fs/cramfs/inode.c - kernel/msm - Gitiles

 /*
  * Compressed rom filesystem for Linux.
  *
  * Copyright (C) 1999 Linus Torvalds.
  *
  * This file is released under the GPL.
  */

 /*
  * These are the VFS interfaces to the compressed rom filesystem.
  * The actual compression is based on zlib, see the other files.
  */

 #include <linux/module.h>
 #include <linux/fs.h>
 #include <linux/pagemap.h>
 #include <linux/init.h>
 #include <linux/string.h>
 #include <linux/blkdev.h>
 #include <linux/cramfs_fs.h>
 #include <linux/slab.h>
 #include <linux/cramfs_fs_sb.h>
 #include <linux/buffer_head.h>
 #include <linux/vfs.h>
 #include <linux/mutex.h>
 #include <asm/semaphore.h>

 #include <asm/uaccess.h>

 static struct super_operations cramfs_ops;
 static struct inode_operations cramfs_dir_inode_operations;
 static const struct file_operations cramfs_directory_operations;
 static const struct address_space_operations cramfs_aops;

 static DEFINE_MUTEX(read_mutex);


 /* These two macros may change in future, to provide better st_ino
    semantics. */
 #define CRAMINO(x)	(((x)->offset && (x)->size)?(x)->offset<<2:1)
 #define OFFSET(x)	((x)->i_ino)


 static int cramfs_iget5_test(struct inode *inode, void *opaque)
 {
 	struct cramfs_inode *cramfs_inode = opaque;

 	if (inode->i_ino != CRAMINO(cramfs_inode))
 		return 0; /* does not match */

 	if (inode->i_ino != 1)
 		return 1;

 	/* all empty directories, char, block, pipe, and sock, share inode #1 */

 	if ((inode->i_mode != cramfs_inode->mode) ||
 	    (inode->i_gid != cramfs_inode->gid) ||
 	    (inode->i_uid != cramfs_inode->uid))
 		return 0; /* does not match */

 	if ((S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode)) &&
 	    (inode->i_rdev != old_decode_dev(cramfs_inode->size)))
 		return 0; /* does not match */

 	return 1; /* matches */
 }

 static int cramfs_iget5_set(struct inode *inode, void *opaque)
 {
 	static struct timespec zerotime;
 	struct cramfs_inode *cramfs_inode = opaque;
 	inode->i_mode = cramfs_inode->mode;
 	inode->i_uid = cramfs_inode->uid;
 	inode->i_size = cramfs_inode->size;
 	inode->i_blocks = (cramfs_inode->size - 1) / 512 + 1;
 	inode->i_gid = cramfs_inode->gid;
 	/* Struct copy intentional */
 	inode->i_mtime = inode->i_atime = inode->i_ctime = zerotime;
 	inode->i_ino = CRAMINO(cramfs_inode);
 	/* inode->i_nlink is left 1 - arguably wrong for directories,
 	   but it's the best we can do without reading the directory
            contents.  1 yields the right result in GNU find, even
 	   without -noleaf option. */
 	if (S_ISREG(inode->i_mode)) {
 		inode->i_fop = &generic_ro_fops;
 		inode->i_data.a_ops = &cramfs_aops;
 	} else if (S_ISDIR(inode->i_mode)) {
 		inode->i_op = &cramfs_dir_inode_operations;
 		inode->i_fop = &cramfs_directory_operations;
 	} else if (S_ISLNK(inode->i_mode)) {
 		inode->i_op = &page_symlink_inode_operations;
 		inode->i_data.a_ops = &cramfs_aops;
 	} else {
 		inode->i_size = 0;
 		inode->i_blocks = 0;
 		init_special_inode(inode, inode->i_mode,
 			old_decode_dev(cramfs_inode->size));
 	}
 	return 0;
 }

 static struct inode *get_cramfs_inode(struct super_block *sb,
 				struct cramfs_inode * cramfs_inode)
 {
 	struct inode *inode = iget5_locked(sb, CRAMINO(cramfs_inode),
 					    cramfs_iget5_test, cramfs_iget5_set,
 					    cramfs_inode);
 	if (inode && (inode->i_state & I_NEW)) {
 		unlock_new_inode(inode);
 	}
 	return inode;
 }

 /*
  * We have our own block cache: don't fill up the buffer cache
  * with the rom-image, because the way the filesystem is set
  * up the accesses should be fairly regular and cached in the
  * page cache and dentry tree anyway..
  *
  * This also acts as a way to guarantee contiguous areas of up to
  * BLKS_PER_BUF*PAGE_CACHE_SIZE, so that the caller doesn't need to
  * worry about end-of-buffer issues even when decompressing a full
  * page cache.
  */
 #define READ_BUFFERS (2)
 /* NEXT_BUFFER(): Loop over [0..(READ_BUFFERS-1)]. */
 #define NEXT_BUFFER(_ix) ((_ix) ^ 1)

