fs/btrfs/zlib.c - kernel/msm-4.19 - Gitiles

 /*
  * 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.
  *
  * Based on jffs2 zlib code:
  * Copyright © 2001-2007 Red Hat, Inc.
  * Created by David Woodhouse <dwmw2@infradead.org>
  */

 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/zlib.h>
 #include <linux/zutil.h>
 #include <linux/vmalloc.h>
 #include <linux/init.h>
 #include <linux/err.h>
 #include <linux/sched.h>
 #include <linux/pagemap.h>
 #include <linux/bio.h>
 #include "compression.h"

 struct workspace {
 	z_stream inf_strm;
 	z_stream def_strm;
 	char *buf;
 	struct list_head list;
 };

 static void zlib_free_workspace(struct list_head *ws)
 {
 	struct workspace *workspace = list_entry(ws, struct workspace, list);

 	vfree(workspace->def_strm.workspace);
 	vfree(workspace->inf_strm.workspace);
 	kfree(workspace->buf);
 	kfree(workspace);
 }

 static struct list_head *zlib_alloc_workspace(void)
 {
 	struct workspace *workspace;

 	workspace = kzalloc(sizeof(*workspace), GFP_NOFS);
 	if (!workspace)
 		return ERR_PTR(-ENOMEM);

 	workspace->def_strm.workspace = vmalloc(zlib_deflate_workspacesize(
 						MAX_WBITS, MAX_MEM_LEVEL));
 	workspace->inf_strm.workspace = vmalloc(zlib_inflate_workspacesize());
 	workspace->buf = kmalloc(PAGE_CACHE_SIZE, GFP_NOFS);
 	if (!workspace->def_strm.workspace ||
 	    !workspace->inf_strm.workspace || !workspace->buf)
 		goto fail;

 	INIT_LIST_HEAD(&workspace->list);

 	return &workspace->list;
 fail:
 	zlib_free_workspace(&workspace->list);
 	return ERR_PTR(-ENOMEM);
 }

 static int zlib_compress_pages(struct list_head *ws,
 			       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 workspace *workspace = list_entry(ws, struct workspace, list);
 	int ret;
 	char *data_in;
 	char *cpage_out;
 	int nr_pages = 0;
 	struct page *in_page = NULL;
 	struct page *out_page = NULL;
 	unsigned long bytes_left;

 	*out_pages = 0;
 	*total_out = 0;
 	*total_in = 0;

 	if (Z_OK != zlib_deflateInit(&workspace->def_strm, 3)) {
 		printk(KERN_WARNING "BTRFS: deflateInit failed\n");
 		ret = -EIO;
 		goto out;
 	}

 	workspace->def_strm.total_in = 0;
 	workspace->def_strm.total_out = 0;

 	in_page = find_get_page(mapping, start >> PAGE_CACHE_SHIFT);
 	data_in = kmap(in_page);

 	out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
 	if (out_page == NULL) {
 		ret = -ENOMEM;
 		goto out;
 	}
 	cpage_out = kmap(out_page);
 	pages[0] = out_page;
 	nr_pages = 1;

 	workspace->def_strm.next_in = data_in;
 	workspace->def_strm.next_out = cpage_out;
 	workspace->def_strm.avail_out = PAGE_CACHE_SIZE;
 	workspace->def_strm.avail_in = min(len, PAGE_CACHE_SIZE);

 	while (workspace->def_strm.total_in < len) {
 		ret = zlib_deflate(&workspace->def_strm, Z_SYNC_FLUSH);
 		if (ret != Z_OK) {
 			printk(KERN_DEBUG "BTRFS: deflate in loop returned %d\n",
 			       ret);
 			zlib_deflateEnd(&workspace->def_strm);
 			ret = -EIO;
 			goto out;
 		}

