/*
   *	linux/mm/filemap_xip.c
   *
   * Copyright (C) 2005 IBM Corporation
   * Author: Carsten Otte <cotte@de.ibm.com>
   *
   * derived from linux/mm/filemap.c - Copyright (C) Linus Torvalds
   *
   */
  
  #include <linux/fs.h>
  #include <linux/pagemap.h>

  #include <linux/export.h>

  #include <linux/uio.h>
  #include <linux/rmap.h>

  #include <linux/mmu_notifier.h>

  #include <linux/sched.h>

  #include <linux/seqlock.h>
  #include <linux/mutex.h>

  #include <linux/gfp.h>

  #include <asm/tlbflush.h>

  #include <asm/io.h>

  
  /*

   * We do use our own empty page to avoid interference with other users
   * of ZERO_PAGE(), such as /dev/zero
   */

  static DEFINE_MUTEX(xip_sparse_mutex);
  static seqcount_t xip_sparse_seq = SEQCNT_ZERO;

  static struct page *__xip_sparse_page;

  /* called under xip_sparse_mutex */

  static struct page *xip_sparse_page(void)
  {
  	if (!__xip_sparse_page) {

  		struct page *page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);

  		if (page)
  			__xip_sparse_page = page;

  	}
  	return __xip_sparse_page;
  }
  
  /*

   * This is a file read routine for execute in place files, and uses

   * the mapping->a_ops->get_xip_mem() function for the actual low-level

   * stuff.
   *
   * Note the struct file* is not used at all.  It may be NULL.
   */

  static ssize_t

  do_xip_mapping_read(struct address_space *mapping,
  		    struct file_ra_state *_ra,
  		    struct file *filp,

  		    char __user *buf,
  		    size_t len,
  		    loff_t *ppos)

  {
  	struct inode *inode = mapping->host;

  	pgoff_t index, end_index;
  	unsigned long offset;

  	loff_t isize, pos;
  	size_t copied = 0, error = 0;

  	BUG_ON(!mapping->a_ops->get_xip_mem);

  	pos = *ppos;
  	index = pos >> PAGE_CACHE_SHIFT;
  	offset = pos & ~PAGE_CACHE_MASK;

  
  	isize = i_size_read(inode);
  	if (!isize)
  		goto out;
  
  	end_index = (isize - 1) >> PAGE_CACHE_SHIFT;

  	do {
  		unsigned long nr, left;
  		void *xip_mem;
  		unsigned long xip_pfn;
  		int zero = 0;

  
  		/* nr is the maximum number of bytes to copy from this page */
  		nr = PAGE_CACHE_SIZE;
  		if (index >= end_index) {
  			if (index > end_index)
  				goto out;
  			nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
  			if (nr <= offset) {
  				goto out;
  			}
  		}
  		nr = nr - offset;

  		if (nr > len - copied)
  			nr = len - copied;

  		error = mapping->a_ops->get_xip_mem(mapping, index, 0,
  							&xip_mem, &xip_pfn);
  		if (unlikely(error)) {
  			if (error == -ENODATA) {

  				/* sparse */

  				zero = 1;
  			} else

  				goto out;

  		}

  
  		/* If users can be writing to this page using arbitrary
  		 * virtual addresses, take care about potential aliasing
  		 * before reading the page on the kernel side.
  		 */
  		if (mapping_writably_mapped(mapping))

  			/* address based flush */ ;

  
  		/*

  		 * Ok, we have the mem, so now we can copy it to user space...

  		 *
  		 * The actor routine returns how many bytes were actually used..
  		 * NOTE! This may not be the same as how much of a user buffer
  		 * we filled up (we may be padding etc), so we can only update
  		 * "pos" here (the actor routine has to update the user buffer
  		 * pointers and the remaining count).
  		 */

  		if (!zero)
  			left = __copy_to_user(buf+copied, xip_mem+offset, nr);
  		else
  			left = __clear_user(buf + copied, nr);

  		if (left) {
  			error = -EFAULT;
  			goto out;
  		}

  		copied += (nr - left);
  		offset += (nr - left);
  		index += offset >> PAGE_CACHE_SHIFT;
  		offset &= ~PAGE_CACHE_MASK;
  	} while (copied < len);

  
  out:

  	*ppos = pos + copied;

  	if (filp)
  		file_accessed(filp);

  
  	return (copied ? copied : error);

  }

  ssize_t

  xip_file_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos)

  {

  	if (!access_ok(VERIFY_WRITE, buf, len))
  		return -EFAULT;

  	return do_xip_mapping_read(filp->f_mapping, &filp->f_ra, filp,
  			    buf, len, ppos);

  }

  EXPORT_SYMBOL_GPL(xip_file_read);

  /*
   * __xip_unmap is invoked from xip_unmap and
   * xip_write
   *
   * This function walks all vmas of the address_space and unmaps the

   * __xip_sparse_page when found at pgoff.

