/*
   *	linux/mm/madvise.c
   *
   * Copyright (C) 1999  Linus Torvalds
   * Copyright (C) 2002  Christoph Hellwig
   */
  
  #include <linux/mman.h>
  #include <linux/pagemap.h>
  #include <linux/syscalls.h>

  #include <linux/mempolicy.h>

  #include <linux/hugetlb.h>

  #include <linux/sched.h>

  
  /*

   * Any behaviour which results in changes to the vma->vm_flags needs to
   * take mmap_sem for writing. Others, which simply traverse vmas, need
   * to only take it for reading.
   */
  static int madvise_need_mmap_write(int behavior)
  {
  	switch (behavior) {
  	case MADV_REMOVE:
  	case MADV_WILLNEED:
  	case MADV_DONTNEED:
  		return 0;
  	default:
  		/* be safe, default to 1. list exceptions explicitly */
  		return 1;
  	}
  }
  
  /*

   * We can potentially split a vm area into separate
   * areas, each area with its own behavior.
   */

  static long madvise_behavior(struct vm_area_struct * vma,
  		     struct vm_area_struct **prev,
  		     unsigned long start, unsigned long end, int behavior)

  {
  	struct mm_struct * mm = vma->vm_mm;
  	int error = 0;

  	pgoff_t pgoff;

  	int new_flags = vma->vm_flags;

  
  	switch (behavior) {

  	case MADV_NORMAL:
  		new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
  		break;

  	case MADV_SEQUENTIAL:

  		new_flags = (new_flags & ~VM_RAND_READ) | VM_SEQ_READ;

  		break;
  	case MADV_RANDOM:

  		new_flags = (new_flags & ~VM_SEQ_READ) | VM_RAND_READ;

  		break;

  	case MADV_DONTFORK:
  		new_flags |= VM_DONTCOPY;
  		break;
  	case MADV_DOFORK:
  		new_flags &= ~VM_DONTCOPY;

  		break;
  	}

  	if (new_flags == vma->vm_flags) {
  		*prev = vma;

  		goto out;

  	}
  
  	pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
  	*prev = vma_merge(mm, *prev, start, end, new_flags, vma->anon_vma,
  				vma->vm_file, pgoff, vma_policy(vma));
  	if (*prev) {
  		vma = *prev;
  		goto success;
  	}
  
  	*prev = vma;

  
  	if (start != vma->vm_start) {
  		error = split_vma(mm, vma, start, 1);
  		if (error)
  			goto out;
  	}
  
  	if (end != vma->vm_end) {
  		error = split_vma(mm, vma, end, 0);
  		if (error)
  			goto out;
  	}

  success:

  	/*
  	 * vm_flags is protected by the mmap_sem held in write mode.
  	 */

  	vma->vm_flags = new_flags;

  
  out:
  	if (error == -ENOMEM)
  		error = -EAGAIN;
  	return error;
  }
  
  /*
   * Schedule all required I/O operations.  Do not wait for completion.
   */
  static long madvise_willneed(struct vm_area_struct * vma,

  			     struct vm_area_struct ** prev,

  			     unsigned long start, unsigned long end)
  {
  	struct file *file = vma->vm_file;

  	if (!file)
  		return -EBADF;

  	if (file->f_mapping->a_ops->get_xip_mem) {

  		/* no bad return value, but ignore advice */
  		return 0;
  	}

  	*prev = vma;

  	start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
  	if (end > vma->vm_end)
  		end = vma->vm_end;
  	end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
  
  	force_page_cache_readahead(file->f_mapping,
  			file, start, max_sane_readahead(end - start));
  	return 0;
  }
  
  /*
   * Application no longer needs these pages.  If the pages are dirty,
   * it's OK to just throw them away.  The app will be more careful about
   * data it wants to keep.  Be sure to free swap resources too.  The

   * zap_page_range call sets things up for shrink_active_list to actually free

   * these pages later if no one else has touched them in the meantime,
   * although we could add these pages to a global reuse list for

   * shrink_active_list to pick up before reclaiming other pages.

   *
   * NB: This interface discards data rather than pushes it out to swap,
   * as some implementations do.  This has performance implications for
   * applications like large transactional databases which want to discard
   * pages in anonymous maps after committing to backing store the data
   * that was kept in them.  There is no reason to write this data out to
   * the swap area if the application is discarding it.
   *
   * An interface that causes the system to free clean pages and flush
   * dirty pages is already available as msync(MS_INVALIDATE).
   */
  static long madvise_dontneed(struct vm_area_struct * vma,

  			     struct vm_area_struct ** prev,

  			     unsigned long start, unsigned long end)
  {

  	*prev = vma;

  	if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))

  		return -EINVAL;
  
  	if (unlikely(vma->vm_flags & VM_NONLINEAR)) {
  		struct zap_details details = {
  			.nonlinear_vma = vma,
  			.last_index = ULONG_MAX,
  		};
  		zap_page_range(vma, start, end - start, &details);
  	} else
  		zap_page_range(vma, start, end - start, NULL);
  	return 0;
  }

  /*
   * Application wants to free up the pages and associated backing store.
   * This is effectively punching a hole into the middle of a file.
   *
   * NOTE: Currently, only shmfs/tmpfs is supported for this operation.
   * Other filesystems return -ENOSYS.
   */
  static long madvise_remove(struct vm_area_struct *vma,

  				struct vm_area_struct **prev,

  				unsigned long start, unsigned long end)
  {
  	struct address_space *mapping;

  	loff_t offset, endoff;
  	int error;

