mm/filemap_xip.c - kernel/msm-4.9 - Gitiles

 /*
  *	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/module.h>
 #include <linux/uio.h>
 #include <linux/rmap.h>
 #include <linux/sched.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 struct page *__xip_sparse_page;

 static struct page *xip_sparse_page(void)
 {
 	if (!__xip_sparse_page) {
 		struct page *page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);

 		if (page) {
 			static DEFINE_SPINLOCK(xip_alloc_lock);
 			spin_lock(&xip_alloc_lock);
 			if (!__xip_sparse_page)
 				__xip_sparse_page = page;
 			else
 				__free_page(page);
 			spin_unlock(&xip_alloc_lock);
 		}
 	}
 	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)
 			nr = len;

 		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;

 	page = __xip_sparse_page;
 	if (!page)
 		return;

 	spin_lock(&mapping->i_mmap_lock);
 	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);
 		if (pte) {
 			/* Nuke the page table entry. */
 			flush_cache_page(vma, address, pte_pfn(*pte));
 			pteval = ptep_clear_flush(vma, address, pte);
 			page_remove_rmap(page, vma);
 			dec_mm_counter(mm, file_rss);
 			BUG_ON(pte_dirty(pteval));
 			pte_unmap_unlock(pte, ptl);
 			page_cache_release(page);
 		}
 	}
 	spin_unlock(&mapping->i_mmap_lock);
 }

 /*
  * 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? */

 	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 */
 		error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 1,
 							&xip_mem, &xip_pfn);
 		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 {
 		/* not shared and writable, use xip_sparse_page() */
 		page = xip_sparse_page();
 		if (!page)
 			return VM_FAULT_OOM;

 		page_cache_get(page);
 		vmf->page = page;
 		return 0;
 	}
 }

 static 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 */
 			status = a_ops->get_xip_mem(mapping, index, 1,
 							&xip_mem, &xip_pfn);
 			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 = remove_suid(filp->f_path.dentry);
 	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);
	/*
	* 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/module.h>
	#include <linux/uio.h>
	#include <linux/rmap.h>
	#include <linux/sched.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 struct page *__xip_sparse_page;

	static struct page *xip_sparse_page(void)
	{
	if (!__xip_sparse_page) {
	struct page *page = alloc_page(GFP_HIGHUSER \| __GFP_ZERO);

	if (page) {
	static DEFINE_SPINLOCK(xip_alloc_lock);
	spin_lock(&xip_alloc_lock);
	if (!__xip_sparse_page)
	__xip_sparse_page = page;
	else
	__free_page(page);
	spin_unlock(&xip_alloc_lock);
	}
	}
	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)
	nr = len;

	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;

	page = __xip_sparse_page;
	if (!page)
	return;

	spin_lock(&mapping->i_mmap_lock);
	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);
	if (pte) {
	/* Nuke the page table entry. */
	flush_cache_page(vma, address, pte_pfn(*pte));
	pteval = ptep_clear_flush(vma, address, pte);
	page_remove_rmap(page, vma);
	dec_mm_counter(mm, file_rss);
	BUG_ON(pte_dirty(pteval));
	pte_unmap_unlock(pte, ptl);
	page_cache_release(page);
	}
	}
	spin_unlock(&mapping->i_mmap_lock);
	}

	/*
	* 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? */

	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 */
	error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 1,
	&xip_mem, &xip_pfn);
	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 {
	/* not shared and writable, use xip_sparse_page() */
	page = xip_sparse_page();
	if (!page)
	return VM_FAULT_OOM;

	page_cache_get(page);
	vmf->page = page;
	return 0;
	}
	}

	static 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 */
	status = a_ops->get_xip_mem(mapping, index, 1,
	&xip_mem, &xip_pfn);
	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 = remove_suid(filp->f_path.dentry);
	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);