/*
 * 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_nohighmem(inode);
                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_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_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_SHIFT;
        offset &= PAGE_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_SHIFT;
                blk_offset += offset;
                if (blk_offset + len > BUFFER_SIZE)
                        continue;
                return read_buffers[i] + blk_offset;
        }

        devsize = mapping->host->i_size >> PAGE_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 */
                                put_page(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_SIZE);
                        kunmap(page);
                        put_page(page);
                } else
                        memset(data, 0, PAGE_SIZE);
                data += PAGE_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_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_SIZE - 1) >> PAGE_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_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_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_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_shared = 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");