/*
 *      fs/libfs.c
 *      Library for filesystems writers.
 */

#include <linux/module.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/mount.h>
#include <linux/vfs.h>
#include <linux/quotaops.h>
#include <linux/mutex.h>
#include <linux/exportfs.h>
#include <linux/writeback.h>
#include <linux/buffer_head.h>

#include <asm/uaccess.h>

static inline int simple_positive(struct dentry *dentry)
{
        return dentry->d_inode && !d_unhashed(dentry);
}

int simple_getattr(struct vfsmount *mnt, struct dentry *dentry,
                   struct kstat *stat)
{
        struct inode *inode = dentry->d_inode;
        generic_fillattr(inode, stat);
        stat->blocks = inode->i_mapping->nrpages << (PAGE_CACHE_SHIFT - 9);
        return 0;
}

int simple_statfs(struct dentry *dentry, struct kstatfs *buf)
{
        buf->f_type = dentry->d_sb->s_magic;
        buf->f_bsize = PAGE_CACHE_SIZE;
        buf->f_namelen = NAME_MAX;
        return 0;
}

/*
 * Retaining negative dentries for an in-memory filesystem just wastes
 * memory and lookup time: arrange for them to be deleted immediately.
 */
static int simple_delete_dentry(const struct dentry *dentry)
{
        return 1;
}

/*
 * Lookup the data. This is trivial - if the dentry didn't already
 * exist, we know it is negative.  Set d_op to delete negative dentries.
 */
struct dentry *simple_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
{
        static const struct dentry_operations simple_dentry_operations = {
                .d_delete = simple_delete_dentry,
        };

        if (dentry->d_name.len > NAME_MAX)
                return ERR_PTR(-ENAMETOOLONG);
        d_set_d_op(dentry, &simple_dentry_operations);
        d_add(dentry, NULL);
        return NULL;
}

int dcache_dir_open(struct inode *inode, struct file *file)
{
        static struct qstr cursor_name = {.len = 1, .name = "."};

        file->private_data = d_alloc(file->f_path.dentry, &cursor_name);

        return file->private_data ? 0 : -ENOMEM;
}

int dcache_dir_close(struct inode *inode, struct file *file)
{
        dput(file->private_data);
        return 0;
}

loff_t dcache_dir_lseek(struct file *file, loff_t offset, int origin)
{
        struct dentry *dentry = file->f_path.dentry;
        mutex_lock(&dentry->d_inode->i_mutex);
        switch (origin) {
                case 1:
                        offset += file->f_pos;
                case 0:
                        if (offset >= 0)
                                break;
                default:
                        mutex_unlock(&dentry->d_inode->i_mutex);
                        return -EINVAL;
        }
        if (offset != file->f_pos) {
                file->f_pos = offset;
                if (file->f_pos >= 2) {
                        struct list_head *p;
                        struct dentry *cursor = file->private_data;
                        loff_t n = file->f_pos - 2;

                        spin_lock(&dentry->d_lock);
                        /* d_lock not required for cursor */
                        list_del(&cursor->d_u.d_child);
                        p = dentry->d_subdirs.next;
                        while (n && p != &dentry->d_subdirs) {
                                struct dentry *next;
                                next = list_entry(p, struct dentry, d_u.d_child);
                                spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);
                                if (simple_positive(next))
                                        n--;
                                spin_unlock(&next->d_lock);
                                p = p->next;
                        }
                        list_add_tail(&cursor->d_u.d_child, p);
                        spin_unlock(&dentry->d_lock);
                }
        }
        mutex_unlock(&dentry->d_inode->i_mutex);
        return offset;
}

/* Relationship between i_mode and the DT_xxx types */
static inline unsigned char dt_type(struct inode *inode)
{
        return (inode->i_mode >> 12) & 15;
}

/*
 * Directory is locked and all positive dentries in it are safe, since
 * for ramfs-type trees they can't go away without unlink() or rmdir(),
 * both impossible due to the lock on directory.
 */

int dcache_readdir(struct file * filp, void * dirent, filldir_t filldir)
{
        struct dentry *dentry = filp->f_path.dentry;
        struct dentry *cursor = filp->private_data;
        struct list_head *p, *q = &cursor->d_u.d_child;
        ino_t ino;
        int i = filp->f_pos;

        switch (i) {
                case 0:
                        ino = dentry->d_inode->i_ino;
                        if (filldir(dirent, ".", 1, i, ino, DT_DIR) < 0)
                                break;
                        filp->f_pos++;
                        i++;
                        /* fallthrough */
                case 1:
                        ino = parent_ino(dentry);
                        if (filldir(dirent, "..", 2, i, ino, DT_DIR) < 0)
                                break;
                        filp->f_pos++;
                        i++;
                        /* fallthrough */
                default:
                        spin_lock(&dentry->d_lock);
                        if (filp->f_pos == 2)
                                list_move(q, &dentry->d_subdirs);

