/*
   *   linux/mm/fremap.c
   * 
   * Explicit pagetable population and nonlinear (random) mappings support.
   *
   * started by Ingo Molnar, Copyright (C) 2002, 2003
   */
  
  #include <linux/mm.h>
  #include <linux/swap.h>
  #include <linux/file.h>
  #include <linux/mman.h>
  #include <linux/pagemap.h>
  #include <linux/swapops.h>
  #include <linux/rmap.h>
  #include <linux/module.h>
  #include <linux/syscalls.h>
  
  #include <asm/mmu_context.h>
  #include <asm/cacheflush.h>
  #include <asm/tlbflush.h>

  static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,

  			unsigned long addr, pte_t *ptep)
  {
  	pte_t pte = *ptep;

  	if (pte_present(pte)) {

  		struct page *page;

  		flush_cache_page(vma, addr, pte_pfn(pte));

  		pte = ptep_clear_flush(vma, addr, ptep);

  		page = vm_normal_page(vma, addr, pte);
  		if (page) {
  			if (pte_dirty(pte))
  				set_page_dirty(page);

  			page_remove_rmap(page, vma);

  			page_cache_release(page);

  			update_hiwater_rss(mm);
  			dec_mm_counter(mm, file_rss);

  		}
  	} else {
  		if (!pte_file(pte))
  			free_swap_and_cache(pte_to_swp_entry(pte));

  		pte_clear_not_present_full(mm, addr, ptep, 0);

  	}
  }
  
  /*

   * Install a file pte to a given virtual memory address, release any
   * previously existing mapping.
   */

  static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,

  		unsigned long addr, unsigned long pgoff, pgprot_t prot)
  {
  	int err = -ENOMEM;
  	pte_t *pte;

  	spinlock_t *ptl;

  	pte = get_locked_pte(mm, addr, &ptl);

  	if (!pte)

  		goto out;

  	if (!pte_none(*pte))
  		zap_pte(mm, vma, addr, pte);

  
  	set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));

  	/*
  	 * We don't need to run update_mmu_cache() here because the "file pte"
  	 * being installed by install_file_pte() is not a real pte - it's a
  	 * non-present entry (like a swap entry), noting what file offset should
  	 * be mapped there when there's a fault (in a non-linear vma where
  	 * that's not obvious).
  	 */

  	pte_unmap_unlock(pte, ptl);
  	err = 0;
  out:

  	return err;
  }

  static int populate_range(struct mm_struct *mm, struct vm_area_struct *vma,
  			unsigned long addr, unsigned long size, pgoff_t pgoff)
  {
  	int err;
  
  	do {
  		err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
  		if (err)
  			return err;
  
  		size -= PAGE_SIZE;
  		addr += PAGE_SIZE;
  		pgoff++;
  	} while (size);
  
          return 0;
  
  }

  /***
   * sys_remap_file_pages - remap arbitrary pages of a shared backing store
   *                        file within an existing vma.
   * @start: start of the remapped virtual memory range
   * @size: size of the remapped virtual memory range
   * @prot: new protection bits of the range
   * @pgoff: to be mapped page of the backing store file
   * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
   *
   * this syscall works purely via pagetables, so it's the most efficient
   * way to map the same (large) file into a given virtual window. Unlike
   * mmap()/mremap() it does not create any new vmas. The new mappings are
   * also safe across swapout.
   *
   * NOTE: the 'prot' parameter right now is ignored, and the vma's default
   * protection is used. Arbitrary protections might be implemented in the
   * future.
   */
  asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
  	unsigned long __prot, unsigned long pgoff, unsigned long flags)
  {
  	struct mm_struct *mm = current->mm;
  	struct address_space *mapping;
  	unsigned long end = start + size;
  	struct vm_area_struct *vma;
  	int err = -EINVAL;
  	int has_write_lock = 0;
  
  	if (__prot)
  		return err;
  	/*
  	 * Sanitize the syscall parameters:
  	 */
  	start = start & PAGE_MASK;
  	size = size & PAGE_MASK;
  
  	/* Does the address range wrap, or is the span zero-sized? */
  	if (start + size <= start)
  		return err;
  
  	/* Can we represent this offset inside this architecture's pte's? */
  #if PTE_FILE_MAX_BITS < BITS_PER_LONG
  	if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
  		return err;
  #endif
  
  	/* We need down_write() to change vma->vm_flags. */
  	down_read(&mm->mmap_sem);
   retry:
  	vma = find_vma(mm, start);
  
  	/*
  	 * Make sure the vma is shared, that it supports prefaulting,
  	 * and that the remapped range is valid and fully within
  	 * the single existing vma.  vm_private_data is used as a

  	 * swapout cursor in a VM_NONLINEAR vma.

  	 */

  	if (!vma || !(vma->vm_flags & VM_SHARED))
  		goto out;
  
  	if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR))
  		goto out;

  	if (!vma->vm_flags & VM_CAN_NONLINEAR)

  		goto out;
  
  	if (end <= start || start < vma->vm_start || end > vma->vm_end)
  		goto out;
  
  	/* Must set VM_NONLINEAR before any pages are populated. */
  	if (!(vma->vm_flags & VM_NONLINEAR)) {
  		/* Don't need a nonlinear mapping, exit success */
  		if (pgoff == linear_page_index(vma, start)) {
  			err = 0;
  			goto out;
  		}
  
  		if (!has_write_lock) {
  			up_read(&mm->mmap_sem);
  			down_write(&mm->mmap_sem);
  			has_write_lock = 1;
  			goto retry;
  		}
  		mapping = vma->vm_file->f_mapping;

  		/*
  		 * page_mkclean doesn't work on nonlinear vmas, so if
  		 * dirty pages need to be accounted, emulate with linear
  		 * vmas.
  		 */
  		if (mapping_cap_account_dirty(mapping)) {
  			unsigned long addr;
  
  			flags &= MAP_NONBLOCK;
  			addr = mmap_region(vma->vm_file, start, size,
  					flags, vma->vm_flags, pgoff, 1);
  			if (IS_ERR_VALUE(addr)) {
  				err = addr;
  			} else {
  				BUG_ON(addr != start);
  				err = 0;
  			}
  			goto out;
  		}

  		spin_lock(&mapping->i_mmap_lock);
  		flush_dcache_mmap_lock(mapping);
  		vma->vm_flags |= VM_NONLINEAR;
  		vma_prio_tree_remove(vma, &mapping->i_mmap);
  		vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
  		flush_dcache_mmap_unlock(mapping);
  		spin_unlock(&mapping->i_mmap_lock);
  	}

  	err = populate_range(mm, vma, start, size, pgoff);
  	if (!err && !(flags & MAP_NONBLOCK)) {
  		if (unlikely(has_write_lock)) {
  			downgrade_write(&mm->mmap_sem);
  			has_write_lock = 0;

  		}

  		make_pages_present(start, start+size);
  	}

  	/*
  	 * We can't clear VM_NONLINEAR because we'd have to do
  	 * it after ->populate completes, and that would prevent
  	 * downgrading the lock.  (Locks can't be upgraded).
  	 */

  out:

  	if (likely(!has_write_lock))
  		up_read(&mm->mmap_sem);
  	else
  		up_write(&mm->mmap_sem);
  
  	return err;
  }