fs/remap_range.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 #include <linux/slab.h>
 #include <linux/stat.h>
 #include <linux/sched/xacct.h>
 #include <linux/fcntl.h>
 #include <linux/file.h>
 #include <linux/uio.h>
 #include <linux/fsnotify.h>
 #include <linux/security.h>
 #include <linux/export.h>
 #include <linux/syscalls.h>
 #include <linux/pagemap.h>
 #include <linux/splice.h>
 #include <linux/compat.h>
 #include <linux/mount.h>
 #include <linux/fs.h>
 #include "internal.h"

 #include <linux/uaccess.h>
 #include <asm/unistd.h>

 /*
  * Performs necessary checks before doing a clone.
  *
  * Can adjust amount of bytes to clone via @req_count argument.
  * Returns appropriate error code that caller should return or
  * zero in case the clone should be allowed.
  */
 static int generic_remap_checks(struct file *file_in, loff_t pos_in,
 				struct file *file_out, loff_t pos_out,
 				loff_t *req_count, unsigned int remap_flags)
 {
 	struct inode *inode_in = file_in->f_mapping->host;
 	struct inode *inode_out = file_out->f_mapping->host;
 	uint64_t count = *req_count;
 	uint64_t bcount;
 	loff_t size_in, size_out;
 	loff_t bs = inode_out->i_sb->s_blocksize;
 	int ret;

 	/* The start of both ranges must be aligned to an fs block. */
 	if (!IS_ALIGNED(pos_in, bs) || !IS_ALIGNED(pos_out, bs))
 		return -EINVAL;

 	/* Ensure offsets don't wrap. */
 	if (pos_in + count < pos_in || pos_out + count < pos_out)
 		return -EINVAL;

 	size_in = i_size_read(inode_in);
 	size_out = i_size_read(inode_out);

 	/* Dedupe requires both ranges to be within EOF. */
 	if ((remap_flags & REMAP_FILE_DEDUP) &&
 	    (pos_in >= size_in || pos_in + count > size_in ||
 	     pos_out >= size_out || pos_out + count > size_out))
 		return -EINVAL;

 	/* Ensure the infile range is within the infile. */
 	if (pos_in >= size_in)
 		return -EINVAL;
 	count = min(count, size_in - (uint64_t)pos_in);

 	ret = generic_write_check_limits(file_out, pos_out, &count);
 	if (ret)
 		return ret;

 	/*
 	 * If the user wanted us to link to the infile's EOF, round up to the
 	 * next block boundary for this check.
 	 *
 	 * Otherwise, make sure the count is also block-aligned, having
 	 * already confirmed the starting offsets' block alignment.
 	 */
 	if (pos_in + count == size_in &&
 	    (!(remap_flags & REMAP_FILE_DEDUP) || pos_out + count == size_out)) {
 		bcount = ALIGN(size_in, bs) - pos_in;
 	} else {
 		if (!IS_ALIGNED(count, bs))
 			count = ALIGN_DOWN(count, bs);
 		bcount = count;
 	}

 	/* Don't allow overlapped cloning within the same file. */
 	if (inode_in == inode_out &&
 	    pos_out + bcount > pos_in &&
 	    pos_out < pos_in + bcount)
 		return -EINVAL;

 	/*
 	 * We shortened the request but the caller can't deal with that, so
 	 * bounce the request back to userspace.
 	 */
 	if (*req_count != count && !(remap_flags & REMAP_FILE_CAN_SHORTEN))
 		return -EINVAL;

 	*req_count = count;
 	return 0;
 }

 static int remap_verify_area(struct file *file, loff_t pos, loff_t len,
 			     bool write)
 {
 	if (unlikely(pos < 0 || len < 0))
 		return -EINVAL;

 	if (unlikely((loff_t) (pos + len) < 0))
 		return -EINVAL;

 	return security_file_permission(file, write ? MAY_WRITE : MAY_READ);
 }

 /*
  * Ensure that we don't remap a partial EOF block in the middle of something
  * else.  Assume that the offsets have already been checked for block
  * alignment.
  *
  * For clone we only link a partial EOF block above or at the destination file's
  * EOF.  For deduplication we accept a partial EOF block only if it ends at the
  * destination file's EOF (can not link it into the middle of a file).
  *
  * Shorten the request if possible.
  */
 static int generic_remap_check_len(struct inode *inode_in,
 				   struct inode *inode_out,
 				   loff_t pos_out,
 				   loff_t *len,
 				   unsigned int remap_flags)
 {
 	u64 blkmask = i_blocksize(inode_in) - 1;
 	loff_t new_len = *len;