                        for (p=q->next; p != &dentry->d_subdirs; p=p->next) {
                                struct dentry *next;
                                next = list_entry(p, struct dentry, d_u.d_child);
                                spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);
                                if (!simple_positive(next)) {
                                        spin_unlock(&next->d_lock);
                                        continue;
                                }

                                spin_unlock(&next->d_lock);
                                spin_unlock(&dentry->d_lock);
                                if (filldir(dirent, next->d_name.name, 
                                            next->d_name.len, filp->f_pos, 
                                            next->d_inode->i_ino, 
                                            dt_type(next->d_inode)) < 0)
                                        return 0;
                                spin_lock(&dentry->d_lock);
                                spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);
                                /* next is still alive */
                                list_move(q, p);
                                spin_unlock(&next->d_lock);
                                p = q;
                                filp->f_pos++;
                        }
                        spin_unlock(&dentry->d_lock);
        }
        return 0;
}

ssize_t generic_read_dir(struct file *filp, char __user *buf, size_t siz, loff_t *ppos)
{
        return -EISDIR;
}

const struct file_operations simple_dir_operations = {
        .open           = dcache_dir_open,
        .release        = dcache_dir_close,
        .llseek         = dcache_dir_lseek,
        .read           = generic_read_dir,
        .readdir        = dcache_readdir,
        .fsync          = noop_fsync,
};

const struct inode_operations simple_dir_inode_operations = {
        .lookup         = simple_lookup,
};

static const struct super_operations simple_super_operations = {
        .statfs         = simple_statfs,
};

/*
 * Common helper for pseudo-filesystems (sockfs, pipefs, bdev - stuff that
 * will never be mountable)
 */
struct dentry *mount_pseudo(struct file_system_type *fs_type, char *name,
        const struct super_operations *ops,
        const struct dentry_operations *dops, unsigned long magic)
{
        struct super_block *s = sget(fs_type, NULL, set_anon_super, NULL);
        struct dentry *dentry;
        struct inode *root;
        struct qstr d_name = {.name = name, .len = strlen(name)};

        if (IS_ERR(s))
                return ERR_CAST(s);

        s->s_flags = MS_NOUSER;
        s->s_maxbytes = MAX_LFS_FILESIZE;
        s->s_blocksize = PAGE_SIZE;
        s->s_blocksize_bits = PAGE_SHIFT;
        s->s_magic = magic;
        s->s_op = ops ? ops : &simple_super_operations;
        s->s_time_gran = 1;
        root = new_inode(s);
        if (!root)
                goto Enomem;
        /*
         * since this is the first inode, make it number 1. New inodes created
         * after this must take care not to collide with it (by passing
         * max_reserved of 1 to iunique).
         */
        root->i_ino = 1;
        root->i_mode = S_IFDIR | S_IRUSR | S_IWUSR;
        root->i_atime = root->i_mtime = root->i_ctime = CURRENT_TIME;
        dentry = d_alloc(NULL, &d_name);
        if (!dentry) {
                iput(root);
                goto Enomem;
        }
        dentry->d_sb = s;
        dentry->d_parent = dentry;
        d_instantiate(dentry, root);
        s->s_root = dentry;
        s->s_d_op = dops;
        s->s_flags |= MS_ACTIVE;
        return dget(s->s_root);

