Re: [PATCH 3/3] btrfs-progs: Create uuid tree with proper contents

[Nikolay Borisov <nborisov@suse.com>]

On 27.12.18 г. 9:13 ч., Qu Wenruo wrote:
> Commit 2a496a5b8b74 ("btrfs-progs: mkfs: precreate the uuid tree")
> creates uuid tree at mkfs time.
> 
> However it doesn't populate uuid tree correctly nor just create an empty
> root.
> It uses create_tree(), which just copies the content of fs root,
> containing meaningless INODE_ITEM:
> 
> v4.15 mkfs (no uuid tree creation) + kernel mount:
>   uuid tree key (UUID_TREE ROOT_ITEM 0)
>   leaf 30572544 items 1 free space 16250 generation 7 owner UUID_TREE
>   leaf 30572544 flags 0x1(WRITTEN) backref revision 1
>   fs uuid 33ecddef-fc86-481a-93ce-846b01c11376
>   chunk uuid 9e58f646-b0da-43ca-9c7d-8bbe3e120246
> 	item 0 key (0x92457c59d31491be UUID_KEY_SUBVOL 0xef908b5e79aa76a1) itemoff 16275 itemsize 8
> 		subvol_id 5
> 
> v4.19.1 mkfs (incorrect one), no kernel mount:
>   uuid tree key (UUID_TREE ROOT_ITEM 0)
>   leaf 30507008 items 2 free space 16061 generation 4 owner UUID_TREE
>   leaf 30507008 flags 0x1(WRITTEN) backref revision 1
>   fs uuid 162f5333-9b5d-4217-877c-ddaeaa79398e
>   chunk uuid 7bc2c5c6-a6d2-4eec-a513-142b549c6541
> 	item 0 key (256 INODE_ITEM 0) itemoff 16123 itemsize 160
> 		generation 3 transid 0 size 0 nbytes 16384
> 		block group 0 mode 40755 links 1 uid 0 gid 0 rdev 0
> 		sequence 0 flags 0x0(none)
> 	item 1 key (256 INODE_REF 256) itemoff 16111 itemsize 12
> 		index 0 namelen 2 name: ..
> 
> This patchset will fix it by populuating uuid tree properly:
> (NOTE: due to tree-checker, kernel doesn't accept empty uuid tree, so we
>  can only fix it by populating uuid tree correctly)
> 
> w/ this patchset, no kernel mount:
>   uuid tree key (UUID_TREE ROOT_ITEM 0)
>   leaf 30507008 items 1 free space 16250 generation 4 owner UUID_TREE
>   leaf 30507008 flags 0x1(WRITTEN) backref revision 1
>   fs uuid ae53079e-dbbc-409b-a565-5326c7b27731
>   chunk uuid b5fb1bea-f20d-4af1-80f8-6ca3f0038d67
> 	item 0 key (0x334ba6b032d89c07 UUID_KEY_SUBVOL 0x86cde09cb78bcca0) itemoff 16275 itemsize 8
> 		subvol_id 5
> 
> For kernel, except tree-checker needs an non-empty uuid tree, both all
> above behavior won't cause problem, but it's always better to keep a
> good standardized behavior.
> 
> Furthermore, to avoid such problem from happening again, rename the
> function create_tree() to create_empty_tree() and create_inode_tree(),
> without an @root parameter to avoid such problem.
> 
> Fixes: 2a496a5b8b74 ("btrfs-progs: mkfs: precreate the uuid tree")
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  disk-io.c     |   4 ++
>  mkfs/common.c | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  mkfs/common.h |   3 ++
>  mkfs/main.c   |  36 +-----------------
>  4 files changed, 112 insertions(+), 34 deletions(-)
> 
> diff --git a/disk-io.c b/disk-io.c
> index 5fafa144c0d3..2cb7f2097fc9 100644
> --- a/disk-io.c
> +++ b/disk-io.c
> @@ -694,6 +694,8 @@ void btrfs_free_fs_info(struct btrfs_fs_info *fs_info)
>  {
>  	if (fs_info->quota_root)
>  		free(fs_info->quota_root);
> +	if (fs_info->uuid_root)
> +		free(fs_info->uuid_root);
>  
>  	free(fs_info->tree_root);
>  	free(fs_info->extent_root);
> @@ -964,6 +966,8 @@ void btrfs_release_all_roots(struct btrfs_fs_info *fs_info)
>  		free_extent_buffer(fs_info->log_root_tree->node);
>  	if (fs_info->chunk_root)
>  		free_extent_buffer(fs_info->chunk_root->node);
> +	if (fs_info->uuid_root)
> +		free_extent_buffer(fs_info->uuid_root->node);
>  }
>  
>  static void free_map_lookup(struct cache_extent *ce)
> diff --git a/mkfs/common.c b/mkfs/common.c
> index f7e3badcf2b9..1f5e1d03a6e3 100644
> --- a/mkfs/common.c
> +++ b/mkfs/common.c
> @@ -23,6 +23,7 @@
>  #include "disk-io.h"
>  #include "volumes.h"
>  #include "utils.h"
> +#include "transaction.h"
>  #include "mkfs/common.h"
>  
>  static u64 reference_root_table[] = {
> @@ -822,4 +823,106 @@ int test_minimum_size(const char *file, u64 min_dev_size)
>  	return 0;
>  }
>  
> +/*
> + * Create a tree with all its content copied from @source
> + *
> + * Caller must ensure @source only has one leaf.
> + */
> +static int __create_tree(struct btrfs_trans_handle *trans,
> +			 struct btrfs_root *root, u64 objectid)
> +{
> +	struct btrfs_fs_info *fs_info = trans->fs_info;
> +	struct btrfs_key location;
> +	struct btrfs_root_item root_item;
> +	struct extent_buffer *tmp;
> +	u8 uuid[BTRFS_UUID_SIZE] = {0};
> +	int ret;
> +
> +	ASSERT(btrfs_header_level(root->node) == 0);
> +
> +	ret = btrfs_copy_root(trans, root, root->node, &tmp, objectid);
> +	if (ret)
> +		return ret;
> +
> +	memcpy(&root_item, &root->root_item, sizeof(root_item));
> +	btrfs_set_root_bytenr(&root_item, tmp->start);
> +	btrfs_set_root_level(&root_item, btrfs_header_level(tmp));
> +	btrfs_set_root_generation(&root_item, trans->transid);
> +	/* clear uuid and o/ctime of source tree */
> +	memcpy(root_item.uuid, uuid, BTRFS_UUID_SIZE);
> +	btrfs_set_stack_timespec_sec(&root_item.otime, 0);
> +	btrfs_set_stack_timespec_sec(&root_item.ctime, 0);
> +	free_extent_buffer(tmp);
> +
> +	location.objectid = objectid;
> +	location.type = BTRFS_ROOT_ITEM_KEY;
> +	location.offset = 0;
> +	ret = btrfs_insert_root(trans, fs_info->tree_root,
> +				&location, &root_item);
> +
> +	return ret;
> +}
> +
> +/*
> + * Create an *EMPTY* tree
> + *
> + * Caller must ensure at the time of calling, csum tree is still empty
> + */
> +static int create_empty_tree(struct btrfs_trans_handle *trans, u64 objectid)
> +{
> +	struct btrfs_root *csum_root = trans->fs_info->csum_root;
> +
> +	ASSERT(btrfs_header_level(csum_root->node) == 0 &&
> +	       btrfs_header_nritems(csum_root->node) == 0);
> +	return __create_tree(trans, csum_root, objectid);

