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

[Nikolay Borisov <nborisov@suse.com>]

On 25.07.19 г. 12:33 ч., Johannes Thumshirn wrote:
> From: David Sterba <dsterba@suse.com>
> 
> Export supported checksum algorithms via sysfs.
> 
> Signed-off-by: David Sterba <dsterba@suse.com>
> Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
> ---
>  fs/btrfs/sysfs.c | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
> 
> diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
> index 9539f8143b7a..920282a3452b 100644
> --- a/fs/btrfs/sysfs.c
> +++ b/fs/btrfs/sysfs.c
> @@ -182,6 +182,30 @@ static umode_t btrfs_feature_visible(struct kobject *kobj,
>  	return mode;
>  }
>  
> +static ssize_t btrfs_checksums_show(struct kobject *kobj,
> +				       struct kobj_attribute *a, char *buf)
> +{
> +	ssize_t ret = 0;
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(btrfs_csums); i++) {
> +		ret += snprintf(buf + ret, PAGE_SIZE, "%s%s",
> +				(i == 0 ? "" : ", "),
> +				btrfs_csums[i].name);
> +
> +	}
> +
> +	ret += snprintf(buf + ret, PAGE_SIZE, "\n");
> +	return ret;
> +}
> +
> +static ssize_t btrfs_checksums_store(struct kobject *kobj,
> +					struct kobj_attribute *a,
> +					const char *buf, size_t count)
> +{
> +	return -EPERM;
> +}
> +
>  BTRFS_FEAT_ATTR_INCOMPAT(mixed_backref, MIXED_BACKREF);
>  BTRFS_FEAT_ATTR_INCOMPAT(default_subvol, DEFAULT_SUBVOL);
>  BTRFS_FEAT_ATTR_INCOMPAT(mixed_groups, MIXED_GROUPS);
> @@ -195,6 +219,14 @@ 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(checksums, S_IRUGO,
> +				      btrfs_checksums_show,
> +				      btrfs_checksums_store),

Since we won't ever support writing to this sysfs just kill
btrfs_checksums_store and simply pass NULL as the last argument to
INIT_KOBJ_ATTR.

> +	.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),
> @@ -208,6 +240,9 @@ 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
>  };
>  
>