/*
   * tiny-shmem.c: simple shmemfs and tmpfs using ramfs code
   *
   * Matt Mackall <mpm@selenic.com> January, 2004
   * derived from mm/shmem.c and fs/ramfs/inode.c
   *
   * This is intended for small system where the benefits of the full
   * shmem code (swap-backed and resource-limited) are outweighed by
   * their complexity. On systems without swap this code should be
   * effectively equivalent, but much lighter weight.
   */
  
  #include <linux/fs.h>
  #include <linux/init.h>

  #include <linux/vfs.h>
  #include <linux/mount.h>
  #include <linux/file.h>
  #include <linux/mm.h>
  #include <linux/module.h>
  #include <linux/swap.h>
  #include <linux/ramfs.h>
  
  static struct file_system_type tmpfs_fs_type = {
  	.name		= "tmpfs",
  	.get_sb		= ramfs_get_sb,
  	.kill_sb	= kill_litter_super,
  };
  
  static struct vfsmount *shm_mnt;
  
  static int __init init_tmpfs(void)
  {

  	BUG_ON(register_filesystem(&tmpfs_fs_type) != 0);

  	shm_mnt = kern_mount(&tmpfs_fs_type);

  	BUG_ON(IS_ERR(shm_mnt));

  	return 0;
  }
  module_init(init_tmpfs)
  
  /*
   * shmem_file_setup - get an unlinked file living in tmpfs
   *
   * @name: name for dentry (to be seen in /proc/<pid>/maps
   * @size: size to be set for the file
   *
   */
  struct file *shmem_file_setup(char *name, loff_t size, unsigned long flags)
  {
  	int error;
  	struct file *file;
  	struct inode *inode;
  	struct dentry *dentry, *root;
  	struct qstr this;
  
  	if (IS_ERR(shm_mnt))
  		return (void *)shm_mnt;
  
  	error = -ENOMEM;
  	this.name = name;
  	this.len = strlen(name);
  	this.hash = 0; /* will go */
  	root = shm_mnt->mnt_root;
  	dentry = d_alloc(root, &this);
  	if (!dentry)
  		goto put_memory;
  
  	error = -ENFILE;
  	file = get_empty_filp();
  	if (!file)
  		goto put_dentry;
  
  	error = -ENOSPC;
  	inode = ramfs_get_inode(root->d_sb, S_IFREG | S_IRWXUGO, 0);
  	if (!inode)
  		goto close_file;
  
  	d_instantiate(dentry, inode);

  	inode->i_nlink = 0;	/* It is unlinked */

  	file->f_vfsmnt = mntget(shm_mnt);
  	file->f_dentry = dentry;
  	file->f_mapping = inode->i_mapping;
  	file->f_op = &ramfs_file_operations;
  	file->f_mode = FMODE_WRITE | FMODE_READ;

  
  	/* notify everyone as to the change of file size */

  	error = do_truncate(dentry, size, 0, file);

  	if (error < 0)
  		goto close_file;

  	return file;
  
  close_file:
  	put_filp(file);
  put_dentry:
  	dput(dentry);
  put_memory:
  	return ERR_PTR(error);
  }
  
  /*
   * shmem_zero_setup - setup a shared anonymous mapping
   *
   * @vma: the vma to be mmapped is prepared by do_mmap_pgoff
   */
  int shmem_zero_setup(struct vm_area_struct *vma)
  {
  	struct file *file;
  	loff_t size = vma->vm_end - vma->vm_start;
  
  	file = shmem_file_setup("dev/zero", size, vma->vm_flags);
  	if (IS_ERR(file))
  		return PTR_ERR(file);
  
  	if (vma->vm_file)
  		fput(vma->vm_file);
  	vma->vm_file = file;
  	vma->vm_ops = &generic_file_vm_ops;
  	return 0;
  }
  
  int shmem_unuse(swp_entry_t entry, struct page *page)
  {
  	return 0;
  }

  
  int shmem_mmap(struct file *file, struct vm_area_struct *vma)
  {
  	file_accessed(file);
  #ifndef CONFIG_MMU
  	return ramfs_nommu_mmap(file, vma);
  #else
  	return 0;
  #endif
  }
  
  #ifndef CONFIG_MMU
  unsigned long shmem_get_unmapped_area(struct file *file,
  				      unsigned long addr,
  				      unsigned long len,
  				      unsigned long pgoff,
  				      unsigned long flags)
  {
  	return ramfs_nommu_get_unmapped_area(file, addr, len, pgoff, flags);
  }
  #endif