Enomem:
        deactivate_locked_super(s);
        return ERR_PTR(-ENOMEM);
}

int simple_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
{
        struct inode *inode = old_dentry->d_inode;

        inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
        inc_nlink(inode);
        ihold(inode);
        dget(dentry);
        d_instantiate(dentry, inode);
        return 0;
}

int simple_empty(struct dentry *dentry)
{
        struct dentry *child;
        int ret = 0;

        spin_lock(&dentry->d_lock);
        list_for_each_entry(child, &dentry->d_subdirs, d_u.d_child) {
                spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
                if (simple_positive(child)) {
                        spin_unlock(&child->d_lock);
                        goto out;
                }
                spin_unlock(&child->d_lock);
        }
        ret = 1;
out:
        spin_unlock(&dentry->d_lock);
        return ret;
}

int simple_unlink(struct inode *dir, struct dentry *dentry)
{
        struct inode *inode = dentry->d_inode;

        inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
        drop_nlink(inode);
        dput(dentry);
        return 0;
}

int simple_rmdir(struct inode *dir, struct dentry *dentry)
{
        if (!simple_empty(dentry))
                return -ENOTEMPTY;

        drop_nlink(dentry->d_inode);
        simple_unlink(dir, dentry);
        drop_nlink(dir);
        return 0;
}

int simple_rename(struct inode *old_dir, struct dentry *old_dentry,
                struct inode *new_dir, struct dentry *new_dentry)
{
        struct inode *inode = old_dentry->d_inode;
        int they_are_dirs = S_ISDIR(old_dentry->d_inode->i_mode);

        if (!simple_empty(new_dentry))
                return -ENOTEMPTY;

        if (new_dentry->d_inode) {
                simple_unlink(new_dir, new_dentry);
                if (they_are_dirs)
                        drop_nlink(old_dir);
        } else if (they_are_dirs) {
                drop_nlink(old_dir);
                inc_nlink(new_dir);
        }

        old_dir->i_ctime = old_dir->i_mtime = new_dir->i_ctime =
                new_dir->i_mtime = inode->i_ctime = CURRENT_TIME;

        return 0;
}

/**
 * simple_setattr - setattr for simple filesystem
 * @dentry: dentry
 * @iattr: iattr structure
 *
 * Returns 0 on success, -error on failure.
 *
 * simple_setattr is a simple ->setattr implementation without a proper
 * implementation of size changes.
 *
 * It can either be used for in-memory filesystems or special files
 * on simple regular filesystems.  Anything that needs to change on-disk
 * or wire state on size changes needs its own setattr method.
 */
int simple_setattr(struct dentry *dentry, struct iattr *iattr)
{
        struct inode *inode = dentry->d_inode;
        int error;

        WARN_ON_ONCE(inode->i_op->truncate);

        error = inode_change_ok(inode, iattr);
        if (error)
                return error;

        if (iattr->ia_valid & ATTR_SIZE)
                truncate_setsize(inode, iattr->ia_size);
        setattr_copy(inode, iattr);
        mark_inode_dirty(inode);
        return 0;
}
EXPORT_SYMBOL(simple_setattr);

int simple_readpage(struct file *file, struct page *page)
{
        clear_highpage(page);
        flush_dcache_page(page);
        SetPageUptodate(page);
        unlock_page(page);
        return 0;
}

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

        index = pos >> PAGE_CACHE_SHIFT;

        page = grab_cache_page_write_begin(mapping, index, flags);
        if (!page)
                return -ENOMEM;

        *pagep = page;

        if (!PageUptodate(page) && (len != PAGE_CACHE_SIZE)) {
                unsigned from = pos & (PAGE_CACHE_SIZE - 1);

                zero_user_segments(page, 0, from, from + len, PAGE_CACHE_SIZE);
        }
        return 0;
}

/**
 * simple_write_end - .write_end helper for non-block-device FSes
 * @available: See .write_end of address_space_operations
 * @file:               "
 * @mapping:            "
 * @pos:                "
 * @len:                "
 * @copied:             "
 * @page:               "
 * @fsdata:             "
 *
 * simple_write_end does the minimum needed for updating a page after writing is
 * done. It has the same API signature as the .write_end of
 * address_space_operations vector. So it can just be set onto .write_end for
 * FSes that don't need any other processing. i_mutex is assumed to be held.
 * Block based filesystems should use generic_write_end().
 * NOTE: Even though i_size might get updated by this function, mark_inode_dirty
 * is not called, so a filesystem that actually does store data in .write_inode
 * should extend on what's done here with a call to mark_inode_dirty() in the
 * case that i_size has changed.
 */
int simple_write_end(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned copied,
                        struct page *page, void *fsdata)
{
        struct inode *inode = page->mapping->host;
        loff_t last_pos = pos + copied;