   */
  static void
  __xip_unmap (struct address_space * mapping,
  		     unsigned long pgoff)
  {
  	struct vm_area_struct *vma;
  	struct mm_struct *mm;
  	struct prio_tree_iter iter;
  	unsigned long address;
  	pte_t *pte;
  	pte_t pteval;

  	spinlock_t *ptl;

  	struct page *page;

  	unsigned count;
  	int locked = 0;
  
  	count = read_seqcount_begin(&xip_sparse_seq);

  	page = __xip_sparse_page;
  	if (!page)
  		return;

  retry:

  	mutex_lock(&mapping->i_mmap_mutex);

  	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
  		mm = vma->vm_mm;
  		address = vma->vm_start +
  			((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
  		BUG_ON(address < vma->vm_start || address >= vma->vm_end);

  		pte = page_check_address(page, mm, address, &ptl, 1);

  		if (pte) {

  			/* Nuke the page table entry. */

  			flush_cache_page(vma, address, pte_pfn(*pte));

  			pteval = ptep_clear_flush_notify(vma, address, pte);

  			page_remove_rmap(page);

  			dec_mm_counter(mm, MM_FILEPAGES);

  			BUG_ON(pte_dirty(pteval));

  			pte_unmap_unlock(pte, ptl);

  			page_cache_release(page);

  		}
  	}

  	mutex_unlock(&mapping->i_mmap_mutex);

  
  	if (locked) {
  		mutex_unlock(&xip_sparse_mutex);
  	} else if (read_seqcount_retry(&xip_sparse_seq, count)) {
  		mutex_lock(&xip_sparse_mutex);
  		locked = 1;
  		goto retry;
  	}

  }
  
  /*

   * xip_fault() is invoked via the vma operations vector for a

   * mapped memory region to read in file data during a page fault.
   *

   * This function is derived from filemap_fault, but used for execute in place

   */

  static int xip_file_fault(struct vm_area_struct *vma, struct vm_fault *vmf)

  {

  	struct file *file = vma->vm_file;

  	struct address_space *mapping = file->f_mapping;
  	struct inode *inode = mapping->host;

  	pgoff_t size;

  	void *xip_mem;
  	unsigned long xip_pfn;
  	struct page *page;
  	int error;

  	/* XXX: are VM_FAULT_ codes OK? */

  again:

  	size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

  	if (vmf->pgoff >= size)
  		return VM_FAULT_SIGBUS;

  	error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 0,
  						&xip_mem, &xip_pfn);
  	if (likely(!error))
  		goto found;
  	if (error != -ENODATA)

  		return VM_FAULT_OOM;

  
  	/* sparse block */

  	if ((vma->vm_flags & (VM_WRITE | VM_MAYWRITE)) &&
  	    (vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) &&

  	    (!(mapping->host->i_sb->s_flags & MS_RDONLY))) {

  		int err;

  		/* maybe shared writable, allocate new block */

  		mutex_lock(&xip_sparse_mutex);

  		error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 1,
  							&xip_mem, &xip_pfn);

  		mutex_unlock(&xip_sparse_mutex);

  		if (error)

  			return VM_FAULT_SIGBUS;

  		/* unmap sparse mappings at pgoff from all other vmas */

  		__xip_unmap(mapping, vmf->pgoff);

  
  found:
  		err = vm_insert_mixed(vma, (unsigned long)vmf->virtual_address,
  							xip_pfn);
  		if (err == -ENOMEM)
  			return VM_FAULT_OOM;
  		BUG_ON(err);
  		return VM_FAULT_NOPAGE;

  	} else {

  		int err, ret = VM_FAULT_OOM;
  
  		mutex_lock(&xip_sparse_mutex);
  		write_seqcount_begin(&xip_sparse_seq);
  		error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 0,
  							&xip_mem, &xip_pfn);
  		if (unlikely(!error)) {
  			write_seqcount_end(&xip_sparse_seq);
  			mutex_unlock(&xip_sparse_mutex);
  			goto again;
  		}
  		if (error != -ENODATA)
  			goto out;

  		/* not shared and writable, use xip_sparse_page() */
  		page = xip_sparse_page();

  		if (!page)

  			goto out;
  		err = vm_insert_page(vma, (unsigned long)vmf->virtual_address,
  							page);
  		if (err == -ENOMEM)
  			goto out;
  
  		ret = VM_FAULT_NOPAGE;
  out:
  		write_seqcount_end(&xip_sparse_seq);
  		mutex_unlock(&xip_sparse_mutex);

  		return ret;

