fs/squashfs/block.c - kernel/common.git - Git at Google

 /*
  * Squashfs - a compressed read only filesystem for Linux
  *
  * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
  * Phillip Lougher <phillip@squashfs.org.uk>
  *
  * 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,
  * 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, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  *
  * block.c
  */

 /*
  * This file implements the low-level routines to read and decompress
  * datablocks and metadata blocks.
  */

 #include <linux/fs.h>
 #include <linux/vfs.h>
 #include <linux/bio.h>
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/pagemap.h>
 #include <linux/buffer_head.h>
 #include <linux/workqueue.h>

 #include "squashfs_fs.h"
 #include "squashfs_fs_sb.h"
 #include "squashfs.h"
 #include "decompressor.h"
 #include "page_actor.h"

 static struct workqueue_struct *squashfs_read_wq;

 struct squashfs_read_request {
 	struct super_block *sb;
 	u64 index;
 	int length;
 	int compressed;
 	int offset;
 	u64 read_end;
 	struct squashfs_page_actor *output;
 	enum {
 		SQUASHFS_COPY,
 		SQUASHFS_DECOMPRESS,
 		SQUASHFS_METADATA,
 	} data_processing;
 	bool synchronous;

 	/*
 	 * If the read is synchronous, it is possible to retrieve information
 	 * about the request by setting these pointers.
 	 */
 	int *res;
 	int *bytes_read;
 	int *bytes_uncompressed;

 	int nr_buffers;
 	struct buffer_head **bh;
 	struct work_struct offload;
 };

 struct squashfs_bio_request {
 	struct buffer_head **bh;
 	int nr_buffers;
 };

 static int squashfs_bio_submit(struct squashfs_read_request *req);

 int squashfs_init_read_wq(void)
 {
 	squashfs_read_wq = create_workqueue("SquashFS read wq");
 	return !!squashfs_read_wq;
 }

 void squashfs_destroy_read_wq(void)
 {
 	flush_workqueue(squashfs_read_wq);
 	destroy_workqueue(squashfs_read_wq);
 }

 static void free_read_request(struct squashfs_read_request *req, int error)
 {
 	if (!req->synchronous)
 		squashfs_page_actor_free(req->output, error);
 	if (req->res)
 		*(req->res) = error;
 	kfree(req->bh);
 	kfree(req);
 }

 static void squashfs_process_blocks(struct squashfs_read_request *req)
 {
 	int error = 0;
 	int bytes, i, length;
 	struct squashfs_sb_info *msblk = req->sb->s_fs_info;
 	struct squashfs_page_actor *actor = req->output;
 	struct buffer_head **bh = req->bh;
 	int nr_buffers = req->nr_buffers;

 	for (i = 0; i < nr_buffers; ++i) {
 		if (!bh[i])
 			continue;
 		wait_on_buffer(bh[i]);
 		if (!buffer_uptodate(bh[i]))
 			error = -EIO;
 	}
 	if (error)
 		goto cleanup;

 	if (req->data_processing == SQUASHFS_METADATA) {
 		/* Extract the length of the metadata block */
 		if (req->offset != msblk->devblksize - 1)
 			length = *((u16 *)(bh[0]->b_data + req->offset));
 		else {
 			length = bh[0]->b_data[req->offset];
 			length |= bh[1]->b_data[0] << 8;
 		}
 		req->compressed = SQUASHFS_COMPRESSED(length);
 		req->data_processing = req->compressed ? SQUASHFS_DECOMPRESS
 						       : SQUASHFS_COPY;
 		length = SQUASHFS_COMPRESSED_SIZE(length);
 		if (req->index + length + 2 > req->read_end) {
 			for (i = 0; i < nr_buffers; ++i)
 				put_bh(bh[i]);
 			kfree(bh);
 			req->length = length;
 			req->index += 2;
 			squashfs_bio_submit(req);
 			return;
 		}
 		req->length = length;
 		req->offset = (req->offset + 2) % PAGE_SIZE;
 		if (req->offset < 2) {
 			put_bh(bh[0]);
 			++bh;
 			--nr_buffers;
 		}
 	}
 	if (req->bytes_read)
 		*(req->bytes_read) = req->length;

 	if (req->data_processing == SQUASHFS_COPY) {
 		squashfs_bh_to_actor(bh, nr_buffers, req->output, req->offset,
 			req->length, msblk->devblksize);
 	} else if (req->data_processing == SQUASHFS_DECOMPRESS) {
 		req->length = squashfs_decompress(msblk, bh, nr_buffers,
 			req->offset, req->length, actor);
 		if (req->length < 0) {
 			error = -EIO;
 			goto cleanup;
 		}
 	}