        /* zero the stale part of the page if we did a short copy */
        if (copied < len) {
                unsigned from = pos & (PAGE_CACHE_SIZE - 1);

                zero_user(page, from + copied, len - copied);
        }

        if (!PageUptodate(page))
                SetPageUptodate(page);
        /*
         * No need to use i_size_read() here, the i_size
         * cannot change under us because we hold the i_mutex.
         */
        if (last_pos > inode->i_size)
                i_size_write(inode, last_pos);

        set_page_dirty(page);
        unlock_page(page);
        page_cache_release(page);

        return copied;
}

/*
 * the inodes created here are not hashed. If you use iunique to generate
 * unique inode values later for this filesystem, then you must take care
 * to pass it an appropriate max_reserved value to avoid collisions.
 */
int simple_fill_super(struct super_block *s, unsigned long magic,
                      struct tree_descr *files)
{
        struct inode *inode;
        struct dentry *root;
        struct dentry *dentry;
        int i;

        s->s_blocksize = PAGE_CACHE_SIZE;
        s->s_blocksize_bits = PAGE_CACHE_SHIFT;
        s->s_magic = magic;
        s->s_op = &simple_super_operations;
        s->s_time_gran = 1;

        inode = new_inode(s);
        if (!inode)
                return -ENOMEM;
        /*
         * because the root inode is 1, the files array must not contain an
         * entry at index 1
         */
        inode->i_ino = 1;
        inode->i_mode = S_IFDIR | 0755;
        inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
        inode->i_op = &simple_dir_inode_operations;
        inode->i_fop = &simple_dir_operations;
        inode->i_nlink = 2;
        root = d_alloc_root(inode);
        if (!root) {
                iput(inode);
                return -ENOMEM;
        }
        for (i = 0; !files->name || files->name[0]; i++, files++) {
                if (!files->name)
                        continue;

                /* warn if it tries to conflict with the root inode */
                if (unlikely(i == 1))
                        printk(KERN_WARNING "%s: %s passed in a files array"
                                "with an index of 1!\n", __func__,
                                s->s_type->name);

                dentry = d_alloc_name(root, files->name);
                if (!dentry)
                        goto out;
                inode = new_inode(s);
                if (!inode)
                        goto out;
                inode->i_mode = S_IFREG | files->mode;
                inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
                inode->i_fop = files->ops;
                inode->i_ino = i;
                d_add(dentry, inode);
        }
        s->s_root = root;
        return 0;
out:
        d_genocide(root);
        dput(root);
        return -ENOMEM;
}

static DEFINE_SPINLOCK(pin_fs_lock);

int simple_pin_fs(struct file_system_type *type, struct vfsmount **mount, int *count)
{
        struct vfsmount *mnt = NULL;
        spin_lock(&pin_fs_lock);
        if (unlikely(!*mount)) {
                spin_unlock(&pin_fs_lock);
                mnt = vfs_kern_mount(type, 0, type->name, NULL);
                if (IS_ERR(mnt))
                        return PTR_ERR(mnt);
                spin_lock(&pin_fs_lock);
                if (!*mount)
                        *mount = mnt;
        }
        mntget(*mount);
        ++*count;
        spin_unlock(&pin_fs_lock);
        mntput(mnt);
        return 0;
}

void simple_release_fs(struct vfsmount **mount, int *count)
{
        struct vfsmount *mnt;
        spin_lock(&pin_fs_lock);
        mnt = *mount;
        if (!--*count)
                *mount = NULL;
        spin_unlock(&pin_fs_lock);
        mntput(mnt);
}

/**
 * simple_read_from_buffer - copy data from the buffer to user space
 * @to: the user space buffer to read to
 * @count: the maximum number of bytes to read
 * @ppos: the current position in the buffer
 * @from: the buffer to read from
 * @available: the size of the buffer
 *
 * The simple_read_from_buffer() function reads up to @count bytes from the
 * buffer @from at offset @ppos into the user space address starting at @to.
 *
 * On success, the number of bytes read is returned and the offset @ppos is
 * advanced by this number, or negative value is returned on error.
 **/
ssize_t simple_read_from_buffer(void __user *to, size_t count, loff_t *ppos,
                                const void *from, size_t available)
{
        loff_t pos = *ppos;
        size_t ret;

        if (pos < 0)
                return -EINVAL;
        if (pos >= available || !count)
                return 0;
        if (count > available - pos)
                count = available - pos;
        ret = copy_to_user(to, from + pos, count);
        if (ret == count)
                return -EFAULT;
        count -= ret;
        *ppos = pos + count;
        return count;
}

