Re: [PATCH v2 2/4] ublk: refactor recovery configuration flag helpers

[Ming Lei <ming.lei@redhat.com>]

On Mon, Sep 16, 2024 at 06:21:53PM -0600, Uday Shankar wrote:
> ublk currently supports the following behaviors on ublk server exit:
> 
> A: outstanding I/Os get errors, subsequently issued I/Os get errors
> B: outstanding I/Os get errors, subsequently issued I/Os queue
> C: outstanding I/Os get reissued, subsequently issued I/Os queue
> 
> and the following behaviors for recovery of preexisting block devices by
> a future incarnation of the ublk server:
> 
> 1: ublk devices stopped on ublk server exit (no recovery possible)
> 2: ublk devices are recoverable using start/end_recovery commands
> 
> The userspace interface allows selection of combinations of these
> behaviors using flags specified at device creation time, namely:
> 
> default behavior: A + 1
> UBLK_F_USER_RECOVERY: B + 2
> UBLK_F_USER_RECOVERY|UBLK_F_USER_RECOVERY_REISSUE: C + 2
> 
> We can't easily change the userspace interface to allow independent
> selection of one of {A, B, C} and one of {1, 2}, but we can refactor the
> internal helpers which test for the flags. Replace the existing helpers
> with the following set:
> 
> ublk_nosrv_should_reissue_outstanding: tests for behavior C
> ublk_nosrv_[dev_]should_queue_io: tests for behavior B
> ublk_nosrv_should_stop_dev: tests for behavior 1
> 
> Signed-off-by: Uday Shankar <ushankar@purestorage.com>
> ---
> Changes since v1 (https://lore.kernel.org/linux-block/20240617194451.435445-3-ushankar@purestorage.com/):
> - Make the fast-path test in ublk_queue_rq access the queue-local copy
>   of the device flags.
> 
>  drivers/block/ublk_drv.c | 63 +++++++++++++++++++++++++++-------------
>  1 file changed, 43 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 5e04a0fcd0b7..b069f4d2b9d2 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -675,22 +675,45 @@ static inline int ublk_queue_cmd_buf_size(struct ublk_device *ub, int q_id)
>  			PAGE_SIZE);
>  }
>  
> -static inline bool ublk_queue_can_use_recovery_reissue(
> -		struct ublk_queue *ubq)
> +/*
> + * Should I/O outstanding to the ublk server when it exits be reissued?
> + * If not, outstanding I/O will get errors.
> + */
> +static inline bool ublk_nosrv_should_reissue_outstanding(struct ublk_device *ub)
>  {
> -	return (ubq->flags & UBLK_F_USER_RECOVERY) &&
> -			(ubq->flags & UBLK_F_USER_RECOVERY_REISSUE);
> +	return (ub->dev_info.flags & UBLK_F_USER_RECOVERY) &&
> +	       (ub->dev_info.flags & UBLK_F_USER_RECOVERY_REISSUE);
>  }
>  
> -static inline bool ublk_queue_can_use_recovery(
> -		struct ublk_queue *ubq)
> +/*
> + * Should I/O issued while there is no ublk server queue? If not, I/O
> + * issued while there is no ublk server will get errors.
> + */
> +static inline bool ublk_nosrv_dev_should_queue_io(struct ublk_device *ub)
> +{
> +	return ub->dev_info.flags & UBLK_F_USER_RECOVERY;
> +}
> +
> +/*
> + * Same as ublk_nosrv_dev_should_queue_io, but uses a queue-local copy
> + * of the device flags for smaller cache footprint - better for fast
> + * paths.
> + */
> +static inline bool ublk_nosrv_should_queue_io(struct ublk_queue *ubq)
>  {
>  	return ubq->flags & UBLK_F_USER_RECOVERY;
>  }
>  
> -static inline bool ublk_can_use_recovery(struct ublk_device *ub)
> +/*
> + * Should ublk devices be stopped (i.e. no recovery possible) when the
> + * ublk server exits? If not, devices can be used again by a future
> + * incarnation of a ublk server via the start_recovery/end_recovery
> + * commands.
> + */
> +static inline bool ublk_nosrv_should_stop_dev(struct ublk_device *ub)
>  {
> -	return ub->dev_info.flags & UBLK_F_USER_RECOVERY;
> +	return (!(ub->dev_info.flags & UBLK_F_USER_RECOVERY)) &&
> +	       (!(ub->dev_info.flags & UBLK_F_USER_RECOVERY_REISSUE));
>  }

It should be enough to check UBLK_F_USER_RECOVERY only since
UBLK_F_USER_RECOVERY_REISSUE implies UBLK_F_USER_RECOVERY.

Otherwise, this patch looks fine.


Thanks, 
Ming