Fixed MTP to work with TWRP

fs/cramfs/Kconfig

@@ -0,0 +1,22 @@
+config CRAMFS
+	tristate "Compressed ROM file system support (cramfs) (OBSOLETE)"
+	depends on BLOCK
+	select ZLIB_INFLATE
+	help
+	  Saying Y here includes support for CramFs (Compressed ROM File
+	  System).  CramFs is designed to be a simple, small, and compressed
+	  file system for ROM based embedded systems.  CramFs is read-only,
+	  limited to 256MB file systems (with 16MB files), and doesn't support
+	  16/32 bits uid/gid, hard links and timestamps.
+
+	  See <file:Documentation/filesystems/cramfs.txt> and
+	  <file:fs/cramfs/README> for further information.
+
+	  To compile this as a module, choose M here: the module will be called
+	  cramfs.  Note that the root file system (the one containing the
+	  directory /) cannot be compiled as a module.
+
+	  This filesystem is obsoleted by SquashFS, which is much better
+	  in terms of performance and features.
+
+	  If unsure, say N.

fs/cramfs/Makefile

@@ -0,0 +1,7 @@
+#
+# Makefile for the linux cramfs routines.
+#
+
+obj-$(CONFIG_CRAMFS) += cramfs.o
+
+cramfs-objs := inode.o uncompress.o

