On Thu, Feb 12, 2026 at 9:07 AM Jason Wang <[email protected]> wrote: > > On Tue, Feb 10, 2026 at 4:26 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. > > --- > > v2: > > * return -EINVAL if ioctl called with version < 2, so userland visible > > reply is kept (Jason). > > --- > > 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 d1da7c15d98b..7458cbaed4c7 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. > > * > > @@ -1947,6 +1950,19 @@ 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; > > @@ -2207,6 +2223,18 @@ 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 = -EINVAL; > > + 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 27832d46084c..8898d9daa777 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; > > Nit: Should we document " /* if VDUSE_API_VERSION >= 2 */ > > But I have an open question, is this better to just introduce a > VDUSE_SET_FEATURES then we can do negotiation to avoid bumping API > versions? >
How do you know if you can call VDUSE_GET_FEATURES and VDUSE_SET_FEATURES then? vduse_ioctl does not even return -ENOIOCMD but -EINVAL if you call the equivalent of VDUSE_GET_FEATURES on current Linux master. Or should the VDUSE instance assume that if the ioctl returns -EINVAL the kernel does not support them?
