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

Max Gurtovoy
2025-12-08T22:09:37Z

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

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