nit: IMO this approach (of using a tree as a prototype) is rather bogus
since you exploit the fact that an arbitrary tree (in this case csum)
*should* be empty and so you use it as the source for another empty
tree. Analogically, further down you exploit the fact that the fs_tree
has a default inode and copy that.

I'd prefer it if every tree was created explicitly so that in the future
when its layout might change we touch the respective function. This is
not critical but it's something to think about.

> +}
>  
> +/*
> + * Create a tree containing an root inode
> + *
> + * Caller must ensure at the time of calling, fs tree only contains 2 items
> + * (one for INODE_ITEM and one for INODE_REF)
> + */
> +int create_inode_tree(struct btrfs_trans_handle *trans, u64 objectid)

This function is really misnamed, since it's creating the
DATA_RELOC_TREE, yet it's called create_inode_tree. Why not simply
create_data_reloc_tree or are you planning on using this function more
than once?

> +{
> +	struct btrfs_root *fs_root = trans->fs_info->fs_root;
> +
> +	ASSERT(btrfs_header_level(fs_root->node) == 0 &&
> +	       btrfs_header_nritems(fs_root->node) == 2);
> +	return __create_tree(trans, fs_root, objectid);
> +}
> +
> +int create_uuid_tree(struct btrfs_trans_handle *trans)
> +{
> +	struct btrfs_fs_info *fs_info = trans->fs_info;
> +	struct btrfs_root *uuid_root = fs_info->uuid_root;
> +	struct btrfs_key key;
> +	int ret;
> +
> +	if (!uuid_root) {

Isn't this always true,  so the conditional here is redundant?

