/*
 * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Licensed under the GPL
 *
 * Ported the filesystem routines to 2.5.
 * 2003-02-10 Petr Baudis <pasky@ucw.cz>
 */

#include <linux/fs.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/statfs.h>
#include "hostfs.h"
#include "init.h"
#include "kern.h"

struct hostfs_inode_info {
        char *host_filename;
        int fd;
        int mode;
        struct inode vfs_inode;
};

static inline struct hostfs_inode_info *HOSTFS_I(struct inode *inode)
{
        return list_entry(inode, struct hostfs_inode_info, vfs_inode);
}

#define FILE_HOSTFS_I(file) HOSTFS_I((file)->f_path.dentry->d_inode)

int hostfs_d_delete(struct dentry *dentry)
{
        return 1;
}

struct dentry_operations hostfs_dentry_ops = {
        .d_delete               = hostfs_d_delete,
};

/* Changed in hostfs_args before the kernel starts running */
static char *root_ino = "";
static int append = 0;

#define HOSTFS_SUPER_MAGIC 0x00c0ffee

static const struct inode_operations hostfs_iops;
static const struct inode_operations hostfs_dir_iops;
static const struct address_space_operations hostfs_link_aops;

#ifndef MODULE
static int __init hostfs_args(char *options, int *add)
{
        char *ptr;

        ptr = strchr(options, ',');
        if (ptr != NULL)
                *ptr++ = '\0';
        if (*options != '\0')
                root_ino = options;

        options = ptr;
        while (options) {
                ptr = strchr(options, ',');
                if (ptr != NULL)
                        *ptr++ = '\0';
                if (*options != '\0') {
                        if (!strcmp(options, "append"))
                                append = 1;
                        else printf("hostfs_args - unsupported option - %s\n",
                                    options);
                }
                options = ptr;
        }
        return 0;
}

__uml_setup("hostfs=", hostfs_args,
"hostfs=<root dir>,<flags>,...\n"
"    This is used to set hostfs parameters.  The root directory argument\n"
"    is used to confine all hostfs mounts to within the specified directory\n"
"    tree on the host.  If this isn't specified, then a user inside UML can\n"
"    mount anything on the host that's accessible to the user that's running\n"
"    it.\n"
"    The only flag currently supported is 'append', which specifies that all\n"
"    files opened by hostfs will be opened in append mode.\n\n"
);
#endif

static char *dentry_name(struct dentry *dentry, int extra)
{
        struct dentry *parent;
        char *root, *name;
        int len;

        len = 0;
        parent = dentry;
        while (parent->d_parent != parent) {
                len += parent->d_name.len + 1;
                parent = parent->d_parent;
        }

        root = HOSTFS_I(parent->d_inode)->host_filename;
        len += strlen(root);
        name = kmalloc(len + extra + 1, GFP_KERNEL);
        if (name == NULL)
                return NULL;

        name[len] = '\0';
        parent = dentry;
        while (parent->d_parent != parent) {
                len -= parent->d_name.len + 1;
                name[len] = '/';
                strncpy(&name[len + 1], parent->d_name.name,
                        parent->d_name.len);
                parent = parent->d_parent;
        }
        strncpy(name, root, strlen(root));
        return name;
}

static char *inode_name(struct inode *ino, int extra)
{
        struct dentry *dentry;

        dentry = list_entry(ino->i_dentry.next, struct dentry, d_alias);
        return dentry_name(dentry, extra);
}

static int read_name(struct inode *ino, char *name)
{
        /*
         * The non-int inode fields are copied into ints by stat_file and
         * then copied into the inode because passing the actual pointers
         * in and having them treated as int * breaks on big-endian machines
         */
        int err;
        int i_mode, i_nlink, i_blksize;
        unsigned long long i_size;
        unsigned long long i_ino;
        unsigned long long i_blocks;

        err = stat_file(name, &i_ino, &i_mode, &i_nlink, &ino->i_uid,
                        &ino->i_gid, &i_size, &ino->i_atime, &ino->i_mtime,
                        &ino->i_ctime, &i_blksize, &i_blocks, -1);
        if (err)
                return err;

