On Thu, Jan 15, 2026 at 9:15 AM Jason Wang <[email protected]> wrote:
>
> On Thu, Jan 15, 2026 at 2:49 AM Eugenio Pérez <[email protected]> wrote:
> >
> > Address Space IDs allows the VDUSE framework to support devices able to
> > expose different virtqueues to different part of the drivers. For
> > example, to let QEMU handle the net device control virtqueue, so QEMU
> > always knows the state of the device like mac address or number of
> > queues enabled, while leaving the dataplane passtrhough to the guest
> > intact. This enables live migration.
> >
> > Expands the VDUSE documentation to explain how to use the new ioctls or
> > the new struct members of old ioctls.
> >
> > Signed-off-by: Eugenio Pérez <[email protected]>
> > ---
> > v12: New in V12. Requested by Jason.
> > ---
> > Documentation/userspace-api/vduse.rst | 49 +++++++++++++++++++++++++++
> > 1 file changed, 49 insertions(+)
> >
> > diff --git a/Documentation/userspace-api/vduse.rst
> > b/Documentation/userspace-api/vduse.rst
> > index bdb880e01132..66110d918815 100644
> > --- a/Documentation/userspace-api/vduse.rst
> > +++ b/Documentation/userspace-api/vduse.rst
> > @@ -230,4 +230,53 @@ able to start the dataplane processing as follows:
> > 5. Inject an interrupt for specific virtqueue with the VDUSE_INJECT_VQ_IRQ
> > ioctl
> > after the used ring is filled.
> >
> > +Enabling ASID (API version 1)
> > +------------------------------
> > +
> > +VDUSE supports per-address-space identifiers (ASIDs) starting with API
> > +version 1. Setup it with ioctl(VDUSE_SET_API_VERSION) on
> > `/dev/vduse/control` and
> > +pass `VDUSE_API_VERSION_1` before creating a new VDUSE instance with
> > +ioctl(VDUSE_CREATE_DEV).
> > +
> > +Afterwards, you can use the member asid of ioctl(VDUSE_IOTLB_GET_INFO) to
> > +select the address space of the IOTLB you are queryng. Similarly, you can
> > use
>
> Should be "querying"
>
> > +ioctl(VDUSE_IOTLB_GET_FD2) to obtain the file descriptor describing an IOVA
>
> Should we fail VDUSE_IOTLB_GET_FD on API version 1 or it is implied for ASID
> 0?
>
ASID 0 is implied at this moment, so future VDUSE devices don't need
to worry about ASID configuration.
> > +region of an specific ASID. Example usage:
> > +
> > +.. code-block:: c
> > +
> > + static void *iova_to_va(int dev_fd, uint32_t asid, uint64_t iova,
> > + uint64_t *len)
> > + {
> > + int fd;
> > + void *addr;
> > + size_t size;
> > + struct vduse_iotlb_entry_v2 entry = { 0 };
> > +
> > + entry.v1.start = iova;
> > + entry.v1.last = iova;
> > + entry.asid = asid;
> > +
> > + fd = ioctl(dev_fd, VDUSE_IOTLB_GET_FD2, &entry);
> > + if (fd < 0)
> > + return NULL;
> > +
> > + size = entry.v1.last - entry.v1.start + 1;
> > + *len = entry.v1.last - iova + 1;
> > + addr = mmap(0, size, perm_to_prot(entry.v1.perm),
> > MAP_SHARED,
> > + fd, entry.v1.offset);
> > + close(fd);
> > + if (addr == MAP_FAILED)
> > + return NULL;
> > +
> > + /*
> > + * Using some data structures such as linked list to store
> > + * the iotlb mapping. The munmap(2) should be called for the
> > + * cached mapping when the corresponding VDUSE_UPDATE_IOTLB
> > + * message is received or the device is reset.
> > + */
> > +
> > + return addr + iova - entry.start;
> > + }
> > +
>
> It looks like we missed the documentation of VDUSE_SET_VQ_GROUP_ASID.
>
> > For more details on the uAPI, please see include/uapi/linux/vduse.h.
> > --
> > 2.52.0
> >
>
> Thanks
>
