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Tue, 27 Aug 2019 11:07:37 +0000 From: Parav Pandit To: Cornelia Huck CC: "alex.williamson@redhat.com" , Jiri Pirko , "kwankhede@nvidia.com" , "davem@davemloft.net" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "netdev@vger.kernel.org" Subject: RE: [PATCH 3/4] mdev: Expose mdev alias in sysfs tree Thread-Topic: [PATCH 3/4] mdev: Expose mdev alias in sysfs tree Thread-Index: AQHVXE6v3Mg2zMVvBUG6schRq+9Lx6cO0OsAgAADYqA= Date: Tue, 27 Aug 2019 11:07:37 +0000 Message-ID: References: <20190826204119.54386-1-parav@mellanox.com> <20190826204119.54386-4-parav@mellanox.com> <20190827124706.7e726794.cohuck@redhat.com> In-Reply-To: <20190827124706.7e726794.cohuck@redhat.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: spf=none (sender IP is ) smtp.mailfrom=parav@mellanox.com; x-originating-ip: [106.51.18.188] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 5556892f-a1f4-47ab-a094-08d72adec557 x-ms-office365-filtering-ht: Tenant x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(7168020)(4627221)(201703031133081)(201702281549075)(8990200)(5600166)(711020)(4605104)(1401327)(4618075)(2017052603328)(7193020);SRVR:AM0PR05MB4161; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: Mellanox.com X-MS-Exchange-CrossTenant-Network-Message-Id: 5556892f-a1f4-47ab-a094-08d72adec557 X-MS-Exchange-CrossTenant-originalarrivaltime: 27 Aug 2019 11:07:37.7315 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: a652971c-7d2e-4d9b-a6a4-d149256f461b X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: gMkHqIWT7VWd931RprbzlvnRRInXkrghuADpYRQ2PFNGYeI0EOhLE7E+z7HTXvp15hjhVGWJXLpws7arHi7gxQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM0PR05MB4161 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: Cornelia Huck > Sent: Tuesday, August 27, 2019 4:17 PM > To: Parav Pandit > Cc: alex.williamson@redhat.com; Jiri Pirko ; > kwankhede@nvidia.com; davem@davemloft.net; kvm@vger.kernel.org; linux- > kernel@vger.kernel.org; netdev@vger.kernel.org > Subject: Re: [PATCH 3/4] mdev: Expose mdev alias in sysfs tree >=20 > On Mon, 26 Aug 2019 15:41:18 -0500 > Parav Pandit wrote: >=20 > > Expose mdev alias as string in a sysfs tree so that such attribute can > > be used to generate netdevice name by systemd/udev or can be used to > > match other kernel objects based on the alias of the mdev. >=20 > What about >=20 > "Expose the optional alias for an mdev device as a sysfs attribute. > This way, userspace tools such as udev may make use of the alias, for exa= mple > to create a netdevice name for the mdev." >=20 Ok. I will change it. > > > > Signed-off-by: Parav Pandit > > --- > > drivers/vfio/mdev/mdev_sysfs.c | 13 +++++++++++++ >=20 > I think the documentation should be updated as well. >=20 > > 1 file changed, 13 insertions(+) > > > > diff --git a/drivers/vfio/mdev/mdev_sysfs.c > > b/drivers/vfio/mdev/mdev_sysfs.c index 43afe0e80b76..59f4e3cc5233 > > 100644 > > --- a/drivers/vfio/mdev/mdev_sysfs.c > > +++ b/drivers/vfio/mdev/mdev_sysfs.c > > @@ -246,7 +246,20 @@ static ssize_t remove_store(struct device *dev, > > struct device_attribute *attr, > > > > static DEVICE_ATTR_WO(remove); > > > > +static ssize_t alias_show(struct device *device, > > + struct device_attribute *attr, char *buf) { > > + struct mdev_device *dev =3D mdev_from_dev(device); > > + > > + if (!dev->alias) > > + return -EOPNOTSUPP; >=20 > I'm wondering how to make this consumable by userspace in the easiest way= . > - As you do now (userspace gets an error when trying to read)? > - Returning an empty value (nothing to see here, move along)? No. This is confusing, to return empty value, because it says that there is= an alias but it is some weird empty string. If there is alias, it shows exactly what it is. If no alias it returns an error code =3D unsupported -> inline with other w= idely used subsystem. > - Or not creating the attribute at all? That would match what userspace > sees on older kernels, so it needs to be able to deal with that New sysfs files can appear. Tool cannot say that I was not expecting this f= ile here. User space is supposed to work with the file they are off interest. Mdev interface has option to specify vendor specific files, though in usual= manner it's not recommended. So there is no old user space, new kernel issue here. > anyway. >=20 > > + > > + return sprintf(buf, "%s\n", dev->alias); } static > > +DEVICE_ATTR_RO(alias); > > + > > static const struct attribute *mdev_device_attrs[] =3D { > > + &dev_attr_alias.attr, > > &dev_attr_remove.attr, > > NULL, > > };