 		/* we're making it bigger, give up */
 		if (workspace->def_strm.total_in > 8192 &&
 		    workspace->def_strm.total_in <
 		    workspace->def_strm.total_out) {
 			ret = -E2BIG;
 			goto out;
 		}
 		/* we need another page for writing out.  Test this
 		 * before the total_in so we will pull in a new page for
 		 * the stream end if required
 		 */
 		if (workspace->def_strm.avail_out == 0) {
 			kunmap(out_page);
 			if (nr_pages == nr_dest_pages) {
 				out_page = NULL;
 				ret = -E2BIG;
 				goto out;
 			}
 			out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
 			if (out_page == NULL) {
 				ret = -ENOMEM;
 				goto out;
 			}
 			cpage_out = kmap(out_page);
 			pages[nr_pages] = out_page;
 			nr_pages++;
 			workspace->def_strm.avail_out = PAGE_CACHE_SIZE;
 			workspace->def_strm.next_out = cpage_out;
 		}
 		/* we're all done */
 		if (workspace->def_strm.total_in >= len)
 			break;

 		/* we've read in a full page, get a new one */
 		if (workspace->def_strm.avail_in == 0) {
 			if (workspace->def_strm.total_out > max_out)
 				break;

 			bytes_left = len - workspace->def_strm.total_in;
 			kunmap(in_page);
 			page_cache_release(in_page);

 			start += PAGE_CACHE_SIZE;
 			in_page = find_get_page(mapping,
 						start >> PAGE_CACHE_SHIFT);
 			data_in = kmap(in_page);
 			workspace->def_strm.avail_in = min(bytes_left,
 							   PAGE_CACHE_SIZE);
 			workspace->def_strm.next_in = data_in;
 		}
 	}
 	workspace->def_strm.avail_in = 0;
 	ret = zlib_deflate(&workspace->def_strm, Z_FINISH);
 	zlib_deflateEnd(&workspace->def_strm);

 	if (ret != Z_STREAM_END) {
 		ret = -EIO;
 		goto out;
 	}

 	if (workspace->def_strm.total_out >= workspace->def_strm.total_in) {
 		ret = -E2BIG;
 		goto out;
 	}

 	ret = 0;
 	*total_out = workspace->def_strm.total_out;
 	*total_in = workspace->def_strm.total_in;
 out:
 	*out_pages = nr_pages;
 	if (out_page)
 		kunmap(out_page);

 	if (in_page) {
 		kunmap(in_page);
 		page_cache_release(in_page);
 	}
 	return ret;
 }

 static int zlib_decompress_biovec(struct list_head *ws, struct page **pages_in,
 				  u64 disk_start,
 				  struct bio_vec *bvec,
 				  int vcnt,
 				  size_t srclen)
 {
 	struct workspace *workspace = list_entry(ws, struct workspace, list);
 	int ret = 0, ret2;
 	int wbits = MAX_WBITS;
 	char *data_in;
 	size_t total_out = 0;
 	unsigned long page_in_index = 0;
 	unsigned long page_out_index = 0;
 	unsigned long total_pages_in = DIV_ROUND_UP(srclen, PAGE_CACHE_SIZE);
 	unsigned long buf_start;
 	unsigned long pg_offset;

 	data_in = kmap(pages_in[page_in_index]);
 	workspace->inf_strm.next_in = data_in;
 	workspace->inf_strm.avail_in = min_t(size_t, srclen, PAGE_CACHE_SIZE);
 	workspace->inf_strm.total_in = 0;

 	workspace->inf_strm.total_out = 0;
 	workspace->inf_strm.next_out = workspace->buf;
 	workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;
 	pg_offset = 0;

 	/* If it's deflate, and it's got no preset dictionary, then
 	   we can tell zlib to skip the adler32 check. */
 	if (srclen > 2 && !(data_in[1] & PRESET_DICT) &&
 	    ((data_in[0] & 0x0f) == Z_DEFLATED) &&
 	    !(((data_in[0]<<8) + data_in[1]) % 31)) {

 		wbits = -((data_in[0] >> 4) + 8);
 		workspace->inf_strm.next_in += 2;
 		workspace->inf_strm.avail_in -= 2;
 	}

 	if (Z_OK != zlib_inflateInit2(&workspace->inf_strm, wbits)) {
 		printk(KERN_WARNING "BTRFS: inflateInit failed\n");
 		return -EIO;
 	}
 	while (workspace->inf_strm.total_in < srclen) {
 		ret = zlib_inflate(&workspace->inf_strm, Z_NO_FLUSH);
 		if (ret != Z_OK && ret != Z_STREAM_END)
 			break;

 		buf_start = total_out;
 		total_out = workspace->inf_strm.total_out;

