fs/btrfs/lzo.c - kernel/msm-4.9 - 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.
  */

 #include <linux/kernel.h>
 #include <linux/slab.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 <linux/lzo.h>
 #include "compression.h"

 #define LZO_LEN	4

 struct workspace {
 	void *mem;
 	void *buf;	/* where decompressed data goes */
 	void *cbuf;	/* where compressed data goes */
 	struct list_head list;
 };

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

 	vfree(workspace->buf);
 	vfree(workspace->cbuf);
 	vfree(workspace->mem);
 	kfree(workspace);
 }

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

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

 	workspace->mem = vmalloc(LZO1X_MEM_COMPRESS);
 	workspace->buf = vmalloc(lzo1x_worst_compress(PAGE_CACHE_SIZE));
 	workspace->cbuf = vmalloc(lzo1x_worst_compress(PAGE_CACHE_SIZE));
 	if (!workspace->mem || !workspace->buf || !workspace->cbuf)
 		goto fail;

 	INIT_LIST_HEAD(&workspace->list);

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

 static inline void write_compress_length(char *buf, size_t len)
 {
 	__le32 dlen;

 	dlen = cpu_to_le32(len);
 	memcpy(buf, &dlen, LZO_LEN);
 }

 static inline size_t read_compress_length(char *buf)
 {
 	__le32 dlen;

 	memcpy(&dlen, buf, LZO_LEN);
 	return le32_to_cpu(dlen);
 }

 static int lzo_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 = 0;
 	char *data_in;
 	char *cpage_out;
 	int nr_pages = 0;
 	struct page *in_page = NULL;
 	struct page *out_page = NULL;
 	unsigned long bytes_left;

 	size_t in_len;
 	size_t out_len;
 	char *buf;
 	unsigned long tot_in = 0;
 	unsigned long tot_out = 0;
 	unsigned long pg_bytes_left;
 	unsigned long out_offset;
 	unsigned long bytes;

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

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

 	/*
 	 * store the size of all chunks of compressed data in
 	 * the first 4 bytes
 	 */
 	out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
 	if (out_page == NULL) {
 		ret = -ENOMEM;
 		goto out;
 	}
 	cpage_out = kmap(out_page);
 	out_offset = LZO_LEN;
 	tot_out = LZO_LEN;
 	pages[0] = out_page;
 	nr_pages = 1;
 	pg_bytes_left = PAGE_CACHE_SIZE - LZO_LEN;

 	/* compress at most one page of data each time */
 	in_len = min(len, PAGE_CACHE_SIZE);
 	while (tot_in < len) {
 		ret = lzo1x_1_compress(data_in, in_len, workspace->cbuf,
 				       &out_len, workspace->mem);
 		if (ret != LZO_E_OK) {
 			printk(KERN_DEBUG "BTRFS: deflate in loop returned %d\n",
 			       ret);
 			ret = -EIO;
 			goto out;
 		}

 		/* store the size of this chunk of compressed data */
 		write_compress_length(cpage_out + out_offset, out_len);
 		tot_out += LZO_LEN;
 		out_offset += LZO_LEN;
 		pg_bytes_left -= LZO_LEN;

 		tot_in += in_len;
 		tot_out += out_len;

 		/* copy bytes from the working buffer into the pages */
 		buf = workspace->cbuf;
 		while (out_len) {
 			bytes = min_t(unsigned long, pg_bytes_left, out_len);

 			memcpy(cpage_out + out_offset, buf, bytes);

 			out_len -= bytes;
 			pg_bytes_left -= bytes;
 			buf += bytes;
 			out_offset += bytes;

 			/*
 			 * we need another page for writing out.
 			 *
 			 * Note if there's less than 4 bytes left, we just
 			 * skip to a new page.
 			 */
 			if ((out_len == 0 && pg_bytes_left < LZO_LEN) ||
 			    pg_bytes_left == 0) {
 				if (pg_bytes_left) {
 					memset(cpage_out + out_offset, 0,
 					       pg_bytes_left);
 					tot_out += pg_bytes_left;
 				}