        ino->i_ino = i_ino;
        ino->i_mode = i_mode;
        ino->i_nlink = i_nlink;
        ino->i_size = i_size;
        ino->i_blocks = i_blocks;
        return 0;
}

static char *follow_link(char *link)
{
        int len, n;
        char *name, *resolved, *end;

        len = 64;
        while (1) {
                n = -ENOMEM;
                name = kmalloc(len, GFP_KERNEL);
                if (name == NULL)
                        goto out;

                n = do_readlink(link, name, len);
                if (n < len)
                        break;
                len *= 2;
                kfree(name);
        }
        if (n < 0)
                goto out_free;

        if (*name == '/')
                return name;

        end = strrchr(link, '/');
        if (end == NULL)
                return name;

        *(end + 1) = '\0';
        len = strlen(link) + strlen(name) + 1;

        resolved = kmalloc(len, GFP_KERNEL);
        if (resolved == NULL) {
                n = -ENOMEM;
                goto out_free;
        }

        sprintf(resolved, "%s%s", link, name);
        kfree(name);
        kfree(link);
        return resolved;

 out_free:
        kfree(name);
 out:
        return ERR_PTR(n);
}

static int read_inode(struct inode *ino)
{
        char *name;
        int err = 0;

        /*
         * Unfortunately, we are called from iget() when we don't have a dentry
         * allocated yet.
         */
        if (list_empty(&ino->i_dentry))
                goto out;

        err = -ENOMEM;
        name = inode_name(ino, 0);
        if (name == NULL)
                goto out;

        if (file_type(name, NULL, NULL) == OS_TYPE_SYMLINK) {
                name = follow_link(name);
                if (IS_ERR(name)) {
                        err = PTR_ERR(name);
                        goto out;
                }
        }

        err = read_name(ino, name);
        kfree(name);
 out:
        return err;
}

int hostfs_statfs(struct dentry *dentry, struct kstatfs *sf)
{
        /*
         * do_statfs uses struct statfs64 internally, but the linux kernel
         * struct statfs still has 32-bit versions for most of these fields,
         * so we convert them here
         */
        int err;
        long long f_blocks;
        long long f_bfree;
        long long f_bavail;
        long long f_files;
        long long f_ffree;

        err = do_statfs(HOSTFS_I(dentry->d_sb->s_root->d_inode)->host_filename,
                        &sf->f_bsize, &f_blocks, &f_bfree, &f_bavail, &f_files,
                        &f_ffree, &sf->f_fsid, sizeof(sf->f_fsid),
                        &sf->f_namelen, sf->f_spare);
        if (err)
                return err;
        sf->f_blocks = f_blocks;
        sf->f_bfree = f_bfree;
        sf->f_bavail = f_bavail;
        sf->f_files = f_files;
        sf->f_ffree = f_ffree;
        sf->f_type = HOSTFS_SUPER_MAGIC;
        return 0;
}

static struct inode *hostfs_alloc_inode(struct super_block *sb)
{
        struct hostfs_inode_info *hi;

        hi = kmalloc(sizeof(*hi), GFP_KERNEL);
        if (hi == NULL)
                return NULL;

        *hi = ((struct hostfs_inode_info) { .host_filename      = NULL,
                                            .fd                 = -1,
                                            .mode               = 0 });
        inode_init_once(&hi->vfs_inode);
        return &hi->vfs_inode;
}

static void hostfs_delete_inode(struct inode *inode)
{
        truncate_inode_pages(&inode->i_data, 0);
        if (HOSTFS_I(inode)->fd != -1) {
                close_file(&HOSTFS_I(inode)->fd);
                HOSTFS_I(inode)->fd = -1;
        }
        clear_inode(inode);
}

static void hostfs_destroy_inode(struct inode *inode)
{
        kfree(HOSTFS_I(inode)->host_filename);

