super.c

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/* Block- or MTD-based romfs
 *
 * Copyright © 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 *
 * Derived from: ROMFS file system, Linux implementation
 *
 * Copyright © 1997-1999  Janos Farkas <[email protected]>
 *
 * Using parts of the minix filesystem
 * Copyright © 1991, 1992  Linus Torvalds
 *
 * and parts of the affs filesystem additionally
 * Copyright © 1993  Ray Burr
 * Copyright © 1996  Hans-Joachim Widmaier
 *
 * Changes
 *                  Changed for 2.1.19 modules
 *  Jan 1997            Initial release
 *  Jun 1997            2.1.43+ changes
 *                  Proper page locking in readpage
 *                  Changed to work with 2.1.45+ fs
 *  Jul 1997            Fixed follow_link
 *          2.1.47
 *                  lookup shouldn't return -ENOENT
 *                  from Horst von Brand:
 *                    fail on wrong checksum
 *                    double unlock_super was possible
 *                    correct namelen for statfs
 *                  spotted by Bill Hawes:
 *                    readlink shouldn't iput()
 *  Jun 1998    2.1.106     from Avery Pennarun: glibc scandir()
 *                    exposed a problem in readdir
 *          2.1.107     code-freeze spellchecker run
 *  Aug 1998            2.1.118+ VFS changes
 *  Sep 1998    2.1.122     another VFS change (follow_link)
 *  Apr 1999    2.2.7       no more EBADF checking in
 *                    lookup/readdir, use ERR_PTR
 *  Jun 1999    2.3.6       d_alloc_root use changed
 *          2.3.9       clean up usage of ENOENT/negative
 *                    dentries in lookup
 *                  clean up page flags setting
 *                    (error, uptodate, locking) in
 *                    in readpage
 *                  use init_special_inode for
 *                    fifos/sockets (and streamline) in
 *                    read_inode, fix _ops table order
 *  Aug 1999    2.3.16      __initfunc() => __init change
 *  Oct 1999    2.3.24      page->owner hack obsoleted
 *  Nov 1999    2.3.27      2.3.25+ page->offset => index change
 *
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

#include <linux/module.h>
#include <linux/string.h>
#include <linux/fs.h>
#include <linux/time.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/blkdev.h>
#include <linux/parser.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/statfs.h>
#include <linux/mtd/super.h>
#include <linux/ctype.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/uaccess.h>
#include "internal.h"

static struct kmem_cache *romfs_inode_cachep;

static const umode_t romfs_modemap[8] = {
    0,          /* hard link */
    S_IFDIR  | 0644,    /* directory */
    S_IFREG  | 0644,    /* regular file */
    S_IFLNK  | 0777,    /* symlink */
    S_IFBLK  | 0600,    /* blockdev */
    S_IFCHR  | 0600,    /* chardev */
    S_IFSOCK | 0644,    /* socket */
    S_IFIFO  | 0644     /* FIFO */
};

static const unsigned char romfs_dtype_table[] = {
    DT_UNKNOWN, DT_DIR, DT_REG, DT_LNK, DT_BLK, DT_CHR, DT_SOCK, DT_FIFO
};

static struct inode *romfs_iget(struct super_block *sb, unsigned long pos);

/*
 * read a page worth of data from the image
 */
static int romfs_readpage(struct file *file, struct page *page)
{
    struct inode *inode = page->mapping->host;
    loff_t offset, size;
    unsigned long fillsize, pos;
    void *buf;
    int ret;

    buf = kmap(page);
    if (!buf)
        return -ENOMEM;

    /* 32 bit warning -- but not for us :) */
    offset = page_offset(page);
    size = i_size_read(inode);
    fillsize = 0;
    ret = 0;
    if (offset < size) {
        size -= offset;
        fillsize = size > PAGE_SIZE ? PAGE_SIZE : size;

        pos = ROMFS_I(inode)->i_dataoffset + offset;

        ret = romfs_dev_read(inode->i_sb, pos, buf, fillsize);
        if (ret < 0) {
            SetPageError(page);
            fillsize = 0;
            ret = -EIO;
        }
    }

    if (fillsize < PAGE_SIZE)
        memset(buf + fillsize, 0, PAGE_SIZE - fillsize);
    if (ret == 0)
        SetPageUptodate(page);

    flush_dcache_page(page);
    kunmap(page);
    unlock_page(page);
    return ret;
}

static const struct address_space_operations romfs_aops = {
    .readpage   = romfs_readpage
};