 				/* we're done, don't allocate new page */
 				if (out_len == 0 && tot_in >= len)
 					break;

 				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;

 				pg_bytes_left = PAGE_CACHE_SIZE;
 				out_offset = 0;
 			}
 		}

 		/* we're making it bigger, give up */
 		if (tot_in > 8192 && tot_in < tot_out) {
 			ret = -E2BIG;
 			goto out;
 		}

 		/* we're all done */
 		if (tot_in >= len)
 			break;

 		if (tot_out > max_out)
 			break;

 		bytes_left = len - tot_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);
 		in_len = min(bytes_left, PAGE_CACHE_SIZE);
 	}

 	if (tot_out > tot_in)
 		goto out;

 	/* store the size of all chunks of compressed data */
 	cpage_out = kmap(pages[0]);
 	write_compress_length(cpage_out, tot_out);

 	kunmap(pages[0]);

 	ret = 0;
 	*total_out = tot_out;
 	*total_in = tot_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 lzo_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;
 	char *data_in;
 	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 buf_offset = 0;
 	unsigned long bytes;
 	unsigned long working_bytes;
 	unsigned long pg_offset;

 	size_t in_len;
 	size_t out_len;
 	unsigned long in_offset;
 	unsigned long in_page_bytes_left;
 	unsigned long tot_in;
 	unsigned long tot_out;
 	unsigned long tot_len;
 	char *buf;
 	bool may_late_unmap, need_unmap;

 	data_in = kmap(pages_in[0]);
 	tot_len = read_compress_length(data_in);

 	tot_in = LZO_LEN;
 	in_offset = LZO_LEN;
 	tot_len = min_t(size_t, srclen, tot_len);
 	in_page_bytes_left = PAGE_CACHE_SIZE - LZO_LEN;

 	tot_out = 0;
 	pg_offset = 0;

 	while (tot_in < tot_len) {
 		in_len = read_compress_length(data_in + in_offset);
 		in_page_bytes_left -= LZO_LEN;
 		in_offset += LZO_LEN;
 		tot_in += LZO_LEN;

 		tot_in += in_len;
 		working_bytes = in_len;
 		may_late_unmap = need_unmap = false;

 		/* fast path: avoid using the working buffer */
 		if (in_page_bytes_left >= in_len) {
 			buf = data_in + in_offset;
 			bytes = in_len;
 			may_late_unmap = true;
 			goto cont;
 		}

 		/* copy bytes from the pages into the working buffer */
 		buf = workspace->cbuf;
 		buf_offset = 0;
 		while (working_bytes) {
 			bytes = min(working_bytes, in_page_bytes_left);

 			memcpy(buf + buf_offset, data_in + in_offset, bytes);
 			buf_offset += bytes;
 cont:
 			working_bytes -= bytes;
 			in_page_bytes_left -= bytes;
 			in_offset += bytes;

 			/* check if we need to pick another page */
 			if ((working_bytes == 0 && in_page_bytes_left < LZO_LEN)
 			    || in_page_bytes_left == 0) {
 				tot_in += in_page_bytes_left;

 				if (working_bytes == 0 && tot_in >= tot_len)
 					break;

 				if (page_in_index + 1 >= total_pages_in) {
 					ret = -EIO;
 					goto done;
 				}

 				if (may_late_unmap)
 					need_unmap = true;
 				else
 					kunmap(pages_in[page_in_index]);

 				data_in = kmap(pages_in[++page_in_index]);

 				in_page_bytes_left = PAGE_CACHE_SIZE;
 				in_offset = 0;
 			}
 		}

 		out_len = lzo1x_worst_compress(PAGE_CACHE_SIZE);
 		ret = lzo1x_decompress_safe(buf, in_len, workspace->buf,
 					    &out_len);
 		if (need_unmap)
 			kunmap(pages_in[page_in_index - 1]);
 		if (ret != LZO_E_OK) {
 			printk(KERN_WARNING "BTRFS: decompress failed\n");
 			ret = -EIO;
 			break;
 		}

 		buf_start = tot_out;
 		tot_out += out_len;