        /*
         * XXX: This should not happen, probably. The check is here for
         * additional safety.
         */
        if (HOSTFS_I(inode)->fd != -1) {
                close_file(&HOSTFS_I(inode)->fd);
                printk(KERN_DEBUG "Closing host fd in .destroy_inode\n");
        }

        kfree(HOSTFS_I(inode));
}

static void hostfs_read_inode(struct inode *inode)
{
        read_inode(inode);
}

static const struct super_operations hostfs_sbops = {
        .alloc_inode    = hostfs_alloc_inode,
        .drop_inode     = generic_delete_inode,
        .delete_inode   = hostfs_delete_inode,
        .destroy_inode  = hostfs_destroy_inode,
        .read_inode     = hostfs_read_inode,
        .statfs         = hostfs_statfs,
};

int hostfs_readdir(struct file *file, void *ent, filldir_t filldir)
{
        void *dir;
        char *name;
        unsigned long long next, ino;
        int error, len;

        name = dentry_name(file->f_path.dentry, 0);
        if (name == NULL)
                return -ENOMEM;
        dir = open_dir(name, &error);
        kfree(name);
        if (dir == NULL)
                return -error;
        next = file->f_pos;
        while ((name = read_dir(dir, &next, &ino, &len)) != NULL) {
                error = (*filldir)(ent, name, len, file->f_pos,
                                   ino, DT_UNKNOWN);
                if (error) break;
                file->f_pos = next;
        }
        close_dir(dir);
        return 0;
}

int hostfs_file_open(struct inode *ino, struct file *file)
{
        char *name;
        int mode = 0, r = 0, w = 0, fd;

        mode = file->f_mode & (FMODE_READ | FMODE_WRITE);
        if ((mode & HOSTFS_I(ino)->mode) == mode)
                return 0;

        /*
         * The file may already have been opened, but with the wrong access,
         * so this resets things and reopens the file with the new access.
         */
        if (HOSTFS_I(ino)->fd != -1) {
                close_file(&HOSTFS_I(ino)->fd);
                HOSTFS_I(ino)->fd = -1;
        }

        HOSTFS_I(ino)->mode |= mode;
        if (HOSTFS_I(ino)->mode & FMODE_READ)
                r = 1;
        if (HOSTFS_I(ino)->mode & FMODE_WRITE)
                w = 1;
        if (w)
                r = 1;

        name = dentry_name(file->f_path.dentry, 0);
        if (name == NULL)
                return -ENOMEM;

        fd = open_file(name, r, w, append);
        kfree(name);
        if (fd < 0)
                return fd;
        FILE_HOSTFS_I(file)->fd = fd;

        return 0;
}

int hostfs_fsync(struct file *file, struct dentry *dentry, int datasync)
{
        return fsync_file(HOSTFS_I(dentry->d_inode)->fd, datasync);
}

static const struct file_operations hostfs_file_fops = {
        .llseek         = generic_file_llseek,
        .read           = do_sync_read,
        .splice_read    = generic_file_splice_read,
        .aio_read       = generic_file_aio_read,
        .aio_write      = generic_file_aio_write,
        .write          = do_sync_write,
        .mmap           = generic_file_mmap,
        .open           = hostfs_file_open,
        .release        = NULL,
        .fsync          = hostfs_fsync,
};

static const struct file_operations hostfs_dir_fops = {
        .llseek         = generic_file_llseek,
        .readdir        = hostfs_readdir,
        .read           = generic_read_dir,
};

int hostfs_writepage(struct page *page, struct writeback_control *wbc)
{
        struct address_space *mapping = page->mapping;
        struct inode *inode = mapping->host;
        char *buffer;
        unsigned long long base;
        int count = PAGE_CACHE_SIZE;
        int end_index = inode->i_size >> PAGE_CACHE_SHIFT;
        int err;

        if (page->index >= end_index)
                count = inode->i_size & (PAGE_CACHE_SIZE-1);

        buffer = kmap(page);
        base = ((unsigned long long) page->index) << PAGE_CACHE_SHIFT;

        err = write_file(HOSTFS_I(inode)->fd, &base, buffer, count);
        if (err != count) {
                ClearPageUptodate(page);
                goto out;
        }

        if (base > inode->i_size)
                inode->i_size = base;

        if (PageError(page))
                ClearPageError(page);
        err = 0;

 out:
        kunmap(page);