 	/* Last page may have trailing bytes not filled */
 	bytes = req->length % PAGE_SIZE;
 	if (bytes && actor->page[actor->pages - 1])
 		zero_user_segment(actor->page[actor->pages - 1], bytes,
 				  PAGE_SIZE);

 cleanup:
 	if (req->bytes_uncompressed)
 		*(req->bytes_uncompressed) = req->length;
 	if (error) {
 		for (i = 0; i < nr_buffers; ++i)
 			if (bh[i])
 				put_bh(bh[i]);
 	}
 	free_read_request(req, error);
 }

 static void read_wq_handler(struct work_struct *work)
 {
 	squashfs_process_blocks(container_of(work,
 		    struct squashfs_read_request, offload));
 }

 static void squashfs_bio_end_io(struct bio *bio)
 {
 	int i;
 	int error = bio->bi_error;
 	struct squashfs_bio_request *bio_req = bio->bi_private;

 	bio_put(bio);

 	for (i = 0; i < bio_req->nr_buffers; ++i) {
 		if (!bio_req->bh[i])
 			continue;
 		if (!error)
 			set_buffer_uptodate(bio_req->bh[i]);
 		else
 			clear_buffer_uptodate(bio_req->bh[i]);
 		unlock_buffer(bio_req->bh[i]);
 	}
 	kfree(bio_req);
 }

 static int bh_is_optional(struct squashfs_read_request *req, int idx)
 {
 	int start_idx, end_idx;
 	struct squashfs_sb_info *msblk = req->sb->s_fs_info;

 	start_idx = (idx * msblk->devblksize - req->offset) / PAGE_CACHE_SIZE;
 	end_idx = ((idx + 1) * msblk->devblksize - req->offset + 1) / PAGE_CACHE_SIZE;
 	if (start_idx >= req->output->pages)
 		return 1;
 	if (start_idx < 0)
 		start_idx = end_idx;
 	if (end_idx >= req->output->pages)
 		end_idx = start_idx;
 	return !req->output->page[start_idx] && !req->output->page[end_idx];
 }

 static int actor_getblks(struct squashfs_read_request *req, u64 block)
 {
 	int i;

 	req->bh = kmalloc_array(req->nr_buffers, sizeof(*(req->bh)), GFP_NOIO);
 	if (!req->bh)
 		return -ENOMEM;

 	for (i = 0; i < req->nr_buffers; ++i) {
 		/*
 		 * When dealing with an uncompressed block, the actor may
 		 * contains NULL pages. There's no need to read the buffers
 		 * associated with these pages.
 		 */
 		if (!req->compressed && bh_is_optional(req, i)) {
 			req->bh[i] = NULL;
 			continue;
 		}
 		req->bh[i] = sb_getblk(req->sb, block + i);
 		if (!req->bh[i]) {
 			while (--i) {
 				if (req->bh[i])
 					put_bh(req->bh[i]);
 			}
 			return -1;
 		}
 	}
 	return 0;
 }

 static int squashfs_bio_submit(struct squashfs_read_request *req)
 {
 	struct bio *bio = NULL;
 	struct buffer_head *bh;
 	struct squashfs_bio_request *bio_req = NULL;
 	int b = 0, prev_block = 0;
 	struct squashfs_sb_info *msblk = req->sb->s_fs_info;

 	u64 read_start = round_down(req->index, msblk->devblksize);
 	u64 read_end = round_up(req->index + req->length, msblk->devblksize);
 	sector_t block = read_start >> msblk->devblksize_log2;
 	sector_t block_end = read_end >> msblk->devblksize_log2;
 	int offset = read_start - round_down(req->index, PAGE_SIZE);
 	int nr_buffers = block_end - block;
 	int blksz = msblk->devblksize;
 	int bio_max_pages = nr_buffers > BIO_MAX_PAGES ? BIO_MAX_PAGES
 						       : nr_buffers;

