Feedback-ID: iac594737:Fastmail
Date:   Thu, 2 Feb 2023 13:41:29 -0500
From:   Demi Marie Obenour <demi@invisiblethingslab.com>
To:     Mike Snitzer <snitzer@kernel.org>
Cc:     Jens Axboe <axboe@kernel.dk>,
        Roger Pau =?utf-8?B?TW9ubsOp?= <roger.pau@citrix.com>,
        Alasdair Kergon <agk@redhat.com>,
        Marek =?utf-8?Q?Marczykowski-G=C3=B3recki?= 
        <marmarek@invisiblethingslab.com>, Juergen Gross <jgross@suse.com>,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        xen-devel@lists.xenproject.org, dm-devel@redhat.com
Subject: Re: [RFC PATCH 0/7] Allow race-free block device handling
Message-ID: <Y9wEF3rWfpiCKc2i@itl-email>
References: <20230126033358.1880-1-demi@invisiblethingslab.com>
 <Y9vp3XDEQAl7TLND@redhat.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
        protocol="application/pgp-signature"; boundary="0LK2ZHUlLOwPgDgy"
Content-Disposition: inline
In-Reply-To: <Y9vp3XDEQAl7TLND@redhat.com>
Precedence: bulk


--0LK2ZHUlLOwPgDgy
Content-Type: text/plain; protected-headers=v1; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable
Date: Thu, 2 Feb 2023 13:41:29 -0500
From: Demi Marie Obenour <demi@invisiblethingslab.com>
To: Mike Snitzer <snitzer@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>,
	Roger Pau =?utf-8?B?TW9ubsOp?= <roger.pau@citrix.com>,
	Alasdair Kergon <agk@redhat.com>,
	Marek =?utf-8?Q?Marczykowski-G=C3=B3recki?= <marmarek@invisiblethingslab.com>,
	Juergen Gross <jgross@suse.com>, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org,
	dm-devel@redhat.com
Subject: Re: [RFC PATCH 0/7] Allow race-free block device handling

On Thu, Feb 02, 2023 at 11:50:37AM -0500, Mike Snitzer wrote:
> On Wed, Jan 25 2023 at 10:33P -0500,
> Demi Marie Obenour <demi@invisiblethingslab.com> wrote:
>=20
> > This work aims to allow userspace to create and destroy block devices
> > in a race-free and leak-free way,
>=20
> "race-free and leak-free way" implies there both races and leaks in
> existing code. You're making claims that are likely very specific to
> your Xen use-case.  Please explain more carefully.

Will do in v2.

> > and to allow them to be exposed to
> > other Xen VMs via blkback without leaks or races.  It=E2=80=99s marked =
as RFC
> > for a few reasons:
> >=20
> > - The code has been only lightly tested.  It might be unstable or
> >   insecure.
> >=20
> > - The DM_DEV_CREATE ioctl gains a new flag.  Unknown flags were
> >   previously ignored, so this could theoretically break buggy userspace
> >   tools.
>=20
> Not seeing a reason that type of DM change is needed. If you feel
> strongly about it send a separate patch and we can discuss it.

Patch 2/7 is the diskseq change.  v2 will contain a revised and tested
version with a greatly expanded commit message.

> > - I have no idea if I got the block device reference counting and
> >   locking correct.
>=20
> Your headers and justifcation for this line of work are really way too
> terse. Please take the time to clearly make the case for your changes
> in both the patch headers and code.

I will expand the commit message in v2, but I am not sure what you want
me to add to the code comments.  Would you mind explaining?
--=20
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

--0LK2ZHUlLOwPgDgy
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
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=aeu1
-----END PGP SIGNATURE-----

--0LK2ZHUlLOwPgDgy--