Re: [PATCH v4 1/6] btrfs: Introduce a function to check if all chunks a OK for degraded rw mount

[Nikolay Borisov <nborisov@suse.com>]

On 28.06.2017 08:43, Qu Wenruo wrote:
> Introduce a new function, btrfs_check_rw_degradable(), to check if all
> chunks in btrfs is OK for degraded rw mount.
> 
> It provides the new basis for accurate btrfs mount/remount and even
> runtime degraded mount check other than old one-size-fit-all method.
> 
> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
>  fs/btrfs/volumes.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  fs/btrfs/volumes.h |  1 +
>  2 files changed, 59 insertions(+)
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index c95f018d4a1e..7a72fbdb8262 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -6817,6 +6817,64 @@ int btrfs_read_sys_array(struct btrfs_fs_info *fs_info)
>  	return -EIO;
>  }
>  
> +/*
> + * Check if all chunks in the fs is OK for read-write degraded mount
> + *
> + * Return true if all chunks meet the minimal RW mount requirement.
> + * Return false if any chunk doesn't meet the minimal RW mount requirement.
> + */
> +bool btrfs_check_rw_degradable(struct btrfs_fs_info *fs_info)
> +{
> +	struct btrfs_mapping_tree *map_tree = &fs_info->mapping_tree;
> +	struct extent_map *em;
> +	u64 next_start = 0;
> +	bool ret = true;
> +
> +	read_lock(&map_tree->map_tree.lock);
> +	em = lookup_extent_mapping(&map_tree->map_tree, 0, (u64)-1);
> +	read_unlock(&map_tree->map_tree.lock);
> +	/* No chunk at all? Return false anyway */
> +	if (!em) {
> +		ret = false;
> +		goto out;
> +	}
> +	while (em) {
> +		struct map_lookup *map;
> +		int missing = 0;
> +		int max_tolerated;
> +		int i;
> +
> +		map = em->map_lookup;
> +		max_tolerated =
> +			btrfs_get_num_tolerated_disk_barrier_failures(
> +					map->type);
> +		for (i = 0; i < map->num_stripes; i++) {
> +			struct btrfs_device *dev = map->stripes[i].dev;
> +
> +			if (!dev || !dev->bdev || dev->missing ||
> +			    dev->last_flush_error)
> +				missing++;
> +		}
> +		if (missing > max_tolerated) {
> +			ret = false;
> +			btrfs_warn(fs_info,
> +	"chunk %llu missing %d devices, max tolerance is %d for writeble mount",
> +				   em->start, missing, max_tolerated);
> +			free_extent_map(em);
> +			goto out;
> +		}
> +		next_start = extent_map_end(em);
> +		free_extent_map(em);
> +
> +		read_lock(&map_tree->map_tree.lock);
> +		em = lookup_extent_mapping(&map_tree->map_tree, next_start,
> +					   (u64)(-1) - next_start);
> +		read_unlock(&map_tree->map_tree.lock);
> +	}
> +out:
> +	return ret;
> +}
> +

Nit but I think in this function it would be best to directly return
true/false based on context rather than having the superfluous goto.

>  int btrfs_read_chunk_tree(struct btrfs_fs_info *fs_info)
>  {
>  	struct btrfs_root *root = fs_info->chunk_root;
> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> index 6f45fd60d15a..a5897c7a7e86 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -543,4 +543,5 @@ struct list_head *btrfs_get_fs_uuids(void);
>  void btrfs_set_fs_info_ptr(struct btrfs_fs_info *fs_info);
>  void btrfs_reset_fs_info_ptr(struct btrfs_fs_info *fs_info);
>  
> +bool btrfs_check_rw_degradable(struct btrfs_fs_info *fs_info);
>  #endif
>