 /*
  * BLKS_PER_BUF_SHIFT should be at least 2 to allow for "compressed"
  * data that takes up more space than the original and with unlucky
  * alignment.
  */
 #define BLKS_PER_BUF_SHIFT	(2)
 #define BLKS_PER_BUF		(1 << BLKS_PER_BUF_SHIFT)
 #define BUFFER_SIZE		(BLKS_PER_BUF*PAGE_CACHE_SIZE)

 static unsigned char read_buffers[READ_BUFFERS][BUFFER_SIZE];
 static unsigned buffer_blocknr[READ_BUFFERS];
 static struct super_block * buffer_dev[READ_BUFFERS];
 static int next_buffer;

 /*
  * Returns a pointer to a buffer containing at least LEN bytes of
  * filesystem starting at byte offset OFFSET into the filesystem.
  */
 static void *cramfs_read(struct super_block *sb, unsigned int offset, unsigned int len)
 {
 	struct address_space *mapping = sb->s_bdev->bd_inode->i_mapping;
 	struct page *pages[BLKS_PER_BUF];
 	unsigned i, blocknr, buffer, unread;
 	unsigned long devsize;
 	char *data;

 	if (!len)
 		return NULL;
 	blocknr = offset >> PAGE_CACHE_SHIFT;
 	offset &= PAGE_CACHE_SIZE - 1;

 	/* Check if an existing buffer already has the data.. */
 	for (i = 0; i < READ_BUFFERS; i++) {
 		unsigned int blk_offset;

 		if (buffer_dev[i] != sb)
 			continue;
 		if (blocknr < buffer_blocknr[i])
 			continue;
 		blk_offset = (blocknr - buffer_blocknr[i]) << PAGE_CACHE_SHIFT;
 		blk_offset += offset;
 		if (blk_offset + len > BUFFER_SIZE)
 			continue;
 		return read_buffers[i] + blk_offset;
 	}

 	devsize = mapping->host->i_size >> PAGE_CACHE_SHIFT;

 	/* Ok, read in BLKS_PER_BUF pages completely first. */
 	unread = 0;
 	for (i = 0; i < BLKS_PER_BUF; i++) {
 		struct page *page = NULL;

 		if (blocknr + i < devsize) {
 			page = read_mapping_page(mapping, blocknr + i, NULL);
 			/* synchronous error? */
 			if (IS_ERR(page))
 				page = NULL;
 		}
 		pages[i] = page;
 	}

 	for (i = 0; i < BLKS_PER_BUF; i++) {
 		struct page *page = pages[i];
 		if (page) {
 			wait_on_page_locked(page);
 			if (!PageUptodate(page)) {
 				/* asynchronous error */
 				page_cache_release(page);
 				pages[i] = NULL;
 			}
 		}
 	}

 	buffer = next_buffer;
 	next_buffer = NEXT_BUFFER(buffer);
 	buffer_blocknr[buffer] = blocknr;
 	buffer_dev[buffer] = sb;

 	data = read_buffers[buffer];
 	for (i = 0; i < BLKS_PER_BUF; i++) {
 		struct page *page = pages[i];
 		if (page) {
 			memcpy(data, kmap(page), PAGE_CACHE_SIZE);
 			kunmap(page);
 			page_cache_release(page);
 		} else
 			memset(data, 0, PAGE_CACHE_SIZE);
 		data += PAGE_CACHE_SIZE;
 	}
 	return read_buffers[buffer] + offset;
 }

 static void cramfs_put_super(struct super_block *sb)
 {
 	kfree(sb->s_fs_info);
 	sb->s_fs_info = NULL;
 }

 static int cramfs_remount(struct super_block *sb, int *flags, char *data)
 {
 	*flags |= MS_RDONLY;
 	return 0;
 }

 static int cramfs_fill_super(struct super_block *sb, void *data, int silent)
 {
 	int i;
 	struct cramfs_super super;
 	unsigned long root_offset;
 	struct cramfs_sb_info *sbi;
 	struct inode *root;

 	sb->s_flags |= MS_RDONLY;

 	sbi = kzalloc(sizeof(struct cramfs_sb_info), GFP_KERNEL);
 	if (!sbi)
 		return -ENOMEM;
 	sb->s_fs_info = sbi;

 	/* Invalidate the read buffers on mount: think disk change.. */
 	mutex_lock(&read_mutex);
 	for (i = 0; i < READ_BUFFERS; i++)
 		buffer_blocknr[i] = -1;

 	/* Read the first block and get the superblock from it */
 	memcpy(&super, cramfs_read(sb, 0, sizeof(super)), sizeof(super));
 	mutex_unlock(&read_mutex);

