深层解决cramfs文件系统不支持nandflash坏块的解决办法

今日在对公司的产品调试时，发现如果nandflash有坏块在cramfs文件系统分区，那么linux系统无法启动，提示如下信息：

uncorrectable error : 
uncorrectable error : 
end_request: I/O error, dev mtdblock0, sector 512
Buffer I/O error on device mtdblock0, logical block 64
uncorrectable error : 
uncorrectable error : 
end_request: I/O error, dev mtdblock0, sector 512
Buffer I/O error on device mtdblock0, logical block 64
uncorrectable error : 
uncorrectable error : 
end_request: I/O error, dev mtdblock0, sector 520
Buffer I/O error on device mtdblock0, logical block 65
uncorrectable error : 
uncorrectable error : 
end_request: I/O error, dev mtdblock0, sector 520
Buffer I/O error on device mtdblock0, logical block 65
Error -5 while decompressing!
802fd844(853)->81526000(4096)
g_serial gadget: g_serial ready
mice: PS/2 mouse device common for all mice
i2c /dev entries driver
at91_i2c at91_i2c: AT91 i2c bus driver.
TCP cubic registered
NET: Registered protocol family 17
VFS: Mounted root (cramfs filesystem) readonly on device 31:0.
Freeing init memory: 124K
init started: BusyBox v1.15.3 (2014-06-24 22:48:57 PDT)
starting pid 360, tty '/dev/console': '-/etc/init.d/rcS'
mount /var as ramfs
mount /proc as proc
mount /sys as sysfs
mount /dev as tmpfs
Starting mdev...
mount /mnt/local as yaffs2
yaffs: dev is 32505857 name is "mtdblock1"
yaffs: passed flags ""
yaffs: Attempting MTD mount on 31.1, "mtdblock1"
yaffs_read_super: isCheckpointed 0
uncorrectable error : 
uncorrectable error : 
end_request: I/O error, dev mtdblock0, sector 512
Buffer I/O error on device mtdblock0, logical block 64
uncorrectable error : 
uncorrectable error : 
end_request: I/O error, dev mtdblock0, sector 512
Buffer I/O error on device mtdblock0, logical block 64
uncorrectable error : 
uncorrectable error : 
end_request: I/O error, dev mtdblock0, sector 520
Buffer I/O error on device mtdblock0, logical block 65
uncorrectable error : 
uncorrectable error : 
end_request: I/O error, dev mtdblock0, sector 520
Buffer I/O error on device mtdblock0, logical block 65
Error -5 while decompressing!
802fd844(853)->81526000(4096)

然后在网上找了一下原因，是由于在nandflash上的cramfs分区上存在坏块，造成linux内核启动失败，于是根据网上的提示在fs/cramfs/inode.c文件中添加如下代码：

struct cramfs_nand_info {
    unsigned int erasesize_shift;
    uint32_t *block_map;
    uint32_t size;
};
static unsigned int cramfs_nand_transfer_offset(struct super_block *sb, unsigned int offset)
{
    struct cramfs_sb_info *sbi = sb->s_fs_info;
    struct cramfs_nand_info *nandinfo;
    nandinfo = (struct cramfs_nand_info *)(sbi + 1);
    if (!nandinfo->erasesize_shift || !nandinfo->block_map)
        return offset;
    if (offset > nandinfo->size)
        return offset;
    return  (offset + nandinfo->block_map[offset >>nandinfo->erasesize_shift]);
}
static void cramfs_fill_nand(struct super_block *sb)
{
    struct cramfs_sb_info *sbi = sb->s_fs_info;
    struct cramfs_nand_info *nandinfo;
    uint32_t *block_map = NULL;
    uint32_t offset = 0;
    nandinfo = (struct cramfs_nand_info *)(sbi + 1);
    if(MAJOR(sb->s_dev) == MTD_BLOCK_MAJOR){
        struct mtd_info *mtd;
        int blocks, i;
        mtd = get_mtd_device(NULL, MINOR(sb->s_dev));
        if(!mtd)
            return;
        if(mtd->type != MTD_NANDFLASH)
            return;
        blocks = mtd->size>>mtd->erasesize_shift;
        block_map = kmalloc(blocks*sizeof(uint32_t), GFP_KERNEL);
        if (!block_map)
            return ;
        for(i = 0; i < blocks; i++){
            if (mtd->block_isbad(mtd, (loff_t)i*mtd->erasesize))
                 offset += mtd->erasesize;
             block_map[i] = offset;
        }
        nandinfo->erasesize_shift = mtd->erasesize_shift;
        nandinfo->block_map = block_map;
        nandinfo->size = (uint32_t) mtd->size;
    }
}