/*
 * read the entries from a directory
 */
static int romfs_readdir(struct file *filp, void *dirent, filldir_t filldir)
{
    struct inode *i = filp->f_dentry->d_inode;
    struct romfs_inode ri;
    unsigned long offset, maxoff;
    int j, ino, nextfh;
    int stored = 0;
    char fsname[ROMFS_MAXFN];   /* XXX dynamic? */
    int ret;

    maxoff = romfs_maxsize(i->i_sb);

    offset = filp->f_pos;
    if (!offset) {
        offset = i->i_ino & ROMFH_MASK;
        ret = romfs_dev_read(i->i_sb, offset, &ri, ROMFH_SIZE);
        if (ret < 0)
            goto out;
        offset = be32_to_cpu(ri.spec) & ROMFH_MASK;
    }

    /* Not really failsafe, but we are read-only... */
    for (;;) {
        if (!offset || offset >= maxoff) {
            offset = maxoff;
            filp->f_pos = offset;
            goto out;
        }
        filp->f_pos = offset;

        /* Fetch inode info */
        ret = romfs_dev_read(i->i_sb, offset, &ri, ROMFH_SIZE);
        if (ret < 0)
            goto out;

        j = romfs_dev_strnlen(i->i_sb, offset + ROMFH_SIZE,
                      sizeof(fsname) - 1);
        if (j < 0)
            goto out;

        ret = romfs_dev_read(i->i_sb, offset + ROMFH_SIZE, fsname, j);
        if (ret < 0)
            goto out;
        fsname[j] = '\0';

        ino = offset;
        nextfh = be32_to_cpu(ri.next);
        if ((nextfh & ROMFH_TYPE) == ROMFH_HRD)
            ino = be32_to_cpu(ri.spec);
        if (filldir(dirent, fsname, j, offset, ino,
                romfs_dtype_table[nextfh & ROMFH_TYPE]) < 0)
            goto out;

        stored++;
        offset = nextfh & ROMFH_MASK;
    }

out:
    return stored;
}

/*
 * look up an entry in a directory
 */
static struct dentry *romfs_lookup(struct inode *dir, struct dentry *dentry,
                   unsigned int flags)
{
    unsigned long offset, maxoff;
    struct inode *inode;
    struct romfs_inode ri;
    const char *name;       /* got from dentry */
    int len, ret;

    offset = dir->i_ino & ROMFH_MASK;
    ret = romfs_dev_read(dir->i_sb, offset, &ri, ROMFH_SIZE);
    if (ret < 0)
        goto error;

    /* search all the file entries in the list starting from the one
     * pointed to by the directory's special data */
    maxoff = romfs_maxsize(dir->i_sb);
    offset = be32_to_cpu(ri.spec) & ROMFH_MASK;

    name = dentry->d_name.name;
    len = dentry->d_name.len;

    for (;;) {
        if (!offset || offset >= maxoff)
            goto out0;

        ret = romfs_dev_read(dir->i_sb, offset, &ri, sizeof(ri));
        if (ret < 0)
            goto error;

        /* try to match the first 16 bytes of name */
        ret = romfs_dev_strcmp(dir->i_sb, offset + ROMFH_SIZE, name,
                       len);
        if (ret < 0)
            goto error;
        if (ret == 1)
            break;

        /* next entry */
        offset = be32_to_cpu(ri.next) & ROMFH_MASK;
    }

    /* Hard link handling */
    if ((be32_to_cpu(ri.next) & ROMFH_TYPE) == ROMFH_HRD)
        offset = be32_to_cpu(ri.spec) & ROMFH_MASK;

    inode = romfs_iget(dir->i_sb, offset);
    if (IS_ERR(inode)) {
        ret = PTR_ERR(inode);
        goto error;
    }
    goto outi;

