linux-kernel - Re: [dm-devel] [PATCH v2 1/3] block: add sysfs entry for discard

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Message-ID: <20120703144509.GA15612@redhat.com>
Date:	Tue, 3 Jul 2012 10:45:09 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, axboe@...nel.dk, snitzer@...hat.com,
	martin.petersen@...cle.com, david@...morbit.com, xfs@....sgi.com,
	dm-devel@...hat.com, hch@....de
Subject: Re: [dm-devel] [PATCH v2 1/3] block: add sysfs entry for
 discard_alignment

On Tue, Jul 03, 2012 at 04:40:40PM +0200, Paolo Bonzini wrote:
> Il 03/07/2012 16:39, Vivek Goyal ha scritto:
> >> > +static inline int bdev_discard_alignment(struct block_device *bdev)
> >> > +{
> >> > +	struct request_queue *q = bdev_get_queue(bdev);
> >> > +
> >> > +	if (bdev != bdev->bd_contains)
> >> > +		return bdev->bd_part->discard_alignment;
> >> > +
> >> > +	return q->limits.discard_alignment;
> >> > +}
> >> > +
> >> >  static inline unsigned int queue_discard_zeroes_data(struct request_queue *q)
> >> >  {
> >> >  	if (q->limits.max_discard_sectors && q->limits.discard_zeroes_data == 1)
> >> > diff --git a/block/blk-lib.c b/block/blk-lib.c
> >> > index b2bde5c..77d8869 100644
> >> > --- a/block/blk-lib.c
> >> > +++ b/block/blk-lib.c
> >> > @@ -58,7 +58,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> >> >  	/* Zero-sector (unknown) and one-sector granularities are the same.  */
> >> >  	granularity = max(q->limits.discard_granularity >> 9, 1U);
> >> >  	mask = granularity - 1;
> >> > -	alignment = (q->limits.discard_alignment >> 9) & mask;
> >> > +	alignment = bdev_discard_alignment(bdev) >> 9;
> > Why are you removing AND with mask operation? I don't see any AND
> > operation being done in bdev_discard_alignment().
> 
> For partitions it is done by queue_limits_discard_alignment.  For disks,
> it shouldn't be necessary at all but I can leave it.

Ok. I am fine with both with and without mask.

Thanks
Vivek
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