pages
   * bio->bi_vcnt is a count of pages
   *
   * After the compressed pages are read, we copy the bytes into the
   * bio we were passed and then call the bio end_io calls
   */
  int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
  				 int mirror_num, unsigned long bio_flags)
  {
  	struct extent_io_tree *tree;
  	struct extent_map_tree *em_tree;
  	struct compressed_bio *cb;
  	struct btrfs_root *root = BTRFS_I(inode)->root;
  	unsigned long uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
  	unsigned long compressed_len;
  	unsigned long nr_pages;

  	unsigned long pg_index;

  	struct page *page;
  	struct block_device *bdev;
  	struct bio *comp_bio;

  	u64 cur_disk_byte = (u64)bio->bi_iter.bi_sector << 9;

  	u64 em_len;
  	u64 em_start;

  	struct extent_map *em;

  	int ret = -ENOMEM;

  	int faili = 0;

  	u32 *sums;

  
  	tree = &BTRFS_I(inode)->io_tree;
  	em_tree = &BTRFS_I(inode)->extent_tree;
  
  	/* we need the actual starting offset of this extent in the file */

  	read_lock(&em_tree->lock);

  	em = lookup_extent_mapping(em_tree,
  				   page_offset(bio->bi_io_vec->bv_page),
  				   PAGE_CACHE_SIZE);

  	read_unlock(&em_tree->lock);

  	if (!em)
  		return -EIO;

  	compressed_len = em->block_len;
  	cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);

  	if (!cb)
  		goto out;

  	atomic_set(&cb->pending_bios, 0);
  	cb->errors = 0;
  	cb->inode = inode;

  	cb->mirror_num = mirror_num;
  	sums = &cb->sums;

  	cb->start = em->orig_start;

  	em_len = em->len;
  	em_start = em->start;

  	free_extent_map(em);

  	em = NULL;

  
  	cb->len = uncompressed_len;
  	cb->compressed_len = compressed_len;

  	cb->compress_type = extent_compress_type(bio_flags);

  	cb->orig_bio = bio;
  
  	nr_pages = (compressed_len + PAGE_CACHE_SIZE - 1) /
  				 PAGE_CACHE_SIZE;

  	cb->compressed_pages = kzalloc(sizeof(struct page *) * nr_pages,

  				       GFP_NOFS);

  	if (!cb->compressed_pages)
  		goto fail1;

  	bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;

  	for (pg_index = 0; pg_index < nr_pages; pg_index++) {
  		cb->compressed_pages[pg_index] = alloc_page(GFP_NOFS |

  							      __GFP_HIGHMEM);

  		if (!cb->compressed_pages[pg_index]) {
  			faili = pg_index - 1;
  			ret = -ENOMEM;

  			goto fail2;

  		}

  	}

  	faili = nr_pages - 1;

  	cb->nr_pages = nr_pages;

  	/* In the parent-locked case, we only locked the range we are
  	 * interested in.  In all other cases, we can opportunistically
  	 * cache decompressed data that goes beyond the requested range. */
  	if (!(bio_flags & EXTENT_BIO_PARENT_LOCKED))
  		add_ra_bio_pages(inode, em_start + em_len, cb);

  	/* include any pages we added in add_ra-bio_pages */
  	uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
  	cb->len = uncompressed_len;

  	comp_bio = compressed_bio_alloc(bdev, cur_disk_byte, GFP_NOFS);

  	if (!comp_bio)
  		goto fail2;

  	comp_bio->bi_private = cb;
  	comp_bio->bi_end_io = end_compressed_bio_read;
  	atomic_inc(&cb->pending_bios);

  	for (pg_index = 0; pg_index < nr_pages; pg_index++) {
  		page = cb->compressed_pages[pg_index];

  		page->mapping = inode->i_mapping;

  		page->index = em_start >> PAGE_CACHE_SHIFT;

  		if (comp_bio->bi_iter.bi_size)

  			ret = tree->ops->merge_bio_hook(READ, page, 0,

  							PAGE_CACHE_SIZE,
  							comp_bio, 0);
  		else
  			ret = 0;

  		page->mapping = NULL;

  		if (ret || bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0) <
  		    PAGE_CACHE_SIZE) {
  			bio_get(comp_bio);
  
  			ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);