 		/* we didn't make progress in this inflate call, we're done */
 		if (buf_start == total_out)
 			break;

 		ret2 = btrfs_decompress_buf2page(workspace->buf, buf_start,
 						 total_out, disk_start,
 						 bvec, vcnt,
 						 &page_out_index, &pg_offset);
 		if (ret2 == 0) {
 			ret = 0;
 			goto done;
 		}

 		workspace->inf_strm.next_out = workspace->buf;
 		workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;

 		if (workspace->inf_strm.avail_in == 0) {
 			unsigned long tmp;
 			kunmap(pages_in[page_in_index]);
 			page_in_index++;
 			if (page_in_index >= total_pages_in) {
 				data_in = NULL;
 				break;
 			}
 			data_in = kmap(pages_in[page_in_index]);
 			workspace->inf_strm.next_in = data_in;
 			tmp = srclen - workspace->inf_strm.total_in;
 			workspace->inf_strm.avail_in = min(tmp,
 							   PAGE_CACHE_SIZE);
 		}
 	}
 	if (ret != Z_STREAM_END)
 		ret = -EIO;
 	else
 		ret = 0;
 done:
 	zlib_inflateEnd(&workspace->inf_strm);
 	if (data_in)
 		kunmap(pages_in[page_in_index]);
 	return ret;
 }

 static int zlib_decompress(struct list_head *ws, unsigned char *data_in,
 			   struct page *dest_page,
 			   unsigned long start_byte,
 			   size_t srclen, size_t destlen)
 {
 	struct workspace *workspace = list_entry(ws, struct workspace, list);
 	int ret = 0;
 	int wbits = MAX_WBITS;
 	unsigned long bytes_left = destlen;
 	unsigned long total_out = 0;
 	char *kaddr;

 	workspace->inf_strm.next_in = data_in;
 	workspace->inf_strm.avail_in = srclen;
 	workspace->inf_strm.total_in = 0;

 	workspace->inf_strm.next_out = workspace->buf;
 	workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;
 	workspace->inf_strm.total_out = 0;
 	/* If it's deflate, and it's got no preset dictionary, then
 	   we can tell zlib to skip the adler32 check. */
 	if (srclen > 2 && !(data_in[1] & PRESET_DICT) &&
 	    ((data_in[0] & 0x0f) == Z_DEFLATED) &&
 	    !(((data_in[0]<<8) + data_in[1]) % 31)) {

 		wbits = -((data_in[0] >> 4) + 8);
 		workspace->inf_strm.next_in += 2;
 		workspace->inf_strm.avail_in -= 2;
 	}

 	if (Z_OK != zlib_inflateInit2(&workspace->inf_strm, wbits)) {
 		printk(KERN_WARNING "BTRFS: inflateInit failed\n");
 		return -EIO;
 	}

 	while (bytes_left > 0) {
 		unsigned long buf_start;
 		unsigned long buf_offset;
 		unsigned long bytes;
 		unsigned long pg_offset = 0;

 		ret = zlib_inflate(&workspace->inf_strm, Z_NO_FLUSH);
 		if (ret != Z_OK && ret != Z_STREAM_END)
 			break;

 		buf_start = total_out;
 		total_out = workspace->inf_strm.total_out;

 		if (total_out == buf_start) {
 			ret = -EIO;
 			break;
 		}

 		if (total_out <= start_byte)
 			goto next;

 		if (total_out > start_byte && buf_start < start_byte)
 			buf_offset = start_byte - buf_start;
 		else
 			buf_offset = 0;

 		bytes = min(PAGE_CACHE_SIZE - pg_offset,
 			    PAGE_CACHE_SIZE - buf_offset);
 		bytes = min(bytes, bytes_left);

 		kaddr = kmap_atomic(dest_page);
 		memcpy(kaddr + pg_offset, workspace->buf + buf_offset, bytes);
 		kunmap_atomic(kaddr);

 		pg_offset += bytes;
 		bytes_left -= bytes;
 next:
 		workspace->inf_strm.next_out = workspace->buf;
 		workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;
 	}

 	if (ret != Z_STREAM_END && bytes_left != 0)
 		ret = -EIO;
 	else
 		ret = 0;

 	zlib_inflateEnd(&workspace->inf_strm);
 	return ret;
 }

 struct btrfs_compress_op btrfs_zlib_compress = {
 	.alloc_workspace	= zlib_alloc_workspace,
 	.free_workspace		= zlib_free_workspace,
 	.compress_pages		= zlib_compress_pages,
 	.decompress_biovec	= zlib_decompress_biovec,
 	.decompress		= zlib_decompress,
 };
	/*
	* 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.
	*
	* Based on jffs2 zlib code:
	* Copyright © 2001-2007 Red Hat, Inc.
	* Created by David Woodhouse <dwmw2@infradead.org>
	*/