    /*
     * it's a bit funky, _lookup needs to return an error code
     * (negative) or a NULL, both as a dentry.  ENOENT should not
     * be returned, instead we need to create a negative dentry by
     * d_add(dentry, NULL); and return 0 as no error.
     * (Although as I see, it only matters on writable file
     * systems).
     */
out0:
    inode = NULL;
outi:
    d_add(dentry, inode);
    ret = 0;
error:
    return ERR_PTR(ret);
}

static const struct file_operations romfs_dir_operations = {
    .read       = generic_read_dir,
    .readdir    = romfs_readdir,
    .llseek     = default_llseek,
};

static const struct inode_operations romfs_dir_inode_operations = {
    .lookup     = romfs_lookup,
};

/*
 * get a romfs inode based on its position in the image (which doubles as the
 * inode number)
 */
static struct inode *romfs_iget(struct super_block *sb, unsigned long pos)
{
    struct romfs_inode_info *inode;
    struct romfs_inode ri;
    struct inode *i;
    unsigned long nlen;
    unsigned nextfh;
    int ret;
    umode_t mode;

    /* we might have to traverse a chain of "hard link" file entries to get
     * to the actual file */
    for (;;) {
        ret = romfs_dev_read(sb, pos, &ri, sizeof(ri));
        if (ret < 0)
            goto error;

        /* XXX: do romfs_checksum here too (with name) */

        nextfh = be32_to_cpu(ri.next);
        if ((nextfh & ROMFH_TYPE) != ROMFH_HRD)
            break;

        pos = be32_to_cpu(ri.spec) & ROMFH_MASK;
    }

    /* determine the length of the filename */
    nlen = romfs_dev_strnlen(sb, pos + ROMFH_SIZE, ROMFS_MAXFN);
    if (IS_ERR_VALUE(nlen))
        goto eio;

    /* get an inode for this image position */
    i = iget_locked(sb, pos);
    if (!i)
        return ERR_PTR(-ENOMEM);

    if (!(i->i_state & I_NEW))
        return i;

    /* precalculate the data offset */
    inode = ROMFS_I(i);
    inode->i_metasize = (ROMFH_SIZE + nlen + 1 + ROMFH_PAD) & ROMFH_MASK;
    inode->i_dataoffset = pos + inode->i_metasize;

    set_nlink(i, 1);        /* Hard to decide.. */
    i->i_size = be32_to_cpu(ri.size);
    i->i_mtime.tv_sec = i->i_atime.tv_sec = i->i_ctime.tv_sec = 0;
    i->i_mtime.tv_nsec = i->i_atime.tv_nsec = i->i_ctime.tv_nsec = 0;

    /* set up mode and ops */
    mode = romfs_modemap[nextfh & ROMFH_TYPE];

    switch (nextfh & ROMFH_TYPE) {
    case ROMFH_DIR:
        i->i_size = ROMFS_I(i)->i_metasize;
        i->i_op = &romfs_dir_inode_operations;
        i->i_fop = &romfs_dir_operations;
        if (nextfh & ROMFH_EXEC)
            mode |= S_IXUGO;
        break;
    case ROMFH_REG:
        i->i_fop = &romfs_ro_fops;
        i->i_data.a_ops = &romfs_aops;
        if (i->i_sb->s_mtd)
            i->i_data.backing_dev_info =
                i->i_sb->s_mtd->backing_dev_info;
        if (nextfh & ROMFH_EXEC)
            mode |= S_IXUGO;
        break;
    case ROMFH_SYM:
        i->i_op = &page_symlink_inode_operations;
        i->i_data.a_ops = &romfs_aops;
        mode |= S_IRWXUGO;
        break;
    default:
        /* depending on MBZ for sock/fifos */
        nextfh = be32_to_cpu(ri.spec);
        init_special_inode(i, mode, MKDEV(nextfh >> 16,
                          nextfh & 0xffff));
        break;
    }

    i->i_mode = mode;

    unlock_new_inode(i);
    return i;

eio:
    ret = -EIO;
error:
    printk(KERN_ERR "ROMFS: read error for inode 0x%lx\n", pos);
    return ERR_PTR(ret);
}