 	/* Do sanity checks on the superblock */
 	if (super.magic != CRAMFS_MAGIC) {
 		/* check at 512 byte offset */
 		mutex_lock(&read_mutex);
 		memcpy(&super, cramfs_read(sb, 512, sizeof(super)), sizeof(super));
 		mutex_unlock(&read_mutex);
 		if (super.magic != CRAMFS_MAGIC) {
 			if (!silent)
 				printk(KERN_ERR "cramfs: wrong magic\n");
 			goto out;
 		}
 	}

 	/* get feature flags first */
 	if (super.flags & ~CRAMFS_SUPPORTED_FLAGS) {
 		printk(KERN_ERR "cramfs: unsupported filesystem features\n");
 		goto out;
 	}

 	/* Check that the root inode is in a sane state */
 	if (!S_ISDIR(super.root.mode)) {
 		printk(KERN_ERR "cramfs: root is not a directory\n");
 		goto out;
 	}
 	root_offset = super.root.offset << 2;
 	if (super.flags & CRAMFS_FLAG_FSID_VERSION_2) {
 		sbi->size=super.size;
 		sbi->blocks=super.fsid.blocks;
 		sbi->files=super.fsid.files;
 	} else {
 		sbi->size=1<<28;
 		sbi->blocks=0;
 		sbi->files=0;
 	}
 	sbi->magic=super.magic;
 	sbi->flags=super.flags;
 	if (root_offset == 0)
 		printk(KERN_INFO "cramfs: empty filesystem");
 	else if (!(super.flags & CRAMFS_FLAG_SHIFTED_ROOT_OFFSET) &&
 		 ((root_offset != sizeof(struct cramfs_super)) &&
 		  (root_offset != 512 + sizeof(struct cramfs_super))))
 	{
 		printk(KERN_ERR "cramfs: bad root offset %lu\n", root_offset);
 		goto out;
 	}

 	/* Set it all up.. */
 	sb->s_op = &cramfs_ops;
 	root = get_cramfs_inode(sb, &super.root);
 	if (!root)
 		goto out;
 	sb->s_root = d_alloc_root(root);
 	if (!sb->s_root) {
 		iput(root);
 		goto out;
 	}
 	return 0;
 out:
 	kfree(sbi);
 	sb->s_fs_info = NULL;
 	return -EINVAL;
 }

 static int cramfs_statfs(struct dentry *dentry, struct kstatfs *buf)
 {
 	struct super_block *sb = dentry->d_sb;

 	buf->f_type = CRAMFS_MAGIC;
 	buf->f_bsize = PAGE_CACHE_SIZE;
 	buf->f_blocks = CRAMFS_SB(sb)->blocks;
 	buf->f_bfree = 0;
 	buf->f_bavail = 0;
 	buf->f_files = CRAMFS_SB(sb)->files;
 	buf->f_ffree = 0;
 	buf->f_namelen = CRAMFS_MAXPATHLEN;
 	return 0;
 }

 /*
  * Read a cramfs directory entry.
  */
 static int cramfs_readdir(struct file *filp, void *dirent, filldir_t filldir)
 {
 	struct inode *inode = filp->f_path.dentry->d_inode;
 	struct super_block *sb = inode->i_sb;
 	char *buf;
 	unsigned int offset;
 	int copied;

 	/* Offset within the thing. */
 	offset = filp->f_pos;
 	if (offset >= inode->i_size)
 		return 0;
 	/* Directory entries are always 4-byte aligned */
 	if (offset & 3)
 		return -EINVAL;

 	buf = kmalloc(256, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;

 	copied = 0;
 	while (offset < inode->i_size) {
 		struct cramfs_inode *de;
 		unsigned long nextoffset;
 		char *name;
 		ino_t ino;
 		mode_t mode;
 		int namelen, error;

 		mutex_lock(&read_mutex);
 		de = cramfs_read(sb, OFFSET(inode) + offset, sizeof(*de)+256);
 		name = (char *)(de+1);

 		/*
 		 * Namelengths on disk are shifted by two
 		 * and the name padded out to 4-byte boundaries
 		 * with zeroes.
 		 */
 		namelen = de->namelen << 2;
 		memcpy(buf, name, namelen);
 		ino = CRAMINO(de);
 		mode = de->mode;
 		mutex_unlock(&read_mutex);
 		nextoffset = offset + sizeof(*de) + namelen;
 		for (;;) {
 			if (!namelen) {
 				kfree(buf);
 				return -EIO;
 			}
 			if (buf[namelen-1])
 				break;
 			namelen--;
 		}
 		error = filldir(dirent, buf, namelen, offset, ino, mode >> 12);
 		if (error)
 			break;

 		offset = nextoffset;
 		filp->f_pos = offset;
 		copied++;
 	}
 	kfree(buf);
 	return 0;
 }

