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Tue, 09 Dec 2025 10:24:15 -0800 (PST) Received: from redhat.com ([80.230.34.255]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47a82d910b2sm3071355e9.14.2025.12.09.10.24.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Dec 2025 10:24:14 -0800 (PST) Date: Tue, 9 Dec 2025 13:24:12 -0500 From: "Michael S. Tsirkin" To: Max Gurtovoy Cc: stefanha@redhat.com, sgarzare@redhat.com, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, oren@nvidia.com, aevdaev@nvidia.com, aaptel@nvidia.com Subject: Re: [PATCH v2 1/1] virtio: add driver_override support Message-ID: <20251209132326-mutt-send-email-mst@kernel.org> References: <20251208220908.9250-1-mgurtovoy@nvidia.com> <20251209113306-mutt-send-email-mst@kernel.org> <49a3aabb-eb28-4149-b845-1bc5afffb985@nvidia.com> <20251209124819-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Dec 09, 2025 at 08:20:45PM +0200, Max Gurtovoy wrote: > > On 09/12/2025 19:48, Michael S. Tsirkin wrote: > > On Tue, Dec 09, 2025 at 07:45:19PM +0200, Max Gurtovoy wrote: > > > On 09/12/2025 18:34, Michael S. Tsirkin wrote: > > > > On Tue, Dec 09, 2025 at 12:09:08AM +0200, Max Gurtovoy wrote: > > > > > Add support for the 'driver_override' attribute to Virtio devices. This > > > > > allows users to control which Virtio bus driver binds to a given Virtio > > > > > device. > > > > > > > > > > If 'driver_override' is not set, the existing behavior is preserved and > > > > > devices will continue to auto-bind to the first matching Virtio bus > > > > > driver. > > > > oh, it's a device driver not the bus driver, actually. > > > Yes. I'll fix the commit message. > > > > > > > > > > > Tested with virtio blk device (virtio core and pci drivers are loaded): > > > > > > > > > > $ modprobe my_virtio_blk > > > > > > > > > > # automatically unbind from virtio_blk driver and override + bind to > > > > > # my_virtio_blk driver. > > > > > $ driverctl -v -b virtio set-override virtio0 my_virtio_blk > > > > > > > > > > In addition, driverctl saves the configuration persistently under > > > > > /etc/driverctl.d/. > > > > what is this "mydriver" though? what are valid examples that > > > > we want to support? > > > This is an example for a custom virtio block driver. > > > > > > It can be any custom virtio-XX driver (XX=FS/NET/..). > > Is "custom" a way to say "out of tree"? > > The driver_override mechanism fits both in-tree/out-of-tree drivers. good to know. which in tree drivers can use it? this is the part that's missing in the commit log. thanks > > > > > > > Signed-off-by: Avraham Evdaev > > > > > Signed-off-by: Max Gurtovoy > > > > > --- > > > > > > > > > > changes from v1: > > > > > - use !strcmp() to compare strings (MST) > > > > > - extend commit msg with example (MST) > > > > > > > > > > --- > > > > > drivers/virtio/virtio.c | 34 ++++++++++++++++++++++++++++++++++ > > > > > include/linux/virtio.h | 4 ++++ > > > > > 2 files changed, 38 insertions(+) > > > > > > > > > > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c > > > > > index a09eb4d62f82..993dc928be49 100644 > > > > > --- a/drivers/virtio/virtio.c > > > > > +++ b/drivers/virtio/virtio.c > > > > > @@ -61,12 +61,41 @@ static ssize_t features_show(struct device *_d, > > > > > } > > > > > static DEVICE_ATTR_RO(features); > > > > > +static ssize_t driver_override_store(struct device *_d, > > > > > + struct device_attribute *attr, > > > > > + const char *buf, size_t count) > > > > > +{ > > > > > + struct virtio_device *dev = dev_to_virtio(_d); > > > > > + int ret; > > > > > + > > > > > + ret = driver_set_override(_d, &dev->driver_override, buf, count); > > > > > + if (ret) > > > > > + return ret; > > > > > + > > > > > + return count; > > > > > +} > > > > > + > > > > > +static ssize_t driver_override_show(struct device *_d, > > > > > + struct device_attribute *attr, char *buf) > > > > > +{ > > > > > + struct virtio_device *dev = dev_to_virtio(_d); > > > > > + ssize_t len; > > > > > + > > > > > + device_lock(_d); > > > > > + len = sysfs_emit(buf, "%s\n", dev->driver_override); > > > > > + device_unlock(_d); > > > > > + > > > > > + return len; > > > > > +} > > > > > +static DEVICE_ATTR_RW(driver_override); > > > > > + > > > > > static struct attribute *virtio_dev_attrs[] = { > > > > > &dev_attr_device.attr, > > > > > &dev_attr_vendor.attr, > > > > > &dev_attr_status.attr, > > > > > &dev_attr_modalias.attr, > > > > > &dev_attr_features.attr, > > > > > + &dev_attr_driver_override.attr, > > > > > NULL, > > > > > }; > > > > > ATTRIBUTE_GROUPS(virtio_dev); > > > > > @@ -88,6 +117,10 @@ static int virtio_dev_match(struct device *_dv, const struct device_driver *_dr) > > > > > struct virtio_device *dev = dev_to_virtio(_dv); > > > > > const struct virtio_device_id *ids; > > > > > + /* Check override first, and if set, only use the named driver */ > > > > > + if (dev->driver_override) > > > > > + return !strcmp(dev->driver_override, _dr->name); > > > > > + > > > > > ids = drv_to_virtio(_dr)->id_table; > > > > > for (i = 0; ids[i].device; i++) > > > > > if (virtio_id_match(dev, &ids[i])) > > > > > @@ -582,6 +615,7 @@ void unregister_virtio_device(struct virtio_device *dev) > > > > > { > > > > > int index = dev->index; /* save for after device release */ > > > > > + kfree(dev->driver_override); > > > > > device_unregister(&dev->dev); > > > > > virtio_debug_device_exit(dev); > > > > > ida_free(&virtio_index_ida, index); > > > > > diff --git a/include/linux/virtio.h b/include/linux/virtio.h > > > > > index db31fc6f4f1f..418bb490bdc6 100644 > > > > > --- a/include/linux/virtio.h > > > > > +++ b/include/linux/virtio.h > > > > > @@ -138,6 +138,9 @@ struct virtio_admin_cmd { > > > > > * @config_lock: protects configuration change reporting > > > > > * @vqs_list_lock: protects @vqs. > > > > > * @dev: underlying device. > > > > > + * @driver_override: driver name to force a match; do not set directly, > > > > > + * because core frees it; use driver_set_override() to > > > > > + * set or clear it. > > > > > * @id: the device type identification (used to match it with a driver). > > > > > * @config: the configuration ops for this device. > > > > > * @vringh_config: configuration ops for host vrings. > > > > > @@ -158,6 +161,7 @@ struct virtio_device { > > > > > spinlock_t config_lock; > > > > > spinlock_t vqs_list_lock; > > > > > struct device dev; > > > > > + const char *driver_override; > > > > > struct virtio_device_id id; > > > > > const struct virtio_config_ops *config; > > > > > const struct vringh_config_ops *vringh_config; > > > > > -- > > > > > 2.18.1