libfs.c en linux

   /*
    *      fs/libfs.c
    *      Library for filesystems writers.
    */
   
   #include <linux/blkdev.h>
   #include <linux/export.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/namei.h>
  #include <linux/exportfs.h>
  #include <linux/writeback.h>
  #include <linux/buffer_head.h> /* sync_mapping_buffers */
  
  #include <asm/uaccess.h>
  
  #include "internal.h"
  
  int simple_getattr(struct vfsmount *mnt, struct dentry *dentry,
                     struct kstat *stat)
  {
          struct inode *inode = d_inode(dentry);
          generic_fillattr(inode, stat);
          stat->blocks = inode->i_mapping->nrpages << (PAGE_SHIFT - 9);
          return 0;
  }
  EXPORT_SYMBOL(simple_getattr);
  
  int simple_statfs(struct dentry *dentry, struct kstatfs *buf)
  {
          buf->f_type = dentry->d_sb->s_magic;
          buf->f_bsize = PAGE_SIZE;
          buf->f_namelen = NAME_MAX;
          return 0;
  }
  EXPORT_SYMBOL(simple_statfs);
  
  /*
   * Retaining negative dentries for an in-memory filesystem just wastes
   * memory and lookup time: arrange for them to be deleted immediately.
   */
  int always_delete_dentry(const struct dentry *dentry)
  {
          return 1;
  }
  EXPORT_SYMBOL(always_delete_dentry);
  
  const struct dentry_operations simple_dentry_operations = {
          .d_delete = always_delete_dentry,
  };
  EXPORT_SYMBOL(simple_dentry_operations);
  
  /*
   * 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, unsigned int flags)
  {
          if (dentry->d_name.len > NAME_MAX)
                  return ERR_PTR(-ENAMETOOLONG);
          if (!dentry->d_sb->s_d_op)
                  d_set_d_op(dentry, &simple_dentry_operations);
          d_add(dentry, NULL);
          return NULL;
  }
  EXPORT_SYMBOL(simple_lookup);
  
  int dcache_dir_open(struct inode *inode, struct file *file)
  {
          static struct qstr cursor_name = QSTR_INIT(".", 1);
  
          file->private_data = d_alloc(file->f_path.dentry, &cursor_name);
  
          return file->private_data ? 0 : -ENOMEM;
  }
  EXPORT_SYMBOL(dcache_dir_open);
  
  int dcache_dir_close(struct inode *inode, struct file *file)
  {
          dput(file->private_data);
          return 0;
  }
  EXPORT_SYMBOL(dcache_dir_close);
  
  loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
  {
          struct dentry *dentry = file->f_path.dentry;
          inode_lock(d_inode(dentry));
          switch (whence) {
                  case 1:
                          offset += file->f_pos;
                  case 0:
                          if (offset >= 0)
                                  break;
                  default:
                         inode_unlock(d_inode(dentry));
                         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_child);
                         p = dentry->d_subdirs.next;
                         while (n && p != &dentry->d_subdirs) {
                                 struct dentry *next;
                                 next = list_entry(p, struct dentry, 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_child, p);
                         spin_unlock(&dentry->d_lock);
                 }
         }
         inode_unlock(d_inode(dentry));
         return offset;
 }
 EXPORT_SYMBOL(dcache_dir_lseek);
 
 /* 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 *file, struct dir_context *ctx)
 {
         struct dentry *dentry = file->f_path.dentry;
         struct dentry *cursor = file->private_data;
         struct list_head *p, *q = &cursor->d_child;
 
         if (!dir_emit_dots(file, ctx))
                 return 0;
         spin_lock(&dentry->d_lock);
         if (ctx->pos == 2)
                 list_move(q, &dentry->d_subdirs);
 
         for (p = q->next; p != &dentry->d_subdirs; p = p->next) {
                 struct dentry *next = list_entry(p, struct dentry, 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 (!dir_emit(ctx, next->d_name.name, next->d_name.len,
                               d_inode(next)->i_ino, dt_type(d_inode(next))))
                         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;
                 ctx->pos++;
         }
         spin_unlock(&dentry->d_lock);
         return 0;
 }
 EXPORT_SYMBOL(dcache_readdir);
 
 ssize_t generic_read_dir(struct file *filp, char __user *buf, size_t siz, loff_t *ppos)
 {
         return -EISDIR;
 }
 EXPORT_SYMBOL(generic_read_dir);
 
 const struct file_operations simple_dir_operations = {
         .open           = dcache_dir_open,
         .release        = dcache_dir_close,
         .llseek         = dcache_dir_lseek,
         .read           = generic_read_dir,
         .iterate        = dcache_readdir,
         .fsync          = noop_fsync,
 };
 EXPORT_SYMBOL(simple_dir_operations);
 
 const struct inode_operations simple_dir_inode_operations = {
         .lookup         = simple_lookup,
 };
 EXPORT_SYMBOL(simple_dir_inode_operations);
 