        unlock_page(page);
        return err;
}

int hostfs_readpage(struct file *file, struct page *page)
{
        char *buffer;
        long long start;
        int err = 0;

        start = (long long) page->index << PAGE_CACHE_SHIFT;
        buffer = kmap(page);
        err = read_file(FILE_HOSTFS_I(file)->fd, &start, buffer,
                        PAGE_CACHE_SIZE);
        if (err < 0)
                goto out;

        memset(&buffer[err], 0, PAGE_CACHE_SIZE - err);

        flush_dcache_page(page);
        SetPageUptodate(page);
        if (PageError(page)) ClearPageError(page);
        err = 0;
 out:
        kunmap(page);
        unlock_page(page);
        return err;
}

int hostfs_write_begin(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned flags,
                        struct page **pagep, void **fsdata)
{
        pgoff_t index = pos >> PAGE_CACHE_SHIFT;

        *pagep = __grab_cache_page(mapping, index);
        if (!*pagep)
                return -ENOMEM;
        return 0;
}

int hostfs_write_end(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned copied,
                        struct page *page, void *fsdata)
{
        struct inode *inode = mapping->host;
        void *buffer;
        unsigned from = pos & (PAGE_CACHE_SIZE - 1);
        int err;

        buffer = kmap(page);
        err = write_file(FILE_HOSTFS_I(file)->fd, &pos, buffer + from, copied);
        kunmap(page);

        if (!PageUptodate(page) && err == PAGE_CACHE_SIZE)
                SetPageUptodate(page);

        /*
         * If err > 0, write_file has added err to pos, so we are comparing
         * i_size against the last byte written.
         */
        if (err > 0 && (pos > inode->i_size))
                inode->i_size = pos;
        unlock_page(page);
        page_cache_release(page);

        return err;
}

static const struct address_space_operations hostfs_aops = {
        .writepage      = hostfs_writepage,
        .readpage       = hostfs_readpage,
        .set_page_dirty = __set_page_dirty_nobuffers,
        .write_begin    = hostfs_write_begin,
        .write_end      = hostfs_write_end,
};

static int init_inode(struct inode *inode, struct dentry *dentry)
{
        char *name;
        int type, err = -ENOMEM;
        int maj, min;
        dev_t rdev = 0;

        if (dentry) {
                name = dentry_name(dentry, 0);
                if (name == NULL)
                        goto out;
                type = file_type(name, &maj, &min);
                /* Reencode maj and min with the kernel encoding.*/
                rdev = MKDEV(maj, min);
                kfree(name);
        }
        else type = OS_TYPE_DIR;

        err = 0;
        if (type == OS_TYPE_SYMLINK)
                inode->i_op = &page_symlink_inode_operations;
        else if (type == OS_TYPE_DIR)
                inode->i_op = &hostfs_dir_iops;
        else inode->i_op = &hostfs_iops;

        if (type == OS_TYPE_DIR) inode->i_fop = &hostfs_dir_fops;
        else inode->i_fop = &hostfs_file_fops;

        if (type == OS_TYPE_SYMLINK)
                inode->i_mapping->a_ops = &hostfs_link_aops;
        else inode->i_mapping->a_ops = &hostfs_aops;

        switch (type) {
        case OS_TYPE_CHARDEV:
                init_special_inode(inode, S_IFCHR, rdev);
                break;
        case OS_TYPE_BLOCKDEV:
                init_special_inode(inode, S_IFBLK, rdev);
                break;
        case OS_TYPE_FIFO:
                init_special_inode(inode, S_IFIFO, 0);
                break;
        case OS_TYPE_SOCK:
                init_special_inode(inode, S_IFSOCK, 0);
                break;
        }
 out:
        return err;
}

int hostfs_create(struct inode *dir, struct dentry *dentry, int mode,
                  struct nameidata *nd)
{
        struct inode *inode;
        char *name;
        int error, fd;

        error = -ENOMEM;
        inode = iget(dir->i_sb, 0);
        if (inode == NULL)
                goto out;

        error = init_inode(inode, dentry);
        if (error)
                goto out_put;

        error = -ENOMEM;
        name = dentry_name(dentry, 0);
        if (name == NULL)
                goto out_put;

        fd = file_create(name,
                         mode & S_IRUSR, mode & S_IWUSR, mode & S_IXUSR,
                         mode & S_IRGRP, mode & S_IWGRP, mode & S_IXGRP,
                         mode & S_IROTH, mode & S_IWOTH, mode & S_IXOTH);
        if (fd < 0)
                error = fd;
        else error = read_name(inode, name);

        kfree(name);
        if (error)
                goto out_put;