fs/cramfs/README

@@ -0,0 +1,168 @@
+Notes on Filesystem Layout
+--------------------------
+
+These notes describe what mkcramfs generates.  Kernel requirements are
+a bit looser, e.g. it doesn't care if the <file_data> items are
+swapped around (though it does care that directory entries (inodes) in
+a given directory are contiguous, as this is used by readdir).
+
+All data is currently in host-endian format; neither mkcramfs nor the
+kernel ever do swabbing.  (See section `Block Size' below.)
+
+<filesystem>:
+	<superblock>
+	<directory_structure>
+	<data>
+
+<superblock>: struct cramfs_super (see cramfs_fs.h).
+
+<directory_structure>:
+	For each file:
+		struct cramfs_inode (see cramfs_fs.h).
+		Filename.  Not generally null-terminated, but it is
+		 null-padded to a multiple of 4 bytes.
+
+The order of inode traversal is described as "width-first" (not to be
+confused with breadth-first); i.e. like depth-first but listing all of
+a directory's entries before recursing down its subdirectories: the
+same order as `ls -AUR' (but without the /^\..*:$/ directory header
+lines); put another way, the same order as `find -type d -exec
+ls -AU1 {} \;'.
+
+Beginning in 2.4.7, directory entries are sorted.  This optimization
+allows cramfs_lookup to return more quickly when a filename does not
+exist, speeds up user-space directory sorts, etc.
+
+<data>:
+	One <file_data> for each file that's either a symlink or a
+	 regular file of non-zero st_size.
+
+<file_data>:
+	nblocks * <block_pointer>
+	 (where nblocks = (st_size - 1) / blksize + 1)
+	nblocks * <block>
+	padding to multiple of 4 bytes
+
+The i'th <block_pointer> for a file stores the byte offset of the
+*end* of the i'th <block> (i.e. one past the last byte, which is the
+same as the start of the (i+1)'th <block> if there is one).  The first
+<block> immediately follows the last <block_pointer> for the file.
+<block_pointer>s are each 32 bits long.
+
+The order of <file_data>'s is a depth-first descent of the directory
+tree, i.e. the same order as `find -size +0 \( -type f -o -type l \)
+-print'.
+
+
+<block>: The i'th <block> is the output of zlib's compress function
+applied to the i'th blksize-sized chunk of the input data.
+(For the last <block> of the file, the input may of course be smaller.)
+Each <block> may be a different size.  (See <block_pointer> above.)
+<block>s are merely byte-aligned, not generally u32-aligned.
+
+
+Holes
+-----
+
+This kernel supports cramfs holes (i.e. [efficient representation of]
+blocks in uncompressed data consisting entirely of NUL bytes), but by
+default mkcramfs doesn't test for & create holes, since cramfs in
+kernels up to at least 2.3.39 didn't support holes.  Run mkcramfs
+with -z if you want it to create files that can have holes in them.
+
+
+Tools
+-----
+
+The cramfs user-space tools, including mkcramfs and cramfsck, are
+located at <http://sourceforge.net/projects/cramfs/>.
+
+
+Future Development
+==================
+
+Block Size
+----------
+
+(Block size in cramfs refers to the size of input data that is
+compressed at a time.  It's intended to be somewhere around
+PAGE_CACHE_SIZE for cramfs_readpage's convenience.)
+
+The superblock ought to indicate the block size that the fs was
+written for, since comments in <linux/pagemap.h> indicate that
+PAGE_CACHE_SIZE may grow in future (if I interpret the comment
+correctly).
+
+Currently, mkcramfs #define's PAGE_CACHE_SIZE as 4096 and uses that
+for blksize, whereas Linux-2.3.39 uses its PAGE_CACHE_SIZE, which in
+turn is defined as PAGE_SIZE (which can be as large as 32KB on arm).
+This discrepancy is a bug, though it's not clear which should be
+changed.
+
+One option is to change mkcramfs to take its PAGE_CACHE_SIZE from
+<asm/page.h>.  Personally I don't like this option, but it does
+require the least amount of change: just change `#define
+PAGE_CACHE_SIZE (4096)' to `#include <asm/page.h>'.  The disadvantage
+is that the generated cramfs cannot always be shared between different
+kernels, not even necessarily kernels of the same architecture if
+PAGE_CACHE_SIZE is subject to change between kernel versions
+(currently possible with arm and ia64).
+
+The remaining options try to make cramfs more sharable.
+
+One part of that is addressing endianness.  The two options here are
+`always use little-endian' (like ext2fs) or `writer chooses
+endianness; kernel adapts at runtime'.  Little-endian wins because of
+code simplicity and little CPU overhead even on big-endian machines.
+
+The cost of swabbing is changing the code to use the le32_to_cpu
+etc. macros as used by ext2fs.  We don't need to swab the compressed
+data, only the superblock, inodes and block pointers.
+
+
+The other part of making cramfs more sharable is choosing a block
+size.  The options are:
+
+  1. Always 4096 bytes.
+
+  2. Writer chooses blocksize; kernel adapts but rejects blocksize >
+     PAGE_CACHE_SIZE.
+
+  3. Writer chooses blocksize; kernel adapts even to blocksize >
+     PAGE_CACHE_SIZE.
+
+It's easy enough to change the kernel to use a smaller value than
+PAGE_CACHE_SIZE: just make cramfs_readpage read multiple blocks.
+
+The cost of option 1 is that kernels with a larger PAGE_CACHE_SIZE
+value don't get as good compression as they can.
+
+The cost of option 2 relative to option 1 is that the code uses
+variables instead of #define'd constants.  The gain is that people
+with kernels having larger PAGE_CACHE_SIZE can make use of that if
+they don't mind their cramfs being inaccessible to kernels with
+smaller PAGE_CACHE_SIZE values.
+
+Option 3 is easy to implement if we don't mind being CPU-inefficient:
+e.g. get readpage to decompress to a buffer of size MAX_BLKSIZE (which
+must be no larger than 32KB) and discard what it doesn't need.
+Getting readpage to read into all the covered pages is harder.
+
+The main advantage of option 3 over 1, 2, is better compression.  The
+cost is greater complexity.  Probably not worth it, but I hope someone
+will disagree.  (If it is implemented, then I'll re-use that code in
+e2compr.)
+
+
+Another cost of 2 and 3 over 1 is making mkcramfs use a different
+block size, but that just means adding and parsing a -b option.
+
+
+Inode Size
+----------
+
+Given that cramfs will probably be used for CDs etc. as well as just
+silicon ROMs, it might make sense to expand the inode a little from
+its current 12 bytes.  Inodes other than the root inode are followed
+by filename, so the expansion doesn't even have to be a multiple of 4
+bytes.