/*
 * allocate a new inode
 */
static struct inode *romfs_alloc_inode(struct super_block *sb)
{
    struct romfs_inode_info *inode;
    inode = kmem_cache_alloc(romfs_inode_cachep, GFP_KERNEL);
    return inode ? &inode->vfs_inode : NULL;
}

/*
 * return a spent inode to the slab cache
 */
static void romfs_i_callback(struct rcu_head *head)
{
    struct inode *inode = container_of(head, struct inode, i_rcu);
    kmem_cache_free(romfs_inode_cachep, ROMFS_I(inode));
}

static void romfs_destroy_inode(struct inode *inode)
{
    call_rcu(&inode->i_rcu, romfs_i_callback);
}

/*
 * get filesystem statistics
 */
static int romfs_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 = ROMFS_MAGIC;
    buf->f_namelen = ROMFS_MAXFN;
    buf->f_bsize = ROMBSIZE;
    buf->f_bfree = buf->f_bavail = buf->f_ffree;
    buf->f_blocks =
        (romfs_maxsize(dentry->d_sb) + ROMBSIZE - 1) >> ROMBSBITS;
    buf->f_fsid.val[0] = (u32)id;
    buf->f_fsid.val[1] = (u32)(id >> 32);
    return 0;
}

/*
 * remounting must involve read-only
 */
static int romfs_remount(struct super_block *sb, int *flags, char *data)
{
    *flags |= MS_RDONLY;
    return 0;
}

static const struct super_operations romfs_super_ops = {
    .alloc_inode    = romfs_alloc_inode,
    .destroy_inode  = romfs_destroy_inode,
    .statfs     = romfs_statfs,
    .remount_fs = romfs_remount,
};

/*
 * checksum check on part of a romfs filesystem
 */
static __u32 romfs_checksum(const void *data, int size)
{
    const __be32 *ptr = data;
    __u32 sum;

    sum = 0;
    size >>= 2;
    while (size > 0) {
        sum += be32_to_cpu(*ptr++);
        size--;
    }
    return sum;
}

/*
 * fill in the superblock
 */
static int romfs_fill_super(struct super_block *sb, void *data, int silent)
{
    struct romfs_super_block *rsb;
    struct inode *root;
    unsigned long pos, img_size;
    const char *storage;
    size_t len;
    int ret;

#ifdef CONFIG_BLOCK
    if (!sb->s_mtd) {
        sb_set_blocksize(sb, ROMBSIZE);
    } else {
        sb->s_blocksize = ROMBSIZE;
        sb->s_blocksize_bits = blksize_bits(ROMBSIZE);
    }
#endif

    sb->s_maxbytes = 0xFFFFFFFF;
    sb->s_magic = ROMFS_MAGIC;
    sb->s_flags |= MS_RDONLY | MS_NOATIME;
    sb->s_op = &romfs_super_ops;

    /* read the image superblock and check it */
    rsb = kmalloc(512, GFP_KERNEL);
    if (!rsb)
        return -ENOMEM;

    sb->s_fs_info = (void *) 512;
    ret = romfs_dev_read(sb, 0, rsb, 512);
    if (ret < 0)
        goto error_rsb;

    img_size = be32_to_cpu(rsb->size);

    if (sb->s_mtd && img_size > sb->s_mtd->size)
        goto error_rsb_inval;

    sb->s_fs_info = (void *) img_size;

    if (rsb->word0 != ROMSB_WORD0 || rsb->word1 != ROMSB_WORD1 ||
        img_size < ROMFH_SIZE) {
        if (!silent)
            printk(KERN_WARNING "VFS:"
                   " Can't find a romfs filesystem on dev %s.\n",
                   sb->s_id);
        goto error_rsb_inval;
    }

    if (romfs_checksum(rsb, min_t(size_t, img_size, 512))) {
        printk(KERN_ERR "ROMFS: bad initial checksum on dev %s.\n",
               sb->s_id);
        goto error_rsb_inval;
    }

    storage = sb->s_mtd ? "MTD" : "the block layer";

    len = strnlen(rsb->name, ROMFS_MAXFN);
    if (!silent)
        printk(KERN_NOTICE "ROMFS: Mounting image '%*.*s' through %s\n",
               (unsigned) len, (unsigned) len, rsb->name, storage);

    kfree(rsb);
    rsb = NULL;

