linux-kernel - Re: [PATCH v2 13/26] raid5: use bio

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Message-ID: <20120911150326.79f066c0@notabene.brown>
Date:	Tue, 11 Sep 2012 15:03:26 +1000
From:	NeilBrown <neilb@...e.de>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, axboe@...nel.dk, tj@...nel.org
Subject: Re: [PATCH v2 13/26] raid5: use bio_reset()

On Mon, 10 Sep 2012 17:22:24 -0700 Kent Overstreet <koverstreet@...gle.com>
wrote:

> Had to shuffle the code around a bit (where bi_rw and bi_end_io were
> set), but shouldn't really be anything tricky here
> 
> Signed-off-by: Kent Overstreet <koverstreet@...gle.com>
> CC: Jens Axboe <axboe@...nel.dk>
> CC: NeilBrown <neilb@...e.de>
> ---
>  drivers/md/raid5.c | 28 ++++++++++++++--------------
>  1 file changed, 14 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 7c19dbe..ebe43f7 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -561,14 +561,6 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
>  		bi = &sh->dev[i].req;
>  		rbi = &sh->dev[i].rreq; /* For writing to replacement */
>  
> -		bi->bi_rw = rw;
> -		rbi->bi_rw = rw;
> -		if (rw & WRITE) {
> -			bi->bi_end_io = raid5_end_write_request;
> -			rbi->bi_end_io = raid5_end_write_request;
> -		} else
> -			bi->bi_end_io = raid5_end_read_request;
> -
>  		rcu_read_lock();
>  		rrdev = rcu_dereference(conf->disks[i].replacement);
>  		smp_mb(); /* Ensure that if rrdev is NULL, rdev won't be */
> @@ -643,7 +635,14 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
>  
>  			set_bit(STRIPE_IO_STARTED, &sh->state);
>  
> +			bio_reset(bi);
>  			bi->bi_bdev = rdev->bdev;
> +			bi->bi_rw = rw;
> +			bi->bi_end_io = (rw & WRITE)
> +				? raid5_end_write_request
> +				: raid5_end_read_request;
> +			bi->bi_private = sh;
> +
>  			pr_debug("%s: for %llu schedule op %ld on disc %d\n",
>  				__func__, (unsigned long long)sh->sector,
>  				bi->bi_rw, i);
> @@ -657,12 +656,9 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
>  			if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags))
>  				bi->bi_rw |= REQ_FLUSH;
>  
> -			bi->bi_flags = 1 << BIO_UPTODATE;
> -			bi->bi_idx = 0;
>  			bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
>  			bi->bi_io_vec[0].bv_offset = 0;
>  			bi->bi_size = STRIPE_SIZE;
> -			bi->bi_next = NULL;
>  			if (rrdev)
>  				set_bit(R5_DOUBLE_LOCKED, &sh->dev[i].flags);
>  			generic_make_request(bi);
> @@ -674,7 +670,14 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
>  
>  			set_bit(STRIPE_IO_STARTED, &sh->state);
>  
> +			bio_reset(rbi);
>  			rbi->bi_bdev = rrdev->bdev;
> +			rbi->bi_rw = rw;
> +			rbi->bi_end_io = (rw & WRITE)
> +				? raid5_end_write_request
> +				: raid5_end_read_request;

'rbi->bi_end_io' can only ever be raid5_end_write_request.  We only get here
on a write.
I'd be OK with 
    BUG_ON(!(rw & WRITE));
but I don't want the condition in the assignment.

The rest looks quite sane.

Thanks
NeilBrown


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