/**
 * simple_write_to_buffer - copy data from user space to the buffer
 * @to: the buffer to write to
 * @available: the size of the buffer
 * @ppos: the current position in the buffer
 * @from: the user space buffer to read from
 * @count: the maximum number of bytes to read
 *
 * The simple_write_to_buffer() function reads up to @count bytes from the user
 * space address starting at @from into the buffer @to at offset @ppos.
 *
 * On success, the number of bytes written is returned and the offset @ppos is
 * advanced by this number, or negative value is returned on error.
 **/
ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos,
                const void __user *from, size_t count)
{
        loff_t pos = *ppos;
        size_t res;

        if (pos < 0)
                return -EINVAL;
        if (pos >= available || !count)
                return 0;
        if (count > available - pos)
                count = available - pos;
        res = copy_from_user(to + pos, from, count);
        if (res == count)
                return -EFAULT;
        count -= res;
        *ppos = pos + count;
        return count;
}

/**
 * memory_read_from_buffer - copy data from the buffer
 * @to: the kernel space buffer to read to
 * @count: the maximum number of bytes to read
 * @ppos: the current position in the buffer
 * @from: the buffer to read from
 * @available: the size of the buffer
 *
 * The memory_read_from_buffer() function reads up to @count bytes from the
 * buffer @from at offset @ppos into the kernel space address starting at @to.
 *
 * On success, the number of bytes read is returned and the offset @ppos is
 * advanced by this number, or negative value is returned on error.
 **/
ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
                                const void *from, size_t available)
{
        loff_t pos = *ppos;

        if (pos < 0)
                return -EINVAL;
        if (pos >= available)
                return 0;
        if (count > available - pos)
                count = available - pos;
        memcpy(to, from + pos, count);
        *ppos = pos + count;

        return count;
}

/*
 * Transaction based IO.
 * The file expects a single write which triggers the transaction, and then
 * possibly a read which collects the result - which is stored in a
 * file-local buffer.
 */

void simple_transaction_set(struct file *file, size_t n)
{
        struct simple_transaction_argresp *ar = file->private_data;

        BUG_ON(n > SIMPLE_TRANSACTION_LIMIT);

        /*
         * The barrier ensures that ar->size will really remain zero until
         * ar->data is ready for reading.
         */
        smp_mb();
        ar->size = n;
}

char *simple_transaction_get(struct file *file, const char __user *buf, size_t size)
{
        struct simple_transaction_argresp *ar;
        static DEFINE_SPINLOCK(simple_transaction_lock);

        if (size > SIMPLE_TRANSACTION_LIMIT - 1)
                return ERR_PTR(-EFBIG);

        ar = (struct simple_transaction_argresp *)get_zeroed_page(GFP_KERNEL);
        if (!ar)
                return ERR_PTR(-ENOMEM);

        spin_lock(&simple_transaction_lock);

        /* only one write allowed per open */
        if (file->private_data) {
                spin_unlock(&simple_transaction_lock);
                free_page((unsigned long)ar);
                return ERR_PTR(-EBUSY);
        }

        file->private_data = ar;

        spin_unlock(&simple_transaction_lock);

        if (copy_from_user(ar->data, buf, size))
                return ERR_PTR(-EFAULT);

        return ar->data;
}

ssize_t simple_transaction_read(struct file *file, char __user *buf, size_t size, loff_t *pos)
{
        struct simple_transaction_argresp *ar = file->private_data;

        if (!ar)
                return 0;
        return simple_read_from_buffer(buf, size, pos, ar->data, ar->size);
}

int simple_transaction_release(struct inode *inode, struct file *file)
{
        free_page((unsigned long)file->private_data);
        return 0;
}

/* Simple attribute files */

struct simple_attr {
        int (*get)(void *, u64 *);
        int (*set)(void *, u64);
        char get_buf[24];       /* enough to store a u64 and "\n\0" */
        char set_buf[24];
        void *data;
        const char *fmt;        /* format for read operation */
        struct mutex mutex;     /* protects access to these buffers */
};

