Re: [PATCH 5/8] btrfs-progs: ctree: Introduce function to create an empty tree

[Lu Fengqi <lufq.fnst@cn.fujitsu.com>]

On 10/27/2017 03:29 PM, Qu Wenruo wrote:
> Introduce a new function, btrfs_create_tree(), to create an empty tree.
> 
> Currently, there is only one caller to create new tree, namely
> data reloc tree in mkfs.
> However it's copying fs tree to create a new root.
> 
> This copy fs tree method is not a good idea if we only need an empty
> tree.
> 
> So here introduce a new function, btrfs_create_tree() to create new
> tree.
> Which will handle the following things:
> 1) New tree root leaf
>     Using generic tree allocation
> 
> 2) New root item in tree root
> 
> 3) Modify special tree root pointers in fs_info
>     Only quota_root is supported yet, but can be expended easily
> 
> This patch provides the basis to implement quota support in mkfs.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>   ctree.c | 109 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>   ctree.h |   2 ++
>   2 files changed, 111 insertions(+)
> 
> diff --git a/ctree.c b/ctree.c
> index 4fc33b14000a..c707be58c413 100644
> --- a/ctree.c
> +++ b/ctree.c
> @@ -22,6 +22,7 @@
>   #include "repair.h"
>   #include "internal.h"
>   #include "sizes.h"
> +#include "utils.h"
>   
>   static int split_node(struct btrfs_trans_handle *trans, struct btrfs_root
>   		      *root, struct btrfs_path *path, int level);
> @@ -136,6 +137,114 @@ int btrfs_copy_root(struct btrfs_trans_handle *trans,
>   	return 0;
>   }
>   
> +/*
> + * Create a new tree root, with root objectid set to @objectid.
> + *
> + * NOTE: Doesn't support tree with non-zero offset, like tree reloc tree.
> + */
> +int btrfs_create_root(struct btrfs_trans_handle *trans,
> +		      struct btrfs_fs_info *fs_info, u64 objectid)
> +{
> +	struct extent_buffer *node;
> +	struct btrfs_root *new_root;
> +	struct btrfs_disk_key disk_key;
> +	struct btrfs_key location;
> +	struct btrfs_root_item root_item = { 0 };
> +	int ret;
> +
> +	new_root = malloc(sizeof(*new_root));
> +	if (!new_root)
> +		return -ENOMEM;
> +
> +	btrfs_setup_root(new_root, fs_info, objectid);
> +	if (!is_fstree(objectid))
> +		new_root->track_dirty = 1;
> +	add_root_to_dirty_list(new_root);

Since add_root_to_dirty_list only add root which track_dirty != 0 to 
dirty list, why not write like the following?

         if (!is_fstree(objectid)) {
                 new_root->track_dirty = 1;
                 add_root_to_dirty_list(new_root);
         }

> +
> +	new_root->objectid = objectid;
> +	new_root->root_key.objectid = objectid;

These have been initialized in btrfs_setup_root, so we don't need to 
initialize again.

> +	new_root->root_key.type = BTRFS_ROOT_ITEM_KEY;
> +	new_root->root_key.offset = 0;
> +
> +	node = btrfs_alloc_free_block(trans, new_root, fs_info->nodesize,
> +				      objectid, &disk_key, 0, 0, 0);
> +	if (IS_ERR(node)) {
> +		ret = PTR_ERR(node);
> +		error("failed to create root node for tree %llu: %d (%s)",
> +		      objectid, ret, strerror(-ret));
> +		return ret;
> +	}
> +	new_root->node = node;
> +
> +	btrfs_set_header_generation(node, trans->transid);
> +	btrfs_set_header_backref_rev(node, BTRFS_MIXED_BACKREF_REV);
> +	btrfs_clear_header_flag(node, BTRFS_HEADER_FLAG_RELOC |
> +				      BTRFS_HEADER_FLAG_WRITTEN);
> +	btrfs_set_header_owner(node, objectid);
> +	btrfs_set_header_nritems(node, 0);
> +	btrfs_set_header_level(node, 0);
> +	write_extent_buffer(node, fs_info->fsid, btrfs_header_fsid(),
> +			    BTRFS_FSID_SIZE);
> +	ret = btrfs_inc_ref(trans, new_root, node, 0);
> +	if (ret < 0)
> +		goto free;
> +
> +	/*
> +	 * Special tree roots may need to modify pointers in @fs_info
> +	 * Only quota is supported yet.
> +	 */
> +	switch (objectid) {
> +	case BTRFS_QUOTA_TREE_OBJECTID:
> +		if (fs_info->quota_root) {
> +			error("quota root already exists");
> +			ret = -EEXIST;
> +			goto free;
> +		}
> +		fs_info->quota_root = new_root;
> +		fs_info->quota_enabled = 1;
> +		break;
> +	/*
> +	 * Essential trees can't be created by this function, yet.
> +	 * As we expect such skeleton exists, or a lot of functions like
> +	 * btrfs_alloc_free_block() doesn't work at all
> +	 */
> +	case BTRFS_ROOT_TREE_OBJECTID:
> +	case BTRFS_EXTENT_TREE_OBJECTID:
> +	case BTRFS_CHUNK_TREE_OBJECTID:
> +	case BTRFS_FS_TREE_OBJECTID:
> +		ret = -EEXIST;
> +		goto free;
> +	default:
> +		/* Subvolume trees don't need special handles */
> +		if (is_fstree(objectid))
> +			break;
> +		/* Other special trees are not supported yet */
> +		ret = -ENOTTY;
> +		goto free;
> +	}
> +	btrfs_mark_buffer_dirty(node);
> +	btrfs_set_root_bytenr(&root_item, btrfs_header_bytenr(node));
> +	btrfs_set_root_level(&root_item, 0);
> +	btrfs_set_root_generation(&root_item, trans->transid);
> +	btrfs_set_root_dirid(&root_item, 0);
> +	btrfs_set_root_refs(&root_item, 1);
> +	btrfs_set_root_used(&root_item, fs_info->nodesize);
> +	location.objectid = objectid;
> +	location.type = BTRFS_ROOT_ITEM_KEY;
> +	location.offset = 0;
> +
> +	ret = btrfs_insert_root(trans, fs_info->tree_root, &location,
> +				&root_item);
> +	if (ret < 0)
> +		goto free;
> +	return ret;
> +
> +free:
> +	free_extent_buffer(node);
> +	free(new_root);
> +	return ret;
> +}
> +
>   /*
>    * check if the tree block can be shared by multiple trees
>    */
> diff --git a/ctree.h b/ctree.h
> index 506b76766579..ac8ce70a55e7 100644
> --- a/ctree.h
> +++ b/ctree.h
> @@ -2558,6 +2558,8 @@ int btrfs_copy_root(struct btrfs_trans_handle *trans,
>   		      struct btrfs_root *root,
>   		      struct extent_buffer *buf,
>   		      struct extent_buffer **cow_ret, u64 new_root_objectid);
> +int btrfs_create_root(struct btrfs_trans_handle *trans,
> +		      struct btrfs_fs_info *fs_info, u64 objectid);
>   int btrfs_extend_item(struct btrfs_root *root, struct btrfs_path *path,
>   		u32 data_size);
>   int btrfs_truncate_item(struct btrfs_root *root, struct btrfs_path *path,
> 


-- 
Thanks,
Lu