Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   "Tian, Kevin" <kevin.tian@intel.com>
To:     Alex Williamson <alex.williamson@redhat.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>
CC:     "jgg@nvidia.com" <jgg@nvidia.com>, "hch@lst.de" <hch@lst.de>,
        "jasowang@redhat.com" <jasowang@redhat.com>,
        "joro@8bytes.org" <joro@8bytes.org>,
        "jean-philippe@linaro.org" <jean-philippe@linaro.org>,
        "parav@mellanox.com" <parav@mellanox.com>,
        "lkml@metux.net" <lkml@metux.net>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "lushenming@huawei.com" <lushenming@huawei.com>,
        "eric.auger@redhat.com" <eric.auger@redhat.com>,
        "corbet@lwn.net" <corbet@lwn.net>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "yi.l.liu@linux.intel.com" <yi.l.liu@linux.intel.com>,
        "Tian, Jun J" <jun.j.tian@intel.com>, "Wu, Hao" <hao.wu@intel.com>,
        "Jiang, Dave" <dave.jiang@intel.com>,
        "jacob.jun.pan@linux.intel.com" <jacob.jun.pan@linux.intel.com>,
        "kwankhede@nvidia.com" <kwankhede@nvidia.com>,
        "robin.murphy@arm.com" <robin.murphy@arm.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        "dwmw2@infradead.org" <dwmw2@infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "baolu.lu@linux.intel.com" <baolu.lu@linux.intel.com>,
        "david@gibson.dropbear.id.au" <david@gibson.dropbear.id.au>,
        "nicolinc@nvidia.com" <nicolinc@nvidia.com>
Subject: RE: [RFC 02/20] vfio: Add device class for /dev/vfio/devices
Thread-Topic: [RFC 02/20] vfio: Add device class for /dev/vfio/devices
Thread-Index: AQHXrSFvz6zvm2xHBUaW/Kl+BWVvQauu6ySAgABTS3A=
Date:   Wed, 22 Sep 2021 00:56:17 +0000
Message-ID: <BN9PR11MB5433C4C1539B3965134391358CA29@BN9PR11MB5433.namprd11.prod.outlook.com>
References: <20210919063848.1476776-1-yi.l.liu@intel.com>
        <20210919063848.1476776-3-yi.l.liu@intel.com>
 <20210921135601.3393f51b.alex.williamson@redhat.com>
In-Reply-To: <20210921135601.3393f51b.alex.williamson@redhat.com>
Accept-Language: en-US
Content-Language: en-US
x-ms-exchange-antispam-messagedata-chunkcount: 1
x-ms-exchange-antispam-messagedata-0: =?us-ascii?Q?0iXhGTTXRnD+qphUE240+yUILUkoTn6wOO1JPZuVOnwTX1NfCGhU4B4teoJ/?=
 =?us-ascii?Q?HvDKIzcr7jCN87pBUVkOZD0XDrrFci0RrHKbGq+rxD1xYgK4tA+65t+Gqj13?=
 =?us-ascii?Q?Ns68ZDAyf/LLp+XquFRkjyyxULN2P1dffvsvVkt9HQwBBj5UTK1VH5vfGxpI?=
 =?us-ascii?Q?t/0JWZi1oWF6wD+w02cLyFrQEX9TpHS+0JTzm9Yn0es5LT6daD9reufc4dl0?=
 =?us-ascii?Q?ZLj6WnkqCzkXlWHxfMpGEq/P8TmGmRGTmbI1CApoX9f8rs1h4tmKRim4gchw?=
 =?us-ascii?Q?iGMR3Q6ANLuFczZXFYFSrzl2CWcO0dfGk7cNnG/A9APtq52/LcZzRsQy4zFX?=
 =?us-ascii?Q?K5uQ9svZkye5VbwPHOUaScjabSSKsnvSyd8CJ4soh4dU8VdGR/JylQq5Km8d?=
 =?us-ascii?Q?fa7OfB75wEZbV1unRGjRCsdEluYzyOBBeW8B4fN/hzvrYV/JbCU0xZwRfrG/?=
 =?us-ascii?Q?2tflJ571Fx8lKHziy6rJ8ON6J9xwpd8Hv4TXpL+uN5qB99JKyfaHlPhoZ9co?=
 =?us-ascii?Q?D3iqfBPFwzWAiDIpyi3Vh81jBEohz8tlOkdO0Z2hqAybtPffQoBdgc+1BxbX?=
 =?us-ascii?Q?3XwUxkknWX6VQUhR76hjTBUgyauCB7+38b3Mhiix0eXED6Fs20/5Q9PhFLrr?=
 =?us-ascii?Q?COJrb2SuyB5jB9CIWJ8M9i+YKYt1yHEUwedVIMKuYAUdDL9reQ8u8yCSujyc?=
 =?us-ascii?Q?mKCr2PEhcZYaZCjtkpVFjBW1W7pQFa8iR4uUdtrXgGdQh5KWgng1AgDKT8hn?=
 =?us-ascii?Q?migC06smKe2l3B6b52dhiQrcnINJfdsjtjhgqTxqb5ecCiQb9S940MGH6ucb?=
 =?us-ascii?Q?XZ6PmQ/tikuaKytOyp9iZxmZfeTIjQpHfkWtgeY25RX6CrjcrzmztYiEUnPQ?=
 =?us-ascii?Q?LwBmAAj9JEaVsGHuSX7acFPxAv0UiQYGnWWoD73YEL9n5VL10fB0dgEB195F?=
 =?us-ascii?Q?eBSYj+hntveDHE7oLY5N+m4coAZEErxNsME/Sp20FuhxMVux8YEaC9L6HpEw?=
 =?us-ascii?Q?UlYTf2EuRe62Dtive5g6J7+NOvwvgkIPTgjNspN05EwGuz0rpFfKhaAkxeEt?=
 =?us-ascii?Q?33DVOe47ULg8mirQUa1FrFV1xM0PXIJ7q0/wsZx10DuEqz5txwlULcuNC4qe?=
 =?us-ascii?Q?R47JF4UWTxbL8ynKAxXnZryqyUoa0nqhEsNF0GhpzcTtwvm17tlKhaUGjNh/?=
 =?us-ascii?Q?eELNGZLjM5/zMvx/nalnRUtShcXdTWkRHSQ9KDONFHGn2L63nirpsgGmCOYl?=
 =?us-ascii?Q?lLWl6wjkXcJr6isFZP+2CWjV7Kspwzh/qLqMuB81B6HNbodxZdzQ9PNzyuje?=
 =?us-ascii?Q?K4s=3D?=
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-AuthSource: BN9PR11MB5433.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 57853485-82b7-4b1e-645a-08d97d63c8cf
X-MS-Exchange-CrossTenant-originalarrivaltime: 22 Sep 2021 00:56:17.1858
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-mailboxtype: HOSTED
X-MS-Exchange-CrossTenant-userprincipalname: D1CJDNAD8wpq62ID39tS1fmQkFtV3egyduwS5zcMdfeWFoQnjn7XzF82+W/bKEPSSLrq0/cST6+7VZIJ5kJogQ==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN6PR11MB1330
X-OriginatorOrg: intel.com
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