  			BUG_ON(ret); /* -ENOMEM */

  			/*
  			 * inc the count before we submit the bio so
  			 * we know the end IO handler won't happen before
  			 * we inc the count.  Otherwise, the cb might get
  			 * freed before we're done setting it up
  			 */
  			atomic_inc(&cb->pending_bios);

  			if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {

  				ret = btrfs_lookup_bio_sums(root, inode,
  							comp_bio, sums);

  				BUG_ON(ret); /* -ENOMEM */

  			}

  			sums += (comp_bio->bi_iter.bi_size +
  				 root->sectorsize - 1) / root->sectorsize;

  
  			ret = btrfs_map_bio(root, READ, comp_bio,
  					    mirror_num, 0);

  			if (ret)
  				bio_endio(comp_bio, ret);

  
  			bio_put(comp_bio);
  
  			comp_bio = compressed_bio_alloc(bdev, cur_disk_byte,
  							GFP_NOFS);

  			BUG_ON(!comp_bio);

  			comp_bio->bi_private = cb;
  			comp_bio->bi_end_io = end_compressed_bio_read;
  
  			bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0);

  		}
  		cur_disk_byte += PAGE_CACHE_SIZE;
  	}
  	bio_get(comp_bio);
  
  	ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);

  	BUG_ON(ret); /* -ENOMEM */

  	if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
  		ret = btrfs_lookup_bio_sums(root, inode, comp_bio, sums);

  		BUG_ON(ret); /* -ENOMEM */

  	}

  
  	ret = btrfs_map_bio(root, READ, comp_bio, mirror_num, 0);

  	if (ret)
  		bio_endio(comp_bio, ret);

  
  	bio_put(comp_bio);
  	return 0;

  
  fail2:

  	while (faili >= 0) {
  		__free_page(cb->compressed_pages[faili]);
  		faili--;
  	}

  
  	kfree(cb->compressed_pages);
  fail1:
  	kfree(cb);
  out:
  	free_extent_map(em);
  	return ret;

  }

  
  static struct list_head comp_idle_workspace[BTRFS_COMPRESS_TYPES];
  static spinlock_t comp_workspace_lock[BTRFS_COMPRESS_TYPES];
  static int comp_num_workspace[BTRFS_COMPRESS_TYPES];
  static atomic_t comp_alloc_workspace[BTRFS_COMPRESS_TYPES];
  static wait_queue_head_t comp_workspace_wait[BTRFS_COMPRESS_TYPES];

  static struct btrfs_compress_op *btrfs_compress_op[] = {

  	&btrfs_zlib_compress,

  	&btrfs_lzo_compress,

  };

  void __init btrfs_init_compress(void)

  {
  	int i;
  
  	for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
  		INIT_LIST_HEAD(&comp_idle_workspace[i]);
  		spin_lock_init(&comp_workspace_lock[i]);
  		atomic_set(&comp_alloc_workspace[i], 0);
  		init_waitqueue_head(&comp_workspace_wait[i]);
  	}

  }
  
  /*
   * this finds an available workspace or allocates a new one
   * ERR_PTR is returned if things go bad.
   */
  static struct list_head *find_workspace(int type)
  {
  	struct list_head *workspace;
  	int cpus = num_online_cpus();
  	int idx = type - 1;
  
  	struct list_head *idle_workspace	= &comp_idle_workspace[idx];
  	spinlock_t *workspace_lock		= &comp_workspace_lock[idx];
  	atomic_t *alloc_workspace		= &comp_alloc_workspace[idx];
  	wait_queue_head_t *workspace_wait	= &comp_workspace_wait[idx];
  	int *num_workspace			= &comp_num_workspace[idx];
  again:
  	spin_lock(workspace_lock);
  	if (!list_empty(idle_workspace)) {
  		workspace = idle_workspace->next;
  		list_del(workspace);
  		(*num_workspace)--;
  		spin_unlock(workspace_lock);
  		return workspace;
  