 /*
  * Lookup and fill in the inode data..
  */
 static struct dentry * cramfs_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
 {
 	unsigned int offset = 0;
 	int sorted;

 	mutex_lock(&read_mutex);
 	sorted = CRAMFS_SB(dir->i_sb)->flags & CRAMFS_FLAG_SORTED_DIRS;
 	while (offset < dir->i_size) {
 		struct cramfs_inode *de;
 		char *name;
 		int namelen, retval;

 		de = cramfs_read(dir->i_sb, OFFSET(dir) + offset, sizeof(*de)+256);
 		name = (char *)(de+1);

 		/* Try to take advantage of sorted directories */
 		if (sorted && (dentry->d_name.name[0] < name[0]))
 			break;

 		namelen = de->namelen << 2;
 		offset += sizeof(*de) + namelen;

 		/* Quick check that the name is roughly the right length */
 		if (((dentry->d_name.len + 3) & ~3) != namelen)
 			continue;

 		for (;;) {
 			if (!namelen) {
 				mutex_unlock(&read_mutex);
 				return ERR_PTR(-EIO);
 			}
 			if (name[namelen-1])
 				break;
 			namelen--;
 		}
 		if (namelen != dentry->d_name.len)
 			continue;
 		retval = memcmp(dentry->d_name.name, name, namelen);
 		if (retval > 0)
 			continue;
 		if (!retval) {
 			struct cramfs_inode entry = *de;
 			mutex_unlock(&read_mutex);
 			d_add(dentry, get_cramfs_inode(dir->i_sb, &entry));
 			return NULL;
 		}
 		/* else (retval < 0) */
 		if (sorted)
 			break;
 	}
 	mutex_unlock(&read_mutex);
 	d_add(dentry, NULL);
 	return NULL;
 }

 static int cramfs_readpage(struct file *file, struct page * page)
 {
 	struct inode *inode = page->mapping->host;
 	u32 maxblock, bytes_filled;
 	void *pgdata;

 	maxblock = (inode->i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 	bytes_filled = 0;
 	if (page->index < maxblock) {
 		struct super_block *sb = inode->i_sb;
 		u32 blkptr_offset = OFFSET(inode) + page->index*4;
 		u32 start_offset, compr_len;

 		start_offset = OFFSET(inode) + maxblock*4;
 		mutex_lock(&read_mutex);
 		if (page->index)
 			start_offset = *(u32 *) cramfs_read(sb, blkptr_offset-4, 4);
 		compr_len = (*(u32 *) cramfs_read(sb, blkptr_offset, 4) - start_offset);
 		mutex_unlock(&read_mutex);
 		pgdata = kmap(page);
 		if (compr_len == 0)
 			; /* hole */
 		else if (compr_len > (PAGE_CACHE_SIZE << 1))
 			printk(KERN_ERR "cramfs: bad compressed blocksize %u\n", compr_len);
 		else {
 			mutex_lock(&read_mutex);
 			bytes_filled = cramfs_uncompress_block(pgdata,
 				 PAGE_CACHE_SIZE,
 				 cramfs_read(sb, start_offset, compr_len),
 				 compr_len);
 			mutex_unlock(&read_mutex);
 		}
 	} else
 		pgdata = kmap(page);
 	memset(pgdata + bytes_filled, 0, PAGE_CACHE_SIZE - bytes_filled);
 	kunmap(page);
 	flush_dcache_page(page);
 	SetPageUptodate(page);
 	unlock_page(page);
 	return 0;
 }

 static const struct address_space_operations cramfs_aops = {
 	.readpage = cramfs_readpage
 };

 /*
  * Our operations:
  */

 /*
  * A directory can only readdir
  */
 static const struct file_operations cramfs_directory_operations = {
 	.llseek		= generic_file_llseek,
 	.read		= generic_read_dir,
 	.readdir	= cramfs_readdir,
 };

 static struct inode_operations cramfs_dir_inode_operations = {
 	.lookup		= cramfs_lookup,
 };

 static struct super_operations cramfs_ops = {
 	.put_super	= cramfs_put_super,
 	.remount_fs	= cramfs_remount,
 	.statfs		= cramfs_statfs,
 };

 static int cramfs_get_sb(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
 {
 	return get_sb_bdev(fs_type, flags, dev_name, data, cramfs_fill_super,
 			   mnt);
 }

 static struct file_system_type cramfs_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "cramfs",
 	.get_sb		= cramfs_get_sb,
 	.kill_sb	= kill_block_super,
 	.fs_flags	= FS_REQUIRES_DEV,
 };

 static int __init init_cramfs_fs(void)
 {
 	int rv;

 	rv = cramfs_uncompress_init();
 	if (rv < 0)
 		return rv;
 	rv = register_filesystem(&cramfs_fs_type);
 	if (rv < 0)
 		cramfs_uncompress_exit();
 	return rv;
 }

 static void __exit exit_cramfs_fs(void)
 {
 	cramfs_uncompress_exit();
 	unregister_filesystem(&cramfs_fs_type);
 }

 module_init(init_cramfs_fs)
 module_exit(exit_cramfs_fs)
 MODULE_LICENSE("GPL");
	/*
	* Compressed rom filesystem for Linux.
	*
	* Copyright (C) 1999 Linus Torvalds.
	*
	* This file is released under the GPL.
	*/

