linux-kernel - Re: dm: introduce a DM_ENFORCE_OPEN

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Date:   Tue, 22 Feb 2022 14:16:13 -0500
From:   Mike Snitzer <snitzer@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Brian Geffon <bgeffon@...gle.com>,
        Alasdair Kergon <agk@...hat.com>, dm-devel@...hat.com,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: dm: introduce a DM_ENFORCE_OPEN_COUNT flag.

On Wed, Feb 02 2022 at  9:42P -0500,
Christoph Hellwig <hch@...radead.org> wrote:

> Withmy block hat on: nak to this.  No block driver has any business at
> all rejecting "too many openers".  In fact any opener but the first of
> a partition is already not counted as an opener, and I plan to complete
> hide the open count from the device driver.

I agree that this proposal exposes controls to userspace that simply
shouldn't be meaningful given the arbitrary nature of openers.  And
preventing openers can result in a race where systemd or some other
service opens before the intended primary consumer of the device.

Seriously brittle and even if finely tuned to have a suitable value
for some niche usecase like android: an absolute hack.

Sorry, not interested in taking this.