Re: [PATCH v2 01/15] block: Make bio_set_ioprio() modify fewer bio->bi_ioprio bits

[Kanchan Joshi <joshi.k@samsung.com>]

On 10/6/2023 1:10 AM, Bart Van Assche wrote:
> A later patch will store the data lifetime in the bio->bi_ioprio member
> before bio_set_ioprio() is called. Make sure that bio_set_ioprio()
> doesn't clear more bits than necessary.
> 
> Cc: Damien Le Moal <dlemoal@kernel.org>
> Cc: Niklas Cassel <niklas.cassel@wdc.com>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>   block/blk-mq.c         |  3 ++-
>   include/linux/ioprio.h | 10 ++++++++++
>   2 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index e2d11183f62e..bc086660ffd3 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2926,7 +2926,8 @@ static void bio_set_ioprio(struct bio *bio)
>   {
>   	/* Nobody set ioprio so far? Initialize it based on task's nice value */
>   	if (IOPRIO_PRIO_CLASS(bio->bi_ioprio) == IOPRIO_CLASS_NONE)
> -		bio->bi_ioprio = get_current_ioprio();
> +		ioprio_set_class_and_level(&bio->bi_ioprio,
> +					   get_current_ioprio());
>   	blkcg_set_ioprio(bio);
>   }
>   
> diff --git a/include/linux/ioprio.h b/include/linux/ioprio.h
> index 7578d4f6a969..f2e768ab4b35 100644
> --- a/include/linux/ioprio.h
> +++ b/include/linux/ioprio.h
> @@ -71,4 +71,14 @@ static inline int ioprio_check_cap(int ioprio)
>   }
>   #endif /* CONFIG_BLOCK */
>   
> +#define IOPRIO_CLASS_LEVEL_MASK ((IOPRIO_CLASS_MASK << IOPRIO_CLASS_SHIFT) | \
> +				 (IOPRIO_LEVEL_MASK << 0))
> +
> +static inline void ioprio_set_class_and_level(u16 *prio, u16 class_level)
> +{
> +	WARN_ON_ONCE(class_level & ~IOPRIO_CLASS_LEVEL_MASK);
> +	*prio &= ~IOPRIO_CLASS_LEVEL_MASK;
> +	*prio |= class_level;

Return of get_current_ioprio() will touch all 16 bits here. So 
user-defined value can alter whatever was set in bio by F2FS (patch 4 in 
this series). Is that not an issue?

And what is the user interface you have in mind. Is it ioprio based, or 
write-hint based or mix of both?