On Thu, Jan 29, 2026 at 3:10 AM Jason Wang <[email protected]> wrote:
>
> 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)?
>
Good point! I got fooled by vduse_dev_ioctl that uses ENOIOCTLCMD as
default. I guess it's too late to change the mismatch. Changing for
V2.
Thanks!
>
> > + 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
>