	/*
	* These are the VFS interfaces to the compressed rom filesystem.
	* The actual compression is based on zlib, see the other files.
	*/

	#include <linux/module.h>
	#include <linux/fs.h>
	#include <linux/pagemap.h>
	#include <linux/init.h>
	#include <linux/string.h>
	#include <linux/blkdev.h>
	#include <linux/cramfs_fs.h>
	#include <linux/slab.h>
	#include <linux/cramfs_fs_sb.h>
	#include <linux/buffer_head.h>
	#include <linux/vfs.h>
	#include <linux/mutex.h>
	#include <asm/semaphore.h>

	#include <asm/uaccess.h>

	static struct super_operations cramfs_ops;
	static struct inode_operations cramfs_dir_inode_operations;
	static const struct file_operations cramfs_directory_operations;
	static const struct address_space_operations cramfs_aops;

	static DEFINE_MUTEX(read_mutex);


	/* These two macros may change in future, to provide better st_ino
	semantics. */
	#define CRAMINO(x) (((x)->offset && (x)->size)?(x)->offset<<2:1)
	#define OFFSET(x) ((x)->i_ino)


	static int cramfs_iget5_test(struct inode inode, void opaque)
	{
	struct cramfs_inode *cramfs_inode = opaque;

	if (inode->i_ino != CRAMINO(cramfs_inode))
	return 0; /* does not match */

	if (inode->i_ino != 1)
	return 1;

	/* all empty directories, char, block, pipe, and sock, share inode #1 */

	if ((inode->i_mode != cramfs_inode->mode) \|\|
	(inode->i_gid != cramfs_inode->gid) \|\|
	(inode->i_uid != cramfs_inode->uid))
	return 0; /* does not match */

	if ((S_ISCHR(inode->i_mode) \|\| S_ISBLK(inode->i_mode)) &&
	(inode->i_rdev != old_decode_dev(cramfs_inode->size)))
	return 0; /* does not match */

	return 1; /* matches */
	}

	static int cramfs_iget5_set(struct inode inode, void opaque)
	{
	static struct timespec zerotime;
	struct cramfs_inode *cramfs_inode = opaque;
	inode->i_mode = cramfs_inode->mode;
	inode->i_uid = cramfs_inode->uid;
	inode->i_size = cramfs_inode->size;
	inode->i_blocks = (cramfs_inode->size - 1) / 512 + 1;
	inode->i_gid = cramfs_inode->gid;
	/* Struct copy intentional */
	inode->i_mtime = inode->i_atime = inode->i_ctime = zerotime;
	inode->i_ino = CRAMINO(cramfs_inode);
	/* inode->i_nlink is left 1 - arguably wrong for directories,
	but it's the best we can do without reading the directory
	contents. 1 yields the right result in GNU find, even
	without -noleaf option. */
	if (S_ISREG(inode->i_mode)) {
	inode->i_fop = &generic_ro_fops;
	inode->i_data.a_ops = &cramfs_aops;
	} else if (S_ISDIR(inode->i_mode)) {
	inode->i_op = &cramfs_dir_inode_operations;
	inode->i_fop = &cramfs_directory_operations;
	} else if (S_ISLNK(inode->i_mode)) {
	inode->i_op = &page_symlink_inode_operations;
	inode->i_data.a_ops = &cramfs_aops;
	} else {
	inode->i_size = 0;
	inode->i_blocks = 0;
	init_special_inode(inode, inode->i_mode,
	old_decode_dev(cramfs_inode->size));
	}
	return 0;
	}

	static struct inode get_cramfs_inode(struct super_block sb,
	struct cramfs_inode * cramfs_inode)
	{
	struct inode *inode = iget5_locked(sb, CRAMINO(cramfs_inode),
	cramfs_iget5_test, cramfs_iget5_set,
	cramfs_inode);
	if (inode && (inode->i_state & I_NEW)) {
	unlock_new_inode(inode);
	}
	return inode;
	}

	/*
	* We have our own block cache: don't fill up the buffer cache
	* with the rom-image, because the way the filesystem is set
	* up the accesses should be fairly regular and cached in the
	* page cache and dentry tree anyway..
	*
	* This also acts as a way to guarantee contiguous areas of up to
	* BLKS_PER_BUF*PAGE_CACHE_SIZE, so that the caller doesn't need to
	* worry about end-of-buffer issues even when decompressing a full
	* page cache.
	*/
	#define READ_BUFFERS (2)
	/* NEXT_BUFFER(): Loop over [0..(READ_BUFFERS-1)]. */
	#define NEXT_BUFFER(_ix) ((_ix) ^ 1)

