[PATCH v3 2/3] vduse: add VDUSE_GET_FEATURES ioctl

Eugenio Pérez
2026-03-10T19:08:19Z

Add an ioctl to allow VDUSE instances to query the available features
supported by the kernel module.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
A simple u64 bitmap is used for feature flags. While a flexible array
could support indefinite expansion, 64 bits is sufficient for the
foreseeable future and simplifies the implementation.

Also, dev_dbg is used for logging rather than dev_err as these can be
triggered from userspace.
---
v3:
* Remove check for API_VERSION < 2
* Add comment about struct vduse_dev_config:vduse_features is only valid
if VDUSE_GET_FEATURES success.

v2:
* return -EINVAL if ioctl called with version < 2, so userland visible
reply is kept (Jason).
---
drivers/vdpa/vdpa_user/vduse_dev.c | 7 +++++++
include/uapi/linux/vduse.h | 7 ++++++-
2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
index d1da7c15d98b..17e0358d3a68 100644
--- a/drivers/vdpa/vdpa_user/vduse_dev.c
+++ b/drivers/vdpa/vdpa_user/vduse_dev.c
@@ -52,6 +52,9 @@

#define IRQ_UNBOUND -1

+/* Supported VDUSE features */
+static const uint64_t vduse_features;
+
/*
* VDUSE instance have not asked the vduse API version, so assume 0.
*
@@ -2207,6 +2210,10 @@ static long vduse_ioctl(struct file *file, unsigned int cmd,
ret = vduse_destroy_dev(name);
break;
}
+ case VDUSE_GET_FEATURES:
+ ret = put_user(vduse_features, (u64 __user *)argp);
+ break;
+
default:
ret = -EINVAL;
break;
diff --git a/include/uapi/linux/vduse.h b/include/uapi/linux/vduse.h
index 361eea511c21..e9b5f32a452d 100644
--- a/include/uapi/linux/vduse.h
+++ b/include/uapi/linux/vduse.h
@@ -33,6 +33,7 @@
* @vq_align: the allocation alignment of virtqueue's metadata
* @ngroups: number of vq groups that VDUSE device declares
* @nas: number of address spaces that VDUSE device declares
+ * @vduse_features: VDUSE features
* @reserved: for future use, needs to be initialized to zero
* @config_size: the size of the configuration space
* @config: the buffer of the configuration space
@@ -49,7 +50,8 @@ struct vduse_dev_config {
__u32 vq_align;
__u32 ngroups; /* if VDUSE_API_VERSION >= 1 */
__u32 nas; /* if VDUSE_API_VERSION >= 1 */
- __u32 reserved[11];
+ __u64 vduse_features; /* if VDUSE_GET_FEATURES is not EINVAL */
+ __u32 reserved[9];
__u32 config_size;
__u8 config[];
};
@@ -63,6 +65,9 @@ struct vduse_dev_config {
*/
#define VDUSE_DESTROY_DEV _IOW(VDUSE_BASE, 0x03, char[VDUSE_NAME_MAX])

+/* Get the VDUSE supported features */
+#define VDUSE_GET_FEATURES _IOR(VDUSE_BASE, 0x04, __u64)
+
/* The ioctls for VDUSE device (/dev/vduse/$NAME) */

/**
--
2.53.0