/* simple_attr_open is called by an actual attribute open file operation
 * to set the attribute specific access operations. */
int simple_attr_open(struct inode *inode, struct file *file,
                     int (*get)(void *, u64 *), int (*set)(void *, u64),
                     const char *fmt)
{
        struct simple_attr *attr;

        attr = kmalloc(sizeof(*attr), GFP_KERNEL);
        if (!attr)
                return -ENOMEM;

        attr->get = get;
        attr->set = set;
        attr->data = inode->i_private;
        attr->fmt = fmt;
        mutex_init(&attr->mutex);

        file->private_data = attr;

        return nonseekable_open(inode, file);
}

int simple_attr_release(struct inode *inode, struct file *file)
{
        kfree(file->private_data);
        return 0;
}

/* read from the buffer that is filled with the get function */
ssize_t simple_attr_read(struct file *file, char __user *buf,
                         size_t len, loff_t *ppos)
{
        struct simple_attr *attr;
        size_t size;
        ssize_t ret;

        attr = file->private_data;

        if (!attr->get)
                return -EACCES;

        ret = mutex_lock_interruptible(&attr->mutex);
        if (ret)
                return ret;

        if (*ppos) {            /* continued read */
                size = strlen(attr->get_buf);
        } else {                /* first read */
                u64 val;
                ret = attr->get(attr->data, &val);
                if (ret)
                        goto out;

                size = scnprintf(attr->get_buf, sizeof(attr->get_buf),
                                 attr->fmt, (unsigned long long)val);
        }

        ret = simple_read_from_buffer(buf, len, ppos, attr->get_buf, size);
out:
        mutex_unlock(&attr->mutex);
        return ret;
}

/* interpret the buffer as a number to call the set function with */
ssize_t simple_attr_write(struct file *file, const char __user *buf,
                          size_t len, loff_t *ppos)
{
        struct simple_attr *attr;
        u64 val;
        size_t size;
        ssize_t ret;

        attr = file->private_data;
        if (!attr->set)
                return -EACCES;

        ret = mutex_lock_interruptible(&attr->mutex);
        if (ret)
                return ret;

        ret = -EFAULT;
        size = min(sizeof(attr->set_buf) - 1, len);
        if (copy_from_user(attr->set_buf, buf, size))
                goto out;

        attr->set_buf[size] = '\0';
        val = simple_strtol(attr->set_buf, NULL, 0);
        ret = attr->set(attr->data, val);
        if (ret == 0)
                ret = len; /* on success, claim we got the whole input */
out:
        mutex_unlock(&attr->mutex);
        return ret;
}

/**
 * generic_fh_to_dentry - generic helper for the fh_to_dentry export operation
 * @sb:         filesystem to do the file handle conversion on
 * @fid:        file handle to convert
 * @fh_len:     length of the file handle in bytes
 * @fh_type:    type of file handle
 * @get_inode:  filesystem callback to retrieve inode
 *
 * This function decodes @fid as long as it has one of the well-known
 * Linux filehandle types and calls @get_inode on it to retrieve the
 * inode for the object specified in the file handle.
 */
struct dentry *generic_fh_to_dentry(struct super_block *sb, struct fid *fid,
                int fh_len, int fh_type, struct inode *(*get_inode)
                        (struct super_block *sb, u64 ino, u32 gen))
{
        struct inode *inode = NULL;

        if (fh_len < 2)
                return NULL;

        switch (fh_type) {
        case FILEID_INO32_GEN:
        case FILEID_INO32_GEN_PARENT:
                inode = get_inode(sb, fid->i32.ino, fid->i32.gen);
                break;
        }

        return d_obtain_alias(inode);
}
EXPORT_SYMBOL_GPL(generic_fh_to_dentry);

/**
 * generic_fh_to_dentry - generic helper for the fh_to_parent export operation
 * @sb:         filesystem to do the file handle conversion on
 * @fid:        file handle to convert
 * @fh_len:     length of the file handle in bytes
 * @fh_type:    type of file handle
 * @get_inode:  filesystem callback to retrieve inode
 *
 * This function decodes @fid as long as it has one of the well-known
 * Linux filehandle types and calls @get_inode on it to retrieve the
 * inode for the _parent_ object specified in the file handle if it
 * is specified in the file handle, or NULL otherwise.
 */
struct dentry *generic_fh_to_parent(struct super_block *sb, struct fid *fid,
                int fh_len, int fh_type, struct inode *(*get_inode)
                        (struct super_block *sb, u64 ino, u32 gen))
{
        struct inode *inode = NULL;

        if (fh_len <= 2)
                return NULL;

        switch (fh_type) {
        case FILEID_INO32_GEN_PARENT:
                inode = get_inode(sb, fid->i32.parent_ino,
                                  (fh_len > 3 ? fid->i32.parent_gen : 0));
                break;
        }

        return d_obtain_alias(inode);
}
EXPORT_SYMBOL_GPL(generic_fh_to_parent);