 	if ((*len & blkmask) == 0)
 		return 0;

 	if (pos_out + *len < i_size_read(inode_out))
 		new_len &= ~blkmask;

 	if (new_len == *len)
 		return 0;

 	if (remap_flags & REMAP_FILE_CAN_SHORTEN) {
 		*len = new_len;
 		return 0;
 	}

 	return (remap_flags & REMAP_FILE_DEDUP) ? -EBADE : -EINVAL;
 }

 /* Read a page's worth of file data into the page cache. */
 static struct page *vfs_dedupe_get_page(struct inode *inode, loff_t offset)
 {
 	struct page *page;

 	page = read_mapping_page(inode->i_mapping, offset >> PAGE_SHIFT, NULL);
 	if (IS_ERR(page))
 		return page;
 	if (!PageUptodate(page)) {
 		put_page(page);
 		return ERR_PTR(-EIO);
 	}
 	return page;
 }

 /*
  * Lock two pages, ensuring that we lock in offset order if the pages are from
  * the same file.
  */
 static void vfs_lock_two_pages(struct page *page1, struct page *page2)
 {
 	/* Always lock in order of increasing index. */
 	if (page1->index > page2->index)
 		swap(page1, page2);

 	lock_page(page1);
 	if (page1 != page2)
 		lock_page(page2);
 }

 /* Unlock two pages, being careful not to unlock the same page twice. */
 static void vfs_unlock_two_pages(struct page *page1, struct page *page2)
 {
 	unlock_page(page1);
 	if (page1 != page2)
 		unlock_page(page2);
 }

 /*
  * Compare extents of two files to see if they are the same.
  * Caller must have locked both inodes to prevent write races.
  */
 static int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
 					 struct inode *dest, loff_t destoff,
 					 loff_t len, bool *is_same)
 {
 	loff_t src_poff;
 	loff_t dest_poff;
 	void *src_addr;
 	void *dest_addr;
 	struct page *src_page;
 	struct page *dest_page;
 	loff_t cmp_len;
 	bool same;
 	int error;

 	error = -EINVAL;
 	same = true;
 	while (len) {
 		src_poff = srcoff & (PAGE_SIZE - 1);
 		dest_poff = destoff & (PAGE_SIZE - 1);
 		cmp_len = min(PAGE_SIZE - src_poff,
 			      PAGE_SIZE - dest_poff);
 		cmp_len = min(cmp_len, len);
 		if (cmp_len <= 0)
 			goto out_error;

 		src_page = vfs_dedupe_get_page(src, srcoff);
 		if (IS_ERR(src_page)) {
 			error = PTR_ERR(src_page);
 			goto out_error;
 		}
 		dest_page = vfs_dedupe_get_page(dest, destoff);
 		if (IS_ERR(dest_page)) {
 			error = PTR_ERR(dest_page);
 			put_page(src_page);
 			goto out_error;
 		}

 		vfs_lock_two_pages(src_page, dest_page);

 		/*
 		 * Now that we've locked both pages, make sure they're still
 		 * mapped to the file data we're interested in.  If not,
 		 * someone is invalidating pages on us and we lose.
 		 */
 		if (!PageUptodate(src_page) || !PageUptodate(dest_page) ||
 		    src_page->mapping != src->i_mapping ||
 		    dest_page->mapping != dest->i_mapping) {
 			same = false;
 			goto unlock;
 		}

 		src_addr = kmap_atomic(src_page);
 		dest_addr = kmap_atomic(dest_page);

 		flush_dcache_page(src_page);
 		flush_dcache_page(dest_page);

 		if (memcmp(src_addr + src_poff, dest_addr + dest_poff, cmp_len))
 			same = false;

 		kunmap_atomic(dest_addr);
 		kunmap_atomic(src_addr);
 unlock:
 		vfs_unlock_two_pages(src_page, dest_page);
 		put_page(dest_page);
 		put_page(src_page);

 		if (!same)
 			break;

 		srcoff += cmp_len;
 		destoff += cmp_len;
 		len -= cmp_len;
 	}

 	*is_same = same;
 	return 0;

 out_error:
 	return error;
 }

 /*
  * Check that the two inodes are eligible for cloning, the ranges make
  * sense, and then flush all dirty data.  Caller must ensure that the
  * inodes have been locked against any other modifications.
  *
  * If there's an error, then the usual negative error code is returned.
  * Otherwise returns 0 with *len set to the request length.
  */
 int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
 				  struct file *file_out, loff_t pos_out,
 				  loff_t *len, unsigned int remap_flags)
 {
 	struct inode *inode_in = file_inode(file_in);
 	struct inode *inode_out = file_inode(file_out);
 	bool same_inode = (inode_in == inode_out);
 	int ret;

