Re: [PATCH 1/3] btrfs-progs: check/lowmem: Check and repair root generation

[Nikolay Borisov <nborisov@suse.com>]

On 9.08.19 г. 9:53 ч., Qu Wenruo wrote:
> Since kernel is going to reject any root item which is newer than super
> block generation, we need to provide a way to fix such problem in
> btrfs-check.
> 
> This patch addes the ability to report and repair root generation in
> lowmem mode.
> 
> This is done by cowing the root node, so we will update the root
> generation along with the root node generation at commit transaction
> time.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  check/mode-common.c | 29 +++++++++++++++++++++++++++++
>  check/mode-common.h |  1 +
>  check/mode-lowmem.c | 16 ++++++++++++++++
>  check/mode-lowmem.h |  1 +
>  4 files changed, 47 insertions(+)
> 
> diff --git a/check/mode-common.c b/check/mode-common.c
> index d5f6c8ef97b1..a5b86a0ac32a 100644
> --- a/check/mode-common.c
> +++ b/check/mode-common.c
> @@ -924,3 +924,32 @@ int check_repair_free_space_inode(struct btrfs_fs_info *fs_info,
>  	}
>  	return ret;
>  }
> +
> +int repair_root_generation(struct btrfs_root *root)
> +{
> +	struct btrfs_trans_handle *trans;
> +	struct btrfs_path path;
> +	struct btrfs_key key;
> +	int ret;
> +
> +	trans = btrfs_start_transaction(root, 1);
> +	if (IS_ERR(trans))
> +		return PTR_ERR(trans);
> +
> +	key.objectid = 0;
> +	key.type = 0;
> +	key.offset = 0;
> +	btrfs_init_path(&path);
> +
> +	/* Here we only CoW the tree root to update the geneartion */
> +	path.lowest_level = btrfs_header_level(root->node);
> +	root->node->flags |= EXTENT_BAD_TRANSID;

Why do you set EXTENT_BAD_TRANSID? This flag is currently used only in
read_tree_block to link blocks which have failed ordinary validation to
the recow_ebs list, and this only happens in case we have a single copy
for this eb. This list is then processed in the main check logic.

So repair_root_generation could possibly be as simple as just linking
root->node to the fs_info->recow_ebs and leave the rest to the existing
logic?

> +
> +	ret = btrfs_search_slot(trans, root, &key, &path, 0, 1);
> +	if (ret < 0)
> +		return ret;
> +
> +	btrfs_release_path(&path);
> +	ret = btrfs_commit_transaction(trans, root);
> +	return ret;
> +}
> diff --git a/check/mode-common.h b/check/mode-common.h
> index 4c169c6e3b29..4a3abeb02c81 100644
> --- a/check/mode-common.h
> +++ b/check/mode-common.h
> @@ -155,4 +155,5 @@ static inline bool is_valid_imode(u32 imode)
>  	return true;
>  }
>  
> +int repair_root_generation(struct btrfs_root *root);
>  #endif
> diff --git a/check/mode-lowmem.c b/check/mode-lowmem.c
> index a2be0e6d7034..bf3b57f5ad2d 100644
> --- a/check/mode-lowmem.c
> +++ b/check/mode-lowmem.c
> @@ -4957,6 +4957,7 @@ static int check_btrfs_root(struct btrfs_root *root, int check_all)
>  	struct btrfs_path path;
>  	struct node_refs nrefs;
>  	struct btrfs_root_item *root_item = &root->root_item;
> +	u64 super_generation = btrfs_super_generation(root->fs_info->super_copy);
>  	int ret;
>  	int level;
>  	int err = 0;
> @@ -4978,6 +4979,21 @@ static int check_btrfs_root(struct btrfs_root *root, int check_all)
>  	level = btrfs_header_level(root->node);
>  	btrfs_init_path(&path);
>  
> +	if (btrfs_root_generation(root_item) > super_generation + 1) {
> +		error(
> +	"invalid root generation for root %llu, have %llu expect (0, %llu)",
> +		      root->root_key.objectid, btrfs_root_generation(root_item),
> +		      super_generation + 1);
> +		err |= INVALID_GENERATION;
> +		if (repair) {
> +			ret = repair_root_generation(root);
> +			if (!ret) {
> +				err &= ~INVALID_GENERATION;
> +				printf("Reset generation for root %llu\n",
> +					root->root_key.objectid);
> +			}
> +		}
> +	}
>  	if (btrfs_root_refs(root_item) > 0 ||
>  	    btrfs_disk_key_objectid(&root_item->drop_progress) == 0) {
>  		path.nodes[level] = root->node;
> diff --git a/check/mode-lowmem.h b/check/mode-lowmem.h
> index d2983fd12eb4..0361fb3382b1 100644
> --- a/check/mode-lowmem.h
> +++ b/check/mode-lowmem.h
> @@ -47,6 +47,7 @@
>  #define INODE_FLAGS_ERROR	(1<<23) /* Invalid inode flags */
>  #define DIR_ITEM_HASH_MISMATCH	(1<<24) /* Dir item hash mismatch */
>  #define INODE_MODE_ERROR	(1<<25) /* Bad inode mode */
> +#define INVALID_GENERATION	(1<<26)	/* Generation is too new */
>  
>  /*
>   * Error bit for low memory mode check.
>