 	/* Setup the request */
 	req->read_end = read_end;
 	req->offset = req->index - read_start;
 	req->nr_buffers = nr_buffers;
 	if (actor_getblks(req, block) < 0)
 		goto getblk_failed;

 	/* Create and submit the BIOs */
 	for (b = 0; b < nr_buffers; ++b, offset += blksz) {
 		bh = req->bh[b];
 		if (!bh || !trylock_buffer(bh))
 			continue;
 		if (buffer_uptodate(bh)) {
 			unlock_buffer(bh);
 			continue;
 		}
 		offset %= PAGE_SIZE;

 		/* Append the buffer to the current BIO if it is contiguous */
 		if (bio && bio_req && prev_block + 1 == b) {
 			if (bio_add_page(bio, bh->b_page, blksz, offset)) {
 				bio_req->nr_buffers += 1;
 				prev_block = b;
 				continue;
 			}
 		}

 		/* Otherwise, submit the current BIO and create a new one */
 		if (bio)
 			submit_bio(READ, bio);
 		bio_req = kcalloc(1, sizeof(struct squashfs_bio_request),
 				  GFP_NOIO);
 		if (!bio_req)
 			goto req_alloc_failed;
 		bio_req->bh = &req->bh[b];
 		bio = bio_alloc(GFP_NOIO, bio_max_pages);
 		if (!bio)
 			goto bio_alloc_failed;
 		bio->bi_bdev = req->sb->s_bdev;
 		bio->bi_iter.bi_sector = (block + b)
 				       << (msblk->devblksize_log2 - 9);
 		bio->bi_private = bio_req;
 		bio->bi_end_io = squashfs_bio_end_io;

 		bio_add_page(bio, bh->b_page, blksz, offset);
 		bio_req->nr_buffers += 1;
 		prev_block = b;
 	}
 	if (bio)
 		submit_bio(READ, bio);

 	if (req->synchronous)
 		squashfs_process_blocks(req);
 	else {
 		INIT_WORK(&req->offload, read_wq_handler);
 		schedule_work(&req->offload);
 	}
 	return 0;

 bio_alloc_failed:
 	kfree(bio_req);
 req_alloc_failed:
 	unlock_buffer(bh);
 	while (--nr_buffers >= b)
 		if (req->bh[nr_buffers])
 			put_bh(req->bh[nr_buffers]);
 	while (--b >= 0)
 		if (req->bh[b])
 			wait_on_buffer(req->bh[b]);
 getblk_failed:
 	free_read_request(req, -ENOMEM);
 	return -ENOMEM;
 }

 static int read_metadata_block(struct squashfs_read_request *req,
 			       u64 *next_index)
 {
 	int ret, error, bytes_read = 0, bytes_uncompressed = 0;
 	struct squashfs_sb_info *msblk = req->sb->s_fs_info;

 	if (req->index + 2 > msblk->bytes_used) {
 		free_read_request(req, -EINVAL);
 		return -EINVAL;
 	}
 	req->length = 2;

 	/* Do not read beyond the end of the device */
 	if (req->index + req->length > msblk->bytes_used)
 		req->length = msblk->bytes_used - req->index;
 	req->data_processing = SQUASHFS_METADATA;

 	/*
 	 * Reading metadata is always synchronous because we don't know the
 	 * length in advance and the function is expected to update
 	 * 'next_index' and return the length.
 	 */
 	req->synchronous = true;
 	req->res = &error;
 	req->bytes_read = &bytes_read;
 	req->bytes_uncompressed = &bytes_uncompressed;

 	TRACE("Metadata block @ 0x%llx, %scompressed size %d, src size %d\n",
 	      req->index, req->compressed ? "" : "un", bytes_read,
 	      req->output->length);

 	ret = squashfs_bio_submit(req);
 	if (ret)
 		return ret;
 	if (error)
 		return error;
 	if (next_index)
 		*next_index += 2 + bytes_read;
 	return bytes_uncompressed;
 }

 static int read_data_block(struct squashfs_read_request *req, int length,
 			   u64 *next_index, bool synchronous)
 {
 	int ret, error = 0, bytes_uncompressed = 0, bytes_read = 0;

 	req->compressed = SQUASHFS_COMPRESSED_BLOCK(length);
 	req->length = length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
 	req->data_processing = req->compressed ? SQUASHFS_DECOMPRESS
 					       : SQUASHFS_COPY;

 	req->synchronous = synchronous;
 	if (synchronous) {
 		req->res = &error;
 		req->bytes_read = &bytes_read;
 		req->bytes_uncompressed = &bytes_uncompressed;
 	}

