/* NOMMU mmap support for RomFS on MTD devices
   *
   * Copyright © 2007 Red Hat, Inc. All Rights Reserved.
   * Written by David Howells (dhowells@redhat.com)
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version
   * 2 of the License, or (at your option) any later version.
   */
  
  #include <linux/mm.h>
  #include <linux/mtd/super.h>
  #include "internal.h"
  
  /*
   * try to determine where a shared mapping can be made
   * - only supported for NOMMU at the moment (MMU can't doesn't copy private
   *   mappings)
   * - attempts to map through to the underlying MTD device
   */
  static unsigned long romfs_get_unmapped_area(struct file *file,
  					     unsigned long addr,
  					     unsigned long len,
  					     unsigned long pgoff,
  					     unsigned long flags)
  {
  	struct inode *inode = file->f_mapping->host;
  	struct mtd_info *mtd = inode->i_sb->s_mtd;

  	unsigned long isize, offset, maxpages, lpages;

  	int ret;

  
  	if (!mtd)

  		return (unsigned long) -ENOSYS;

  	/* the mapping mustn't extend beyond the EOF */
  	lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;

  	isize = i_size_read(inode);
  	offset = pgoff << PAGE_SHIFT;

  
  	maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
  	if ((pgoff >= maxpages) || (maxpages - pgoff < lpages))

  		return (unsigned long) -EINVAL;

  	if (addr != 0)
  		return (unsigned long) -EINVAL;

  	if (len > mtd->size || pgoff >= (mtd->size >> PAGE_SHIFT))
  		return (unsigned long) -EINVAL;

  	offset += ROMFS_I(inode)->i_dataoffset;
  	if (offset > mtd->size - len)
  		return (unsigned long) -EINVAL;

  	ret = mtd_get_unmapped_area(mtd, len, offset, flags);
  	if (ret == -EOPNOTSUPP)
  		ret = -ENOSYS;
  	return (unsigned long) ret;

  }
  
  /*
   * permit a R/O mapping to be made directly through onto an MTD device if
   * possible
   */
  static int romfs_mmap(struct file *file, struct vm_area_struct *vma)
  {
  	return vma->vm_flags & (VM_SHARED | VM_MAYSHARE) ? 0 : -ENOSYS;
  }
  
  const struct file_operations romfs_ro_fops = {
  	.llseek			= generic_file_llseek,
  	.read			= do_sync_read,
  	.aio_read		= generic_file_aio_read,
  	.splice_read		= generic_file_splice_read,
  	.mmap			= romfs_mmap,
  	.get_unmapped_area	= romfs_get_unmapped_area,
  };