text: /*
   * Resizable simple ram filesystem for Linux.
   *
   * Copyright (C) 2000 Linus Torvalds.
   *               2000 Transmeta Corp.
   *
   * Usage limits added by David Gibson, Linuxcare Australia.
   * This file is released under the GPL.
   */
  
  /*
   * NOTE! This filesystem is probably most useful
   * not as a real filesystem, but as an example of
   * how virtual filesystems can be written.
   *
   * It doesn't get much simpler than this. Consider
   * that this file implements the full semantics of
   * a POSIX-compliant read-write filesystem.
   *
   * Note in particular how the filesystem does not
   * need to implement any data structures of its own
   * to keep track of the virtual data: using the VFS
   * caches is sufficient.
   */
  
  #include <linux/module.h>
  #include <linux/fs.h>
  #include <linux/pagemap.h>
  #include <linux/init.h>
  #include <linux/string.h>
  #include <linux/locks.h>
  
  #include <asm/uaccess.h>
  
  /* some random number */
  #define RAMFS_MAGIC	0x858458f6
  
  static struct super_operations ramfs_ops;
  static struct address_space_operations ramfs_aops;
  static struct file_operations ramfs_file_operations;
  static struct inode_operations ramfs_dir_inode_operations;
  
  static int ramfs_statfs(struct super_block *sb, struct statfs *buf)
  {
  	buf->f_type = RAMFS_MAGIC;
  	buf->f_bsize = PAGE_CACHE_SIZE;
  	buf->f_namelen = 255;
  	return 0;
  }
  
  /*
   * Lookup the data. This is trivial - if the dentry didn't already
   * exist, we know it is negative.
   */
  static struct dentry * ramfs_lookup(struct inode *dir, struct dentry *dentry)
  {
  	d_add(dentry, NULL);
  	return NULL;
  }
  
  /*
   * Read a page. Again trivial. If it didn't already exist
   * in the page cache, it is zero-filled.
   */
  static int ramfs_readpage(struct file *file, struct page * page)
  {
  	if (!Page_Uptodate(page)) {
  		memset(kmap(page), 0, PAGE_CACHE_SIZE);
  		kunmap(page);
  		flush_dcache_page(page);
  		SetPageUptodate(page);
  	}
  	UnlockPage(page);
  	return 0;
  }
  
  static int ramfs_prepare_write(struct file *file, struct page *page, unsigned offset, unsigned to)
  {
  	void *addr = kmap(page);
  	if (!Page_Uptodate(page)) {
  		memset(addr, 0, PAGE_CACHE_SIZE);
  		flush_dcache_page(page);
  		SetPageUptodate(page);
  	}
  	SetPageDirty(page);
  	return 0;
  }
  
  static int ramfs_commit_write(struct file *file, struct page *page, unsigned offset, unsigned to)
  {
  	struct inode *inode = page->mapping->host;
  	loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
  
  	kunmap(page);
  	if (pos > inode->i_size)
  		inode->i_size = pos;
  	return 0;
  }
  
  struct inode *ramfs_get_inode(struct super_block *sb, int mode, int dev)
  {
  	struct inode * inode = new_inode(sb);
  
  	if (inode) {
  		inode->i_mode = mode;
  		inode->i_uid = current->fsuid;
  		inode->i_gid = current->fsgid;
  		inode->i_blksize = PAGE_CACHE_SIZE;
  		inode->i_blocks = 0;
  		inode->i_rdev = NODEV;
  		inode->i_mapping->a_ops = &ramfs_aops;
  		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
  		switch (mode & S_IFMT) {
  		default:
  			init_special_inode(inode, mode, dev);
  			break;
  		case S_IFREG:
  			inode->i_fop = &ramfs_file_operations;
  			break;
  		case S_IFDIR:
  			inode->i_op = &ramfs_dir_inode_operations;
  			inode->i_fop = &dcache_dir_ops;
  			break;
  		case S_IFLNK:
  			inode->i_op = &page_symlink_inode_operations;
  			break;
  		}
  	}
  	return inode;
  }
  
  /*
   * File creation. Allocate an inode, and we're done..
   */
  static int ramfs_mknod(struct inode *dir, struct dentry *dentry, int mode, int dev)
  {
  	struct inode * inode = ramfs_get_inode(dir->i_sb, mode, dev);
  	int error = -ENOSPC;
  
  	if (inode) {
  		d_instantiate(dentry, inode);
  		dget(dentry);		/* Extra count - pin the dentry in core */
  		error = 0;
  	}
  	return error;
  }
  
  static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, int mode)
  {
  	return ramfs_mknod(dir, dentry, mode | S_IFDIR, 0);
  }
  
  static int ramfs_create(struct inode *dir, struct dentry *dentry, int mode)
  {
  	return ramfs_mknod(dir, dentry, mode | S_IFREG, 0);
  }
  
  /*
   * Link a file..
   */
  static int ramfs_link(struct dentry *old_dentry, struct inode * dir, struct dentry * dentry)
  {
  	struct inode *inode = old_dentry->d_inode;
  
  	if (S_ISDIR(inode->i_mode))
  		return -EPERM;
  
  	inode->i_nlink++;
  	atomic_inc(&inode->i_count);	/* New dentry reference */
  	dget(dentry);		/* Extra pinning count for the created dentry */
  	d_instantiate(dentry, inode);
  	return 0;
  }
  
  static inline int ramfs_positive(struct dentry *dentry)
  {
  	return dentry->d_inode && !d_unhashed(dentry);
  }
  