 	TRACE("Data block @ 0x%llx, %scompressed size %d, src size %d\n",
 	      req->index, req->compressed ? "" : "un", req->length,
 	      req->output->length);

 	ret = squashfs_bio_submit(req);
 	if (ret)
 		return ret;
 	if (synchronous)
 		ret = error ? error : bytes_uncompressed;
 	if (next_index)
 		*next_index += length;
 	return ret;
 }

 /*
  * Read and decompress a metadata block or datablock.  Length is non-zero
  * if a datablock is being read (the size is stored elsewhere in the
  * filesystem), otherwise the length is obtained from the first two bytes of
  * the metadata block.  A bit in the length field indicates if the block
  * is stored uncompressed in the filesystem (usually because compression
  * generated a larger block - this does occasionally happen with compression
  * algorithms).
  */
 static int __squashfs_read_data(struct super_block *sb, u64 index, int length,
 	u64 *next_index, struct squashfs_page_actor *output, bool sync)
 {
 	struct squashfs_read_request *req;

 	req = kcalloc(1, sizeof(struct squashfs_read_request), GFP_KERNEL);
 	if (!req) {
 		if (!sync)
 			squashfs_page_actor_free(output, -ENOMEM);
 		return -ENOMEM;
 	}

 	req->sb = sb;
 	req->index = index;
 	req->output = output;

 	if (next_index)
 		*next_index = index;

 	if (length)
 		length = read_data_block(req, length, next_index, sync);
 	else
 		length = read_metadata_block(req, next_index);

 	if (length < 0) {
 		ERROR("squashfs_read_data failed to read block 0x%llx\n",
 		      (unsigned long long)index);
 		return -EIO;
 	}

 	return length;
 }

 int squashfs_read_data(struct super_block *sb, u64 index, int length,
 	u64 *next_index, struct squashfs_page_actor *output)
 {
 	return __squashfs_read_data(sb, index, length, next_index, output,
 				    true);
 }

 int squashfs_read_data_async(struct super_block *sb, u64 index, int length,
 	u64 *next_index, struct squashfs_page_actor *output)
 {

 	return __squashfs_read_data(sb, index, length, next_index, output,
 				    false);
 }
	/*
	* Squashfs - a compressed read only filesystem for Linux
	*
	* Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
	* Phillip Lougher <phillip@squashfs.org.uk>
	*
	* 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,
	* 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, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
	*
	* block.c
	*/

	/*
	* This file implements the low-level routines to read and decompress
	* datablocks and metadata blocks.
	*/

	#include <linux/fs.h>
	#include <linux/vfs.h>
	#include <linux/bio.h>
	#include <linux/slab.h>
	#include <linux/string.h>
	#include <linux/pagemap.h>
	#include <linux/buffer_head.h>
	#include <linux/workqueue.h>

	#include "squashfs_fs.h"
	#include "squashfs_fs_sb.h"
	#include "squashfs.h"
	#include "decompressor.h"
	#include "page_actor.h"

	static struct workqueue_struct *squashfs_read_wq;

	struct squashfs_read_request {
	struct super_block *sb;
	u64 index;
	int length;
	int compressed;
	int offset;
	u64 read_end;
	struct squashfs_page_actor *output;
	enum {
	SQUASHFS_COPY,
	SQUASHFS_DECOMPRESS,
	SQUASHFS_METADATA,
	} data_processing;
	bool synchronous;

