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Wed, 22 Sep 2021 00:56:17 +0000 From: "Tian, Kevin" To: Alex Williamson , "Liu, Yi L" CC: "jgg@nvidia.com" , "hch@lst.de" , "jasowang@redhat.com" , "joro@8bytes.org" , "jean-philippe@linaro.org" , "parav@mellanox.com" , "lkml@metux.net" , "pbonzini@redhat.com" , "lushenming@huawei.com" , "eric.auger@redhat.com" , "corbet@lwn.net" , "Raj, Ashok" , "yi.l.liu@linux.intel.com" , "Tian, Jun J" , "Wu, Hao" , "Jiang, Dave" , "jacob.jun.pan@linux.intel.com" , "kwankhede@nvidia.com" , "robin.murphy@arm.com" , "kvm@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "dwmw2@infradead.org" , "linux-kernel@vger.kernel.org" , "baolu.lu@linux.intel.com" , "david@gibson.dropbear.id.au" , "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: 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-Has-Attach: X-MS-TNEF-Correlator: authentication-results: redhat.com; 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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: X-Mailing-List: kvm@vger.kernel.org > From: Alex Williamson > Sent: Wednesday, September 22, 2021 3:56 AM >=20 > On Sun, 19 Sep 2021 14:38:30 +0800 > Liu Yi L 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 > > --- > > 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