	#include <linux/kernel.h>
	#include <linux/slab.h>
	#include <linux/zlib.h>
	#include <linux/zutil.h>
	#include <linux/vmalloc.h>
	#include <linux/init.h>
	#include <linux/err.h>
	#include <linux/sched.h>
	#include <linux/pagemap.h>
	#include <linux/bio.h>
	#include "compression.h"

	struct workspace {
	z_stream inf_strm;
	z_stream def_strm;
	char *buf;
	struct list_head list;
	};

	static void zlib_free_workspace(struct list_head *ws)
	{
	struct workspace *workspace = list_entry(ws, struct workspace, list);

	vfree(workspace->def_strm.workspace);
	vfree(workspace->inf_strm.workspace);
	kfree(workspace->buf);
	kfree(workspace);
	}

	static struct list_head *zlib_alloc_workspace(void)
	{
	struct workspace *workspace;

	workspace = kzalloc(sizeof(*workspace), GFP_NOFS);
	if (!workspace)
	return ERR_PTR(-ENOMEM);

	workspace->def_strm.workspace = vmalloc(zlib_deflate_workspacesize(
	MAX_WBITS, MAX_MEM_LEVEL));
	workspace->inf_strm.workspace = vmalloc(zlib_inflate_workspacesize());
	workspace->buf = kmalloc(PAGE_CACHE_SIZE, GFP_NOFS);
	if (!workspace->def_strm.workspace \|\|
	!workspace->inf_strm.workspace \|\| !workspace->buf)
	goto fail;

	INIT_LIST_HEAD(&workspace->list);

	return &workspace->list;
	fail:
	zlib_free_workspace(&workspace->list);
	return ERR_PTR(-ENOMEM);
	}

	static int zlib_compress_pages(struct list_head *ws,
	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 workspace *workspace = list_entry(ws, struct workspace, list);
	int ret;
	char *data_in;
	char *cpage_out;
	int nr_pages = 0;
	struct page *in_page = NULL;
	struct page *out_page = NULL;
	unsigned long bytes_left;

	*out_pages = 0;
	*total_out = 0;
	*total_in = 0;

	if (Z_OK != zlib_deflateInit(&workspace->def_strm, 3)) {
	printk(KERN_WARNING "BTRFS: deflateInit failed\n");
	ret = -EIO;
	goto out;
	}

	workspace->def_strm.total_in = 0;
	workspace->def_strm.total_out = 0;

	in_page = find_get_page(mapping, start >> PAGE_CACHE_SHIFT);
	data_in = kmap(in_page);

	out_page = alloc_page(GFP_NOFS \| __GFP_HIGHMEM);
	if (out_page == NULL) {
	ret = -ENOMEM;
	goto out;
	}
	cpage_out = kmap(out_page);
	pages[0] = out_page;
	nr_pages = 1;

	workspace->def_strm.next_in = data_in;
	workspace->def_strm.next_out = cpage_out;
	workspace->def_strm.avail_out = PAGE_CACHE_SIZE;
	workspace->def_strm.avail_in = min(len, PAGE_CACHE_SIZE);

	while (workspace->def_strm.total_in < len) {
	ret = zlib_deflate(&workspace->def_strm, Z_SYNC_FLUSH);
	if (ret != Z_OK) {
	printk(KERN_DEBUG "BTRFS: deflate in loop returned %d\n",
	ret);
	zlib_deflateEnd(&workspace->def_strm);
	ret = -EIO;
	goto out;
	}