	/*
	* If the read is synchronous, it is possible to retrieve information
	* about the request by setting these pointers.
	*/
	int *res;
	int *bytes_read;
	int *bytes_uncompressed;

	int nr_buffers;
	struct buffer_head **bh;
	struct work_struct offload;
	};

	struct squashfs_bio_request {
	struct buffer_head **bh;
	int nr_buffers;
	};

	static int squashfs_bio_submit(struct squashfs_read_request *req);

	int squashfs_init_read_wq(void)
	{
	squashfs_read_wq = create_workqueue("SquashFS read wq");
	return !!squashfs_read_wq;
	}

	void squashfs_destroy_read_wq(void)
	{
	flush_workqueue(squashfs_read_wq);
	destroy_workqueue(squashfs_read_wq);
	}

	static void free_read_request(struct squashfs_read_request *req, int error)
	{
	if (!req->synchronous)
	squashfs_page_actor_free(req->output, error);
	if (req->res)
	*(req->res) = error;
	kfree(req->bh);
	kfree(req);
	}

	static void squashfs_process_blocks(struct squashfs_read_request *req)
	{
	int error = 0;
	int bytes, i, length;
	struct squashfs_sb_info *msblk = req->sb->s_fs_info;
	struct squashfs_page_actor *actor = req->output;
	struct buffer_head **bh = req->bh;
	int nr_buffers = req->nr_buffers;

	for (i = 0; i < nr_buffers; ++i) {
	if (!bh[i])
	continue;
	wait_on_buffer(bh[i]);
	if (!buffer_uptodate(bh[i]))
	error = -EIO;
	}
	if (error)
	goto cleanup;

	if (req->data_processing == SQUASHFS_METADATA) {
	/* Extract the length of the metadata block */
	if (req->offset != msblk->devblksize - 1)
	length = ((u16 )(bh[0]->b_data + req->offset));
	else {
	length = bh[0]->b_data[req->offset];
	length \|= bh[1]->b_data[0] << 8;
	}
	req->compressed = SQUASHFS_COMPRESSED(length);
	req->data_processing = req->compressed ? SQUASHFS_DECOMPRESS
	: SQUASHFS_COPY;
	length = SQUASHFS_COMPRESSED_SIZE(length);
	if (req->index + length + 2 > req->read_end) {
	for (i = 0; i < nr_buffers; ++i)
	put_bh(bh[i]);
	kfree(bh);
	req->length = length;
	req->index += 2;
	squashfs_bio_submit(req);
	return;
	}
	req->length = length;
	req->offset = (req->offset + 2) % PAGE_SIZE;
	if (req->offset < 2) {
	put_bh(bh[0]);
	++bh;
	--nr_buffers;
	}
	}
	if (req->bytes_read)
	*(req->bytes_read) = req->length;

	if (req->data_processing == SQUASHFS_COPY) {
	squashfs_bh_to_actor(bh, nr_buffers, req->output, req->offset,
	req->length, msblk->devblksize);
	} else if (req->data_processing == SQUASHFS_DECOMPRESS) {
	req->length = squashfs_decompress(msblk, bh, nr_buffers,
	req->offset, req->length, actor);
	if (req->length < 0) {
	error = -EIO;
	goto cleanup;
	}
	}

	/* Last page may have trailing bytes not filled */
	bytes = req->length % PAGE_SIZE;
	if (bytes && actor->page[actor->pages - 1])
	zero_user_segment(actor->page[actor->pages - 1], bytes,
	PAGE_SIZE);

	cleanup:
	if (req->bytes_uncompressed)
	*(req->bytes_uncompressed) = req->length;
	if (error) {
	for (i = 0; i < nr_buffers; ++i)
	if (bh[i])
	put_bh(bh[i]);
	}
	free_read_request(req, error);
	}

	static void read_wq_handler(struct work_struct *work)
	{
	squashfs_process_blocks(container_of(work,
	struct squashfs_read_request, offload));
	}

	static void squashfs_bio_end_io(struct bio *bio)
	{
	int i;
	int error = bio->bi_error;
	struct squashfs_bio_request *bio_req = bio->bi_private;

	bio_put(bio);

	for (i = 0; i < bio_req->nr_buffers; ++i) {
	if (!bio_req->bh[i])
	continue;
	if (!error)
	set_buffer_uptodate(bio_req->bh[i]);
	else
	clear_buffer_uptodate(bio_req->bh[i]);
	unlock_buffer(bio_req->bh[i]);
	}
	kfree(bio_req);
	}

	static int bh_is_optional(struct squashfs_read_request *req, int idx)
	{
	int start_idx, end_idx;
	struct squashfs_sb_info *msblk = req->sb->s_fs_info;

