linux-kernel - The question about blkdev_issue_discard and discard

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Date:	Thu, 22 Mar 2012 17:04:07 +0400
From:	Andrew Wagin <avagin@...il.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	linux-kernel@...r.kernel.org
Subject: The question about blkdev_issue_discard and discard_granularity

Hello Jens,

I'm developing a virtual disk (aka ploop). Now I'm adding support of
discard requests. A block size of ploop may be customized, so I want
that a discard request contains only whole blocks. I found a queue's
parameter discard_granularity and set it correctly, but nothing's
changed. A kernel continues sending bio with size smaller than
discard_granularity and with unaligned borders.

I found that max_discard_sectors is aligned according with discard_granularity.

Why are bi->bi_size and bi->bi_sector not aligned according with
discard_granularity?

If it's just because nobody did this, I can do.

Thanks,
Andrey
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