//—————————— 在cramfs_read函数中进行如下修改 ——————————–

-  sbi = kzalloc(sizeof(struct cramfs_sb_info), GFP_KERNEL);
+ sbi = kzalloc(sizeof(struct cramfs_sb_info) + sizeof(struct cramfs_nand_info), GFP_KERNEL);
    if (!sbi)
    return -ENOMEM;
    sb->s_fs_info = sbi;
+    
+ cramfs_fill_nand(sb);
+ mutex_lock(&read_mutex);
for (i = 0; i < READ_BUFFERS; i++)
        buffer_blocknr[i] = -1;
if (!len)
        return NULL;
+ offset = cramfs_nand_transfer_offset(sb, offset);
blocknr = offset >> PAGE_CACHE_SHIFT;
offset &= PAGE_CACHE_SIZE - 1;
但是发现修改完成之后，能够启动cramfs文件系统，但是在shell中使用一部分命令时会提示如下错误：

Error -5 while decompressing!
802fd844(853)->81526000(4096)
于是分析cramfs文件系统的内部机制，发现cramfs文件系统将以页(4K)为单位进行寻址,如果我们使用的nandflash为1GB的，则1block = 32page，而cramfs在读取文件数据时，通过文件的偏移位置offset和文件长度len，去读取文件，然后解压数据。
根据上述的修改，我们只会去判断文件的起始位置是否在nandflash上是否是坏块，如果一个文件起始位置在block N的最后一个页，但是占用10个页，而block N+1为坏块，那么这个时候我们读取的数据将会出错。如图1所示：

因此，我们好需要增加一个页机制，判断页是否在nandflash的坏块上，同时也改进了上述的连续坏块处理算法，改进之后的inode.c文件源代码如下：

/*
 * 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/uaccess.h>
#include <linux/mtd/mtd.h>
#include <linux/mtd/super.h>

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 uint8_t *page_isbad_blocks;//add by pengrui,used to mark this pages whether in bad blocks

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)
//add zhjch
struct cramfs_nand_info
{
    unsigned int erasesize_shift;
    unsigned int *block_map;
    unsigned int size;
};

static unsigned int cramfs_nand_transfer_offset(struct super_block *sb, unsigned int offset)
{
    struct cramfs_sb_info *sbi = sb->s_fs_info;
    struct cramfs_nand_info *nandinfo;
    nandinfo = (struct cramfs_nand_info *)(sbi + 1);
    if (!nandinfo->erasesize_shift || !nandinfo->block_map)
        return offset;
    if (offset > nandinfo->size)
        return offset;
    return  (offset + nandinfo->block_map[offset >> nandinfo->erasesize_shift]);
}
static void cramfs_fill_nand(struct super_block *sb)
{
    struct cramfs_sb_info *sbi = sb->s_fs_info;
    struct cramfs_nand_info *nandinfo;
    unsigned int *block_map = NULL;
    unsigned int offset = 0;
    unsigned int offset_t = 0;
    unsigned int flag = 0x0;
    unsigned int pagenr;//add by pengrui
    nandinfo = (struct cramfs_nand_info *)(sbi + 1);
    if(MAJOR(sb->s_dev) == MTD_BLOCK_MAJOR)
    {
        struct mtd_info *mtd;
        int blocks, i;
        mtd = get_mtd_device(NULL, MINOR(sb->s_dev));
        if(!mtd)
            return;
        if(mtd->type != MTD_NANDFLASH)
            return;
        blocks = mtd->size >> mtd->erasesize_shift;
    pagenr = 1<<(mtd->erasesize_shift-PAGE_CACHE_SHIFT);//add by pengrui
        block_map = kmalloc(blocks * sizeof(uint32_t), GFP_KERNEL);
        if (!block_map)
            return ;
    //add by pengrui
    page_isbad_blocks = kmalloc(pagenr*blocks*sizeof(uint8_t),GFP_KERNEL);
        if (!page_isbad_blocks)
            return ;
    memset(page_isbad_blocks,0x0,pagenr*blocks);

