Re: [PATCH v9 3/3] btrfs: create read policy sysfs attribute, pid

[David Sterba <dsterba@suse.cz>]

On Thu, Oct 22, 2020 at 03:43:37PM +0800, Anand Jain wrote:
> Add
> 
>  /sys/fs/btrfs/UUID/read_policy
> 
> attribute so that the read policy for the raid1, raid1c34 and raid10 can
> be tuned.
> 
> When this attribute is read, it shall show all available policies, with
> active policy being with in [ ]. The read_policy attribute can be written
> using one of the items listed in there.
> 
> For example:
>   $cat /sys/fs/btrfs/UUID/read_policy
>   [pid]
>   $echo pid > /sys/fs/btrfs/UUID/read_policy
> 
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
> v9: fix C coding style, static const char*
> v5: 
>   Title rename: old: btrfs: sysfs, add read_policy attribute
>   Uses the btrfs_strmatch() helper (BTRFS_READ_POLICY_NAME_MAX dropped).
>   Use the table for the policy names.
>   Rename len to ret.
>   Use a simple logic to prefix space in btrfs_read_policy_show()
>   Reviewed-by: Josef Bacik <josef@toxicpanda.com> dropped.
> 
> v4:-
> v3: rename [by_pid] to [pid]
> v2: v2: check input len before strip and kstrdup
> 
>  fs/btrfs/sysfs.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 49 insertions(+)
> 
> diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
> index 5ea262d289c6..e23ae3643527 100644
> --- a/fs/btrfs/sysfs.c
> +++ b/fs/btrfs/sysfs.c
> @@ -883,6 +883,54 @@ static int btrfs_strmatch(const char *given, const char *golden)
>  	return -EINVAL;
>  }
>  
> +static const char * const btrfs_read_policy_name[] = { "pid" };
> +
> +static ssize_t btrfs_read_policy_show(struct kobject *kobj,
> +				      struct kobj_attribute *a, char *buf)
> +{
> +	int i;
> +	ssize_t ret = 0;
> +	struct btrfs_fs_devices *fs_devices = to_fs_devs(kobj);
> +
> +	for (i = 0; i < BTRFS_NR_READ_POLICY; i++) {
> +		if (fs_devices->read_policy == i)
> +			ret += snprintf(buf + ret, PAGE_SIZE - ret, "%s[%s]",

All snprintf have been upgraded to scnprintf as it does have sane
behaviour when the buffer is not large enough.

> +					(ret == 0 ? "" : " "),
> +					btrfs_read_policy_name[i]);
> +		else
> +			ret += snprintf(buf + ret, PAGE_SIZE - ret, "%s%s",
> +					(ret == 0 ? "" : " "),
> +					btrfs_read_policy_name[i]);
> +	}
> +
> +	ret += snprintf(buf + ret, PAGE_SIZE - ret, "\n");
> +
> +	return ret;
> +}