	/* we're making it bigger, give up */
	if (workspace->def_strm.total_in > 8192 &&
	workspace->def_strm.total_in <
	workspace->def_strm.total_out) {
	ret = -E2BIG;
	goto out;
	}
	/* we need another page for writing out. Test this
	* before the total_in so we will pull in a new page for
	* the stream end if required
	*/
	if (workspace->def_strm.avail_out == 0) {
	kunmap(out_page);
	if (nr_pages == nr_dest_pages) {
	out_page = NULL;
	ret = -E2BIG;
	goto out;
	}
	out_page = alloc_page(GFP_NOFS \| __GFP_HIGHMEM);
	if (out_page == NULL) {
	ret = -ENOMEM;
	goto out;
	}
	cpage_out = kmap(out_page);
	pages[nr_pages] = out_page;
	nr_pages++;
	workspace->def_strm.avail_out = PAGE_CACHE_SIZE;
	workspace->def_strm.next_out = cpage_out;
	}
	/* we're all done */
	if (workspace->def_strm.total_in >= len)
	break;

	/* we've read in a full page, get a new one */
	if (workspace->def_strm.avail_in == 0) {
	if (workspace->def_strm.total_out > max_out)
	break;

	bytes_left = len - workspace->def_strm.total_in;
	kunmap(in_page);
	page_cache_release(in_page);

	start += PAGE_CACHE_SIZE;
	in_page = find_get_page(mapping,
	start >> PAGE_CACHE_SHIFT);
	data_in = kmap(in_page);
	workspace->def_strm.avail_in = min(bytes_left,
	PAGE_CACHE_SIZE);
	workspace->def_strm.next_in = data_in;
	}
	}
	workspace->def_strm.avail_in = 0;
	ret = zlib_deflate(&workspace->def_strm, Z_FINISH);
	zlib_deflateEnd(&workspace->def_strm);

	if (ret != Z_STREAM_END) {
	ret = -EIO;
	goto out;
	}

	if (workspace->def_strm.total_out >= workspace->def_strm.total_in) {
	ret = -E2BIG;
	goto out;
	}

	ret = 0;
	*total_out = workspace->def_strm.total_out;
	*total_in = workspace->def_strm.total_in;
	out:
	*out_pages = nr_pages;
	if (out_page)
	kunmap(out_page);

	if (in_page) {
	kunmap(in_page);
	page_cache_release(in_page);
	}
	return ret;
	}

	static int zlib_decompress_biovec(struct list_head ws, struct page *pages_in,
	u64 disk_start,
	struct bio_vec *bvec,
	int vcnt,
	size_t srclen)
	{
	struct workspace *workspace = list_entry(ws, struct workspace, list);
	int ret = 0, ret2;
	int wbits = MAX_WBITS;
	char *data_in;
	size_t total_out = 0;
	unsigned long page_in_index = 0;
	unsigned long page_out_index = 0;
	unsigned long total_pages_in = DIV_ROUND_UP(srclen, PAGE_CACHE_SIZE);
	unsigned long buf_start;
	unsigned long pg_offset;

	data_in = kmap(pages_in[page_in_index]);
	workspace->inf_strm.next_in = data_in;
	workspace->inf_strm.avail_in = min_t(size_t, srclen, PAGE_CACHE_SIZE);
	workspace->inf_strm.total_in = 0;

	workspace->inf_strm.total_out = 0;
	workspace->inf_strm.next_out = workspace->buf;
	workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;
	pg_offset = 0;

	/* If it's deflate, and it's got no preset dictionary, then
	we can tell zlib to skip the adler32 check. */
	if (srclen > 2 && !(data_in[1] & PRESET_DICT) &&
	((data_in[0] & 0x0f) == Z_DEFLATED) &&
	!(((data_in[0]<<8) + data_in[1]) % 31)) {

	wbits = -((data_in[0] >> 4) + 8);
	workspace->inf_strm.next_in += 2;
	workspace->inf_strm.avail_in -= 2;
	}

	if (Z_OK != zlib_inflateInit2(&workspace->inf_strm, wbits)) {
	printk(KERN_WARNING "BTRFS: inflateInit failed\n");
	return -EIO;
	}
	while (workspace->inf_strm.total_in < srclen) {
	ret = zlib_inflate(&workspace->inf_strm, Z_NO_FLUSH);
	if (ret != Z_OK && ret != Z_STREAM_END)
	break;

	buf_start = total_out;
	total_out = workspace->inf_strm.total_out;

