[PATCH v4 3/4] vduse: add VDUSE_SET_FEATURES ioctl

["Eugenio Pérez" <eperezma@redhat.com>]

Add an ioctl to allow VDUSE instances to set the VDUSE features
supported by the userland VDUSE instance.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
v4: New in v4.
---
 drivers/vdpa/vdpa_user/vduse_dev.c | 24 ++++++++++++++++++++++++
 include/uapi/linux/vduse.h         |  3 +++
 2 files changed, 27 insertions(+)

diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
index e1930e38df7a..4d561b9fbf5e 100644
--- a/drivers/vdpa/vdpa_user/vduse_dev.c
+++ b/drivers/vdpa/vdpa_user/vduse_dev.c
@@ -160,6 +160,7 @@ struct vduse_dev_msg {
 
 struct vduse_control {
 	u64 api_version;
+	u64 vduse_features;
 };
 
 static DEFINE_MUTEX(vduse_lock);
@@ -2349,7 +2350,29 @@ static long vduse_ioctl(struct file *file, unsigned int cmd,
 	case VDUSE_GET_FEATURES:
 		ret = put_user(vduse_features, (u64 __user *)argp);
 		break;
+	case VDUSE_SET_FEATURES: {
+		u64 features;
 
+		ret = -EFAULT;
+		if (get_user(features, (u64 __user *)argp)) {
+			dev_dbg(vduse_ctrl_dev, "Could not get vduse features");
+			break;
+		}
+
+		ret = -EINVAL;
+		if (features & ~vduse_features) {
+			dev_dbg(vduse_ctrl_dev,
+				"Invalid features in %llx, expected %llx",
+				features, vduse_features);
+			break;
+		}
+
+		ret = 0;
+		control->vduse_features = features;
+		dev_dbg(vduse_ctrl_dev, "Set features %llx", features);
+
+		break;
+	}
 	default:
 		ret = -EINVAL;
 		break;
@@ -2376,6 +2399,7 @@ static int vduse_open(struct inode *inode, struct file *file)
 		return -ENOMEM;
 
 	control->api_version = VDUSE_API_VERSION_NOT_ASKED;
+	control->vduse_features = 0;
 	file->private_data = control;
 
 	return 0;
diff --git a/include/uapi/linux/vduse.h b/include/uapi/linux/vduse.h
index 89aa3b448c0a..f14c965bb7f6 100644
--- a/include/uapi/linux/vduse.h
+++ b/include/uapi/linux/vduse.h
@@ -66,6 +66,9 @@ struct vduse_dev_config {
 /* Get the VDUSE supported features */
 #define VDUSE_GET_FEATURES	_IOR(VDUSE_BASE, 0x04, __u64)
 
+/* Set the VDUSE features */
+#define VDUSE_SET_FEATURES	_IOW(VDUSE_BASE, 0x05, __u64)
+
 /* The ioctls for VDUSE device (/dev/vduse/$NAME) */
 
 /**
-- 
2.55.0