Re: [PATCH v2 1/1] virtio: add driver_override support

Stefan Hajnoczi
2025-12-09T15:49:05Z

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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.
>
> 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

Why a second virtio-blk driver implementation? Please explain the use
case.

Thanks,
Stefan

> In addition, driverctl saves the configuration persistently under
> /etc/driverctl.d/.
>
> Signed-off-by: Avraham Evdaev <aevdaev@nvidia.com>
> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> ---
>
> 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
>

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