Re: [PATCH 3/4] btrfs: sysfs: export supported checksums

[Nikolay Borisov <nborisov@suse.com>]

On 7.10.19 г. 12:11 ч., Johannes Thumshirn wrote:
> From: David Sterba <dsterba@suse.com>
> 
> Export supported checksum algorithms via sysfs.
> 
> Co-developed-by: David Sterba <dsterba@suse.com> 
> Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
> ---
>  fs/btrfs/ctree.c |  5 +++++
>  fs/btrfs/ctree.h |  2 ++
>  fs/btrfs/sysfs.c | 33 +++++++++++++++++++++++++++++++++
>  3 files changed, 40 insertions(+)
> 
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index b66509ee62eb..5debd74dc61c 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -53,6 +53,11 @@ const char *btrfs_super_csum_name(u16 csum_type)
>  	return btrfs_csums[csum_type].name;
>  }
>  
> +size_t btrfs_get_num_csums(void)
> +{
> +	return ARRAY_SIZE(btrfs_csums);
> +}

nit: This function is used only once and the ARRAY_SIZE() macro is
descriptive enough, why not just remove it and opencoude the call to
array_size

> +
>  struct btrfs_path *btrfs_alloc_path(void)
>  {
>  	return kmem_cache_zalloc(btrfs_path_cachep, GFP_NOFS);
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index d17e79a40930..0180554f6970 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -2165,6 +2165,8 @@ BTRFS_SETGET_STACK_FUNCS(super_uuid_tree_generation, struct btrfs_super_block,
>  
>  int btrfs_super_csum_size(const struct btrfs_super_block *s);
>  const char *btrfs_super_csum_name(u16 csum_type);
> +size_t btrfs_get_num_csums(void);
> +
>  
>  /*
>   * The leaf data grows from end-to-front in the node.
> diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
> index f6d3c80f2e28..aeebbdfe1a98 100644
> --- a/fs/btrfs/sysfs.c
> +++ b/fs/btrfs/sysfs.c
> @@ -246,6 +246,28 @@ static umode_t btrfs_feature_visible(struct kobject *kobj,
>  	return mode;
>  }
>  
> +static ssize_t btrfs_supported_checksums_show(struct kobject *kobj,
> +					      struct kobj_attribute *a,
> +					      char *buf)
> +{
> +	ssize_t ret = 0;
> +	int i;
> +
> +	for (i = 0; i < btrfs_get_num_csums(); i++) {
> +		/*
> +		 * This "trick" only works as long as 'enum btrfs_csum_type' has
> +		 * no holes in it
> +		 */
> +		ret += snprintf(buf + ret, PAGE_SIZE - ret, "%s%s",
> +				(i == 0 ? "" : ", "),
> +				btrfs_super_csum_name(i));
> +
> +	}
> +
> +	ret += snprintf(buf + ret, PAGE_SIZE - ret, "\n");
> +	return ret;
> +}
> +
>  BTRFS_FEAT_ATTR_INCOMPAT(mixed_backref, MIXED_BACKREF);
>  BTRFS_FEAT_ATTR_INCOMPAT(default_subvol, DEFAULT_SUBVOL);
>  BTRFS_FEAT_ATTR_INCOMPAT(mixed_groups, MIXED_GROUPS);
> @@ -259,6 +281,14 @@ BTRFS_FEAT_ATTR_INCOMPAT(no_holes, NO_HOLES);
>  BTRFS_FEAT_ATTR_INCOMPAT(metadata_uuid, METADATA_UUID);
>  BTRFS_FEAT_ATTR_COMPAT_RO(free_space_tree, FREE_SPACE_TREE);
>  
> +static struct btrfs_feature_attr btrfs_attr_features_checksums_name = {
> +	.kobj_attr = __INIT_KOBJ_ATTR(supported_checksums, S_IRUGO,
> +				      btrfs_supported_checksums_show,
> +				      NULL),
> +	.feature_set	= FEAT_INCOMPAT,
> +	.feature_bit	= 0,
> +};
> +
>  static struct attribute *btrfs_supported_feature_attrs[] = {
>  	BTRFS_FEAT_ATTR_PTR(mixed_backref),
>  	BTRFS_FEAT_ATTR_PTR(default_subvol),
> @@ -272,6 +302,9 @@ static struct attribute *btrfs_supported_feature_attrs[] = {
>  	BTRFS_FEAT_ATTR_PTR(no_holes),
>  	BTRFS_FEAT_ATTR_PTR(metadata_uuid),
>  	BTRFS_FEAT_ATTR_PTR(free_space_tree),
> +
> +	&btrfs_attr_features_checksums_name.kobj_attr.attr,
> +
>  	NULL
>  };
>  
>