        HOSTFS_I(inode)->fd = fd;
        HOSTFS_I(inode)->mode = FMODE_READ | FMODE_WRITE;
        d_instantiate(dentry, inode);
        return 0;

 out_put:
        iput(inode);
 out:
        return error;
}

struct dentry *hostfs_lookup(struct inode *ino, struct dentry *dentry,
                             struct nameidata *nd)
{
        struct inode *inode;
        char *name;
        int err;

        err = -ENOMEM;
        inode = iget(ino->i_sb, 0);
        if (inode == NULL)
                goto out;

        err = init_inode(inode, dentry);
        if (err)
                goto out_put;

        err = -ENOMEM;
        name = dentry_name(dentry, 0);
        if (name == NULL)
                goto out_put;

        err = read_name(inode, name);
        kfree(name);
        if (err == -ENOENT) {
                iput(inode);
                inode = NULL;
        }
        else if (err)
                goto out_put;

        d_add(dentry, inode);
        dentry->d_op = &hostfs_dentry_ops;
        return NULL;

 out_put:
        iput(inode);
 out:
        return ERR_PTR(err);
}

static char *inode_dentry_name(struct inode *ino, struct dentry *dentry)
{
        char *file;
        int len;

        file = inode_name(ino, dentry->d_name.len + 1);
        if (file == NULL)
                return NULL;
        strcat(file, "/");
        len = strlen(file);
        strncat(file, dentry->d_name.name, dentry->d_name.len);
        file[len + dentry->d_name.len] = '\0';
        return file;
}

int hostfs_link(struct dentry *to, struct inode *ino, struct dentry *from)
{
        char *from_name, *to_name;
        int err;

        if ((from_name = inode_dentry_name(ino, from)) == NULL)
                return -ENOMEM;
        to_name = dentry_name(to, 0);
        if (to_name == NULL) {
                kfree(from_name);
                return -ENOMEM;
        }
        err = link_file(to_name, from_name);
        kfree(from_name);
        kfree(to_name);
        return err;
}

int hostfs_unlink(struct inode *ino, struct dentry *dentry)
{
        char *file;
        int err;

        if ((file = inode_dentry_name(ino, dentry)) == NULL)
                return -ENOMEM;
        if (append)
                return -EPERM;

        err = unlink_file(file);
        kfree(file);
        return err;
}

int hostfs_symlink(struct inode *ino, struct dentry *dentry, const char *to)
{
        char *file;
        int err;

        if ((file = inode_dentry_name(ino, dentry)) == NULL)
                return -ENOMEM;
        err = make_symlink(file, to);
        kfree(file);
        return err;
}

int hostfs_mkdir(struct inode *ino, struct dentry *dentry, int mode)
{
        char *file;
        int err;

        if ((file = inode_dentry_name(ino, dentry)) == NULL)
                return -ENOMEM;
        err = do_mkdir(file, mode);
        kfree(file);
        return err;
}

int hostfs_rmdir(struct inode *ino, struct dentry *dentry)
{
        char *file;
        int err;

        if ((file = inode_dentry_name(ino, dentry)) == NULL)
                return -ENOMEM;
        err = do_rmdir(file);
        kfree(file);
        return err;
}

int hostfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
{
        struct inode *inode;
        char *name;
        int err = -ENOMEM;

        inode = iget(dir->i_sb, 0);
        if (inode == NULL)
                goto out;

        err = init_inode(inode, dentry);
        if (err)
                goto out_put;

        err = -ENOMEM;
        name = dentry_name(dentry, 0);
        if (name == NULL)
                goto out_put;

