Re: [PATCH 2/2] btrfs: sysfs, add read_policy attribute

[Josef Bacik <josef@toxicpanda.com>]

On 1/5/20 10:14 AM, Anand Jain wrote:
> Add
> 
>   /sys/fs/btrfs/UUID/read_policy
> 
> attribute so that the read policy for the raid1 and raid10 chunks can be
> tuned.
> 
> When this attribute is read, it shall show all available policies, and
> the active policy is with in [ ], read_policy attribute can be written
> using one of the items showed in the read.
> 
> For example:
> cat /sys/fs/btrfs/UUID/read_policy
> [by_pid]
> echo by_pid > /sys/fs/btrfs/UUID/read_policy
> echo -n by_pid > /sys/fs/btrfs/UUID/read_policy
> 
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
>   fs/btrfs/sysfs.c   | 67 ++++++++++++++++++++++++++++++++++++++++++++++
>   fs/btrfs/volumes.h |  1 +
>   2 files changed, 68 insertions(+)
> 
> diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
> index d414b98fb27f..ae2935184d75 100644
> --- a/fs/btrfs/sysfs.c
> +++ b/fs/btrfs/sysfs.c
> @@ -642,6 +642,72 @@ static ssize_t btrfs_checksum_show(struct kobject *kobj,
>   
>   BTRFS_ATTR(, checksum, btrfs_checksum_show);
>   
> +static const inline char *btrfs_read_policy_name(enum btrfs_read_policy_type type)
> +{
> +	switch (type) {
> +	case BTRFS_READ_BY_PID:
> +		return "by_pid";
> +	default:
> +		return "null";
> +	}
> +}
> +
> +static ssize_t btrfs_read_policy_show(struct kobject *kobj,
> +				      struct kobj_attribute *a, char *buf)
> +{
> +	int i;
> +	ssize_t len = 0;
> +	struct btrfs_fs_devices *fs_devices = to_fs_devs(kobj);
> +
> +	for (i = 0; i < BTRFS_NR_READ_POLICY_TYPE; i++) {
> +		if (len)
> +			len += snprintf(buf + len, PAGE_SIZE, " ");
> +		if (fs_devices->read_policy == i)
> +			len += snprintf(buf + len, PAGE_SIZE, "[%s]",
> +					btrfs_read_policy_name(i));
> +		else
> +			len += snprintf(buf + len, PAGE_SIZE, "%s",
> +					btrfs_read_policy_name(i));
> +	}
> +
> +	len += snprintf(buf + len, PAGE_SIZE, "\n");
> +
> +	return len;
> +}
> +
> +static ssize_t btrfs_read_policy_store(struct kobject *kobj,
> +				       struct kobj_attribute *a,
> +				       const char *buf, size_t len)
> +{
> +	int i;
> +	char *stripped;
> +	char *policy_name;
> +	struct btrfs_fs_devices *fs_devices = to_fs_devs(kobj);
> +
> +	policy_name = kstrdup(buf, GFP_KERNEL);
> +	if (!policy_name)
> +		return -ENOMEM;
> +
> +	stripped = strstrip(policy_name);
> +	if (strlen(stripped) > BTRFS_READ_POLICY_NAME_MAX) {
> +		kfree(policy_name);
> +		return -EINVAL;
> +	}

We have the len passed to us, let's do the length check _before_ we arbitrarily 
kstrdup().  Thanks,

Josef