xfs: refactor clonerange preparation into a separate helper

Refactor all the reflink preparation steps into a separate helper
that we'll use to land all the upcoming fixes for insufficient input
checks.

This rework also moves the invalidation of the destination range to
the prep function so that it is done before the range is remapped.
This ensures that nobody can access the data in range being remapped
until the remap is complete.

[dgc: fix xfs_reflink_remap_prep() return value and caller check to
handle vfs_clone_file_prep_inodes() returning 0 to mean "nothing to
do". ]

[dgc: make sure length changed by vfs_clone_file_prep_inodes() gets
propagated back to XFS code that does the remapping. ]
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_reflink.c

@@ -1220,35 +1220,47 @@ xfs_iolock_two_inodes_and_break_layout(
 	return 0;
 }
 
+/* Unlock both inodes after they've been prepped for a range clone. */
+STATIC void
+xfs_reflink_remap_unlock(
+	struct file		*file_in,
+	struct file		*file_out)
+{
+	struct inode		*inode_in = file_inode(file_in);
+	struct xfs_inode	*src = XFS_I(inode_in);
+	struct inode		*inode_out = file_inode(file_out);
+	struct xfs_inode	*dest = XFS_I(inode_out);
+	bool			same_inode = (inode_in == inode_out);
+
+	xfs_iunlock(dest, XFS_MMAPLOCK_EXCL);
+	if (!same_inode)
+		xfs_iunlock(src, XFS_MMAPLOCK_SHARED);
+	inode_unlock(inode_out);
+	if (!same_inode)
+		inode_unlock_shared(inode_in);
+}
+
 /*
- * Link a range of blocks from one file to another.
+ * Prepare two files for range cloning.  Upon a successful return both inodes
+ * will have the iolock and mmaplock held, the page cache of the out file
+ * will be truncated, and any leases on the out file will have been broken.
  */
-int
-xfs_reflink_remap_range(
+STATIC int
+xfs_reflink_remap_prep(
 	struct file		*file_in,
 	loff_t			pos_in,
 	struct file		*file_out,
 	loff_t			pos_out,
-	u64			len,
+	u64			*len,
 	bool			is_dedupe)
 {
 	struct inode		*inode_in = file_inode(file_in);
 	struct xfs_inode	*src = XFS_I(inode_in);
 	struct inode		*inode_out = file_inode(file_out);
 	struct xfs_inode	*dest = XFS_I(inode_out);
-	struct xfs_mount	*mp = src->i_mount;
 	bool			same_inode = (inode_in == inode_out);
-	xfs_fileoff_t		sfsbno, dfsbno;
-	xfs_filblks_t		fsblen;
-	xfs_extlen_t		cowextsize;
 	ssize_t			ret;
 
-	if (!xfs_sb_version_hasreflink(&mp->m_sb))
-		return -EOPNOTSUPP;
-
-	if (XFS_FORCED_SHUTDOWN(mp))
-		return -EIO;
-
 	/* Lock both files against IO */
 	ret = xfs_iolock_two_inodes_and_break_layout(inode_in, inode_out);
 	if (ret)
@@ -1270,7 +1282,7 @@ xfs_reflink_remap_range(
 		goto out_unlock;
 
 	ret = vfs_clone_file_prep_inodes(inode_in, pos_in, inode_out, pos_out,
-			&len, is_dedupe);
+			len, is_dedupe);
 	if (ret <= 0)
 		goto out_unlock;
 
@@ -1279,8 +1291,6 @@ xfs_reflink_remap_range(
 	if (ret)
 		goto out_unlock;
 
-	trace_xfs_reflink_remap_range(src, pos_in, len, dest, pos_out);
-
 	/*
 	 * Clear out post-eof preallocations because we don't have page cache
 	 * backing the delayed allocations and they'll never get freed on
@@ -1297,6 +1307,51 @@ xfs_reflink_remap_range(
 	if (ret)
 		goto out_unlock;
 
+	/* Zap any page cache for the destination file's range. */
+	truncate_inode_pages_range(&inode_out->i_data, pos_out,
+				   PAGE_ALIGN(pos_out + *len) - 1);
+	return 1;
+out_unlock:
+	xfs_reflink_remap_unlock(file_in, file_out);
+	return ret;
+}
+
+/*
+ * Link a range of blocks from one file to another.
+ */
+int
+xfs_reflink_remap_range(
+	struct file		*file_in,
+	loff_t			pos_in,
+	struct file		*file_out,
+	loff_t			pos_out,
+	u64			len,
+	bool			is_dedupe)
+{
+	struct inode		*inode_in = file_inode(file_in);
+	struct xfs_inode	*src = XFS_I(inode_in);
+	struct inode		*inode_out = file_inode(file_out);
+	struct xfs_inode	*dest = XFS_I(inode_out);
+	struct xfs_mount	*mp = src->i_mount;
+	xfs_fileoff_t		sfsbno, dfsbno;
+	xfs_filblks_t		fsblen;
+	xfs_extlen_t		cowextsize;
+	ssize_t			ret;
+
+	if (!xfs_sb_version_hasreflink(&mp->m_sb))
+		return -EOPNOTSUPP;
+
+	if (XFS_FORCED_SHUTDOWN(mp))
+		return -EIO;
+
+	/* Prepare and then clone file data. */
+	ret = xfs_reflink_remap_prep(file_in, pos_in, file_out, pos_out,
+			&len, is_dedupe);
+	if (ret <= 0)
+		return ret;
+
+	trace_xfs_reflink_remap_range(src, pos_in, len, dest, pos_out);
+
 	dfsbno = XFS_B_TO_FSBT(mp, pos_out);
 	sfsbno = XFS_B_TO_FSBT(mp, pos_in);
 	fsblen = XFS_B_TO_FSB(mp, len);
@@ -1305,10 +1360,6 @@ xfs_reflink_remap_range(
 	if (ret)
 		goto out_unlock;
 
-	/* Zap any page cache for the destination file's range. */
-	truncate_inode_pages_range(&inode_out->i_data, pos_out,
-				   PAGE_ALIGN(pos_out + len) - 1);
-
 	/*
 	 * Carry the cowextsize hint from src to dest if we're sharing the
 	 * entire source file to the entire destination file, the source file
@@ -1325,12 +1376,7 @@ xfs_reflink_remap_range(
 			is_dedupe);
 
 out_unlock:
-	xfs_iunlock(dest, XFS_MMAPLOCK_EXCL);
-	if (!same_inode)
-		xfs_iunlock(src, XFS_MMAPLOCK_SHARED);
-	inode_unlock(inode_out);
-	if (!same_inode)
-		inode_unlock_shared(inode_in);
+	xfs_reflink_remap_unlock(file_in, file_out);
 	if (ret)
 		trace_xfs_reflink_remap_range_error(dest, ret, _RET_IP_);
 	return ret;