 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;
         struct dentry *dentry;
         struct inode *root;
         struct qstr d_name = QSTR_INIT(name, strlen(name));
 
         s = sget(fs_type, NULL, set_anon_super, MS_NOUSER, NULL);
         if (IS_ERR(s))
                 return ERR_CAST(s);
 
         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(s, &d_name);
         if (!dentry) {
                 iput(root);
                 goto Enomem;
         }
         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);
 }
 EXPORT_SYMBOL(mount_pseudo);
 
 int simple_open(struct inode *inode, struct file *file)
 {
         if (inode->i_private)
                 file->private_data = inode->i_private;
         return 0;
 }
 EXPORT_SYMBOL(simple_open);
 
 int simple_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
 {
         struct inode *inode = d_inode(old_dentry);
 
         inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
         inc_nlink(inode);
         ihold(inode);
         dget(dentry);
         d_instantiate(dentry, inode);
         return 0;
 }
 EXPORT_SYMBOL(simple_link);
 
 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_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;
 }
 EXPORT_SYMBOL(simple_empty);
 
 int simple_unlink(struct inode *dir, struct dentry *dentry)
 {
         struct inode *inode = d_inode(dentry);
 
         inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
         drop_nlink(inode);
         dput(dentry);
         return 0;
 }
 EXPORT_SYMBOL(simple_unlink);
 
 int simple_rmdir(struct inode *dir, struct dentry *dentry)
 {
         if (!simple_empty(dentry))
                 return -ENOTEMPTY;
 
         drop_nlink(d_inode(dentry));
         simple_unlink(dir, dentry);
         drop_nlink(dir);
         return 0;
 }
 EXPORT_SYMBOL(simple_rmdir);
 
 int simple_rename(struct inode *old_dir, struct dentry *old_dentry,
                 struct inode *new_dir, struct dentry *new_dentry)
 {
         struct inode *inode = d_inode(old_dentry);
         int they_are_dirs = d_is_dir(old_dentry);
 
         if (!simple_empty(new_dentry))
                 return -ENOTEMPTY;
 
         if (d_really_is_positive(new_dentry)) {
                 simple_unlink(new_dir, new_dentry);
                 if (they_are_dirs) {
                         drop_nlink(d_inode(new_dentry));
                         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;
 }
 EXPORT_SYMBOL(simple_rename);
 
 /**
  * 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 = d_inode(dentry);
         int error;
 
         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;
 }
 EXPORT_SYMBOL(simple_readpage);
 
 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_SHIFT;
 
         page = grab_cache_page_write_begin(mapping, index, flags);
         if (!page)
                 return -ENOMEM;
 
         *pagep = page;
 
         if (!PageUptodate(page) && (len != PAGE_SIZE)) {
                 unsigned from = pos & (PAGE_SIZE - 1);
 
                 zero_user_segments(page, 0, from, from + len, PAGE_SIZE);
         }
         return 0;
 }
 EXPORT_SYMBOL(simple_write_begin);
 
 /**
  * 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_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);
         put_page(page);
 
         return copied;
 }
 EXPORT_SYMBOL(simple_write_end);
 
 /*
  * 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_SIZE;
         s->s_blocksize_bits = PAGE_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;
         set_nlink(inode, 2);
         root = d_make_root(inode);
         if (!root)
                 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) {
                         dput(dentry);
                         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);
         shrink_dcache_parent(root);
         dput(root);
         return -ENOMEM;
 }
 EXPORT_SYMBOL(simple_fill_super);
 
 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, MS_KERNMOUNT, 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;
 }
 EXPORT_SYMBOL(simple_pin_fs);
 
 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);
 }
 EXPORT_SYMBOL(simple_release_fs);
 
