Btrfs: sectorsize align offsets in fiemap

We've been hitting BUG()'s in btrfs_cont_expand and btrfs_fallocate and anywhere
else that calls btrfs_get_extent while running xfstests 13 in a loop.  This is
because fiemap is calling btrfs_get_extent with non-sectorsize aligned offsets,
which will end up adding mappings that are not sectorsize aligned, which will
cause problems in some cases for subsequent calls to btrfs_get_extent for
similar areas that are sectorsize aligned.  With this patch I ran xfstests 13 in
a loop for a couple of hours and didn't hit the problem that I could previously
hit in at most 20 minutes.  Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>

fs/btrfs/extent_io.c

@@ -3366,6 +3366,9 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 		return -ENOMEM;
 	path->leave_spinning = 1;
 
+	start = ALIGN(start, BTRFS_I(inode)->root->sectorsize);
+	len = ALIGN(len, BTRFS_I(inode)->root->sectorsize);
+
 	/*
 	 * lookup the last file extent.  We're not using i_size here
 	 * because there might be preallocation past i_size
@@ -3413,7 +3416,7 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 	lock_extent_bits(&BTRFS_I(inode)->io_tree, start, start + len, 0,
 			 &cached_state, GFP_NOFS);
 
-	em = get_extent_skip_holes(inode, off, last_for_get_extent,
+	em = get_extent_skip_holes(inode, start, last_for_get_extent,
 				   get_extent);
 	if (!em)
 		goto out;