	/* we didn't make progress in this inflate call, we're done */
	if (buf_start == total_out)
	break;

	ret2 = btrfs_decompress_buf2page(workspace->buf, buf_start,
	total_out, disk_start,
	bvec, vcnt,
	&page_out_index, &pg_offset);
	if (ret2 == 0) {
	ret = 0;
	goto done;
	}

	workspace->inf_strm.next_out = workspace->buf;
	workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;

	if (workspace->inf_strm.avail_in == 0) {
	unsigned long tmp;
	kunmap(pages_in[page_in_index]);
	page_in_index++;
	if (page_in_index >= total_pages_in) {
	data_in = NULL;
	break;
	}
	data_in = kmap(pages_in[page_in_index]);
	workspace->inf_strm.next_in = data_in;
	tmp = srclen - workspace->inf_strm.total_in;
	workspace->inf_strm.avail_in = min(tmp,
	PAGE_CACHE_SIZE);
	}
	}
	if (ret != Z_STREAM_END)
	ret = -EIO;
	else
	ret = 0;
	done:
	zlib_inflateEnd(&workspace->inf_strm);
	if (data_in)
	kunmap(pages_in[page_in_index]);
	return ret;
	}

	static int zlib_decompress(struct list_head ws, unsigned char data_in,
	struct page *dest_page,
	unsigned long start_byte,
	size_t srclen, size_t destlen)
	{
	struct workspace *workspace = list_entry(ws, struct workspace, list);
	int ret = 0;
	int wbits = MAX_WBITS;
	unsigned long bytes_left = destlen;
	unsigned long total_out = 0;
	char *kaddr;

	workspace->inf_strm.next_in = data_in;
	workspace->inf_strm.avail_in = srclen;
	workspace->inf_strm.total_in = 0;

	workspace->inf_strm.next_out = workspace->buf;
	workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;
	workspace->inf_strm.total_out = 0;
	/* If it's deflate, and it's got no preset dictionary, then
	we can tell zlib to skip the adler32 check. */
	if (srclen > 2 && !(data_in[1] & PRESET_DICT) &&
	((data_in[0] & 0x0f) == Z_DEFLATED) &&
	!(((data_in[0]<<8) + data_in[1]) % 31)) {

	wbits = -((data_in[0] >> 4) + 8);
	workspace->inf_strm.next_in += 2;
	workspace->inf_strm.avail_in -= 2;
	}

	if (Z_OK != zlib_inflateInit2(&workspace->inf_strm, wbits)) {
	printk(KERN_WARNING "BTRFS: inflateInit failed\n");
	return -EIO;
	}

	while (bytes_left > 0) {
	unsigned long buf_start;
	unsigned long buf_offset;
	unsigned long bytes;
	unsigned long pg_offset = 0;

	ret = zlib_inflate(&workspace->inf_strm, Z_NO_FLUSH);
	if (ret != Z_OK && ret != Z_STREAM_END)
	break;

	buf_start = total_out;
	total_out = workspace->inf_strm.total_out;

	if (total_out == buf_start) {
	ret = -EIO;
	break;
	}

	if (total_out <= start_byte)
	goto next;

	if (total_out > start_byte && buf_start < start_byte)
	buf_offset = start_byte - buf_start;
	else
	buf_offset = 0;

	bytes = min(PAGE_CACHE_SIZE - pg_offset,
	PAGE_CACHE_SIZE - buf_offset);
	bytes = min(bytes, bytes_left);

	kaddr = kmap_atomic(dest_page);
	memcpy(kaddr + pg_offset, workspace->buf + buf_offset, bytes);
	kunmap_atomic(kaddr);

	pg_offset += bytes;
	bytes_left -= bytes;
	next:
	workspace->inf_strm.next_out = workspace->buf;
	workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;
	}

	if (ret != Z_STREAM_END && bytes_left != 0)
	ret = -EIO;
	else
	ret = 0;

	zlib_inflateEnd(&workspace->inf_strm);
	return ret;
	}

	struct btrfs_compress_op btrfs_zlib_compress = {
	.alloc_workspace = zlib_alloc_workspace,
	.free_workspace = zlib_free_workspace,
	.compress_pages = zlib_compress_pages,
	.decompress_biovec = zlib_decompress_biovec,
	.decompress = zlib_decompress,
	};