  	}
  	if (atomic_read(alloc_workspace) > cpus) {
  		DEFINE_WAIT(wait);
  
  		spin_unlock(workspace_lock);
  		prepare_to_wait(workspace_wait, &wait, TASK_UNINTERRUPTIBLE);
  		if (atomic_read(alloc_workspace) > cpus && !*num_workspace)
  			schedule();
  		finish_wait(workspace_wait, &wait);
  		goto again;
  	}
  	atomic_inc(alloc_workspace);
  	spin_unlock(workspace_lock);
  
  	workspace = btrfs_compress_op[idx]->alloc_workspace();
  	if (IS_ERR(workspace)) {
  		atomic_dec(alloc_workspace);
  		wake_up(workspace_wait);
  	}
  	return workspace;
  }
  
  /*
   * put a workspace struct back on the list or free it if we have enough
   * idle ones sitting around
   */
  static void free_workspace(int type, struct list_head *workspace)
  {
  	int idx = type - 1;
  	struct list_head *idle_workspace	= &comp_idle_workspace[idx];
  	spinlock_t *workspace_lock		= &comp_workspace_lock[idx];
  	atomic_t *alloc_workspace		= &comp_alloc_workspace[idx];
  	wait_queue_head_t *workspace_wait	= &comp_workspace_wait[idx];
  	int *num_workspace			= &comp_num_workspace[idx];
  
  	spin_lock(workspace_lock);
  	if (*num_workspace < num_online_cpus()) {
  		list_add_tail(workspace, idle_workspace);
  		(*num_workspace)++;
  		spin_unlock(workspace_lock);
  		goto wake;
  	}
  	spin_unlock(workspace_lock);
  
  	btrfs_compress_op[idx]->free_workspace(workspace);
  	atomic_dec(alloc_workspace);
  wake:

  	smp_mb();

  	if (waitqueue_active(workspace_wait))
  		wake_up(workspace_wait);
  }
  
  /*
   * cleanup function for module exit
   */
  static void free_workspaces(void)
  {
  	struct list_head *workspace;
  	int i;
  
  	for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
  		while (!list_empty(&comp_idle_workspace[i])) {
  			workspace = comp_idle_workspace[i].next;
  			list_del(workspace);
  			btrfs_compress_op[i]->free_workspace(workspace);
  			atomic_dec(&comp_alloc_workspace[i]);
  		}
  	}
  }
  
  /*
   * given an address space and start/len, compress the bytes.
   *
   * pages are allocated to hold the compressed result and stored
   * in 'pages'
   *
   * out_pages is used to return the number of pages allocated.  There
   * may be pages allocated even if we return an error
   *
   * total_in is used to return the number of bytes actually read.  It
   * may be smaller then len if we had to exit early because we
   * ran out of room in the pages array or because we cross the
   * max_out threshold.
   *
   * total_out is used to return the total number of compressed bytes
   *
   * max_out tells us the max number of bytes that we're allowed to
   * stuff into pages
   */
  int btrfs_compress_pages(int type, struct address_space *mapping,
  			 u64 start, unsigned long len,
  			 struct page **pages,
  			 unsigned long nr_dest_pages,
  			 unsigned long *out_pages,
  			 unsigned long *total_in,
  			 unsigned long *total_out,
  			 unsigned long max_out)
  {
  	struct list_head *workspace;
  	int ret;
  
  	workspace = find_workspace(type);
  	if (IS_ERR(workspace))
  		return -1;
  
  	ret = btrfs_compress_op[type-1]->compress_pages(workspace, mapping,
  						      start, len, pages,
  						      nr_dest_pages, out_pages,
  						      total_in, total_out,
  						      max_out);
  	free_workspace(type, workspace);
  	return ret;
  }
  
  /*
   * pages_in is an array of pages with compressed data.
   *
   * disk_start is the starting logical offset of this array in the file
   *
   * bvec is a bio_vec of pages from the file that we want to decompress into
   *
   * vcnt is the count of pages in the biovec
   *
   * srclen is the number of bytes in pages_in
   *
   * The basic idea is that we have a bio that was created by readpages.
   * The pages in the bio are for the uncompressed data, and they may not
   * be contiguous.  They all correspond to the range of bytes covered by
   * the compressed extent.
   */

  static int btrfs_decompress_biovec(int type, struct page **pages_in,
  				   u64 disk_start, struct bio_vec *bvec,
  				   int vcnt, size_t srclen)