fs/cramfs/inode.c

@@ -0,0 +1,611 @@
+/*
+ * 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.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#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/slab.h>
+#include <linux/vfs.h>
+#include <linux/mutex.h>
+#include <uapi/linux/cramfs_fs.h>
+#include <linux/uaccess.h>
+
+#include "internal.h"
+
+/*
+ * cramfs super-block data in memory
+ */
+struct cramfs_sb_info {
+	unsigned long magic;
+	unsigned long size;
+	unsigned long blocks;
+	unsigned long files;
+	unsigned long flags;
+};
+
+static inline struct cramfs_sb_info *CRAMFS_SB(struct super_block *sb)
+{
+	return sb->s_fs_info;
+}
+
+static const struct super_operations cramfs_ops;
+static const 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 macros may change in future, to provide better st_ino semantics. */
+#define OFFSET(x)	((x)->i_ino)
+
+static unsigned long cramino(const struct cramfs_inode *cino, unsigned int offset)
+{
+	if (!cino->offset)
+		return offset + 1;
+	if (!cino->size)
+		return offset + 1;
+
+	/*
+	 * The file mode test fixes buggy mkcramfs implementations where
+	 * cramfs_inode->offset is set to a non zero value for entries
+	 * which did not contain data, like devices node and fifos.
+	 */
+	switch (cino->mode & S_IFMT) {
+	case S_IFREG:
+	case S_IFDIR:
+	case S_IFLNK:
+		return cino->offset << 2;
+	default:
+		break;
+	}
+	return offset + 1;
+}
+
+static struct inode *get_cramfs_inode(struct super_block *sb,
+	const struct cramfs_inode *cramfs_inode, unsigned int offset)
+{
+	struct inode *inode;
+	static struct timespec zerotime;
+
+	inode = iget_locked(sb, cramino(cramfs_inode, offset));
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+	if (!(inode->i_state & I_NEW))
+		return inode;
+
+	switch (cramfs_inode->mode & S_IFMT) {
+	case S_IFREG:
+		inode->i_fop = &generic_ro_fops;
+		inode->i_data.a_ops = &cramfs_aops;
+		break;
+	case S_IFDIR:
+		inode->i_op = &cramfs_dir_inode_operations;
+		inode->i_fop = &cramfs_directory_operations;
+		break;
+	case S_IFLNK:
+		inode->i_op = &page_symlink_inode_operations;
+		inode->i_data.a_ops = &cramfs_aops;
+		break;
+	default:
+		init_special_inode(inode, cramfs_inode->mode,
+				old_decode_dev(cramfs_inode->size));
+	}
+
+	inode->i_mode = cramfs_inode->mode;
+	i_uid_write(inode, cramfs_inode->uid);
+	i_gid_write(inode, cramfs_inode->gid);
+
+	/* if the lower 2 bits are zero, the inode contains data */
+	if (!(inode->i_ino & 3)) {
+		inode->i_size = cramfs_inode->size;
+		inode->i_blocks = (cramfs_inode->size - 1) / 512 + 1;
+	}
+
+	/* Struct copy intentional */
+	inode->i_mtime = inode->i_atime = inode->i_ctime = zerotime;
+	/* 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. */
+
+	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;
+	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. */
+	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_kill_sb(struct super_block *sb)
+{
+	struct cramfs_sb_info *sbi = CRAMFS_SB(sb);
+
+	kill_block_super(sb);
+	kfree(sbi);
+}
+
+static int cramfs_remount(struct super_block *sb, int *flags, char *data)
+{
+	sync_filesystem(sb);
+	*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 for wrong endianness */
+		if (super.magic == CRAMFS_MAGIC_WEND) {
+			if (!silent)
+				pr_err("wrong endianness\n");
+			return -EINVAL;
+		}
+
+		/* 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 (super.magic == CRAMFS_MAGIC_WEND && !silent)
+				pr_err("wrong endianness\n");
+			else if (!silent)
+				pr_err("wrong magic\n");
+			return -EINVAL;
+		}
+	}
+
+	/* get feature flags first */
+	if (super.flags & ~CRAMFS_SUPPORTED_FLAGS) {
+		pr_err("unsupported filesystem features\n");
+		return -EINVAL;
+	}
+
+	/* Check that the root inode is in a sane state */
+	if (!S_ISDIR(super.root.mode)) {
+		pr_err("root is not a directory\n");
+		return -EINVAL;
+	}
+	/* correct strange, hard-coded permissions of mkcramfs */
+	super.root.mode |= (S_IRUSR | S_IXUSR | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
+
+	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)
+		pr_info("empty filesystem");
+	else if (!(super.flags & CRAMFS_FLAG_SHIFTED_ROOT_OFFSET) &&
+		 ((root_offset != sizeof(struct cramfs_super)) &&