 /**
  * 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;
 }
 EXPORT_SYMBOL(simple_read_from_buffer);
 
 /**
  * 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;
 }
 EXPORT_SYMBOL(simple_write_to_buffer);
 
 /**
  * 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;
 }
 EXPORT_SYMBOL(memory_read_from_buffer);
 
 /*
  * 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;
 }
 EXPORT_SYMBOL(simple_transaction_set);
 
 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;
 }
 EXPORT_SYMBOL(simple_transaction_get);
 
 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);
 }
 EXPORT_SYMBOL(simple_transaction_read);
 
 int simple_transaction_release(struct inode *inode, struct file *file)
 {
         free_page((unsigned long)file->private_data);
         return 0;
 }
 EXPORT_SYMBOL(simple_transaction_release);
 
 /* 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);
 }
 EXPORT_SYMBOL_GPL(simple_attr_open);
 
 int simple_attr_release(struct inode *inode, struct file *file)
 {
         kfree(file->private_data);
         return 0;
 }
 EXPORT_SYMBOL_GPL(simple_attr_release); /* GPL-only?  This?  Really? */
 
 /* 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;
 }
 EXPORT_SYMBOL_GPL(simple_attr_read);
 
 /* 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_strtoll(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;
 }
 EXPORT_SYMBOL_GPL(simple_attr_write);
 
 /**
  * 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_parent - 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
  * @start:      start offset in bytes
  * @end:        end offset in bytes (inclusive)
  * @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, loff_t start, loff_t end,
                                  int datasync)
 {
         struct inode *inode = file->f_mapping->host;
         int err;
         int ret;
 
         err = filemap_write_and_wait_range(inode->i_mapping, start, end);
         if (err)
                 return err;
 
         inode_lock(inode);
         ret = sync_mapping_buffers(inode->i_mapping);
         if (!(inode->i_state & I_DIRTY_ALL))
                 goto out;
         if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
                 goto out;
 
         err = sync_inode_metadata(inode, 1);
         if (ret == 0)
                 ret = err;
 
 out:
         inode_unlock(inode);
         return ret;
 }
 EXPORT_SYMBOL(__generic_file_fsync);
 
 /**
  * generic_file_fsync - generic fsync implementation for simple filesystems
  *                      with flush
  * @file:       file to synchronize
  * @start:      start offset in bytes
  * @end:        end offset in bytes (inclusive)
  * @datasync:   only synchronize essential metadata if true
  *
  */
 
 int generic_file_fsync(struct file *file, loff_t start, loff_t end,
                        int datasync)
 {
         struct inode *inode = file->f_mapping->host;
         int err;
 
         err = __generic_file_fsync(file, start, end, datasync);
         if (err)
                 return err;
         return blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
 }
 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_SHIFT - blocksize_bits);
 
         if (unlikely(num_blocks == 0))
                 return 0;
 
         if ((blocksize_bits < 9) || (blocksize_bits > PAGE_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, loff_t start, loff_t end, int datasync)
 {
         return 0;
 }
 EXPORT_SYMBOL(noop_fsync);
 
 /* Because kfree isn't assignment-compatible with void(void*) ;-/ */
 void kfree_link(void *p)
 {
         kfree(p);
 }
 EXPORT_SYMBOL(kfree_link);
 
 /*
  * nop .set_page_dirty method so that people can use .page_mkwrite on
  * anon inodes.
  */
 static int anon_set_page_dirty(struct page *page)
 {
         return 0;
 };
 
 /*
  * A single inode exists for all anon_inode files. Contrary to pipes,
  * anon_inode inodes have no associated per-instance data, so we need
  * only allocate one of them.
  */
 struct inode *alloc_anon_inode(struct super_block *s)
 {
         static const struct address_space_operations anon_aops = {
                 .set_page_dirty = anon_set_page_dirty,
         };
         struct inode *inode = new_inode_pseudo(s);
 
         if (!inode)
                 return ERR_PTR(-ENOMEM);
 
         inode->i_ino = get_next_ino();
         inode->i_mapping->a_ops = &anon_aops;
 
