On Wed, Jan 28, 2026 at 8:45 PM Eugenio Pérez <[email protected]> wrote:
>
> Add an ioctl to allow VDUSE instances to query the available features
> supported by the kernel module.
>
> Signed-off-by: Eugenio Pérez <[email protected]>
> ---
> 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.
> ---
> drivers/vdpa/vdpa_user/vduse_dev.c | 28 ++++++++++++++++++++++++++++
> include/uapi/linux/vduse.h | 7 ++++++-
> 2 files changed, 34 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c
> b/drivers/vdpa/vdpa_user/vduse_dev.c
> index 551ccde0b856..e7da69c2ad71 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.
> *
> @@ -1977,6 +1980,19 @@ static bool vduse_validate_config(struct
> vduse_dev_config *config,
> sizeof(config->reserved)))
> return false;
>
> + if (api_version < VDUSE_API_VERSION_2) {
> + if (config->vduse_features) {
> + dev_dbg(vduse_ctrl_dev,
> + "config->vduse_features with version %llu",
> + api_version);
> + return false;
> + }
> + } else {
> + if (config->vduse_features & ~vduse_features)
> + return false;
> + }
> +
> +
> if (api_version < VDUSE_API_VERSION_1 &&
> (config->ngroups || config->nas))
> return false;
> @@ -2237,6 +2253,18 @@ static long vduse_ioctl(struct file *file, unsigned
> int cmd,
> ret = vduse_destroy_dev(name);
> break;
> }
> + case VDUSE_GET_FEATURES:
> + if (control->api_version < VDUSE_API_VERSION_2) {
> + dev_dbg(vduse_ctrl_dev,
> + "VDUSE_GET_FEATURES ioctl with version %llu",
> + control->api_version);
> + ret = -ENOIOCTLCMD;
Should we stick to -EINVAL (see below)?
> + break;
> + }
> +
> + 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 dea89ed281a7..1f68e556cbf2 100644
> --- a/include/uapi/linux/vduse.h
> +++ b/include/uapi/linux/vduse.h
> @@ -37,6 +37,7 @@
> * @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
> @@ -53,7 +54,8 @@ 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;
> + __u32 reserved[9];
> __u32 config_size;
> __u8 config[];
> };
> @@ -67,6 +69,9 @@ 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) */
>
> /**
> --
> 2.52.0
>
Thanks