+		  (root_offset != 512 + sizeof(struct cramfs_super))))
+	{
+		pr_err("bad root offset %lu\n", root_offset);
+		return -EINVAL;
+	}
+
+	/* Set it all up.. */
+	sb->s_op = &cramfs_ops;
+	root = get_cramfs_inode(sb, &super.root, 0);
+	if (IS_ERR(root))
+		return PTR_ERR(root);
+	sb->s_root = d_make_root(root);
+	if (!sb->s_root)
+		return -ENOMEM;
+	return 0;
+}
+
+static int cramfs_statfs(struct dentry *dentry, struct kstatfs *buf)
+{
+	struct super_block *sb = dentry->d_sb;
+	u64 id = huge_encode_dev(sb->s_bdev->bd_dev);
+
+	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_fsid.val[0] = (u32)id;
+	buf->f_fsid.val[1] = (u32)(id >> 32);
+	buf->f_namelen = CRAMFS_MAXPATHLEN;
+	return 0;
+}
+
+/*
+ * Read a cramfs directory entry.
+ */
+static int cramfs_readdir(struct file *file, struct dir_context *ctx)
+{
+	struct inode *inode = file_inode(file);
+	struct super_block *sb = inode->i_sb;
+	char *buf;
+	unsigned int offset;
+
+	/* Offset within the thing. */
+	if (ctx->pos >= inode->i_size)
+		return 0;
+	offset = ctx->pos;
+	/* Directory entries are always 4-byte aligned */
+	if (offset & 3)
+		return -EINVAL;
+
+	buf = kmalloc(CRAMFS_MAXPATHLEN, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	while (offset < inode->i_size) {
+		struct cramfs_inode *de;
+		unsigned long nextoffset;
+		char *name;
+		ino_t ino;
+		umode_t mode;
+		int namelen;
+
+		mutex_lock(&read_mutex);
+		de = cramfs_read(sb, OFFSET(inode) + offset, sizeof(*de)+CRAMFS_MAXPATHLEN);
+		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, OFFSET(inode) + offset);
+		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--;
+		}
+		if (!dir_emit(ctx, buf, namelen, ino, mode >> 12))
+			break;
+
+		ctx->pos = offset = nextoffset;
+	}
+	kfree(buf);
+	return 0;
+}
+
+/*
+ * Lookup and fill in the inode data..
+ */
+static struct dentry *cramfs_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
+{
+	unsigned int offset = 0;
+	struct inode *inode = NULL;
+	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;
+		int dir_off = OFFSET(dir) + offset;
+
+		de = cramfs_read(dir->i_sb, dir_off, sizeof(*de)+CRAMFS_MAXPATHLEN);
+		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) {
+				inode = ERR_PTR(-EIO);
+				goto out;
+			}
+			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) {
+			inode = get_cramfs_inode(dir->i_sb, de, dir_off);
+			break;
+		}
+		/* else (retval < 0) */
+		if (sorted)
+			break;
+	}
+out:
+	mutex_unlock(&read_mutex);
+	if (IS_ERR(inode))
+		return ERR_CAST(inode);
+	d_add(dentry, inode);
+	return NULL;
+}
+
+static int cramfs_readpage(struct file *file, struct page *page)
+{
+	struct inode *inode = page->mapping->host;
+	u32 maxblock;
+	int bytes_filled;
+	void *pgdata;
+
+	maxblock = (inode->i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
+	bytes_filled = 0;
+	pgdata = kmap(page);
+
+	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);
+
+		if (compr_len == 0)
+			; /* hole */
+		else if (unlikely(compr_len > (PAGE_CACHE_SIZE << 1))) {
+			pr_err("bad compressed blocksize %u\n",
+				compr_len);
+			goto err;
+		} 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);
+			if (unlikely(bytes_filled < 0))
+				goto err;
+		}
+	}
+
+	memset(pgdata + bytes_filled, 0, PAGE_CACHE_SIZE - bytes_filled);
+	flush_dcache_page(page);
+	kunmap(page);
+	SetPageUptodate(page);
+	unlock_page(page);
+	return 0;
+
+err:
+	kunmap(page);
+	ClearPageUptodate(page);
+	SetPageError(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,
+	.iterate	= cramfs_readdir,
+};
+
+static const struct inode_operations cramfs_dir_inode_operations = {
+	.lookup		= cramfs_lookup,
+};
+
+static const struct super_operations cramfs_ops = {
+	.remount_fs	= cramfs_remount,
+	.statfs		= cramfs_statfs,
+};
+
+static struct dentry *cramfs_mount(struct file_system_type *fs_type,
+	int flags, const char *dev_name, void *data)
+{
+	return mount_bdev(fs_type, flags, dev_name, data, cramfs_fill_super);
+}
+
+static struct file_system_type cramfs_fs_type = {
+	.owner		= THIS_MODULE,
+	.name		= "cramfs",
+	.mount		= cramfs_mount,
+	.kill_sb	= cramfs_kill_sb,
+	.fs_flags	= FS_REQUIRES_DEV,
+};
+MODULE_ALIAS_FS("cramfs");
+
+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");