        init_special_inode(inode, mode, dev);
        err = do_mknod(name, mode, MAJOR(dev), MINOR(dev));
        if (err)
                goto out_free;

        err = read_name(inode, name);
        kfree(name);
        if (err)
                goto out_put;

        d_instantiate(dentry, inode);
        return 0;

 out_free:
        kfree(name);
 out_put:
        iput(inode);
 out:
        return err;
}

int hostfs_rename(struct inode *from_ino, struct dentry *from,
                  struct inode *to_ino, struct dentry *to)
{
        char *from_name, *to_name;
        int err;

        if ((from_name = inode_dentry_name(from_ino, from)) == NULL)
                return -ENOMEM;
        if ((to_name = inode_dentry_name(to_ino, to)) == NULL) {
                kfree(from_name);
                return -ENOMEM;
        }
        err = rename_file(from_name, to_name);
        kfree(from_name);
        kfree(to_name);
        return err;
}

int hostfs_permission(struct inode *ino, int desired, struct nameidata *nd)
{
        char *name;
        int r = 0, w = 0, x = 0, err;

        if (desired & MAY_READ) r = 1;
        if (desired & MAY_WRITE) w = 1;
        if (desired & MAY_EXEC) x = 1;
        name = inode_name(ino, 0);
        if (name == NULL)
                return -ENOMEM;

        if (S_ISCHR(ino->i_mode) || S_ISBLK(ino->i_mode) ||
            S_ISFIFO(ino->i_mode) || S_ISSOCK(ino->i_mode))
                err = 0;
        else
                err = access_file(name, r, w, x);
        kfree(name);
        if (!err)
                err = generic_permission(ino, desired, NULL);
        return err;
}

int hostfs_setattr(struct dentry *dentry, struct iattr *attr)
{
        struct hostfs_iattr attrs;
        char *name;
        int err;

        int fd = HOSTFS_I(dentry->d_inode)->fd;

        err = inode_change_ok(dentry->d_inode, attr);
        if (err)
                return err;

        if (append)
                attr->ia_valid &= ~ATTR_SIZE;

        attrs.ia_valid = 0;
        if (attr->ia_valid & ATTR_MODE) {
                attrs.ia_valid |= HOSTFS_ATTR_MODE;
                attrs.ia_mode = attr->ia_mode;
        }
        if (attr->ia_valid & ATTR_UID) {
                attrs.ia_valid |= HOSTFS_ATTR_UID;
                attrs.ia_uid = attr->ia_uid;
        }
        if (attr->ia_valid & ATTR_GID) {
                attrs.ia_valid |= HOSTFS_ATTR_GID;
                attrs.ia_gid = attr->ia_gid;
        }
        if (attr->ia_valid & ATTR_SIZE) {
                attrs.ia_valid |= HOSTFS_ATTR_SIZE;
                attrs.ia_size = attr->ia_size;
        }
        if (attr->ia_valid & ATTR_ATIME) {
                attrs.ia_valid |= HOSTFS_ATTR_ATIME;
                attrs.ia_atime = attr->ia_atime;
        }
        if (attr->ia_valid & ATTR_MTIME) {
                attrs.ia_valid |= HOSTFS_ATTR_MTIME;
                attrs.ia_mtime = attr->ia_mtime;
        }
        if (attr->ia_valid & ATTR_CTIME) {
                attrs.ia_valid |= HOSTFS_ATTR_CTIME;
                attrs.ia_ctime = attr->ia_ctime;
        }
        if (attr->ia_valid & ATTR_ATIME_SET) {
                attrs.ia_valid |= HOSTFS_ATTR_ATIME_SET;
        }
        if (attr->ia_valid & ATTR_MTIME_SET) {
                attrs.ia_valid |= HOSTFS_ATTR_MTIME_SET;
        }
        name = dentry_name(dentry, 0);
        if (name == NULL)
                return -ENOMEM;
        err = set_attr(name, &attrs, fd);
        kfree(name);
        if (err)
                return err;