	/*
	* BLKS_PER_BUF_SHIFT should be at least 2 to allow for "compressed"
	* data that takes up more space than the original and with unlucky
	* alignment.
	*/
	#define BLKS_PER_BUF_SHIFT (2)
	#define BLKS_PER_BUF (1 << BLKS_PER_BUF_SHIFT)
	#define BUFFER_SIZE (BLKS_PER_BUF*PAGE_CACHE_SIZE)

	static unsigned char read_buffers[READ_BUFFERS][BUFFER_SIZE];
	static unsigned buffer_blocknr[READ_BUFFERS];
	static struct super_block * buffer_dev[READ_BUFFERS];
	static int next_buffer;

	/*
	* Returns a pointer to a buffer containing at least LEN bytes of
	* filesystem starting at byte offset OFFSET into the filesystem.
	*/
	static void cramfs_read(struct super_block sb, unsigned int offset, unsigned int len)
	{
	struct address_space *mapping = sb->s_bdev->bd_inode->i_mapping;
	struct page *pages[BLKS_PER_BUF];
	unsigned i, blocknr, buffer, unread;
	unsigned long devsize;
	char *data;

	if (!len)
	return NULL;
	blocknr = offset >> PAGE_CACHE_SHIFT;
	offset &= PAGE_CACHE_SIZE - 1;

	/* Check if an existing buffer already has the data.. */
	for (i = 0; i < READ_BUFFERS; i++) {
	unsigned int blk_offset;

	if (buffer_dev[i] != sb)
	continue;
	if (blocknr < buffer_blocknr[i])
	continue;
	blk_offset = (blocknr - buffer_blocknr[i]) << PAGE_CACHE_SHIFT;
	blk_offset += offset;
	if (blk_offset + len > BUFFER_SIZE)
	continue;
	return read_buffers[i] + blk_offset;
	}

	devsize = mapping->host->i_size >> PAGE_CACHE_SHIFT;

	/* Ok, read in BLKS_PER_BUF pages completely first. */
	unread = 0;
	for (i = 0; i < BLKS_PER_BUF; i++) {
	struct page *page = NULL;

	if (blocknr + i < devsize) {
	page = read_mapping_page(mapping, blocknr + i, NULL);
	/* synchronous error? */
	if (IS_ERR(page))
	page = NULL;
	}
	pages[i] = page;
	}

	for (i = 0; i < BLKS_PER_BUF; i++) {
	struct page *page = pages[i];
	if (page) {
	wait_on_page_locked(page);
	if (!PageUptodate(page)) {
	/* asynchronous error */
	page_cache_release(page);
	pages[i] = NULL;
	}
	}
	}

	buffer = next_buffer;
	next_buffer = NEXT_BUFFER(buffer);
	buffer_blocknr[buffer] = blocknr;
	buffer_dev[buffer] = sb;

	data = read_buffers[buffer];
	for (i = 0; i < BLKS_PER_BUF; i++) {
	struct page *page = pages[i];
	if (page) {
	memcpy(data, kmap(page), PAGE_CACHE_SIZE);
	kunmap(page);
	page_cache_release(page);
	} else
	memset(data, 0, PAGE_CACHE_SIZE);
	data += PAGE_CACHE_SIZE;
	}
	return read_buffers[buffer] + offset;
	}

	static void cramfs_put_super(struct super_block *sb)
	{
	kfree(sb->s_fs_info);
	sb->s_fs_info = NULL;
	}

	static int cramfs_remount(struct super_block sb, int flags, char *data)
	{
	*flags \|= MS_RDONLY;
	return 0;
	}

	static int cramfs_fill_super(struct super_block sb, void data, int silent)
	{
	int i;
	struct cramfs_super super;
	unsigned long root_offset;
	struct cramfs_sb_info *sbi;
	struct inode *root;

	sb->s_flags \|= MS_RDONLY;

	sbi = kzalloc(sizeof(struct cramfs_sb_info), GFP_KERNEL);
	if (!sbi)
	return -ENOMEM;
	sb->s_fs_info = sbi;

	/* Invalidate the read buffers on mount: think disk change.. */
	mutex_lock(&read_mutex);
	for (i = 0; i < READ_BUFFERS; i++)
	buffer_blocknr[i] = -1;

	/* Read the first block and get the superblock from it */
	memcpy(&super, cramfs_read(sb, 0, sizeof(super)), sizeof(super));
	mutex_unlock(&read_mutex);