fs/cramfs/internal.h

@@ -0,0 +1,4 @@
+/* Uncompression interfaces to the underlying zlib */
+int cramfs_uncompress_block(void *dst, int dstlen, void *src, int srclen);
+int cramfs_uncompress_init(void);
+void cramfs_uncompress_exit(void);

fs/cramfs/uncompress.c

@@ -0,0 +1,79 @@
+/*
+ * uncompress.c
+ *
+ * (C) Copyright 1999 Linus Torvalds
+ *
+ * cramfs interfaces to the uncompression library. There's really just
+ * three entrypoints:
+ *
+ *  - cramfs_uncompress_init() - called to initialize the thing.
+ *  - cramfs_uncompress_exit() - tell me when you're done
+ *  - cramfs_uncompress_block() - uncompress a block.
+ *
+ * NOTE NOTE NOTE! The uncompression is entirely single-threaded. We
+ * only have one stream, and we'll initialize it only once even if it
+ * then is used by multiple filesystems.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/vmalloc.h>
+#include <linux/zlib.h>
+#include "internal.h"
+
+static z_stream stream;
+static int initialized;
+
+/* Returns length of decompressed data. */
+int cramfs_uncompress_block(void *dst, int dstlen, void *src, int srclen)
+{
+	int err;
+
+	stream.next_in = src;
+	stream.avail_in = srclen;
+
+	stream.next_out = dst;
+	stream.avail_out = dstlen;
+
+	err = zlib_inflateReset(&stream);
+	if (err != Z_OK) {
+		pr_err("zlib_inflateReset error %d\n", err);
+		zlib_inflateEnd(&stream);
+		zlib_inflateInit(&stream);
+	}
+
+	err = zlib_inflate(&stream, Z_FINISH);
+	if (err != Z_STREAM_END)
+		goto err;
+	return stream.total_out;
+
+err:
+	pr_err("Error %d while decompressing!\n", err);
+	pr_err("%p(%d)->%p(%d)\n", src, srclen, dst, dstlen);
+	return -EIO;
+}
+
+int cramfs_uncompress_init(void)
+{
+	if (!initialized++) {
+		stream.workspace = vmalloc(zlib_inflate_workspacesize());
+		if (!stream.workspace) {
+			initialized = 0;
+			return -ENOMEM;
+		}
+		stream.next_in = NULL;
+		stream.avail_in = 0;
+		zlib_inflateInit(&stream);
+	}
+	return 0;
+}
+
+void cramfs_uncompress_exit(void)
+{
+	if (!--initialized) {
+		zlib_inflateEnd(&stream);
+		vfree(stream.workspace);
+	}
+}