/* file-nommu.c: no-MMU version of ramfs
   *
   * Copyright (C) 2005 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/module.h>
  #include <linux/fs.h>

  #include <linux/mm.h>

  #include <linux/pagemap.h>
  #include <linux/highmem.h>
  #include <linux/init.h>
  #include <linux/string.h>

  #include <linux/backing-dev.h>
  #include <linux/ramfs.h>

  #include <linux/pagevec.h>
  #include <linux/mman.h>

  #include <linux/sched.h>

  #include <linux/slab.h>

  
  #include <asm/uaccess.h>
  #include "internal.h"
  
  static int ramfs_nommu_setattr(struct dentry *, struct iattr *);

  static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
  						   unsigned long addr,
  						   unsigned long len,
  						   unsigned long pgoff,
  						   unsigned long flags);
  static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma);

  static unsigned ramfs_mmap_capabilities(struct file *file)
  {
  	return NOMMU_MAP_DIRECT | NOMMU_MAP_COPY | NOMMU_MAP_READ |
  		NOMMU_MAP_WRITE | NOMMU_MAP_EXEC;
  }

  const struct file_operations ramfs_file_operations = {

  	.mmap_capabilities	= ramfs_mmap_capabilities,

  	.mmap			= ramfs_nommu_mmap,
  	.get_unmapped_area	= ramfs_nommu_get_unmapped_area,

  	.read_iter		= generic_file_read_iter,

  	.write_iter		= generic_file_write_iter,

  	.fsync			= noop_fsync,

  	.splice_read		= generic_file_splice_read,

  	.splice_write		= iter_file_splice_write,

  	.llseek			= generic_file_llseek,
  };

  const struct inode_operations ramfs_file_inode_operations = {

  	.setattr		= ramfs_nommu_setattr,
  	.getattr		= simple_getattr,
  };
  
  /*****************************************************************************/
  /*
   * add a contiguous set of pages into a ramfs inode when it's truncated from
   * size 0 on the assumption that it's going to be used for an mmap of shared
   * memory
   */

  int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)

  {

  	unsigned long npages, xpages, loop;

  	struct page *pages;
  	unsigned order;
  	void *data;
  	int ret;

  	gfp_t gfp = mapping_gfp_mask(inode->i_mapping);

  
  	/* make various checks */
  	order = get_order(newsize);
  	if (unlikely(order >= MAX_ORDER))

  		return -EFBIG;

  	ret = inode_newsize_ok(inode, newsize);
  	if (ret)
  		return ret;

  
  	i_size_write(inode, newsize);
  
  	/* allocate enough contiguous pages to be able to satisfy the
  	 * request */

  	pages = alloc_pages(gfp, order);

  	if (!pages)
  		return -ENOMEM;
  
  	/* split the high-order page into an array of single pages */
  	xpages = 1UL << order;
  	npages = (newsize + PAGE_SIZE - 1) >> PAGE_SHIFT;

  	split_page(pages, order);

  
  	/* trim off any pages we don't actually require */
  	for (loop = npages; loop < xpages; loop++)
  		__free_page(pages + loop);
  
  	/* clear the memory we allocated */
  	newsize = PAGE_SIZE * npages;
  	data = page_address(pages);
  	memset(data, 0, newsize);
  
  	/* attach all the pages to the inode's address space */

  	for (loop = 0; loop < npages; loop++) {
  		struct page *page = pages + loop;

  		ret = add_to_page_cache_lru(page, inode->i_mapping, loop,

  					gfp);

  		if (ret < 0)
  			goto add_error;

  		/* prevent the page from being discarded on memory pressure */
  		SetPageDirty(page);

  		SetPageUptodate(page);

  		unlock_page(page);

  		put_page(page);

  	}

  	return 0;

  add_error:

  	while (loop < npages)
  		__free_page(pages + loop++);

  	return ret;
  }
  
  /*****************************************************************************/
  /*

   *
   */
  static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size)
  {
  	int ret;
  
  	/* assume a truncate from zero size is going to be for the purposes of
  	 * shared mmap */
  	if (size == 0) {
  		if (unlikely(newsize >> 32))
  			return -EFBIG;
  
  		return ramfs_nommu_expand_for_mapping(inode, newsize);
  	}
  
  	/* check that a decrease in size doesn't cut off any shared mappings */
  	if (newsize < size) {

  		ret = nommu_shrink_inode_mappings(inode, size, newsize);

  		if (ret < 0)
  			return ret;
  	}

  	truncate_setsize(inode, newsize);
  	return 0;

  }
  
  /*****************************************************************************/
  /*
   * handle a change of attributes
   * - we're specifically interested in a change of size
   */
  static int ramfs_nommu_setattr(struct dentry *dentry, struct iattr *ia)
  {

  	struct inode *inode = d_inode(dentry);

  	unsigned int old_ia_valid = ia->ia_valid;
  	int ret = 0;

  	/* POSIX UID/GID verification for setting inode attributes */

  	ret = setattr_prepare(dentry, ia);

  	if (ret)
  		return ret;

  	/* pick out size-changing events */
  	if (ia->ia_valid & ATTR_SIZE) {

  		loff_t size = inode->i_size;

  		if (ia->ia_size != size) {
  			ret = ramfs_nommu_resize(inode, ia->ia_size, size);
  			if (ret < 0 || ia->ia_valid == ATTR_SIZE)
  				goto out;
  		} else {
  			/* we skipped the truncate but must still update
  			 * timestamps
  			 */
  			ia->ia_valid |= ATTR_MTIME|ATTR_CTIME;
  		}
  	}

  	setattr_copy(inode, ia);

   out:
  	ia->ia_valid = old_ia_valid;
  	return ret;
  }
  
  /*****************************************************************************/
  /*
   * try to determine where a shared mapping can be made
   * - we require that:
   *   - the pages to be mapped must exist
   *   - the pages be physically contiguous in sequence
   */

  static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,

  					    unsigned long addr, unsigned long len,
  					    unsigned long pgoff, unsigned long flags)
  {
  	unsigned long maxpages, lpages, nr, loop, ret;

  	struct inode *inode = file_inode(file);

  	struct page **pages = NULL, **ptr, *page;
  	loff_t isize;

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

  	ret = -ENOSYS;

  	maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
  	if (pgoff >= maxpages)
  		goto out;
  
  	if (maxpages - pgoff < lpages)
  		goto out;
  
  	/* gang-find the pages */

  	pages = kcalloc(lpages, sizeof(struct page *), GFP_KERNEL);

  	if (!pages)

  		goto out_free;

  
  	nr = find_get_pages(inode->i_mapping, pgoff, lpages, pages);
  	if (nr != lpages)

  		goto out_free_pages; /* leave if some pages were missing */

  
  	/* check the pages for physical adjacency */
  	ptr = pages;
  	page = *ptr++;
  	page++;
  	for (loop = lpages; loop > 1; loop--)
  		if (*ptr++ != page++)

  			goto out_free_pages;

  
  	/* okay - all conditions fulfilled */
  	ret = (unsigned long) page_address(pages[0]);

  out_free_pages:
  	ptr = pages;
  	for (loop = nr; loop > 0; loop--)
  		put_page(*ptr++);
  out_free:
  	kfree(pages);
  out:

  	return ret;
  }
  
  /*****************************************************************************/
  /*

   * set up a mapping for shared memory segments

   */

  static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)

  {

  	if (!(vma->vm_flags & (VM_SHARED | VM_MAYSHARE)))

  		return -ENOSYS;
  
  	file_accessed(file);
  	vma->vm_ops = &generic_file_vm_ops;
  	return 0;

  }