linux-kernel - Re: [dm-devel] [PATCH 19/32] block: add helper to get data dir from op

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Date:	Thu, 5 Nov 2015 11:34:07 -0600
From:	Mike Christie <mchristi@...hat.com>
To:	Bart Van Assche <bart.vanassche@...disk.com>,
	device-mapper development <dm-devel@...hat.com>,
	linux-fsdevel@...r.kernel.org, linux-raid@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	drbd-dev@...ts.linbit.com
Subject: Re: [dm-devel] [PATCH 19/32] block: add helper to get data dir from
 op

On 11/04/2015 04:44 PM, Bart Van Assche wrote:
> On 11/04/2015 02:08 PM, mchristi@...hat.com wrote:
>> From: Mike Christie <mchristi@...hat.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@...hat.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.
> 

I can do that. You are right in how they are used. I just did the above,
to follow the other *_data_dir calls.

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