	/* Do sanity checks on the superblock */
	if (super.magic != CRAMFS_MAGIC) {
	/* check at 512 byte offset */
	mutex_lock(&read_mutex);
	memcpy(&super, cramfs_read(sb, 512, sizeof(super)), sizeof(super));
	mutex_unlock(&read_mutex);
	if (super.magic != CRAMFS_MAGIC) {
	if (!silent)
	printk(KERN_ERR "cramfs: wrong magic\n");
	goto out;
	}
	}

	/* get feature flags first */
	if (super.flags & ~CRAMFS_SUPPORTED_FLAGS) {
	printk(KERN_ERR "cramfs: unsupported filesystem features\n");
	goto out;
	}

	/* Check that the root inode is in a sane state */
	if (!S_ISDIR(super.root.mode)) {
	printk(KERN_ERR "cramfs: root is not a directory\n");
	goto out;
	}
	root_offset = super.root.offset << 2;
	if (super.flags & CRAMFS_FLAG_FSID_VERSION_2) {
	sbi->size=super.size;
	sbi->blocks=super.fsid.blocks;
	sbi->files=super.fsid.files;
	} else {
	sbi->size=1<<28;
	sbi->blocks=0;
	sbi->files=0;
	}
	sbi->magic=super.magic;
	sbi->flags=super.flags;
	if (root_offset == 0)
	printk(KERN_INFO "cramfs: empty filesystem");
	else if (!(super.flags & CRAMFS_FLAG_SHIFTED_ROOT_OFFSET) &&
	((root_offset != sizeof(struct cramfs_super)) &&
	(root_offset != 512 + sizeof(struct cramfs_super))))
	{
	printk(KERN_ERR "cramfs: bad root offset %lu\n", root_offset);
	goto out;
	}

	/* Set it all up.. */
	sb->s_op = &cramfs_ops;
	root = get_cramfs_inode(sb, &super.root);
	if (!root)
	goto out;
	sb->s_root = d_alloc_root(root);
	if (!sb->s_root) {
	iput(root);
	goto out;
	}
	return 0;
	out:
	kfree(sbi);
	sb->s_fs_info = NULL;
	return -EINVAL;
	}

	static int cramfs_statfs(struct dentry dentry, struct kstatfs buf)
	{
	struct super_block *sb = dentry->d_sb;

	buf->f_type = CRAMFS_MAGIC;
	buf->f_bsize = PAGE_CACHE_SIZE;
	buf->f_blocks = CRAMFS_SB(sb)->blocks;
	buf->f_bfree = 0;
	buf->f_bavail = 0;
	buf->f_files = CRAMFS_SB(sb)->files;
	buf->f_ffree = 0;
	buf->f_namelen = CRAMFS_MAXPATHLEN;
	return 0;
	}

	/*
	* Read a cramfs directory entry.
	*/
	static int cramfs_readdir(struct file filp, void dirent, filldir_t filldir)
	{
	struct inode *inode = filp->f_path.dentry->d_inode;
	struct super_block *sb = inode->i_sb;
	char *buf;
	unsigned int offset;
	int copied;

	/* Offset within the thing. */
	offset = filp->f_pos;
	if (offset >= inode->i_size)
	return 0;
	/* Directory entries are always 4-byte aligned */
	if (offset & 3)
	return -EINVAL;

	buf = kmalloc(256, GFP_KERNEL);
	if (!buf)
	return -ENOMEM;

	copied = 0;
	while (offset < inode->i_size) {
	struct cramfs_inode *de;
	unsigned long nextoffset;
	char *name;
	ino_t ino;
	mode_t mode;
	int namelen, error;

	mutex_lock(&read_mutex);
	de = cramfs_read(sb, OFFSET(inode) + offset, sizeof(*de)+256);
	name = (char *)(de+1);

	/*
	* Namelengths on disk are shifted by two
	* and the name padded out to 4-byte boundaries
	* with zeroes.
	*/
	namelen = de->namelen << 2;
	memcpy(buf, name, namelen);
	ino = CRAMINO(de);
	mode = de->mode;
	mutex_unlock(&read_mutex);
	nextoffset = offset + sizeof(*de) + namelen;
	for (;;) {
	if (!namelen) {
	kfree(buf);
	return -EIO;
	}
	if (buf[namelen-1])
	break;
	namelen--;
	}
	error = filldir(dirent, buf, namelen, offset, ino, mode >> 12);
	if (error)
	break;

	offset = nextoffset;
	filp->f_pos = offset;
	copied++;
	}
	kfree(buf);
	return 0;
	}

