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From: Christoph Hellwig <hch@infradead.org>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	Christoph Hellwig <hch@infradead.org>,
	linux-block@vger.kernel.org,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	xfs <linux-xfs@vger.kernel.org>
Subject: Re: [PATCH] loop: fix no-unmap write-zeroes request behavior
Date: Fri, 11 Oct 2019 00:51:44 -0700
Message-ID: <20191011075144.GA26033@infradead.org> (raw)
In-Reply-To: <20191010170239.GC13098@magnolia>

On Thu, Oct 10, 2019 at 10:02:39AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Currently, if the loop device receives a WRITE_ZEROES request, it asks
> the underlying filesystem to punch out the range.  This behavior is
> correct if unmapping is allowed.  However, a NOUNMAP request means that
> the caller forbids us from freeing the storage backing the range, so
> punching out the range is incorrect behavior.

It doesn't really forbid, as most protocols don't have a way for forbid
deallocation.  It requests not to.

Otherwise this looks fine, although I would have implemented it slightly
differently:

>  	case REQ_OP_FLUSH:
>  		return lo_req_flush(lo, rq);
>  	case REQ_OP_DISCARD:
> -	case REQ_OP_WRITE_ZEROES:
>  		return lo_discard(lo, rq, pos);
> +	case REQ_OP_WRITE_ZEROES:
> +		return lo_zeroout(lo, rq, pos);

This could just become:

	case REQ_OP_WRITE_ZEROES:
		if (rq->cmd_flags & REQ_NOUNMAP))
			return lo_zeroout(lo, rq, pos);
		/*FALLTHRU*/
	case REQ_OP_DISCARD:
		return lo_discard(lo, rq, pos);

  reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-10 17:02 Darrick J. Wong
2019-10-11  7:51 ` Christoph Hellwig [this message]
2019-10-11 16:05 ` [PATCH v2] " Darrick J. Wong
2019-10-14  7:28   ` Christoph Hellwig
2019-10-14 15:50 ` [PATCH v3] " Darrick J. Wong
2019-10-14 16:39   ` Eric Sandeen
2019-10-14 17:00     ` Darrick J. Wong
2019-10-15  7:58   ` Christoph Hellwig

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