 	/* Don't touch certain kinds of inodes */
 	if (IS_IMMUTABLE(inode_out))
 		return -EPERM;

 	if (IS_SWAPFILE(inode_in) || IS_SWAPFILE(inode_out))
 		return -ETXTBSY;

 	/* Don't reflink dirs, pipes, sockets... */
 	if (S_ISDIR(inode_in->i_mode) || S_ISDIR(inode_out->i_mode))
 		return -EISDIR;
 	if (!S_ISREG(inode_in->i_mode) || !S_ISREG(inode_out->i_mode))
 		return -EINVAL;

 	/* Zero length dedupe exits immediately; reflink goes to EOF. */
 	if (*len == 0) {
 		loff_t isize = i_size_read(inode_in);

 		if ((remap_flags & REMAP_FILE_DEDUP) || pos_in == isize)
 			return 0;
 		if (pos_in > isize)
 			return -EINVAL;
 		*len = isize - pos_in;
 		if (*len == 0)
 			return 0;
 	}

 	/* Check that we don't violate system file offset limits. */
 	ret = generic_remap_checks(file_in, pos_in, file_out, pos_out, len,
 			remap_flags);
 	if (ret)
 		return ret;

 	/* Wait for the completion of any pending IOs on both files */
 	inode_dio_wait(inode_in);
 	if (!same_inode)
 		inode_dio_wait(inode_out);

 	ret = filemap_write_and_wait_range(inode_in->i_mapping,
 			pos_in, pos_in + *len - 1);
 	if (ret)
 		return ret;

 	ret = filemap_write_and_wait_range(inode_out->i_mapping,
 			pos_out, pos_out + *len - 1);
 	if (ret)
 		return ret;

 	/*
 	 * Check that the extents are the same.
 	 */
 	if (remap_flags & REMAP_FILE_DEDUP) {
 		bool		is_same = false;

 		ret = vfs_dedupe_file_range_compare(inode_in, pos_in,
 				inode_out, pos_out, *len, &is_same);
 		if (ret)
 			return ret;
 		if (!is_same)
 			return -EBADE;
 	}

 	ret = generic_remap_check_len(inode_in, inode_out, pos_out, len,
 			remap_flags);
 	if (ret)
 		return ret;

 	/* If can't alter the file contents, we're done. */
 	if (!(remap_flags & REMAP_FILE_DEDUP))
 		ret = file_modified(file_out);

 	return ret;
 }
 EXPORT_SYMBOL(generic_remap_file_range_prep);

 loff_t do_clone_file_range(struct file *file_in, loff_t pos_in,
 			   struct file *file_out, loff_t pos_out,
 			   loff_t len, unsigned int remap_flags)
 {
 	loff_t ret;

 	WARN_ON_ONCE(remap_flags & REMAP_FILE_DEDUP);

 	/*
 	 * FICLONE/FICLONERANGE ioctls enforce that src and dest files are on
 	 * the same mount. Practically, they only need to be on the same file
 	 * system.
 	 */
 	if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
 		return -EXDEV;

 	ret = generic_file_rw_checks(file_in, file_out);
 	if (ret < 0)
 		return ret;

 	if (!file_in->f_op->remap_file_range)
 		return -EOPNOTSUPP;

 	ret = remap_verify_area(file_in, pos_in, len, false);
 	if (ret)
 		return ret;

 	ret = remap_verify_area(file_out, pos_out, len, true);
 	if (ret)
 		return ret;

 	ret = file_in->f_op->remap_file_range(file_in, pos_in,
 			file_out, pos_out, len, remap_flags);
 	if (ret < 0)
 		return ret;

 	fsnotify_access(file_in);
 	fsnotify_modify(file_out);
 	return ret;
 }
 EXPORT_SYMBOL(do_clone_file_range);

 loff_t vfs_clone_file_range(struct file *file_in, loff_t pos_in,
 			    struct file *file_out, loff_t pos_out,
 			    loff_t len, unsigned int remap_flags)
 {
 	loff_t ret;

 	file_start_write(file_out);
 	ret = do_clone_file_range(file_in, pos_in, file_out, pos_out, len,
 				  remap_flags);
 	file_end_write(file_out);

 	return ret;
 }
 EXPORT_SYMBOL(vfs_clone_file_range);