 		ret2 = btrfs_decompress_buf2page(workspace->buf, buf_start,
 						 tot_out, disk_start,
 						 bvec, vcnt,
 						 &page_out_index, &pg_offset);
 		if (ret2 == 0)
 			break;
 	}
 done:
 	kunmap(pages_in[page_in_index]);
 	if (!ret)
 		btrfs_clear_biovec_end(bvec, vcnt, page_out_index, pg_offset);
 	return ret;
 }

 static int lzo_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);
 	size_t in_len;
 	size_t out_len;
 	size_t tot_len;
 	int ret = 0;
 	char *kaddr;
 	unsigned long bytes;

 	BUG_ON(srclen < LZO_LEN);

 	tot_len = read_compress_length(data_in);
 	data_in += LZO_LEN;

 	in_len = read_compress_length(data_in);
 	data_in += LZO_LEN;

 	out_len = PAGE_CACHE_SIZE;
 	ret = lzo1x_decompress_safe(data_in, in_len, workspace->buf, &out_len);
 	if (ret != LZO_E_OK) {
 		printk(KERN_WARNING "BTRFS: decompress failed!\n");
 		ret = -EIO;
 		goto out;
 	}

 	if (out_len < start_byte) {
 		ret = -EIO;
 		goto out;
 	}

 	/*
 	 * the caller is already checking against PAGE_SIZE, but lets
 	 * move this check closer to the memcpy/memset
 	 */
 	destlen = min_t(unsigned long, destlen, PAGE_SIZE);
 	bytes = min_t(unsigned long, destlen, out_len - start_byte);

 	kaddr = kmap_atomic(dest_page);
 	memcpy(kaddr, workspace->buf + start_byte, bytes);

 	/*
 	 * btrfs_getblock is doing a zero on the tail of the page too,
 	 * but this will cover anything missing from the decompressed
 	 * data.
 	 */
 	if (bytes < destlen)
 		memset(kaddr+bytes, 0, destlen-bytes);
 	kunmap_atomic(kaddr);
 out:
 	return ret;
 }

 const struct btrfs_compress_op btrfs_lzo_compress = {
 	.alloc_workspace	= lzo_alloc_workspace,
 	.free_workspace		= lzo_free_workspace,
 	.compress_pages		= lzo_compress_pages,
 	.decompress_biovec	= lzo_decompress_biovec,
 	.decompress		= lzo_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.
	*/

	#include <linux/kernel.h>
	#include <linux/slab.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 <linux/lzo.h>
	#include "compression.h"

	#define LZO_LEN 4

	struct workspace {
	void *mem;
	void buf; / where decompressed data goes */
	void cbuf; / where compressed data goes */
	struct list_head list;
	};

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

	vfree(workspace->buf);
	vfree(workspace->cbuf);
	vfree(workspace->mem);
	kfree(workspace);
	}

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

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

	workspace->mem = vmalloc(LZO1X_MEM_COMPRESS);
	workspace->buf = vmalloc(lzo1x_worst_compress(PAGE_CACHE_SIZE));
	workspace->cbuf = vmalloc(lzo1x_worst_compress(PAGE_CACHE_SIZE));
	if (!workspace->mem \|\| !workspace->buf \|\| !workspace->cbuf)
	goto fail;

	INIT_LIST_HEAD(&workspace->list);

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

	static inline void write_compress_length(char *buf, size_t len)
	{
	__le32 dlen;

	dlen = cpu_to_le32(len);
	memcpy(buf, &dlen, LZO_LEN);
	}

	static inline size_t read_compress_length(char *buf)
	{
	__le32 dlen;

	memcpy(&dlen, buf, LZO_LEN);
	return le32_to_cpu(dlen);
	}

	static int lzo_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 = 0;
	char *data_in;
	char *cpage_out;
	int nr_pages = 0;
	struct page *in_page = NULL;
	struct page *out_page = NULL;
	unsigned long bytes_left;

	size_t in_len;
	size_t out_len;
	char *buf;
	unsigned long tot_in = 0;
	unsigned long tot_out = 0;
	unsigned long pg_bytes_left;
	unsigned long out_offset;
	unsigned long bytes;