  	*prev = NULL;	/* tell sys_madvise we drop mmap_sem */

  	if (vma->vm_flags & (VM_LOCKED|VM_NONLINEAR|VM_HUGETLB))
  		return -EINVAL;
  
  	if (!vma->vm_file || !vma->vm_file->f_mapping
  		|| !vma->vm_file->f_mapping->host) {
  			return -EINVAL;
  	}

  	if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) != (VM_SHARED|VM_WRITE))
  		return -EACCES;

  	mapping = vma->vm_file->f_mapping;
  
  	offset = (loff_t)(start - vma->vm_start)
  			+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
  	endoff = (loff_t)(end - vma->vm_start - 1)
  			+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);

  
  	/* vmtruncate_range needs to take i_mutex and i_alloc_sem */

  	up_read(&current->mm->mmap_sem);

  	error = vmtruncate_range(mapping->host, offset, endoff);

  	down_read(&current->mm->mmap_sem);

  	return error;

  }

  static long
  madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
  		unsigned long start, unsigned long end, int behavior)

  {

  	long error;

  	switch (behavior) {

  	case MADV_DOFORK:
  		if (vma->vm_flags & VM_IO) {
  			error = -EINVAL;
  			break;
  		}
  	case MADV_DONTFORK:

  	case MADV_NORMAL:
  	case MADV_SEQUENTIAL:
  	case MADV_RANDOM:

  		error = madvise_behavior(vma, prev, start, end, behavior);

  		break;

  	case MADV_REMOVE:

  		error = madvise_remove(vma, prev, start, end);

  		break;

  
  	case MADV_WILLNEED:

  		error = madvise_willneed(vma, prev, start, end);

  		break;
  
  	case MADV_DONTNEED:

  		error = madvise_dontneed(vma, prev, start, end);

  		break;
  
  	default:
  		error = -EINVAL;
  		break;
  	}

  	return error;
  }
  
  /*
   * The madvise(2) system call.
   *
   * Applications can use madvise() to advise the kernel how it should
   * handle paging I/O in this VM area.  The idea is to help the kernel
   * use appropriate read-ahead and caching techniques.  The information
   * provided is advisory only, and can be safely disregarded by the
   * kernel without affecting the correct operation of the application.
   *
   * behavior values:
   *  MADV_NORMAL - the default behavior is to read clusters.  This
   *		results in some read-ahead and read-behind.
   *  MADV_RANDOM - the system should read the minimum amount of data
   *		on any access, since it is unlikely that the appli-
   *		cation will need more than what it asks for.
   *  MADV_SEQUENTIAL - pages in the given range will probably be accessed
   *		once, so they can be aggressively read ahead, and
   *		can be freed soon after they are accessed.
   *  MADV_WILLNEED - the application is notifying the system to read
   *		some pages ahead.
   *  MADV_DONTNEED - the application is finished with the given range,
   *		so the kernel can free resources associated with it.

   *  MADV_REMOVE - the application wants to free up the given range of
   *		pages and associated backing store.

   *
   * return values:
   *  zero    - success
   *  -EINVAL - start + len < 0, start is not page-aligned,
   *		"behavior" is not a valid value, or application
   *		is attempting to release locked or shared pages.
   *  -ENOMEM - addresses in the specified range are not currently
   *		mapped, or are outside the AS of the process.
   *  -EIO    - an I/O error occurred while paging in data.
   *  -EBADF  - map exists, but area maps something that isn't a file.
   *  -EAGAIN - a kernel resource was temporarily unavailable.
   */
  asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior)
  {

  	unsigned long end, tmp;
  	struct vm_area_struct * vma, *prev;

  	int unmapped_error = 0;
  	int error = -EINVAL;

  	int write;

  	size_t len;

  	write = madvise_need_mmap_write(behavior);
  	if (write)

  		down_write(&current->mm->mmap_sem);
  	else
  		down_read(&current->mm->mmap_sem);

  
  	if (start & ~PAGE_MASK)
  		goto out;
  	len = (len_in + ~PAGE_MASK) & PAGE_MASK;
  
  	/* Check to see whether len was rounded up from small -ve to zero */
  	if (len_in && !len)
  		goto out;
  
  	end = start + len;
  	if (end < start)
  		goto out;
  
  	error = 0;
  	if (end == start)
  		goto out;
  
  	/*
  	 * If the interval [start,end) covers some unmapped address
  	 * ranges, just ignore them, but return -ENOMEM at the end.

  	 * - different from the way of handling in mlock etc.

  	 */

  	vma = find_vma_prev(current->mm, start, &prev);

  	if (vma && start > vma->vm_start)
  		prev = vma;

  	for (;;) {
  		/* Still start < end. */
  		error = -ENOMEM;
  		if (!vma)
  			goto out;

  		/* Here start < (end|vma->vm_end). */

  		if (start < vma->vm_start) {
  			unmapped_error = -ENOMEM;
  			start = vma->vm_start;

  			if (start >= end)
  				goto out;

  		}

  		/* Here vma->vm_start <= start < (end|vma->vm_end) */
  		tmp = vma->vm_end;
  		if (end < tmp)
  			tmp = end;

  		/* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
  		error = madvise_vma(vma, &prev, start, tmp, behavior);

  		if (error)
  			goto out;

  		start = tmp;

  		if (prev && start < prev->vm_end)

  			start = prev->vm_end;
  		error = unmapped_error;
  		if (start >= end)
  			goto out;

  		if (prev)
  			vma = prev->vm_next;
  		else	/* madvise_remove dropped mmap_sem */
  			vma = find_vma(current->mm, start);

  	}

  out:

  	if (write)

  		up_write(&current->mm->mmap_sem);
  	else
  		up_read(&current->mm->mmap_sem);

  	return error;
  }