 /* Check whether we are allowed to dedupe the destination file */
 static bool allow_file_dedupe(struct file *file)
 {
 	struct user_namespace *mnt_userns = file_mnt_user_ns(file);
 	struct inode *inode = file_inode(file);

 	if (capable(CAP_SYS_ADMIN))
 		return true;
 	if (file->f_mode & FMODE_WRITE)
 		return true;
 	if (uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode)))
 		return true;
 	if (!inode_permission(mnt_userns, inode, MAY_WRITE))
 		return true;
 	return false;
 }

 loff_t vfs_dedupe_file_range_one(struct file *src_file, loff_t src_pos,
 				 struct file *dst_file, loff_t dst_pos,
 				 loff_t len, unsigned int remap_flags)
 {
 	loff_t ret;

 	WARN_ON_ONCE(remap_flags & ~(REMAP_FILE_DEDUP |
 				     REMAP_FILE_CAN_SHORTEN));

 	ret = mnt_want_write_file(dst_file);
 	if (ret)
 		return ret;

 	/*
 	 * This is redundant if called from vfs_dedupe_file_range(), but other
 	 * callers need it and it's not performance sesitive...
 	 */
 	ret = remap_verify_area(src_file, src_pos, len, false);
 	if (ret)
 		goto out_drop_write;

 	ret = remap_verify_area(dst_file, dst_pos, len, true);
 	if (ret)
 		goto out_drop_write;

 	ret = -EPERM;
 	if (!allow_file_dedupe(dst_file))
 		goto out_drop_write;

 	ret = -EXDEV;
 	if (src_file->f_path.mnt != dst_file->f_path.mnt)
 		goto out_drop_write;

 	ret = -EISDIR;
 	if (S_ISDIR(file_inode(dst_file)->i_mode))
 		goto out_drop_write;

 	ret = -EINVAL;
 	if (!dst_file->f_op->remap_file_range)
 		goto out_drop_write;

 	if (len == 0) {
 		ret = 0;
 		goto out_drop_write;
 	}

 	ret = dst_file->f_op->remap_file_range(src_file, src_pos, dst_file,
 			dst_pos, len, remap_flags | REMAP_FILE_DEDUP);
 out_drop_write:
 	mnt_drop_write_file(dst_file);

 	return ret;
 }
 EXPORT_SYMBOL(vfs_dedupe_file_range_one);

 int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same)
 {
 	struct file_dedupe_range_info *info;
 	struct inode *src = file_inode(file);
 	u64 off;
 	u64 len;
 	int i;
 	int ret;
 	u16 count = same->dest_count;
 	loff_t deduped;

 	if (!(file->f_mode & FMODE_READ))
 		return -EINVAL;

 	if (same->reserved1 || same->reserved2)
 		return -EINVAL;

 	off = same->src_offset;
 	len = same->src_length;

 	if (S_ISDIR(src->i_mode))
 		return -EISDIR;

 	if (!S_ISREG(src->i_mode))
 		return -EINVAL;

 	if (!file->f_op->remap_file_range)
 		return -EOPNOTSUPP;

 	ret = remap_verify_area(file, off, len, false);
 	if (ret < 0)
 		return ret;
 	ret = 0;

 	if (off + len > i_size_read(src))
 		return -EINVAL;

 	/* Arbitrary 1G limit on a single dedupe request, can be raised. */
 	len = min_t(u64, len, 1 << 30);

 	/* pre-format output fields to sane values */
 	for (i = 0; i < count; i++) {
 		same->info[i].bytes_deduped = 0ULL;
 		same->info[i].status = FILE_DEDUPE_RANGE_SAME;
 	}

 	for (i = 0, info = same->info; i < count; i++, info++) {
 		struct fd dst_fd = fdget(info->dest_fd);
 		struct file *dst_file = dst_fd.file;

 		if (!dst_file) {
 			info->status = -EBADF;
 			goto next_loop;
 		}

 		if (info->reserved) {
 			info->status = -EINVAL;
 			goto next_fdput;
 		}

 		deduped = vfs_dedupe_file_range_one(file, off, dst_file,
 						    info->dest_offset, len,
 						    REMAP_FILE_CAN_SHORTEN);
 		if (deduped == -EBADE)
 			info->status = FILE_DEDUPE_RANGE_DIFFERS;
 		else if (deduped < 0)
 			info->status = deduped;
 		else
 			info->bytes_deduped = len;