	start_idx = (idx * msblk->devblksize - req->offset) / PAGE_CACHE_SIZE;
	end_idx = ((idx + 1) * msblk->devblksize - req->offset + 1) / PAGE_CACHE_SIZE;
	if (start_idx >= req->output->pages)
	return 1;
	if (start_idx < 0)
	start_idx = end_idx;
	if (end_idx >= req->output->pages)
	end_idx = start_idx;
	return !req->output->page[start_idx] && !req->output->page[end_idx];
	}

	static int actor_getblks(struct squashfs_read_request *req, u64 block)
	{
	int i;

	req->bh = kmalloc_array(req->nr_buffers, sizeof(*(req->bh)), GFP_NOIO);
	if (!req->bh)
	return -ENOMEM;

	for (i = 0; i < req->nr_buffers; ++i) {
	/*
	* When dealing with an uncompressed block, the actor may
	* contains NULL pages. There's no need to read the buffers
	* associated with these pages.
	*/
	if (!req->compressed && bh_is_optional(req, i)) {
	req->bh[i] = NULL;
	continue;
	}
	req->bh[i] = sb_getblk(req->sb, block + i);
	if (!req->bh[i]) {
	while (--i) {
	if (req->bh[i])
	put_bh(req->bh[i]);
	}
	return -1;
	}
	}
	return 0;
	}

	static int squashfs_bio_submit(struct squashfs_read_request *req)
	{
	struct bio *bio = NULL;
	struct buffer_head *bh;
	struct squashfs_bio_request *bio_req = NULL;
	int b = 0, prev_block = 0;
	struct squashfs_sb_info *msblk = req->sb->s_fs_info;

	u64 read_start = round_down(req->index, msblk->devblksize);
	u64 read_end = round_up(req->index + req->length, msblk->devblksize);
	sector_t block = read_start >> msblk->devblksize_log2;
	sector_t block_end = read_end >> msblk->devblksize_log2;
	int offset = read_start - round_down(req->index, PAGE_SIZE);
	int nr_buffers = block_end - block;
	int blksz = msblk->devblksize;
	int bio_max_pages = nr_buffers > BIO_MAX_PAGES ? BIO_MAX_PAGES
	: nr_buffers;

	/* Setup the request */
	req->read_end = read_end;
	req->offset = req->index - read_start;
	req->nr_buffers = nr_buffers;
	if (actor_getblks(req, block) < 0)
	goto getblk_failed;

	/* Create and submit the BIOs */
	for (b = 0; b < nr_buffers; ++b, offset += blksz) {
	bh = req->bh[b];
	if (!bh \|\| !trylock_buffer(bh))
	continue;
	if (buffer_uptodate(bh)) {
	unlock_buffer(bh);
	continue;
	}
	offset %= PAGE_SIZE;

	/* Append the buffer to the current BIO if it is contiguous */
	if (bio && bio_req && prev_block + 1 == b) {
	if (bio_add_page(bio, bh->b_page, blksz, offset)) {
	bio_req->nr_buffers += 1;
	prev_block = b;
	continue;
	}
	}

	/* Otherwise, submit the current BIO and create a new one */
	if (bio)
	submit_bio(READ, bio);
	bio_req = kcalloc(1, sizeof(struct squashfs_bio_request),
	GFP_NOIO);
	if (!bio_req)
	goto req_alloc_failed;
	bio_req->bh = &req->bh[b];
	bio = bio_alloc(GFP_NOIO, bio_max_pages);
	if (!bio)
	goto bio_alloc_failed;
	bio->bi_bdev = req->sb->s_bdev;
	bio->bi_iter.bi_sector = (block + b)
	<< (msblk->devblksize_log2 - 9);
	bio->bi_private = bio_req;
	bio->bi_end_io = squashfs_bio_end_io;

	bio_add_page(bio, bh->b_page, blksz, offset);
	bio_req->nr_buffers += 1;
	prev_block = b;
	}
	if (bio)
	submit_bio(READ, bio);

	if (req->synchronous)
	squashfs_process_blocks(req);
	else {
	INIT_WORK(&req->offload, read_wq_handler);
	schedule_work(&req->offload);
	}
	return 0;

