Re: [PATCH 2/2] btrfs: pretty print leaked root name

[David Sterba <dsterba@suse.cz>]

On Thu, Sep 03, 2020 at 02:29:51PM -0400, Josef Bacik wrote:
> I'm a actual human being so am incapable of converting u64 to s64 in my
> head, so add a helper to get the pretty name of a root objectid and use
> that helper to spit out the name for any special roots for leaked roots,
> so I don't have to scratch my head and figure out which root I messed up
> the refs for.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> ---
>  fs/btrfs/disk-io.c    |  6 ++++--
>  fs/btrfs/print-tree.c | 39 +++++++++++++++++++++++++++++++++++++++
>  fs/btrfs/print-tree.h |  3 +++
>  3 files changed, 46 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index 7147237d9bf0..71beb9493ab4 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -1504,10 +1504,12 @@ void btrfs_check_leaked_roots(struct btrfs_fs_info *fs_info)
>  	struct btrfs_root *root;
>  
>  	while (!list_empty(&fs_info->allocated_roots)) {
> +		char buf[BTRFS_ROOT_NAME_BUF_LEN];
> +
>  		root = list_first_entry(&fs_info->allocated_roots,
>  					struct btrfs_root, leak_list);
> -		btrfs_err(fs_info, "leaked root %llu-%llu refcount %d",
> -			  root->root_key.objectid, root->root_key.offset,
> +		btrfs_err(fs_info, "leaked root %s refcount %d",
> +			  btrfs_root_name(root->root_key.objectid, buf),
>  			  refcount_read(&root->refs));
>  		while (refcount_read(&root->refs) > 1)
>  			btrfs_put_root(root);
> diff --git a/fs/btrfs/print-tree.c b/fs/btrfs/print-tree.c
> index 80567c11ec12..d0370075a719 100644
> --- a/fs/btrfs/print-tree.c
> +++ b/fs/btrfs/print-tree.c
> @@ -7,6 +7,45 @@
>  #include "disk-io.h"
>  #include "print-tree.h"
>  
> +struct name_map {
> +	u64 id;
> +	char *name;

	const char* or maybe even a fixed length string, removing the
	_TREE suffix

> +};
> +
> +static const struct name_map root_map[] = {
> +	{ BTRFS_ROOT_TREE_OBJECTID,		"ROOT_TREE"		},
> +	{ BTRFS_EXTENT_TREE_OBJECTID,		"EXTENT_TREE"		},
> +	{ BTRFS_CHUNK_TREE_OBJECTID,		"CHUNK_TREE"		},
> +	{ BTRFS_DEV_TREE_OBJECTID,		"DEV_TREE"		},
> +	{ BTRFS_FS_TREE_OBJECTID,		"FS_TREE"		},
> +	{ BTRFS_ROOT_TREE_DIR_OBJECTID,		"ROOT_TREE_DIR"		},

This is not a tree id

> +	{ BTRFS_CSUM_TREE_OBJECTID,		"CSUM_TREE"		},
> +	{ BTRFS_TREE_LOG_OBJECTID,		"TREE_LOG"		},
> +	{ BTRFS_QUOTA_TREE_OBJECTID,		"QUOTA_TREE"		},
> +	{ BTRFS_UUID_TREE_OBJECTID,		"UUID_TREE"		},
> +	{ BTRFS_FREE_SPACE_TREE_OBJECTID,	"FREE_SPACE_TREE"	},
> +	{ BTRFS_DATA_RELOC_TREE_OBJECTID,	"DATA_RELOC_TREE"	},

I've noticed we have the id -> str mapping already in
btrfs_lockdep_keysets, so there could be just one such structure and
we'd add wrappers around that.

Also the C99 initializers should be used.

> +};
> +
> +char *btrfs_root_name(u64 objectid, char *buf)
> +{
> +	int i;
> +
> +	if (objectid == BTRFS_TREE_RELOC_OBJECTID) {
> +		snprintf(buf, BTRFS_ROOT_NAME_BUF_LEN,
> +			 "TREE_RELOC offset=%llu", objectid);

The reloc tree is an outlier here so I wonder if we'd rather have a nice
pretty printer of the tree root name and deal with the oddities where
required rather than inside the helper. In this case there would have to
be some conditionals in btrfs_check_leaked_roots, as we can't do that in
the format string.