 next_fdput:
 		fdput(dst_fd);
 next_loop:
 		if (fatal_signal_pending(current))
 			break;
 	}
 	return ret;
 }
 EXPORT_SYMBOL(vfs_dedupe_file_range);
	// SPDX-License-Identifier: GPL-2.0-only
	#include <linux/slab.h>
	#include <linux/stat.h>
	#include <linux/sched/xacct.h>
	#include <linux/fcntl.h>
	#include <linux/file.h>
	#include <linux/uio.h>
	#include <linux/fsnotify.h>
	#include <linux/security.h>
	#include <linux/export.h>
	#include <linux/syscalls.h>
	#include <linux/pagemap.h>
	#include <linux/splice.h>
	#include <linux/compat.h>
	#include <linux/mount.h>
	#include <linux/fs.h>
	#include "internal.h"

	#include <linux/uaccess.h>
	#include <asm/unistd.h>

	/*
	* Performs necessary checks before doing a clone.
	*
	* Can adjust amount of bytes to clone via @req_count argument.
	* Returns appropriate error code that caller should return or
	* zero in case the clone should be allowed.
	*/
	static int generic_remap_checks(struct file *file_in, loff_t pos_in,
	struct file *file_out, loff_t pos_out,
	loff_t *req_count, unsigned int remap_flags)
	{
	struct inode *inode_in = file_in->f_mapping->host;
	struct inode *inode_out = file_out->f_mapping->host;
	uint64_t count = *req_count;
	uint64_t bcount;
	loff_t size_in, size_out;
	loff_t bs = inode_out->i_sb->s_blocksize;
	int ret;

	/* The start of both ranges must be aligned to an fs block. */
	if (!IS_ALIGNED(pos_in, bs) \|\| !IS_ALIGNED(pos_out, bs))
	return -EINVAL;

	/* Ensure offsets don't wrap. */
	if (pos_in + count < pos_in \|\| pos_out + count < pos_out)
	return -EINVAL;

	size_in = i_size_read(inode_in);
	size_out = i_size_read(inode_out);

	/* Dedupe requires both ranges to be within EOF. */
	if ((remap_flags & REMAP_FILE_DEDUP) &&
	(pos_in >= size_in \|\| pos_in + count > size_in \|\|
	pos_out >= size_out \|\| pos_out + count > size_out))
	return -EINVAL;

	/* Ensure the infile range is within the infile. */
	if (pos_in >= size_in)
	return -EINVAL;
	count = min(count, size_in - (uint64_t)pos_in);

	ret = generic_write_check_limits(file_out, pos_out, &count);
	if (ret)
	return ret;

	/*
	* If the user wanted us to link to the infile's EOF, round up to the
	* next block boundary for this check.
	*
	* Otherwise, make sure the count is also block-aligned, having
	* already confirmed the starting offsets' block alignment.
	*/
	if (pos_in + count == size_in &&
	(!(remap_flags & REMAP_FILE_DEDUP) \|\| pos_out + count == size_out)) {
	bcount = ALIGN(size_in, bs) - pos_in;
	} else {
	if (!IS_ALIGNED(count, bs))
	count = ALIGN_DOWN(count, bs);
	bcount = count;
	}

	/* Don't allow overlapped cloning within the same file. */
	if (inode_in == inode_out &&
	pos_out + bcount > pos_in &&
	pos_out < pos_in + bcount)
	return -EINVAL;

	/*
	* We shortened the request but the caller can't deal with that, so
	* bounce the request back to userspace.
	*/
	if (*req_count != count && !(remap_flags & REMAP_FILE_CAN_SHORTEN))
	return -EINVAL;

