From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
Subject: Re: [PATCH v7 4/6] block: loop: prepare for supporing direct IO
Date: Mon, 27 Jul 2015 01:40:20 -0700
Message-ID: <20150727084020.GA28336@infradead.org>
References: <1437061068-26118-1-git-send-email-ming.lei@canonical.com>
 <1437061068-26118-5-git-send-email-ming.lei@canonical.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Return-path: <linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Content-Disposition: inline
In-Reply-To: <1437061068-26118-5-git-send-email-ming.lei-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>
Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
To: Ming Lei <ming.lei-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>
Cc: Jens Axboe <axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, "Justin M. Forbes" <jforbes-rxtnV0ftBwyoClj4AeEUq9i2O/JbrIOy@public.gmane.org>, Jeff Moyer <jmoyer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
List-Id: linux-api@vger.kernel.org

> +	/*
> +	 * loop block's logical block size is 512, now
> +	 * we support direct I/O only if the backing
> +	 * block devices' minimize I/O size is 512 and
> +	 * the offset is aligned with 512.
> +	 */
> +	if (dio) {
> +		if (inode->i_sb->s_bdev &&
> +			bdev_io_min(inode->i_sb->s_bdev) == 512 &&
> +			!(lo->lo_offset & 511))

Why the hardcoded value?  I suspect this should be more like:

	if (dio && inode->i_sb->s_bdev &&
	    (lo->lo_offset & (bdev_io_min(inode->i_sb->s_bdev) - 1)) != 0)
		dio = false;

> +	blk_mq_freeze_queue(lo->lo_queue);
> +	lo->use_dio = use_dio;
> +	if (use_dio)
> +		lo->lo_flags |= LO_FLAGS_DIRECT_IO;
> +	else
> +		lo->lo_flags &= ~LO_FLAGS_DIRECT_IO;
> +	blk_mq_unfreeze_queue(lo->lo_queue);

Locking?