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

To: Vivek Goyal <vgoyal@xxxxxxxxxx>
Subject: Re: [dm-devel] [PATCH v2 1/3] block: add sysfs entry for discard_alignment
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Date: Tue, 03 Jul 2012 16:40:40 +0200
Cc: linux-kernel@xxxxxxxxxxxxxxx, axboe@xxxxxxxxx, snitzer@xxxxxxxxxx, martin.petersen@xxxxxxxxxx, david@xxxxxxxxxxxxx, xfs@xxxxxxxxxxx, dm-devel@xxxxxxxxxx, hch@xxxxxx
In-reply-to: <20120703143949.GE11272@xxxxxxxxxx>
References: <1341235225-27551-1-git-send-email-pbonzini@xxxxxxxxxx> <1341235225-27551-2-git-send-email-pbonzini@xxxxxxxxxx> <20120703023442.GB3586@xxxxxxxxxx> <4FF2DCB1.2090704@xxxxxxxxxx> <20120703140048.GC11272@xxxxxxxxxx> <4FF2FFEE.4000401@xxxxxxxxxx> <20120703143949.GE11272@xxxxxxxxxx>
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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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