	bio_alloc_failed:
	kfree(bio_req);
	req_alloc_failed:
	unlock_buffer(bh);
	while (--nr_buffers >= b)
	if (req->bh[nr_buffers])
	put_bh(req->bh[nr_buffers]);
	while (--b >= 0)
	if (req->bh[b])
	wait_on_buffer(req->bh[b]);
	getblk_failed:
	free_read_request(req, -ENOMEM);
	return -ENOMEM;
	}

	static int read_metadata_block(struct squashfs_read_request *req,
	u64 *next_index)
	{
	int ret, error, bytes_read = 0, bytes_uncompressed = 0;
	struct squashfs_sb_info *msblk = req->sb->s_fs_info;

	if (req->index + 2 > msblk->bytes_used) {
	free_read_request(req, -EINVAL);
	return -EINVAL;
	}
	req->length = 2;

	/* Do not read beyond the end of the device */
	if (req->index + req->length > msblk->bytes_used)
	req->length = msblk->bytes_used - req->index;
	req->data_processing = SQUASHFS_METADATA;

	/*
	* Reading metadata is always synchronous because we don't know the
	* length in advance and the function is expected to update
	* 'next_index' and return the length.
	*/
	req->synchronous = true;
	req->res = &error;
	req->bytes_read = &bytes_read;
	req->bytes_uncompressed = &bytes_uncompressed;

	TRACE("Metadata block @ 0x%llx, %scompressed size %d, src size %d\n",
	req->index, req->compressed ? "" : "un", bytes_read,
	req->output->length);

	ret = squashfs_bio_submit(req);
	if (ret)
	return ret;
	if (error)
	return error;
	if (next_index)
	*next_index += 2 + bytes_read;
	return bytes_uncompressed;
	}

	static int read_data_block(struct squashfs_read_request *req, int length,
	u64 *next_index, bool synchronous)
	{
	int ret, error = 0, bytes_uncompressed = 0, bytes_read = 0;

	req->compressed = SQUASHFS_COMPRESSED_BLOCK(length);
	req->length = length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
	req->data_processing = req->compressed ? SQUASHFS_DECOMPRESS
	: SQUASHFS_COPY;

	req->synchronous = synchronous;
	if (synchronous) {
	req->res = &error;
	req->bytes_read = &bytes_read;
	req->bytes_uncompressed = &bytes_uncompressed;
	}

	TRACE("Data block @ 0x%llx, %scompressed size %d, src size %d\n",
	req->index, req->compressed ? "" : "un", req->length,
	req->output->length);

	ret = squashfs_bio_submit(req);
	if (ret)
	return ret;
	if (synchronous)
	ret = error ? error : bytes_uncompressed;
	if (next_index)
	*next_index += length;
	return ret;
	}

	/*
	* Read and decompress a metadata block or datablock. Length is non-zero
	* if a datablock is being read (the size is stored elsewhere in the
	* filesystem), otherwise the length is obtained from the first two bytes of
	* the metadata block. A bit in the length field indicates if the block
	* is stored uncompressed in the filesystem (usually because compression
	* generated a larger block - this does occasionally happen with compression
	* algorithms).
	*/
	static int __squashfs_read_data(struct super_block *sb, u64 index, int length,
	u64 next_index, struct squashfs_page_actor output, bool sync)
	{
	struct squashfs_read_request *req;

	req = kcalloc(1, sizeof(struct squashfs_read_request), GFP_KERNEL);
	if (!req) {
	if (!sync)
	squashfs_page_actor_free(output, -ENOMEM);
	return -ENOMEM;
	}

	req->sb = sb;
	req->index = index;
	req->output = output;

	if (next_index)
	*next_index = index;

	if (length)
	length = read_data_block(req, length, next_index, sync);
	else
	length = read_metadata_block(req, next_index);

	if (length < 0) {
	ERROR("squashfs_read_data failed to read block 0x%llx\n",
	(unsigned long long)index);
	return -EIO;
	}

	return length;
	}

	int squashfs_read_data(struct super_block *sb, u64 index, int length,
	u64 next_index, struct squashfs_page_actor output)
	{
	return __squashfs_read_data(sb, index, length, next_index, output,
	true);
	}

	int squashfs_read_data_async(struct super_block *sb, u64 index, int length,
	u64 next_index, struct squashfs_page_actor output)
	{

	return __squashfs_read_data(sb, index, length, next_index, output,
	false);
	}