	*req_count = count;
	return 0;
	}

	static int remap_verify_area(struct file *file, loff_t pos, loff_t len,
	bool write)
	{
	if (unlikely(pos < 0 \|\| len < 0))
	return -EINVAL;

	if (unlikely((loff_t) (pos + len) < 0))
	return -EINVAL;

	return security_file_permission(file, write ? MAY_WRITE : MAY_READ);
	}

	/*
	* Ensure that we don't remap a partial EOF block in the middle of something
	* else. Assume that the offsets have already been checked for block
	* alignment.
	*
	* For clone we only link a partial EOF block above or at the destination file's
	* EOF. For deduplication we accept a partial EOF block only if it ends at the
	* destination file's EOF (can not link it into the middle of a file).
	*
	* Shorten the request if possible.
	*/
	static int generic_remap_check_len(struct inode *inode_in,
	struct inode *inode_out,
	loff_t pos_out,
	loff_t *len,
	unsigned int remap_flags)
	{
	u64 blkmask = i_blocksize(inode_in) - 1;
	loff_t new_len = *len;

	if ((*len & blkmask) == 0)
	return 0;

	if (pos_out + *len < i_size_read(inode_out))
	new_len &= ~blkmask;

	if (new_len == *len)
	return 0;

	if (remap_flags & REMAP_FILE_CAN_SHORTEN) {
	*len = new_len;
	return 0;
	}

	return (remap_flags & REMAP_FILE_DEDUP) ? -EBADE : -EINVAL;
	}

	/* Read a page's worth of file data into the page cache. */
	static struct page vfs_dedupe_get_page(struct inode inode, loff_t offset)
	{
	struct page *page;

	page = read_mapping_page(inode->i_mapping, offset >> PAGE_SHIFT, NULL);
	if (IS_ERR(page))
	return page;
	if (!PageUptodate(page)) {
	put_page(page);
	return ERR_PTR(-EIO);
	}
	return page;
	}

	/*
	* Lock two pages, ensuring that we lock in offset order if the pages are from
	* the same file.
	*/
	static void vfs_lock_two_pages(struct page page1, struct page page2)
	{
	/* Always lock in order of increasing index. */
	if (page1->index > page2->index)
	swap(page1, page2);

	lock_page(page1);
	if (page1 != page2)
	lock_page(page2);
	}

	/* Unlock two pages, being careful not to unlock the same page twice. */
	static void vfs_unlock_two_pages(struct page page1, struct page page2)
	{
	unlock_page(page1);
	if (page1 != page2)
	unlock_page(page2);
	}

	/*
	* Compare extents of two files to see if they are the same.
	* Caller must have locked both inodes to prevent write races.
	*/
	static int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
	struct inode *dest, loff_t destoff,
	loff_t len, bool *is_same)
	{
	loff_t src_poff;
	loff_t dest_poff;
	void *src_addr;
	void *dest_addr;
	struct page *src_page;
	struct page *dest_page;
	loff_t cmp_len;
	bool same;
	int error;

	error = -EINVAL;
	same = true;
	while (len) {
	src_poff = srcoff & (PAGE_SIZE - 1);
	dest_poff = destoff & (PAGE_SIZE - 1);
	cmp_len = min(PAGE_SIZE - src_poff,
	PAGE_SIZE - dest_poff);
	cmp_len = min(cmp_len, len);
	if (cmp_len <= 0)
	goto out_error;

	src_page = vfs_dedupe_get_page(src, srcoff);
	if (IS_ERR(src_page)) {
	error = PTR_ERR(src_page);
	goto out_error;
	}
	dest_page = vfs_dedupe_get_page(dest, destoff);
	if (IS_ERR(dest_page)) {
	error = PTR_ERR(dest_page);
	put_page(src_page);
	goto out_error;
	}

	vfs_lock_two_pages(src_page, dest_page);

	/*
	* Now that we've locked both pages, make sure they're still
	* mapped to the file data we're interested in. If not,
	* someone is invalidating pages on us and we lose.
	*/
	if (!PageUptodate(src_page) \|\| !PageUptodate(dest_page) \|\|
	src_page->mapping != src->i_mapping \|\|
	dest_page->mapping != dest->i_mapping) {
	same = false;
	goto unlock;
	}

	src_addr = kmap_atomic(src_page);
	dest_addr = kmap_atomic(dest_page);

	flush_dcache_page(src_page);
	flush_dcache_page(dest_page);

	if (memcmp(src_addr + src_poff, dest_addr + dest_poff, cmp_len))
	same = false;

	kunmap_atomic(dest_addr);
	kunmap_atomic(src_addr);
	unlock:
	vfs_unlock_two_pages(src_page, dest_page);
	put_page(dest_page);
	put_page(src_page);

	if (!same)
	break;

	srcoff += cmp_len;
	destoff += cmp_len;
	len -= cmp_len;
	}

	*is_same = same;
	return 0;

	out_error:
	return error;
	}

	/*
	* Check that the two inodes are eligible for cloning, the ranges make
	* sense, and then flush all dirty data. Caller must ensure that the
	* inodes have been locked against any other modifications.
	*
	* If there's an error, then the usual negative error code is returned.
	* Otherwise returns 0 with *len set to the request length.
	*/
	int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
	struct file *file_out, loff_t pos_out,
	loff_t *len, unsigned int remap_flags)
	{
	struct inode *inode_in = file_inode(file_in);
	struct inode *inode_out = file_inode(file_out);
	bool same_inode = (inode_in == inode_out);
	int ret;