> From: Alex Williamson <alex.williamson@redhat.com>
> Sent: Wednesday, September 22, 2021 3:56 AM
>=20
> On Sun, 19 Sep 2021 14:38:30 +0800
> Liu Yi L <yi.l.liu@intel.com> wrote:
>=20
> > This patch introduces a new interface (/dev/vfio/devices/$DEVICE) for
> > userspace to directly open a vfio device w/o relying on container/group
> > (/dev/vfio/$GROUP). Anything related to group is now hidden behind
> > iommufd (more specifically in iommu core by this RFC) in a device-centr=
ic
> > manner.
> >
> > In case a device is exposed in both legacy and new interfaces (see next
> > patch for how to decide it), this patch also ensures that when the devi=
ce
> > is already opened via one interface then the other one must be blocked.
> >
> > Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> > ---
> >  drivers/vfio/vfio.c  | 228 +++++++++++++++++++++++++++++++++++++++----
> >  include/linux/vfio.h |   2 +
> >  2 files changed, 213 insertions(+), 17 deletions(-)
> >
> > diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> > index 02cc51ce6891..84436d7abedd 100644
> > --- a/drivers/vfio/vfio.c
> > +++ b/drivers/vfio/vfio.c
> ...
> > @@ -2295,6 +2436,52 @@ static struct miscdevice vfio_dev =3D {
> >  	.mode =3D S_IRUGO | S_IWUGO,
> >  };
> >
> > +static char *vfio_device_devnode(struct device *dev, umode_t *mode)
> > +{
> > +	return kasprintf(GFP_KERNEL, "vfio/devices/%s", dev_name(dev));
> > +}
>=20
> dev_name() doesn't provide us with any uniqueness guarantees, so this
> could potentially generate naming conflicts.  The similar scheme for
> devices within an iommu group appends an instance number if a conflict
> occurs, but that solution doesn't work here where the name isn't just a
> link to the actual device.  Devices within an iommu group are also
> likely associated within a bus_type, so the potential for conflict is
> pretty negligible, that's not the case as vfio is adopted for new
> device types.  Thanks,
>=20

This is also our concern. Thanks for confirming it. Appreciate if you
can help think out some better alternative to deal with it.

Thanks
Kevin