// SPDX-License-Identifier: GPL-2.0

  /*
   *	linux/mm/msync.c
   *
   * Copyright (C) 1994-1999  Linus Torvalds
   */
  
  /*
   * The msync() system call.
   */

  #include <linux/fs.h>

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

  #include <linux/file.h>

  #include <linux/syscalls.h>

  #include <linux/sched.h>

  /*
   * MS_SYNC syncs the entire file - including mappings.
   *

   * MS_ASYNC does not start I/O (it used to, up to 2.5.67).
   * Nor does it marks the relevant pages dirty (it used to up to 2.6.17).
   * Now it doesn't do anything, since dirty pages are properly tracked.
   *
   * The application may now run fsync() to

   * write out the dirty pages and wait on the writeout and check the result.
   * Or the application may run fadvise(FADV_DONTNEED) against the fd to start
   * async writeout immediately.

   * So by _not_ starting I/O in MS_ASYNC we provide complete flexibility to

   * applications.
   */

  SYSCALL_DEFINE3(msync, unsigned long, start, size_t, len, int, flags)

  {
  	unsigned long end;

  	struct mm_struct *mm = current->mm;

  	struct vm_area_struct *vma;

  	int unmapped_error = 0;
  	int error = -EINVAL;

  	start = untagged_addr(start);

  	if (flags & ~(MS_ASYNC | MS_INVALIDATE | MS_SYNC))
  		goto out;

  	if (offset_in_page(start))

  		goto out;
  	if ((flags & MS_ASYNC) && (flags & MS_SYNC))
  		goto out;
  	error = -ENOMEM;
  	len = (len + ~PAGE_MASK) & PAGE_MASK;
  	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.
  	 */

  	mmap_read_lock(mm);

  	vma = find_vma(mm, start);
  	for (;;) {

  		struct file *file;

  		loff_t fstart, fend;

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

  		/* Here start < vma->vm_end. */
  		if (start < vma->vm_start) {

  			start = vma->vm_start;

  			if (start >= end)
  				goto out_unlock;
  			unmapped_error = -ENOMEM;

  		}
  		/* Here vma->vm_start <= start < vma->vm_end. */

  		if ((flags & MS_INVALIDATE) &&
  				(vma->vm_flags & VM_LOCKED)) {
  			error = -EBUSY;
  			goto out_unlock;

  		}

  		file = vma->vm_file;

  		fstart = (start - vma->vm_start) +
  			 ((loff_t)vma->vm_pgoff << PAGE_SHIFT);

  		fend = fstart + (min(end, vma->vm_end) - start) - 1;

  		start = vma->vm_end;

  		if ((flags & MS_SYNC) && file &&

  				(vma->vm_flags & VM_SHARED)) {

  			get_file(file);

  			mmap_read_unlock(mm);

  			error = vfs_fsync_range(file, fstart, fend, 1);

  			fput(file);

  			if (error || start >= end)
  				goto out;

  			mmap_read_lock(mm);

  			vma = find_vma(mm, start);

  		} else {

  			if (start >= end) {
  				error = 0;
  				goto out_unlock;
  			}

  			vma = vma->vm_next;
  		}

  	}

  out_unlock:

  	mmap_read_unlock(mm);

  out:

  	return error ? : unmapped_error;

  }