> +		ret = create_empty_tree(trans, BTRFS_UUID_TREE_OBJECTID);
> +		if (ret < 0) {
> +			errno = -ret;
> +			error("failed to create uuid root: %m");
> +			return ret;
> +		}
> +		key.objectid = BTRFS_UUID_TREE_OBJECTID;
> +		key.type = BTRFS_ROOT_ITEM_KEY;
> +		key.offset = 0;
> +		uuid_root = btrfs_read_fs_root_no_cache(fs_info, &key);
> +		if (IS_ERR(uuid_root)) {
> +			errno = -PTR_ERR(uuid_root);
> +			error("failed to read uuid root: %m");
> +			return PTR_ERR(uuid_root);
> +		}
> +		fs_info->uuid_root = uuid_root;
> +	}
> +	ret = btrfs_uuid_tree_add(trans, fs_info->fs_root->root_item.uuid,
> +				  BTRFS_UUID_KEY_SUBVOL,
> +				  fs_info->fs_root->root_key.objectid);
> +	if (ret < 0) {
> +		errno = -ret;
> +		error("failed to add uuid tree entry for fs root: %m");
> +	}
> +	return ret;
> +}
> diff --git a/mkfs/common.h b/mkfs/common.h
> index 28912906d0a9..adb5d561c38d 100644
> --- a/mkfs/common.h
> +++ b/mkfs/common.h
> @@ -75,4 +75,7 @@ int test_num_disk_vs_raid(u64 metadata_profile, u64 data_profile,
>  int test_status_for_mkfs(const char *file, bool force_overwrite);
>  int test_dev_for_mkfs(const char *file, int force_overwrite);
>  
> +int create_uuid_tree(struct btrfs_trans_handle *trans);
> +int create_inode_tree(struct btrfs_trans_handle *trans, u64 objectid);
> +
>  #endif
> diff --git a/mkfs/main.c b/mkfs/main.c
> index b6748f7fe853..ea3d1ae80e5e 100644
> --- a/mkfs/main.c
> +++ b/mkfs/main.c
> @@ -309,38 +309,6 @@ static int create_raid_groups(struct btrfs_trans_handle *trans,
>  	return ret;
>  }
>  
> -static int create_tree(struct btrfs_trans_handle *trans,
> -			struct btrfs_root *root, u64 objectid)
> -{
> -	struct btrfs_key location;
> -	struct btrfs_root_item root_item;
> -	struct extent_buffer *tmp;
> -	u8 uuid[BTRFS_UUID_SIZE] = {0};
> -	int ret;
> -
> -	ret = btrfs_copy_root(trans, root, root->node, &tmp, objectid);
> -	if (ret)
> -		return ret;
> -
> -	memcpy(&root_item, &root->root_item, sizeof(root_item));
> -	btrfs_set_root_bytenr(&root_item, tmp->start);
> -	btrfs_set_root_level(&root_item, btrfs_header_level(tmp));
> -	btrfs_set_root_generation(&root_item, trans->transid);
> -	/* clear uuid and o/ctime of source tree */
> -	memcpy(root_item.uuid, uuid, BTRFS_UUID_SIZE);
> -	btrfs_set_stack_timespec_sec(&root_item.otime, 0);
> -	btrfs_set_stack_timespec_sec(&root_item.ctime, 0);
> -	free_extent_buffer(tmp);
> -
> -	location.objectid = objectid;
> -	location.type = BTRFS_ROOT_ITEM_KEY;
> -	location.offset = 0;
> -	ret = btrfs_insert_root(trans, root->fs_info->tree_root,
> -				&location, &root_item);
> -
> -	return ret;
> -}
> -
>  static void print_usage(int ret)
>  {
>  	printf("Usage: mkfs.btrfs [options] dev [ dev ... ]\n");
> @@ -1203,13 +1171,13 @@ raid_groups:
>  		goto out;
>  	}
>  
> -	ret = create_tree(trans, root, BTRFS_DATA_RELOC_TREE_OBJECTID);
> +	ret = create_inode_tree(trans, BTRFS_DATA_RELOC_TREE_OBJECTID);
>  	if (ret) {
>  		error("unable to create data reloc tree: %d", ret);
>  		goto out;
>  	}
>  
> -	ret = create_tree(trans, root, BTRFS_UUID_TREE_OBJECTID);
> +	ret = create_uuid_tree(trans);
>  	if (ret)
>  		warning(
>  	"unable to create uuid tree, will be created after mount: %d", ret);
>