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

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Message-ID: <20210315132509.GD30489@veeam.com>
Date:   Mon, 15 Mar 2021 16:25:09 +0300
From:   Sergei Shtepa <sergei.shtepa@...am.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     Mike Snitzer <snitzer@...hat.com>,
        Alasdair Kergon <agk@...hat.com>,
        Hannes Reinecke <hare@...e.de>, Jens Axboe <axboe@...nel.dk>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        Pavel Tide <Pavel.TIde@...am.com>
Subject: Re: [PATCH v7 3/3] dm: add DM_INTERPOSED_FLAG

The 03/14/2021 12:30, Christoph Hellwig wrote:
> 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.

I suppose this cannot be implemented, since we need to change the behavior
for block devices that already have been opened.

-- 
Sergei Shtepa
Veeam Software developer.