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From:   Martijn Coenen <maco@android.com>
Date:   Mon, 27 Apr 2020 22:34:35 +0200
Message-ID: <CAB0TPYGZc_n-b5xtNsbJxEiqpLMqE=RcXGuy7C2vbY18mKZ6_A@mail.gmail.com>
Subject: Re: [PATCH v3 0/9] Add a new LOOP_SET_FD_AND_STATUS ioctl
To:     Christoph Hellwig <hch@lst.de>
Cc:     Jens Axboe <axboe@kernel.dk>, Ming Lei <ming.lei@redhat.com>,
        Narayan Kamath <narayan@google.com>,
        Zimuzo Ezeozue <zezeozue@google.com>, kernel-team@android.com,
        linux-block <linux-block@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Martijn Coenen <maco@google.com>,
        Bart Van Assche <bvanassche@acm.org>,
        Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>,
        Jaegeuk Kim <jaegeuk@kernel.org>
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Hi Christoph,

On Mon, Apr 27, 2020 at 7:06 PM Christoph Hellwig <hch@lst.de> wrote:
>
> I've just been looking over the loop driver for other reasons,
> and noticed that setting the block size still isn't possible
> with LOOP_SET_FD_AND_STATUS as far as I can tell.  Might that
> be worth it?

That's a good point, I didn't think about it because that path is no
longer slow in our setup, but I think it makes sense to include it.

> Also maybe an explicit direct I/O flag, and maybe
> enough padding with a future proof flags bitmap that we can easily
> extend it for new features if they pop up?

Sounds good. I'm thinking these flags should be separate from
LO_FLAGS_; even though there is already a LO_FLAGS_DIRECT_IO, as far
as I can tell it can only be used to tell whether it's enabled, not to
actually enable it. And it would just get confusing if we add more
flags later. Maybe something like LO_FD_STATUS_FLAG_DIRECT_IO ?

Thanks,
Martijn