Re: [PATCH v3 01/19] block: Add PR callouts for read keys and reservation

[Bart Van Assche <bvanassche@xxxxxxx>]

On 10/26/22 16:19, Mike Christie wrote:
> +struct pr_keys {
> +	u32	generation;
> +	u32	num_keys;
> +	u64	keys[];
> +};
> +
> +struct pr_held_reservation {
> +	u64		key;
> +	u32		generation;
> +	enum pr_type	type;
> +};
> +
>   struct pr_ops {
>   	int (*pr_register)(struct block_device *bdev, u64 old_key, u64 new_key,
>   			u32 flags);
> @@ -14,6 +26,18 @@ struct pr_ops {
>   	int (*pr_preempt)(struct block_device *bdev, u64 old_key, u64 new_key,
>   			enum pr_type type, bool abort);
>   	int (*pr_clear)(struct block_device *bdev, u64 key);
> +	/*
> +	 * pr_read_keys - Read the registered keys and return them in the
> +	 * pr_keys->keys array. The keys array will have been allocated at the
> +	 * end of the pr_keys struct and is keys_len bytes. If there are more
> +	 * keys than can fit in the array, success will still be returned and
> +	 * pr_keys->num_keys will reflect the total number of keys the device
> +	 * contains, so the caller can retry with a larger array.
> +	 */
> +	int (*pr_read_keys)(struct block_device *bdev,
> +			struct pr_keys *keys_info, u32 keys_len);
> +	int (*pr_read_reservation)(struct block_device *bdev,
> +			struct pr_held_reservation *rsv);
>   };

Is there any pr_read_keys() implementation that won't have to divide 
@keys_len by 8? How about leaving out that argument and making callers 
store the number of elements in the keys[] array in the num_keys member 
before calling pr_read_keys()?

Thanks,

Bart.