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[PATCH 4/6] vduse: add VDUSE_GET_FEATURES ioctl

Eugenio Pérez posted 6 patches 1 week, 2 days ago
[PATCH 4/6] vduse: add VDUSE_GET_FEATURES ioctl
Posted by Eugenio Pérez 1 week, 2 days ago 
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.
---
 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;
+			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
Re: [PATCH 4/6] vduse: add VDUSE_GET_FEATURES ioctl
Posted by Jason Wang 1 week, 2 days ago 
On Wed, Jan 28, 2026 at 8:45 PM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> 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.
> ---
>  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
Re: [PATCH 4/6] vduse: add VDUSE_GET_FEATURES ioctl
Posted by Eugenio Perez Martin 1 week, 2 days ago 
On Thu, Jan 29, 2026 at 3:10 AM Jason Wang <jasowang@redhat.com> wrote:
>
> On Wed, Jan 28, 2026 at 8:45 PM Eugenio Pérez <eperezma@redhat.com> wrote:
> >
> > 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.
> > ---
> >  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
>

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