/* Block- or MTD-based romfs
 *
 * Copyright © 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * Derived from: ROMFS file system, Linux implementation
 *
 * Copyright © 1997-1999  Janos Farkas <chexum@shadow.banki.hu>
 *
 * 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 read_folio
 *                                      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 read_folio
 *                                      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.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#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/fs_context.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 <linux/major.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_read_folio(struct file *file, struct folio *folio)
{
        struct inode *inode = folio->mapping->host;
        loff_t offset, size;
        unsigned long fillsize, pos;
        void *buf;
        int ret;

        buf = kmap_local_folio(folio, 0);

        offset = folio_pos(folio);
        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) {
                        fillsize = 0;
                        ret = -EIO;
                }
        }

        buf = folio_zero_tail(folio, fillsize, buf + fillsize);
        kunmap_local(buf);
        folio_end_read(folio, ret == 0);
        return ret;
}

static const struct address_space_operations romfs_aops = {
        .read_folio     = romfs_read_folio
};

/*
 * read the entries from a directory
 */
static int romfs_readdir(struct file *file, struct dir_context *ctx)
{
        struct inode *i = file_inode(file);
        struct romfs_inode ri;
        unsigned long offset, maxoff;
        int j, ino, nextfh;
        char fsname[ROMFS_MAXFN];       /* XXX dynamic? */
        int ret;

        maxoff = romfs_maxsize(i->i_sb);

        offset = ctx->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;
                        ctx->pos = offset;
                        goto out;
                }
                ctx->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 (!dir_emit(ctx, fsname, j, ino,
                            romfs_dtype_table[nextfh & ROMFH_TYPE]))
                        goto out;

                offset = nextfh & ROMFH_MASK;
        }
out:
        return 0;
}

/*
 * 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 = NULL;
        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)
                        break;

                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) {
                        /* 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);
                        break;
                }

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

        return d_splice_alias(inode, dentry);
error:
        return ERR_PTR(ret);
}

static const struct file_operations romfs_dir_operations = {
        .read           = generic_read_dir,
        .iterate_shared = romfs_readdir,
        .llseek         = generic_file_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 (!(inode_state_read_once(i) & 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);
        inode_set_mtime_to_ts(i,
                              inode_set_atime_to_ts(i, inode_set_ctime(i, 0, 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 (nextfh & ROMFH_EXEC)
                        mode |= S_IXUGO;
                break;
        case ROMFH_SYM:
                i->i_op = &page_symlink_inode_operations;
                inode_nohighmem(i);
                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;
        i->i_blocks = (i->i_size + 511) >> 9;

        unlock_new_inode(i);
        return i;

eio:
        ret = -EIO;
error:
        pr_err("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 = alloc_inode_sb(sb, romfs_inode_cachep, GFP_KERNEL);
        return inode ? &inode->vfs_inode : NULL;
}

/*
 * return a spent inode to the slab cache
 */
static void romfs_free_inode(struct inode *inode)
{
        kmem_cache_free(romfs_inode_cachep, ROMFS_I(inode));
}

/*
 * get filesystem statistics
 */
static int romfs_statfs(struct dentry *dentry, struct kstatfs *buf)
{
        struct super_block *sb = dentry->d_sb;
        u64 id = 0;

        /* When calling huge_encode_dev(),
         * use sb->s_bdev->bd_dev when,
         *   - CONFIG_ROMFS_ON_BLOCK defined
         * use sb->s_dev when,
         *   - CONFIG_ROMFS_ON_BLOCK undefined and
         *   - CONFIG_ROMFS_ON_MTD defined
         * leave id as 0 when,
         *   - CONFIG_ROMFS_ON_BLOCK undefined and
         *   - CONFIG_ROMFS_ON_MTD undefined
         */
        if (sb->s_bdev)
                id = huge_encode_dev(sb->s_bdev->bd_dev);
        else if (sb->s_dev)
                id = huge_encode_dev(sb->s_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 = u64_to_fsid(id);
        return 0;
}

/*
 * remounting must involve read-only
 */
static int romfs_reconfigure(struct fs_context *fc)
{
        sync_filesystem(fc->root->d_sb);
        fc->sb_flags |= SB_RDONLY;
        return 0;
}

static const struct super_operations romfs_super_ops = {
        .alloc_inode    = romfs_alloc_inode,
        .free_inode     = romfs_free_inode,
        .statfs         = romfs_statfs,
};

/*
 * 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, struct fs_context *fc)
{
        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) {
                if (!sb_set_blocksize(sb, ROMBSIZE)) {
                        errorf(fc, "romfs: unable to set blocksize\n");
                        return -EINVAL;
                }
        } 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 |= SB_RDONLY | SB_NOATIME;
        sb->s_time_min = 0;
        sb->s_time_max = 0;
        sb->s_op = &romfs_super_ops;

#ifdef CONFIG_ROMFS_ON_MTD
        /* Use same dev ID from the underlying mtdblock device */
        if (sb->s_mtd)
                sb->s_dev = MKDEV(MTD_BLOCK_MAJOR, sb->s_mtd->index);
#endif
        /* 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 (!(fc->sb_flags & SB_SILENT))
                        errorf(fc, "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))) {
                pr_err("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 (!(fc->sb_flags & SB_SILENT))
                pr_notice("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))
                return PTR_ERR(root);

        sb->s_root = d_make_root(root);
        if (!sb->s_root)
                return -ENOMEM;

        return 0;

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

/*
 * get a superblock for mounting
 */
static int romfs_get_tree(struct fs_context *fc)
{
        int ret = -EINVAL;

#ifdef CONFIG_ROMFS_ON_MTD
        ret = get_tree_mtd(fc, romfs_fill_super);
#endif
#ifdef CONFIG_ROMFS_ON_BLOCK
        if (ret == -EINVAL)
                ret = get_tree_bdev(fc, romfs_fill_super);
#endif
        return ret;
}

static const struct fs_context_operations romfs_context_ops = {
        .get_tree       = romfs_get_tree,
        .reconfigure    = romfs_reconfigure,
};

/*
 * Set up the filesystem mount context.
 */
static int romfs_init_fs_context(struct fs_context *fc)
{
        fc->ops = &romfs_context_ops;
        return 0;
}

/*
 * destroy a romfs superblock in the appropriate manner
 */
static void romfs_kill_sb(struct super_block *sb)
{
        generic_shutdown_super(sb);

#ifdef CONFIG_ROMFS_ON_MTD
        if (sb->s_mtd) {
                put_mtd_device(sb->s_mtd);
                sb->s_mtd = NULL;
        }
#endif
#ifdef CONFIG_ROMFS_ON_BLOCK
        if (sb->s_bdev) {
                sync_blockdev(sb->s_bdev);
                bdev_fput(sb->s_bdev_file);
        }
#endif
}

static struct file_system_type romfs_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "romfs",
        .init_fs_context = romfs_init_fs_context,
        .kill_sb        = romfs_kill_sb,
        .fs_flags       = FS_REQUIRES_DEV,
};
MODULE_ALIAS_FS("romfs");

/*
 * 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;

        pr_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_ACCOUNT,
                                  romfs_i_init_once);

        if (!romfs_inode_cachep) {
                pr_err("Failed to initialise inode cache\n");
                return -ENOMEM;
        }
        ret = register_filesystem(&romfs_fs_type);
        if (ret) {
                pr_err("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 */