btrfs: check for relocation inodes on zoned btrfs in should_nocow

Prepare for allowing preallocation for relocation inodes.
Reviewed-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -1944,7 +1944,15 @@ int btrfs_run_delalloc_range(struct btrfs_inode *inode, struct page *locked_page
 	const bool zoned = btrfs_is_zoned(inode->root->fs_info);
 
 	if (should_nocow(inode, start, end)) {
-		ASSERT(!zoned);
+		/*
+		 * Normally on a zoned device we're only doing COW writes, but
+		 * in case of relocation on a zoned filesystem we have taken
+		 * precaution, that we're only writing sequentially. It's safe
+		 * to use run_delalloc_nocow() here, like for  regular
+		 * preallocated inodes.
+		 */
+		ASSERT(!zoned ||
+		       (zoned && btrfs_is_data_reloc_root(inode->root)));
 		ret = run_delalloc_nocow(inode, locked_page, start, end,
 					 page_started, nr_written);
 	} else if (!inode_can_compress(inode) ||