linux-kernel - Re: [PATCH v7 3/3] dm: add DM_INTERPOSED

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Message-ID: <20210314093038.GC3773360@infradead.org>
Date:   Sun, 14 Mar 2021 09:30:38 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Sergei Shtepa <sergei.shtepa@...am.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Mike Snitzer <snitzer@...hat.com>,
        Alasdair Kergon <agk@...hat.com>,
        Hannes Reinecke <hare@...e.de>, Jens Axboe <axboe@...nel.dk>,
        dm-devel@...hat.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        pavel.tide@...am.com
Subject: Re: [PATCH v7 3/3] dm: add DM_INTERPOSED_FLAG

On Fri, Mar 12, 2021 at 06:44:55PM +0300, Sergei Shtepa wrote:
> DM_INTERPOSED_FLAG allow to create DM targets on "the fly".
> Underlying block device opens without a flag FMODE_EXCL.
> DM target receives bio from the original device via
> bdev_interposer.

This is more of a philopical comment, but the idea of just letting the
interposed reopen the device by itself seems like a bad idea.  I think
that is probably better hidden in the block layer interposer attachment
function, which could do the extra blkdev_get_by_dev for the caller.