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Date:   Fri, 30 Aug 2019 08:50:24 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Martijn Coenen <maco@android.com>
Cc:     axboe@kernel.dk, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, gregkh@linuxfoundatio.org,
        kernel-team@android.com, narayan@google.com, dariofreni@google.com,
        ioffe@google.com, jiyong@google.com, maco@google.com
Subject: Re: [PATCH] loop: change queue block size to match when using DIO.
Message-ID: <20190830155024.GA23882@infradead.org>
References: <20190828103229.191853-1-maco@android.com>
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On Wed, Aug 28, 2019 at 12:32:29PM +0200, Martijn Coenen wrote:
> The loop driver assumes that if the passed in fd is opened with
> O_DIRECT, the caller wants to use direct I/O on the loop device.
> However, if the underlying filesystem has a different block size than
> the loop block queue, direct I/O can't be enabled. Instead of requiring
> userspace to manually change the blocksize and re-enable direct I/O,
> just change the queue block size to match.

Why can't we enable the block device in that case?  All the usual
block filesystems support 512 byte aligned direct I/O with a 4k
file system block size (as long as the underlying block device
sector size is also 512 bytes).