	/* Don't touch certain kinds of inodes */
	if (IS_IMMUTABLE(inode_out))
	return -EPERM;

	if (IS_SWAPFILE(inode_in) \|\| IS_SWAPFILE(inode_out))
	return -ETXTBSY;

	/* Don't reflink dirs, pipes, sockets... */
	if (S_ISDIR(inode_in->i_mode) \|\| S_ISDIR(inode_out->i_mode))
	return -EISDIR;
	if (!S_ISREG(inode_in->i_mode) \|\| !S_ISREG(inode_out->i_mode))
	return -EINVAL;

	/* Zero length dedupe exits immediately; reflink goes to EOF. */
	if (*len == 0) {
	loff_t isize = i_size_read(inode_in);

	if ((remap_flags & REMAP_FILE_DEDUP) \|\| pos_in == isize)
	return 0;
	if (pos_in > isize)
	return -EINVAL;
	*len = isize - pos_in;
	if (*len == 0)
	return 0;
	}

	/* Check that we don't violate system file offset limits. */
	ret = generic_remap_checks(file_in, pos_in, file_out, pos_out, len,
	remap_flags);
	if (ret)
	return ret;

	/* Wait for the completion of any pending IOs on both files */
	inode_dio_wait(inode_in);
	if (!same_inode)
	inode_dio_wait(inode_out);

	ret = filemap_write_and_wait_range(inode_in->i_mapping,
	pos_in, pos_in + *len - 1);
	if (ret)
	return ret;

	ret = filemap_write_and_wait_range(inode_out->i_mapping,
	pos_out, pos_out + *len - 1);
	if (ret)
	return ret;

	/*
	* Check that the extents are the same.
	*/
	if (remap_flags & REMAP_FILE_DEDUP) {
	bool is_same = false;

	ret = vfs_dedupe_file_range_compare(inode_in, pos_in,
	inode_out, pos_out, *len, &is_same);
	if (ret)
	return ret;
	if (!is_same)
	return -EBADE;
	}

	ret = generic_remap_check_len(inode_in, inode_out, pos_out, len,
	remap_flags);
	if (ret)
	return ret;

	/* If can't alter the file contents, we're done. */
	if (!(remap_flags & REMAP_FILE_DEDUP))
	ret = file_modified(file_out);

	return ret;
	}
	EXPORT_SYMBOL(generic_remap_file_range_prep);

	loff_t do_clone_file_range(struct file *file_in, loff_t pos_in,
	struct file *file_out, loff_t pos_out,
	loff_t len, unsigned int remap_flags)
	{
	loff_t ret;

	WARN_ON_ONCE(remap_flags & REMAP_FILE_DEDUP);

	/*
	* FICLONE/FICLONERANGE ioctls enforce that src and dest files are on
	* the same mount. Practically, they only need to be on the same file
	* system.
	*/
	if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
	return -EXDEV;

	ret = generic_file_rw_checks(file_in, file_out);
	if (ret < 0)
	return ret;

	if (!file_in->f_op->remap_file_range)
	return -EOPNOTSUPP;

	ret = remap_verify_area(file_in, pos_in, len, false);
	if (ret)
	return ret;

	ret = remap_verify_area(file_out, pos_out, len, true);
	if (ret)
	return ret;

	ret = file_in->f_op->remap_file_range(file_in, pos_in,
	file_out, pos_out, len, remap_flags);
	if (ret < 0)
	return ret;

	fsnotify_access(file_in);
	fsnotify_modify(file_out);
	return ret;
	}
	EXPORT_SYMBOL(do_clone_file_range);

	loff_t vfs_clone_file_range(struct file *file_in, loff_t pos_in,
	struct file *file_out, loff_t pos_out,
	loff_t len, unsigned int remap_flags)
	{
	loff_t ret;

	file_start_write(file_out);
	ret = do_clone_file_range(file_in, pos_in, file_out, pos_out, len,
	remap_flags);
	file_end_write(file_out);

	return ret;
	}
	EXPORT_SYMBOL(vfs_clone_file_range);