        for(i = 0; i < blocks; i++)
        {
        //new to zhjch
        offset = 0x0;
        flag = 0x0;
        while (mtd->block_isbad(mtd, ((loff_t)i * mtd->erasesize)+offset))
            {   
        int m;
        offset += mtd->erasesize;
        //offset_t += offset;
        //add by pengrui,fill this pages flag
        for( m=0; m<pagenr; m++)
            page_isbad_blocks[i*pagenr + m] = 0x1;
        if((i*mtd->erasesize + offset) >mtd->size)
        {
            break;
        } 
        flag++;
        }
        offset_t +=offset;
            block_map[i] = offset_t;
        if(flag>=2)
        offset_t-=(flag-1)*mtd->erasesize;
        }
        nandinfo->erasesize_shift = mtd->erasesize_shift;
        nandinfo->block_map = block_map;
        nandinfo->size = (uint32_t) mtd->size;
    }
}
//add by zhjch end
static int cramfs_iget5_test(struct inode *inode, void *opaque)
{
    struct cramfs_inode *cramfs_inode = opaque;
    return inode->i_ino == CRAMINO(cramfs_inode) && inode->i_ino != 1;
}

static int cramfs_iget5_set(struct inode *inode, void *opaque)
{
    struct cramfs_inode *cramfs_inode = opaque;
    inode->i_ino = CRAMINO(cramfs_inode);
    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);
    static struct timespec zerotime;

    if (inode && (inode->i_state & I_NEW)) {
        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_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 {
            init_special_inode(inode, inode->i_mode,
                old_decode_dev(cramfs_inode->size));
        }
        unlock_new_inode(inode);
    }
    return inode;
}

static void cramfs_drop_inode(struct inode *inode)
{
    if (inode->i_ino == 1)
        generic_delete_inode(inode);
    else
        generic_drop_inode(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 mtd_info *mtd;
    struct address_space *mapping = sb->s_bdev->bd_inode->i_mapping;
    struct page *pages[BLKS_PER_BUF];
    unsigned i, blocknr, pagenr, buffer;
    unsigned long devsize;
    char *data;
    int flag = 0;

    if (!len)
        return NULL;
        //add by pengrui
    mtd = get_mtd_device(NULL, MINOR(sb->s_dev));
        if(!mtd)
            return NULL;
        if(mtd->type != MTD_NANDFLASH)
            return NULL;
    offset = cramfs_nand_transfer_offset(sb, offset);

    blocknr = offset >> PAGE_CACHE_SHIFT;
    pagenr = 1<<(mtd->erasesize_shift-PAGE_CACHE_SHIFT);//add by pengrui
    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) {//old
            //add by pengrui,just check page whether in bad block
            unsigned int pagenum = 0x0;
            pagenum = blocknr+i;
            while(page_isbad_blocks[pagenum])
            {
                pagenum+=pagenr;
            }
            page = read_mapping_page_async(mapping, pagenum, 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;
    //old
    //sbi = kzalloc(sizeof(struct cramfs_sb_info), GFP_KERNEL);
    //new
    sbi = kzalloc(sizeof(struct cramfs_sb_info) + sizeof(struct cramfs_nand_info), GFP_KERNEL);
    if (!sbi)
        return -ENOMEM;
    sb->s_fs_info = sbi;
    //new
    /*add patch for skipping bad nand*/
    cramfs_fill_nand(sb);
    /* 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 endianess */
        if (super.magic == CRAMFS_MAGIC_WEND) {
            if (!silent)
                printk(KERN_ERR "cramfs: wrong endianess\n");
            goto out;
        }

        /* 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)
                printk(KERN_ERR "cramfs: wrong endianess\n");
            else 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;
    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 *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(CRAMFS_MAXPATHLEN, 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)+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);
        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)+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) {
                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;
    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("cramfs: 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,
    .readdir    = cramfs_readdir,
};

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

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

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)
{
    kfree(page_isbad_blocks);
    cramfs_uncompress_exit();
    unregister_filesystem(&cramfs_fs_type);
}

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