	/*
	* Lookup and fill in the inode data..
	*/
	static struct dentry * cramfs_lookup(struct inode dir, struct dentry dentry, struct nameidata *nd)
	{
	unsigned int offset = 0;
	int sorted;

	mutex_lock(&read_mutex);
	sorted = CRAMFS_SB(dir->i_sb)->flags & CRAMFS_FLAG_SORTED_DIRS;
	while (offset < dir->i_size) {
	struct cramfs_inode *de;
	char *name;
	int namelen, retval;

	de = cramfs_read(dir->i_sb, OFFSET(dir) + offset, sizeof(*de)+256);
	name = (char *)(de+1);

	/* Try to take advantage of sorted directories */
	if (sorted && (dentry->d_name.name[0] < name[0]))
	break;

	namelen = de->namelen << 2;
	offset += sizeof(*de) + namelen;

	/* Quick check that the name is roughly the right length */
	if (((dentry->d_name.len + 3) & ~3) != namelen)
	continue;

	for (;;) {
	if (!namelen) {
	mutex_unlock(&read_mutex);
	return ERR_PTR(-EIO);
	}
	if (name[namelen-1])
	break;
	namelen--;
	}
	if (namelen != dentry->d_name.len)
	continue;
	retval = memcmp(dentry->d_name.name, name, namelen);
	if (retval > 0)
	continue;
	if (!retval) {
	struct cramfs_inode entry = *de;
	mutex_unlock(&read_mutex);
	d_add(dentry, get_cramfs_inode(dir->i_sb, &entry));
	return NULL;
	}
	/* else (retval < 0) */
	if (sorted)
	break;
	}
	mutex_unlock(&read_mutex);
	d_add(dentry, NULL);
	return NULL;
	}

	static int cramfs_readpage(struct file file, struct page page)
	{
	struct inode *inode = page->mapping->host;
	u32 maxblock, bytes_filled;
	void *pgdata;

	maxblock = (inode->i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
	bytes_filled = 0;
	if (page->index < maxblock) {
	struct super_block *sb = inode->i_sb;
	u32 blkptr_offset = OFFSET(inode) + page->index*4;
	u32 start_offset, compr_len;

	start_offset = OFFSET(inode) + maxblock*4;
	mutex_lock(&read_mutex);
	if (page->index)
	start_offset = (u32 ) cramfs_read(sb, blkptr_offset-4, 4);
	compr_len = ((u32 ) cramfs_read(sb, blkptr_offset, 4) - start_offset);
	mutex_unlock(&read_mutex);
	pgdata = kmap(page);
	if (compr_len == 0)
	; /* hole */
	else if (compr_len > (PAGE_CACHE_SIZE << 1))
	printk(KERN_ERR "cramfs: bad compressed blocksize %u\n", compr_len);
	else {
	mutex_lock(&read_mutex);
	bytes_filled = cramfs_uncompress_block(pgdata,
	PAGE_CACHE_SIZE,
	cramfs_read(sb, start_offset, compr_len),
	compr_len);
	mutex_unlock(&read_mutex);
	}
	} else
	pgdata = kmap(page);
	memset(pgdata + bytes_filled, 0, PAGE_CACHE_SIZE - bytes_filled);
	kunmap(page);
	flush_dcache_page(page);
	SetPageUptodate(page);
	unlock_page(page);
	return 0;
	}

	static const struct address_space_operations cramfs_aops = {
	.readpage = cramfs_readpage
	};

	/*
	* Our operations:
	*/

	/*
	* A directory can only readdir
	*/
	static const struct file_operations cramfs_directory_operations = {
	.llseek = generic_file_llseek,
	.read = generic_read_dir,
	.readdir = cramfs_readdir,
	};

	static struct inode_operations cramfs_dir_inode_operations = {
	.lookup = cramfs_lookup,
	};

	static struct super_operations cramfs_ops = {
	.put_super = cramfs_put_super,
	.remount_fs = cramfs_remount,
	.statfs = cramfs_statfs,
	};

	static int cramfs_get_sb(struct file_system_type *fs_type,
	int flags, const char dev_name, void data, struct vfsmount *mnt)
	{
	return get_sb_bdev(fs_type, flags, dev_name, data, cramfs_fill_super,
	mnt);
	}

	static struct file_system_type cramfs_fs_type = {
	.owner = THIS_MODULE,
	.name = "cramfs",
	.get_sb = cramfs_get_sb,
	.kill_sb = kill_block_super,
	.fs_flags = FS_REQUIRES_DEV,
	};

	static int __init init_cramfs_fs(void)
	{
	int rv;

	rv = cramfs_uncompress_init();
	if (rv < 0)
	return rv;
	rv = register_filesystem(&cramfs_fs_type);
	if (rv < 0)
	cramfs_uncompress_exit();
	return rv;
	}

	static void __exit exit_cramfs_fs(void)
	{
	cramfs_uncompress_exit();
	unregister_filesystem(&cramfs_fs_type);
	}

	module_init(init_cramfs_fs)
	module_exit(exit_cramfs_fs)
	MODULE_LICENSE("GPL");