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

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

	/*
	* store the size of all chunks of compressed data in
	* the first 4 bytes
	*/
	out_page = alloc_page(GFP_NOFS \| __GFP_HIGHMEM);
	if (out_page == NULL) {
	ret = -ENOMEM;
	goto out;
	}
	cpage_out = kmap(out_page);
	out_offset = LZO_LEN;
	tot_out = LZO_LEN;
	pages[0] = out_page;
	nr_pages = 1;
	pg_bytes_left = PAGE_CACHE_SIZE - LZO_LEN;

	/* compress at most one page of data each time */
	in_len = min(len, PAGE_CACHE_SIZE);
	while (tot_in < len) {
	ret = lzo1x_1_compress(data_in, in_len, workspace->cbuf,
	&out_len, workspace->mem);
	if (ret != LZO_E_OK) {
	printk(KERN_DEBUG "BTRFS: deflate in loop returned %d\n",
	ret);
	ret = -EIO;
	goto out;
	}

	/* store the size of this chunk of compressed data */
	write_compress_length(cpage_out + out_offset, out_len);
	tot_out += LZO_LEN;
	out_offset += LZO_LEN;
	pg_bytes_left -= LZO_LEN;

	tot_in += in_len;
	tot_out += out_len;

	/* copy bytes from the working buffer into the pages */
	buf = workspace->cbuf;
	while (out_len) {
	bytes = min_t(unsigned long, pg_bytes_left, out_len);

	memcpy(cpage_out + out_offset, buf, bytes);

	out_len -= bytes;
	pg_bytes_left -= bytes;
	buf += bytes;
	out_offset += bytes;

	/*
	* we need another page for writing out.
	*
	* Note if there's less than 4 bytes left, we just
	* skip to a new page.
	*/
	if ((out_len == 0 && pg_bytes_left < LZO_LEN) \|\|
	pg_bytes_left == 0) {
	if (pg_bytes_left) {
	memset(cpage_out + out_offset, 0,
	pg_bytes_left);
	tot_out += pg_bytes_left;
	}

	/* we're done, don't allocate new page */
	if (out_len == 0 && tot_in >= len)
	break;

	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;

	pg_bytes_left = PAGE_CACHE_SIZE;
	out_offset = 0;
	}
	}

	/* we're making it bigger, give up */
	if (tot_in > 8192 && tot_in < tot_out) {
	ret = -E2BIG;
	goto out;
	}

	/* we're all done */
	if (tot_in >= len)
	break;

	if (tot_out > max_out)
	break;

	bytes_left = len - tot_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);
	in_len = min(bytes_left, PAGE_CACHE_SIZE);
	}

	if (tot_out > tot_in)
	goto out;

	/* store the size of all chunks of compressed data */
	cpage_out = kmap(pages[0]);
	write_compress_length(cpage_out, tot_out);

	kunmap(pages[0]);

	ret = 0;
	*total_out = tot_out;
	*total_in = tot_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 lzo_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;
	char *data_in;
	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 buf_offset = 0;
	unsigned long bytes;
	unsigned long working_bytes;
	unsigned long pg_offset;

	size_t in_len;
	size_t out_len;
	unsigned long in_offset;
	unsigned long in_page_bytes_left;
	unsigned long tot_in;
	unsigned long tot_out;
	unsigned long tot_len;
	char *buf;
	bool may_late_unmap, need_unmap;

	data_in = kmap(pages_in[0]);
	tot_len = read_compress_length(data_in);

	tot_in = LZO_LEN;
	in_offset = LZO_LEN;
	tot_len = min_t(size_t, srclen, tot_len);
	in_page_bytes_left = PAGE_CACHE_SIZE - LZO_LEN;

	tot_out = 0;
	pg_offset = 0;

	while (tot_in < tot_len) {
	in_len = read_compress_length(data_in + in_offset);
	in_page_bytes_left -= LZO_LEN;
	in_offset += LZO_LEN;
	tot_in += LZO_LEN;

	tot_in += in_len;
	working_bytes = in_len;
	may_late_unmap = need_unmap = false;