         /*
          * Mark the inode dirty from the very beginning,
          * that way it will never be moved to the dirty
          * list because mark_inode_dirty() will think
          * that it already _is_ on the dirty list.
          */
         inode->i_state = I_DIRTY;
         inode->i_mode = S_IRUSR | S_IWUSR;
         inode->i_uid = current_fsuid();
         inode->i_gid = current_fsgid();
         inode->i_flags |= S_PRIVATE;
         inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
         return inode;
 }
 EXPORT_SYMBOL(alloc_anon_inode);
 
 /**
  * simple_nosetlease - generic helper for prohibiting leases
  * @filp: file pointer
  * @arg: type of lease to obtain
  * @flp: new lease supplied for insertion
  * @priv: private data for lm_setup operation
  *
  * Generic helper for filesystems that do not wish to allow leases to be set.
  * All arguments are ignored and it just returns -EINVAL.
  */
 int
 simple_nosetlease(struct file *filp, long arg, struct file_lock **flp,
                   void **priv)
 {
         return -EINVAL;
 }
 EXPORT_SYMBOL(simple_nosetlease);
 
 const char *simple_get_link(struct dentry *dentry, struct inode *inode,
                             struct delayed_call *done)
 {
         return inode->i_link;
 }
 EXPORT_SYMBOL(simple_get_link);
 
 const struct inode_operations simple_symlink_inode_operations = {
         .get_link = simple_get_link,
         .readlink = generic_readlink
 };
 EXPORT_SYMBOL(simple_symlink_inode_operations);
 
 /*
  * Operations for a permanently empty directory.
  */
 static struct dentry *empty_dir_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
 {
         return ERR_PTR(-ENOENT);
 }
 
 static int empty_dir_getattr(struct vfsmount *mnt, struct dentry *dentry,
                                  struct kstat *stat)
 {
         struct inode *inode = d_inode(dentry);
         generic_fillattr(inode, stat);
         return 0;
 }
 
 static int empty_dir_setattr(struct dentry *dentry, struct iattr *attr)
 {
         return -EPERM;
 }
 
 static int empty_dir_setxattr(struct dentry *dentry, const char *name,
                               const void *value, size_t size, int flags)
 {
         return -EOPNOTSUPP;
 }
 
 static ssize_t empty_dir_getxattr(struct dentry *dentry, const char *name,
                                   void *value, size_t size)
 {
         return -EOPNOTSUPP;
 }
 
 static int empty_dir_removexattr(struct dentry *dentry, const char *name)
 {
         return -EOPNOTSUPP;
 }
 
 static ssize_t empty_dir_listxattr(struct dentry *dentry, char *list, size_t size)
 {
         return -EOPNOTSUPP;
 }
 
 static const struct inode_operations empty_dir_inode_operations = {
         .lookup         = empty_dir_lookup,
         .permission     = generic_permission,
         .setattr        = empty_dir_setattr,
         .getattr        = empty_dir_getattr,
         .setxattr       = empty_dir_setxattr,
         .getxattr       = empty_dir_getxattr,
         .removexattr    = empty_dir_removexattr,
         .listxattr      = empty_dir_listxattr,
 };
 
 static loff_t empty_dir_llseek(struct file *file, loff_t offset, int whence)
 {
         /* An empty directory has two entries . and .. at offsets 0 and 1 */
         return generic_file_llseek_size(file, offset, whence, 2, 2);
 }
 
 static int empty_dir_readdir(struct file *file, struct dir_context *ctx)
 {
         dir_emit_dots(file, ctx);
         return 0;
 }
 
 static const struct file_operations empty_dir_operations = {
         .llseek         = empty_dir_llseek,
         .read           = generic_read_dir,
         .iterate        = empty_dir_readdir,
         .fsync          = noop_fsync,
 };
 
 
 void make_empty_dir_inode(struct inode *inode)
 {
         set_nlink(inode, 2);
         inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO;
         inode->i_uid = GLOBAL_ROOT_UID;
         inode->i_gid = GLOBAL_ROOT_GID;
         inode->i_rdev = 0;
         inode->i_size = 0;
         inode->i_blkbits = PAGE_SHIFT;
         inode->i_blocks = 0;
 
         inode->i_op = &empty_dir_inode_operations;
         inode->i_fop = &empty_dir_operations;
 }
 
 bool is_empty_dir_inode(struct inode *inode)
 {
         return (inode->i_fop == &empty_dir_operations) &&
                 (inode->i_op == &empty_dir_inode_operations);
 }