  {
  	struct list_head *workspace;
  	int ret;
  
  	workspace = find_workspace(type);
  	if (IS_ERR(workspace))
  		return -ENOMEM;
  
  	ret = btrfs_compress_op[type-1]->decompress_biovec(workspace, pages_in,
  							 disk_start,
  							 bvec, vcnt, srclen);
  	free_workspace(type, workspace);
  	return ret;
  }
  
  /*
   * a less complex decompression routine.  Our compressed data fits in a
   * single page, and we want to read a single page out of it.
   * start_byte tells us the offset into the compressed data we're interested in
   */
  int btrfs_decompress(int type, unsigned char *data_in, struct page *dest_page,
  		     unsigned long start_byte, size_t srclen, size_t destlen)
  {
  	struct list_head *workspace;
  	int ret;
  
  	workspace = find_workspace(type);
  	if (IS_ERR(workspace))
  		return -ENOMEM;
  
  	ret = btrfs_compress_op[type-1]->decompress(workspace, data_in,
  						  dest_page, start_byte,
  						  srclen, destlen);
  
  	free_workspace(type, workspace);
  	return ret;
  }

  void btrfs_exit_compress(void)

  {
  	free_workspaces();
  }

  
  /*
   * Copy uncompressed data from working buffer to pages.
   *
   * buf_start is the byte offset we're of the start of our workspace buffer.
   *
   * total_out is the last byte of the buffer
   */
  int btrfs_decompress_buf2page(char *buf, unsigned long buf_start,
  			      unsigned long total_out, u64 disk_start,
  			      struct bio_vec *bvec, int vcnt,

  			      unsigned long *pg_index,

  			      unsigned long *pg_offset)
  {
  	unsigned long buf_offset;
  	unsigned long current_buf_start;
  	unsigned long start_byte;
  	unsigned long working_bytes = total_out - buf_start;
  	unsigned long bytes;
  	char *kaddr;

  	struct page *page_out = bvec[*pg_index].bv_page;

  
  	/*
  	 * start byte is the first byte of the page we're currently
  	 * copying into relative to the start of the compressed data.
  	 */
  	start_byte = page_offset(page_out) - disk_start;
  
  	/* we haven't yet hit data corresponding to this page */
  	if (total_out <= start_byte)
  		return 1;
  
  	/*
  	 * the start of the data we care about is offset into
  	 * the middle of our working buffer
  	 */
  	if (total_out > start_byte && buf_start < start_byte) {
  		buf_offset = start_byte - buf_start;
  		working_bytes -= buf_offset;
  	} else {
  		buf_offset = 0;
  	}
  	current_buf_start = buf_start;
  
  	/* copy bytes from the working buffer into the pages */
  	while (working_bytes > 0) {
  		bytes = min(PAGE_CACHE_SIZE - *pg_offset,
  			    PAGE_CACHE_SIZE - buf_offset);
  		bytes = min(bytes, working_bytes);

  		kaddr = kmap_atomic(page_out);

  		memcpy(kaddr + *pg_offset, buf + buf_offset, bytes);

  		if (*pg_index == (vcnt - 1) && *pg_offset == 0)
  			memset(kaddr + bytes, 0, PAGE_CACHE_SIZE - bytes);

  		kunmap_atomic(kaddr);

  		flush_dcache_page(page_out);
  
  		*pg_offset += bytes;
  		buf_offset += bytes;
  		working_bytes -= bytes;
  		current_buf_start += bytes;
  
  		/* check if we need to pick another page */
  		if (*pg_offset == PAGE_CACHE_SIZE) {

  			(*pg_index)++;
  			if (*pg_index >= vcnt)

  				return 0;

  			page_out = bvec[*pg_index].bv_page;

  			*pg_offset = 0;
  			start_byte = page_offset(page_out) - disk_start;
  
  			/*
  			 * make sure our new page is covered by this
  			 * working buffer
  			 */
  			if (total_out <= start_byte)
  				return 1;
  
  			/*
  			 * the next page in the biovec might not be adjacent
  			 * to the last page, but it might still be found
  			 * inside this working buffer. bump our offset pointer
  			 */
  			if (total_out > start_byte &&
  			    current_buf_start < start_byte) {
  				buf_offset = start_byte - buf_start;
  				working_bytes = total_out - start_byte;
  				current_buf_start = buf_start + buf_offset;
  			}
  		}
  	}
  
  	return 1;
  }