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From: Bart Van Assche <bart.vanassche@sandisk.com>
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Date: Wed, 4 Nov 2015 14:44:03 -0800
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Cc: Mike Christie <mchristi@redhat.com>
Subject: Re: [Drbd-dev] [dm-devel] [PATCH 19/32] block: add helper to get
 data dir from op
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On 11/04/2015 02:08 PM, mchristi@redhat.com wrote:
> From: Mike Christie <mchristi@redhat.com>
>
> In later patches the op will no longer be a bitmap, so we will
> not have REQ_WRITE set for all non reads like discard, flush,
> and write same. Drivers will still want to treat them as writes
> for accounting reasons, so this patch adds a helper to translate
> a op to a data direction.
>
> Signed-off-by: Mike Christie <mchristi@redhat.com>
> ---
>   include/linux/blkdev.h | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 19c2e94..cf5f518 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -586,6 +586,18 @@ static inline void queue_flag_clear(unsigned int flag, struct request_queue *q)
>
>   #define list_entry_rq(ptr)	list_entry((ptr), struct request, queuelist)
>
> +/*
> + * Non REQ_OP_WRITE requests like discard, write same, etc, are
> + * considered WRITEs.
> + */
> +static inline int op_to_data_dir(int op)
> +{
> +	if (op == REQ_OP_READ)
> +		return READ;
> +	else
> +		return WRITE;
> +}
> +
>   #define rq_data_dir(rq)		((int)((rq)->cmd_flags & 1))
>
>   /*
>

How about introducing two functions - op_is_write() and op_is_read() ? I 
think that approach will result in shorter and easier to read code in 
the contexts where these functions are used.

Bart.