	/* Check whether we are allowed to dedupe the destination file */
	static bool allow_file_dedupe(struct file *file)
	{
	struct user_namespace *mnt_userns = file_mnt_user_ns(file);
	struct inode *inode = file_inode(file);

	if (capable(CAP_SYS_ADMIN))
	return true;
	if (file->f_mode & FMODE_WRITE)
	return true;
	if (uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode)))
	return true;
	if (!inode_permission(mnt_userns, inode, MAY_WRITE))
	return true;
	return false;
	}

	loff_t vfs_dedupe_file_range_one(struct file *src_file, loff_t src_pos,
	struct file *dst_file, loff_t dst_pos,
	loff_t len, unsigned int remap_flags)
	{
	loff_t ret;

	WARN_ON_ONCE(remap_flags & ~(REMAP_FILE_DEDUP \|
	REMAP_FILE_CAN_SHORTEN));

	ret = mnt_want_write_file(dst_file);
	if (ret)
	return ret;

	/*
	* This is redundant if called from vfs_dedupe_file_range(), but other
	* callers need it and it's not performance sesitive...
	*/
	ret = remap_verify_area(src_file, src_pos, len, false);
	if (ret)
	goto out_drop_write;

	ret = remap_verify_area(dst_file, dst_pos, len, true);
	if (ret)
	goto out_drop_write;

	ret = -EPERM;
	if (!allow_file_dedupe(dst_file))
	goto out_drop_write;

	ret = -EXDEV;
	if (src_file->f_path.mnt != dst_file->f_path.mnt)
	goto out_drop_write;

	ret = -EISDIR;
	if (S_ISDIR(file_inode(dst_file)->i_mode))
	goto out_drop_write;

	ret = -EINVAL;
	if (!dst_file->f_op->remap_file_range)
	goto out_drop_write;

	if (len == 0) {
	ret = 0;
	goto out_drop_write;
	}

	ret = dst_file->f_op->remap_file_range(src_file, src_pos, dst_file,
	dst_pos, len, remap_flags \| REMAP_FILE_DEDUP);
	out_drop_write:
	mnt_drop_write_file(dst_file);

	return ret;
	}
	EXPORT_SYMBOL(vfs_dedupe_file_range_one);

	int vfs_dedupe_file_range(struct file file, struct file_dedupe_range same)
	{
	struct file_dedupe_range_info *info;
	struct inode *src = file_inode(file);
	u64 off;
	u64 len;
	int i;
	int ret;
	u16 count = same->dest_count;
	loff_t deduped;

	if (!(file->f_mode & FMODE_READ))
	return -EINVAL;

	if (same->reserved1 \|\| same->reserved2)
	return -EINVAL;

	off = same->src_offset;
	len = same->src_length;

	if (S_ISDIR(src->i_mode))
	return -EISDIR;

	if (!S_ISREG(src->i_mode))
	return -EINVAL;

	if (!file->f_op->remap_file_range)
	return -EOPNOTSUPP;

	ret = remap_verify_area(file, off, len, false);
	if (ret < 0)
	return ret;
	ret = 0;

	if (off + len > i_size_read(src))
	return -EINVAL;

	/* Arbitrary 1G limit on a single dedupe request, can be raised. */
	len = min_t(u64, len, 1 << 30);

	/* pre-format output fields to sane values */
	for (i = 0; i < count; i++) {
	same->info[i].bytes_deduped = 0ULL;
	same->info[i].status = FILE_DEDUPE_RANGE_SAME;
	}

	for (i = 0, info = same->info; i < count; i++, info++) {
	struct fd dst_fd = fdget(info->dest_fd);
	struct file *dst_file = dst_fd.file;

	if (!dst_file) {
	info->status = -EBADF;
	goto next_loop;
	}

	if (info->reserved) {
	info->status = -EINVAL;
	goto next_fdput;
	}

	deduped = vfs_dedupe_file_range_one(file, off, dst_file,
	info->dest_offset, len,
	REMAP_FILE_CAN_SHORTEN);
	if (deduped == -EBADE)
	info->status = FILE_DEDUPE_RANGE_DIFFERS;
	else if (deduped < 0)
	info->status = deduped;
	else
	info->bytes_deduped = len;

	next_fdput:
	fdput(dst_fd);
	next_loop:
	if (fatal_signal_pending(current))
	break;
	}
	return ret;
	}
	EXPORT_SYMBOL(vfs_dedupe_file_range);