        return inode_setattr(dentry->d_inode, attr);
}

static const struct inode_operations hostfs_iops = {
        .create         = hostfs_create,
        .link           = hostfs_link,
        .unlink         = hostfs_unlink,
        .symlink        = hostfs_symlink,
        .mkdir          = hostfs_mkdir,
        .rmdir          = hostfs_rmdir,
        .mknod          = hostfs_mknod,
        .rename         = hostfs_rename,
        .permission     = hostfs_permission,
        .setattr        = hostfs_setattr,
};

static const struct inode_operations hostfs_dir_iops = {
        .create         = hostfs_create,
        .lookup         = hostfs_lookup,
        .link           = hostfs_link,
        .unlink         = hostfs_unlink,
        .symlink        = hostfs_symlink,
        .mkdir          = hostfs_mkdir,
        .rmdir          = hostfs_rmdir,
        .mknod          = hostfs_mknod,
        .rename         = hostfs_rename,
        .permission     = hostfs_permission,
        .setattr        = hostfs_setattr,
};

int hostfs_link_readpage(struct file *file, struct page *page)
{
        char *buffer, *name;
        int err;

        buffer = kmap(page);
        name = inode_name(page->mapping->host, 0);
        if (name == NULL)
                return -ENOMEM;
        err = do_readlink(name, buffer, PAGE_CACHE_SIZE);
        kfree(name);
        if (err == PAGE_CACHE_SIZE)
                err = -E2BIG;
        else if (err > 0) {
                flush_dcache_page(page);
                SetPageUptodate(page);
                if (PageError(page)) ClearPageError(page);
                err = 0;
        }
        kunmap(page);
        unlock_page(page);
        return err;
}

static const struct address_space_operations hostfs_link_aops = {
        .readpage       = hostfs_link_readpage,
};

static int hostfs_fill_sb_common(struct super_block *sb, void *d, int silent)
{
        struct inode *root_inode;
        char *host_root_path, *req_root = d;
        int err;

        sb->s_blocksize = 1024;
        sb->s_blocksize_bits = 10;
        sb->s_magic = HOSTFS_SUPER_MAGIC;
        sb->s_op = &hostfs_sbops;

        /* NULL is printed as <NULL> by sprintf: avoid that. */
        if (req_root == NULL)
                req_root = "";

        err = -ENOMEM;
        host_root_path = kmalloc(strlen(root_ino) + 1
                                 + strlen(req_root) + 1, GFP_KERNEL);
        if (host_root_path == NULL)
                goto out;

        sprintf(host_root_path, "%s/%s", root_ino, req_root);

        root_inode = iget(sb, 0);
        if (root_inode == NULL)
                goto out_free;

        err = init_inode(root_inode, NULL);
        if (err)
                goto out_put;

        HOSTFS_I(root_inode)->host_filename = host_root_path;
        /*
         * Avoid that in the error path, iput(root_inode) frees again
         * host_root_path through hostfs_destroy_inode!
         */
        host_root_path = NULL;

        err = -ENOMEM;
        sb->s_root = d_alloc_root(root_inode);
        if (sb->s_root == NULL)
                goto out_put;

        err = read_inode(root_inode);
        if (err) {
                /* No iput in this case because the dput does that for us */
                dput(sb->s_root);
                sb->s_root = NULL;
                goto out;
        }

        return 0;

out_put:
        iput(root_inode);
out_free:
        kfree(host_root_path);
out:
        return err;
}

static int hostfs_read_sb(struct file_system_type *type,
                          int flags, const char *dev_name,
                          void *data, struct vfsmount *mnt)
{
        return get_sb_nodev(type, flags, data, hostfs_fill_sb_common, mnt);
}

static struct file_system_type hostfs_type = {

        .owner          = THIS_MODULE,
        .name           = "hostfs",
        .get_sb         = hostfs_read_sb,
        .kill_sb        = kill_anon_super,
        .fs_flags       = 0,
};

static int __init init_hostfs(void)
{
        return register_filesystem(&hostfs_type);
}

static void __exit exit_hostfs(void)
{
        unregister_filesystem(&hostfs_type);
}

module_init(init_hostfs)
module_exit(exit_hostfs)
MODULE_LICENSE("GPL");