/**
 * generic_file_fsync - generic fsync implementation for simple filesystems
 * @file:       file to synchronize
 * @datasync:   only synchronize essential metadata if true
 *
 * This is a generic implementation of the fsync method for simple
 * filesystems which track all non-inode metadata in the buffers list
 * hanging off the address_space structure.
 */
int generic_file_fsync(struct file *file, int datasync)
{
        struct inode *inode = file->f_mapping->host;
        int err;
        int ret;

        ret = sync_mapping_buffers(inode->i_mapping);
        if (!(inode->i_state & I_DIRTY))
                return ret;
        if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
                return ret;

        err = sync_inode_metadata(inode, 1);
        if (ret == 0)
                ret = err;
        return ret;
}
EXPORT_SYMBOL(generic_file_fsync);

/**
 * generic_check_addressable - Check addressability of file system
 * @blocksize_bits:     log of file system block size
 * @num_blocks:         number of blocks in file system
 *
 * Determine whether a file system with @num_blocks blocks (and a
 * block size of 2**@blocksize_bits) is addressable by the sector_t
 * and page cache of the system.  Return 0 if so and -EFBIG otherwise.
 */
int generic_check_addressable(unsigned blocksize_bits, u64 num_blocks)
{
        u64 last_fs_block = num_blocks - 1;
        u64 last_fs_page =
                last_fs_block >> (PAGE_CACHE_SHIFT - blocksize_bits);

        if (unlikely(num_blocks == 0))
                return 0;

        if ((blocksize_bits < 9) || (blocksize_bits > PAGE_CACHE_SHIFT))
                return -EINVAL;

        if ((last_fs_block > (sector_t)(~0ULL) >> (blocksize_bits - 9)) ||
            (last_fs_page > (pgoff_t)(~0ULL))) {
                return -EFBIG;
        }
        return 0;
}
EXPORT_SYMBOL(generic_check_addressable);

/*
 * No-op implementation of ->fsync for in-memory filesystems.
 */
int noop_fsync(struct file *file, int datasync)
{
        return 0;
}

EXPORT_SYMBOL(dcache_dir_close);
EXPORT_SYMBOL(dcache_dir_lseek);
EXPORT_SYMBOL(dcache_dir_open);
EXPORT_SYMBOL(dcache_readdir);
EXPORT_SYMBOL(generic_read_dir);
EXPORT_SYMBOL(mount_pseudo);
EXPORT_SYMBOL(simple_write_begin);
EXPORT_SYMBOL(simple_write_end);
EXPORT_SYMBOL(simple_dir_inode_operations);
EXPORT_SYMBOL(simple_dir_operations);
EXPORT_SYMBOL(simple_empty);
EXPORT_SYMBOL(simple_fill_super);
EXPORT_SYMBOL(simple_getattr);
EXPORT_SYMBOL(simple_link);
EXPORT_SYMBOL(simple_lookup);
EXPORT_SYMBOL(simple_pin_fs);
EXPORT_SYMBOL(simple_readpage);
EXPORT_SYMBOL(simple_release_fs);
EXPORT_SYMBOL(simple_rename);
EXPORT_SYMBOL(simple_rmdir);
EXPORT_SYMBOL(simple_statfs);
EXPORT_SYMBOL(noop_fsync);
EXPORT_SYMBOL(simple_unlink);
EXPORT_SYMBOL(simple_read_from_buffer);
EXPORT_SYMBOL(simple_write_to_buffer);
EXPORT_SYMBOL(memory_read_from_buffer);
EXPORT_SYMBOL(simple_transaction_set);
EXPORT_SYMBOL(simple_transaction_get);
EXPORT_SYMBOL(simple_transaction_read);
EXPORT_SYMBOL(simple_transaction_release);
EXPORT_SYMBOL_GPL(simple_attr_open);
EXPORT_SYMBOL_GPL(simple_attr_release);
EXPORT_SYMBOL_GPL(simple_attr_read);
EXPORT_SYMBOL_GPL(simple_attr_write);