Re: [PATCH] loop: Add LOOP_SET_FD_WITH_OFFSET ioctl.

From: Christoph Hellwig <hch@lst.de>
To: Martijn Coenen <maco@android.com>
Cc: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>,
	Christoph Hellwig <hch@lst.de>,
	Bart Van Assche <bvanassche@acm.org>,
	Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>,
	linux-block <linux-block@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	kernel-team@android.com
Subject: Re: [PATCH] loop: Add LOOP_SET_FD_WITH_OFFSET ioctl.
Date: Tue, 31 Mar 2020 09:48:28 +0200	[thread overview]
Message-ID: <20200331074828.GA24372@lst.de> (raw)
In-Reply-To: <CAB0TPYG4N-2Gg95VwQuQBQ8rvjC=4NQJP4syJWS3Q6CO28HzTQ@mail.gmail.com>

On Mon, Mar 30, 2020 at 10:06:41AM +0200, Martijn Coenen wrote:
> Hi Ming,
> 
> On Mon, Mar 30, 2020 at 3:00 AM Ming Lei <ming.lei@redhat.com> wrote:
> > The new ioctl LOOP_SET_FD_WITH_OFFSET looks not generic enough, could
> > you consider to add one ioctl LOOP_SET_FD_AND_STATUS to cover both
> > SET_FD and SET_STATUS so that using two ioctl() to setup loop can become
> > deprecated finally?
> 
> I originally started out doing that. However, it is a significantly
> larger refactoring of the loop driver, and it makes things like error
> handling more complex. I thought configuring loop with an offset is
> the most common case. But if there's a preference to do an ioctl that
> takes the full status, I can work on that.

I think the full blown set fd an status would seem a lot more useful,
or even better a LOOP_CTL_ADD variant that sets up everything important
on the character device so that we avoid the half set up block devices
entirely.