    /* find the root directory */
    pos = (ROMFH_SIZE + len + 1 + ROMFH_PAD) & ROMFH_MASK;

    root = romfs_iget(sb, pos);
    if (IS_ERR(root))
        goto error;

    sb->s_root = d_make_root(root);
    if (!sb->s_root)
        goto error;

    return 0;

error:
    return -EINVAL;
error_rsb_inval:
    ret = -EINVAL;
error_rsb:
    kfree(rsb);
    return ret;
}

/*
 * get a superblock for mounting
 */
static struct dentry *romfs_mount(struct file_system_type *fs_type,
            int flags, const char *dev_name,
            void *data)
{
    struct dentry *ret = ERR_PTR(-EINVAL);

#ifdef CONFIG_ROMFS_ON_MTD
    ret = mount_mtd(fs_type, flags, dev_name, data, romfs_fill_super);
#endif
#ifdef CONFIG_ROMFS_ON_BLOCK
    if (ret == ERR_PTR(-EINVAL))
        ret = mount_bdev(fs_type, flags, dev_name, data,
                  romfs_fill_super);
#endif
    return ret;
}

/*
 * destroy a romfs superblock in the appropriate manner
 */
static void romfs_kill_sb(struct super_block *sb)
{
#ifdef CONFIG_ROMFS_ON_MTD
    if (sb->s_mtd) {
        kill_mtd_super(sb);
        return;
    }
#endif
#ifdef CONFIG_ROMFS_ON_BLOCK
    if (sb->s_bdev) {
        kill_block_super(sb);
        return;
    }
#endif
}

static struct file_system_type romfs_fs_type = {
    .owner      = THIS_MODULE,
    .name       = "romfs",
    .mount      = romfs_mount,
    .kill_sb    = romfs_kill_sb,
    .fs_flags   = FS_REQUIRES_DEV,
};

/*
 * inode storage initialiser
 */
static void romfs_i_init_once(void *_inode)
{
    struct romfs_inode_info *inode = _inode;

    inode_init_once(&inode->vfs_inode);
}

/*
 * romfs module initialisation
 */
static int __init init_romfs_fs(void)
{
    int ret;

    printk(KERN_INFO "ROMFS MTD (C) 2007 Red Hat, Inc.\n");

    romfs_inode_cachep =
        kmem_cache_create("romfs_i",
                  sizeof(struct romfs_inode_info), 0,
                  SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD,
                  romfs_i_init_once);

    if (!romfs_inode_cachep) {
        printk(KERN_ERR
               "ROMFS error: Failed to initialise inode cache\n");
        return -ENOMEM;
    }
    ret = register_filesystem(&romfs_fs_type);
    if (ret) {
        printk(KERN_ERR "ROMFS error: Failed to register filesystem\n");
        goto error_register;
    }
    return 0;

error_register:
    kmem_cache_destroy(romfs_inode_cachep);
    return ret;
}

/*
 * romfs module removal
 */
static void __exit exit_romfs_fs(void)
{
    unregister_filesystem(&romfs_fs_type);
    /*
     * Make sure all delayed rcu free inodes are flushed before we
     * destroy cache.
     */
    rcu_barrier();
    kmem_cache_destroy(romfs_inode_cachep);
}

module_init(init_romfs_fs);
module_exit(exit_romfs_fs);

MODULE_DESCRIPTION("Direct-MTD Capable RomFS");
MODULE_AUTHOR("Red Hat, Inc.");
MODULE_LICENSE("GPL"); /* Actually dual-licensed, but it doesn't matter for */