linux-kernel - Re: [PATCH 2/5] block: add request->io_data

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Message-ID: <20200413135212.GA60335@mtj.duckdns.org>
Date:   Mon, 13 Apr 2020 09:52:12 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Bart Van Assche <bvanassche@....org>
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...r.kernel.org,
        cgroups@...r.kernel.org, newella@...com, josef@...icpanda.com
Subject: Re: [PATCH 2/5] block: add request->io_data_len

Hello,

On Wed, Apr 08, 2020 at 08:44:17PM -0700, Bart Van Assche wrote:
> On 2020-04-08 13:14, Tejun Heo wrote:
> > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> > index 32868fbedc9e..bfd34c6a27ef 100644
> > --- a/include/linux/blkdev.h
> > +++ b/include/linux/blkdev.h
> > @@ -142,6 +142,14 @@ struct request {
> >  
> >  	/* the following two fields are internal, NEVER access directly */
> >  	unsigned int __data_len;	/* total data len */
> > +#ifdef CONFIG_BLK_RQ_IO_DATA_LEN
> > +	/*
> > +	 * Total data len at the time of issue. This doesn't get deducted by
> > +	 * blk_update_request() and can be used by completion path to determine
> > +	 * the request size.
> > +	 */
> > +	unsigned int io_data_len;
> > +#endif
> >  	sector_t __sector;		/* sector cursor */
> >  
> >  	struct bio *bio;
> 
> So we have one struct member with the description "total data len" and
> another struct member with the description "total data len at the time
> of issue"? How could one not get confused by these descriptions?

The new one explicitly says it doesn't get deducted by update_request.

> This change makes the comment above __data_len incorrect. Please update
> that comment or move io_data_len in front of that comment.

Sure.

> How does this change interact with the code in drivers/scsi/sd.c that
> manipulates __data_len directly?

It doesn't.

Thanks.

-- 
tejun