  /*
   * Check that a directory is empty (this works
   * for regular files too, they'll just always be
   * considered empty..).
   *
   * Note that an empty directory can still have
   * children, they just all have to be negative..
   */
  static int ramfs_empty(struct dentry *dentry)
  {
  	struct list_head *list;
  
  	spin_lock(&dcache_lock);
  	list = dentry->d_subdirs.next;
  
  	while (list != &dentry->d_subdirs) {
  		struct dentry *de = list_entry(list, struct dentry, d_child);
  
  		if (ramfs_positive(de)) {
  			spin_unlock(&dcache_lock);
  			return 0;
  		}
  		list = list->next;
  	}
  	spin_unlock(&dcache_lock);
  	return 1;
  }
  
  /*
   * This works for both directories and regular files.
   * (non-directories will always have empty subdirs)
   */
  static int ramfs_unlink(struct inode * dir, struct dentry *dentry)
  {
  	int retval = -ENOTEMPTY;
  
  	if (ramfs_empty(dentry)) {
  		struct inode *inode = dentry->d_inode;
  
  		inode->i_nlink--;
  		dput(dentry);			/* Undo the count from "create" - this does all the work */
  		retval = 0;
  	}
  	return retval;
  }
  
  #define ramfs_rmdir ramfs_unlink
  
  /*
   * The VFS layer already does all the dentry stuff for rename,
   * we just have to decrement the usage count for the target if
   * it exists so that the VFS layer correctly free's it when it
   * gets overwritten.
   */
  static int ramfs_rename(struct inode * old_dir, struct dentry *old_dentry, struct inode * new_dir,struct dentry *new_dentry)
  {
  	int error = -ENOTEMPTY;
  
  	if (ramfs_empty(new_dentry)) {
  		struct inode *inode = new_dentry->d_inode;
  		if (inode) {
  			inode->i_nlink--;
  			dput(new_dentry);
  		}
  		error = 0;
  	}
  	return error;
  }
  
  static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname)
  {
  	int error;
  
  	error = ramfs_mknod(dir, dentry, S_IFLNK | S_IRWXUGO, 0);
  	if (!error) {
  		int l = strlen(symname)+1;
  		struct inode *inode = dentry->d_inode;
  		error = block_symlink(inode, symname, l);
  	}
  	return error;
  }
  
  static int ramfs_sync_file(struct file * file, struct dentry *dentry, int datasync)
  {
  	return 0;
  }
  
  static struct address_space_operations ramfs_aops = {
  	readpage:	ramfs_readpage,
  	writepage:	fail_writepage,
  	prepare_write:	ramfs_prepare_write,
  	commit_write:	ramfs_commit_write
  };
  
  static struct file_operations ramfs_file_operations = {
  	read:		generic_file_read,
  	write:		generic_file_write,
  	mmap:		generic_file_mmap,
  	fsync:		ramfs_sync_file,
  };
  
  static struct inode_operations ramfs_dir_inode_operations = {
  	create:		ramfs_create,
  	lookup:		ramfs_lookup,
  	link:		ramfs_link,
  	unlink:		ramfs_unlink,
  	symlink:	ramfs_symlink,
  	mkdir:		ramfs_mkdir,
  	rmdir:		ramfs_rmdir,
  	mknod:		ramfs_mknod,
  	rename:		ramfs_rename,
  };
  
  static struct super_operations ramfs_ops = {
  	statfs:		ramfs_statfs,
  	put_inode:	force_delete,
  };
  
  static struct super_block *ramfs_read_super(struct super_block * sb, void * data, int silent)
  {
  	struct inode * inode;
  	struct dentry * root;
  
  	sb->s_blocksize = PAGE_CACHE_SIZE;
  	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
  	sb->s_magic = RAMFS_MAGIC;
  	sb->s_op = &ramfs_ops;
  	inode = ramfs_get_inode(sb, S_IFDIR | 0755, 0);
  	if (!inode)
  		return NULL;
  
  	root = d_alloc_root(inode);
  	if (!root) {
  		iput(inode);
  		return NULL;
  	}
  	sb->s_root = root;
  	return sb;
  }
  
  static DECLARE_FSTYPE(ramfs_fs_type, "ramfs", ramfs_read_super, FS_LITTER);
  static DECLARE_FSTYPE(rootfs_fs_type, "rootfs", ramfs_read_super, FS_NOMOUNT|FS_LITTER);
  
  static int __init init_ramfs_fs(void)
  {
  	return register_filesystem(&ramfs_fs_type);
  }
  
  static void __exit exit_ramfs_fs(void)
  {
  	unregister_filesystem(&ramfs_fs_type);
  }
  
  module_init(init_ramfs_fs)
  module_exit(exit_ramfs_fs)
  
  int __init init_rootfs(void)
  {
  	return register_filesystem(&rootfs_fs_type);
  }
  
  MODULE_LICENSE("GPL");
  
  