	/* fast path: avoid using the working buffer */
	if (in_page_bytes_left >= in_len) {
	buf = data_in + in_offset;
	bytes = in_len;
	may_late_unmap = true;
	goto cont;
	}

	/* copy bytes from the pages into the working buffer */
	buf = workspace->cbuf;
	buf_offset = 0;
	while (working_bytes) {
	bytes = min(working_bytes, in_page_bytes_left);

	memcpy(buf + buf_offset, data_in + in_offset, bytes);
	buf_offset += bytes;
	cont:
	working_bytes -= bytes;
	in_page_bytes_left -= bytes;
	in_offset += bytes;

	/* check if we need to pick another page */
	if ((working_bytes == 0 && in_page_bytes_left < LZO_LEN)
	\|\| in_page_bytes_left == 0) {
	tot_in += in_page_bytes_left;

	if (working_bytes == 0 && tot_in >= tot_len)
	break;

	if (page_in_index + 1 >= total_pages_in) {
	ret = -EIO;
	goto done;
	}

	if (may_late_unmap)
	need_unmap = true;
	else
	kunmap(pages_in[page_in_index]);

	data_in = kmap(pages_in[++page_in_index]);

	in_page_bytes_left = PAGE_CACHE_SIZE;
	in_offset = 0;
	}
	}

	out_len = lzo1x_worst_compress(PAGE_CACHE_SIZE);
	ret = lzo1x_decompress_safe(buf, in_len, workspace->buf,
	&out_len);
	if (need_unmap)
	kunmap(pages_in[page_in_index - 1]);
	if (ret != LZO_E_OK) {
	printk(KERN_WARNING "BTRFS: decompress failed\n");
	ret = -EIO;
	break;
	}

	buf_start = tot_out;
	tot_out += out_len;

	ret2 = btrfs_decompress_buf2page(workspace->buf, buf_start,
	tot_out, disk_start,
	bvec, vcnt,
	&page_out_index, &pg_offset);
	if (ret2 == 0)
	break;
	}
	done:
	kunmap(pages_in[page_in_index]);
	if (!ret)
	btrfs_clear_biovec_end(bvec, vcnt, page_out_index, pg_offset);
	return ret;
	}

	static int lzo_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);
	size_t in_len;
	size_t out_len;
	size_t tot_len;
	int ret = 0;
	char *kaddr;
	unsigned long bytes;

	BUG_ON(srclen < LZO_LEN);

	tot_len = read_compress_length(data_in);
	data_in += LZO_LEN;

	in_len = read_compress_length(data_in);
	data_in += LZO_LEN;

	out_len = PAGE_CACHE_SIZE;
	ret = lzo1x_decompress_safe(data_in, in_len, workspace->buf, &out_len);
	if (ret != LZO_E_OK) {
	printk(KERN_WARNING "BTRFS: decompress failed!\n");
	ret = -EIO;
	goto out;
	}

	if (out_len < start_byte) {
	ret = -EIO;
	goto out;
	}

	/*
	* the caller is already checking against PAGE_SIZE, but lets
	* move this check closer to the memcpy/memset
	*/
	destlen = min_t(unsigned long, destlen, PAGE_SIZE);
	bytes = min_t(unsigned long, destlen, out_len - start_byte);

	kaddr = kmap_atomic(dest_page);
	memcpy(kaddr, workspace->buf + start_byte, bytes);

	/*
	* btrfs_getblock is doing a zero on the tail of the page too,
	* but this will cover anything missing from the decompressed
	* data.
	*/
	if (bytes < destlen)
	memset(kaddr+bytes, 0, destlen-bytes);
	kunmap_atomic(kaddr);
	out:
	return ret;
	}

	const struct btrfs_compress_op btrfs_lzo_compress = {
	.alloc_workspace = lzo_alloc_workspace,
	.free_workspace = lzo_free_workspace,
	.compress_pages = lzo_compress_pages,
	.decompress_biovec = lzo_decompress_biovec,
	.decompress = lzo_decompress,
	};