  	}

  }

  static const struct vm_operations_struct xip_file_vm_ops = {

  	.fault	= xip_file_fault,

  };
  
  int xip_file_mmap(struct file * file, struct vm_area_struct * vma)
  {

  	BUG_ON(!file->f_mapping->a_ops->get_xip_mem);

  
  	file_accessed(file);
  	vma->vm_ops = &xip_file_vm_ops;

  	vma->vm_flags |= VM_CAN_NONLINEAR | VM_MIXEDMAP;

  	return 0;
  }
  EXPORT_SYMBOL_GPL(xip_file_mmap);
  
  static ssize_t

  __xip_file_write(struct file *filp, const char __user *buf,
  		  size_t count, loff_t pos, loff_t *ppos)

  {

  	struct address_space * mapping = filp->f_mapping;

  	const struct address_space_operations *a_ops = mapping->a_ops;

  	struct inode 	*inode = mapping->host;
  	long		status = 0;

  	size_t		bytes;

  	ssize_t		written = 0;

  	BUG_ON(!mapping->a_ops->get_xip_mem);

  	do {
  		unsigned long index;
  		unsigned long offset;
  		size_t copied;

  		void *xip_mem;
  		unsigned long xip_pfn;

  
  		offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
  		index = pos >> PAGE_CACHE_SHIFT;
  		bytes = PAGE_CACHE_SIZE - offset;
  		if (bytes > count)
  			bytes = count;

  		status = a_ops->get_xip_mem(mapping, index, 0,
  						&xip_mem, &xip_pfn);
  		if (status == -ENODATA) {

  			/* we allocate a new page unmap it */

  			mutex_lock(&xip_sparse_mutex);

  			status = a_ops->get_xip_mem(mapping, index, 1,
  							&xip_mem, &xip_pfn);

  			mutex_unlock(&xip_sparse_mutex);

  			if (!status)

  				/* unmap page at pgoff from all other vmas */
  				__xip_unmap(mapping, index);

  		}

  		if (status)

  			break;

  		copied = bytes -

  			__copy_from_user_nocache(xip_mem + offset, buf, bytes);

  		if (likely(copied > 0)) {
  			status = copied;
  
  			if (status >= 0) {
  				written += status;
  				count -= status;
  				pos += status;
  				buf += status;

  			}
  		}
  		if (unlikely(copied != bytes))
  			if (status >= 0)
  				status = -EFAULT;
  		if (status < 0)
  			break;
  	} while (count);
  	*ppos = pos;
  	/*
  	 * No need to use i_size_read() here, the i_size

  	 * cannot change under us because we hold i_mutex.

  	 */
  	if (pos > inode->i_size) {
  		i_size_write(inode, pos);
  		mark_inode_dirty(inode);
  	}
  
  	return written ? written : status;
  }

  ssize_t
  xip_file_write(struct file *filp, const char __user *buf, size_t len,
  	       loff_t *ppos)

  {

  	struct address_space *mapping = filp->f_mapping;
  	struct inode *inode = mapping->host;
  	size_t count;
  	loff_t pos;
  	ssize_t ret;

  	mutex_lock(&inode->i_mutex);

  	if (!access_ok(VERIFY_READ, buf, len)) {
  		ret=-EFAULT;
  		goto out_up;

  	}

  	pos = *ppos;

  	count = len;

  
  	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);

  	/* We can write back this queue in page reclaim */
  	current->backing_dev_info = mapping->backing_dev_info;

  	ret = generic_write_checks(filp, &pos, &count, S_ISBLK(inode->i_mode));
  	if (ret)
  		goto out_backing;

  	if (count == 0)

  		goto out_backing;

  	ret = file_remove_suid(filp);

  	if (ret)
  		goto out_backing;

  	file_update_time(filp);

  	ret = __xip_file_write (filp, buf, count, pos, ppos);

   out_backing:
  	current->backing_dev_info = NULL;
   out_up:

  	mutex_unlock(&inode->i_mutex);

  	return ret;
  }

  EXPORT_SYMBOL_GPL(xip_file_write);

  
  /*
   * truncate a page used for execute in place

   * functionality is analog to block_truncate_page but does use get_xip_mem

   * to get the page instead of page cache
   */
  int
  xip_truncate_page(struct address_space *mapping, loff_t from)
  {
  	pgoff_t index = from >> PAGE_CACHE_SHIFT;
  	unsigned offset = from & (PAGE_CACHE_SIZE-1);
  	unsigned blocksize;
  	unsigned length;

  	void *xip_mem;
  	unsigned long xip_pfn;
  	int err;

  	BUG_ON(!mapping->a_ops->get_xip_mem);

  
  	blocksize = 1 << mapping->host->i_blkbits;
  	length = offset & (blocksize - 1);
  
  	/* Block boundary? Nothing to do */
  	if (!length)
  		return 0;
  
  	length = blocksize - length;

  	err = mapping->a_ops->get_xip_mem(mapping, index, 0,
  						&xip_mem, &xip_pfn);
  	if (unlikely(err)) {
  		if (err == -ENODATA)

  			/* Hole? No need to truncate */
  			return 0;

  		else

  			return err;

  	}

  	memset(xip_mem + offset, 0, length);

  	return 0;

  }
  EXPORT_SYMBOL_GPL(xip_truncate_page);