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

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Message-ID: <4FF30468.30407@redhat.com>
Date:	Tue, 03 Jul 2012 16:40:40 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Vivek Goyal <vgoyal@...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

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.

paolo

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