diff --git a/vhost_user_backend/Cargo.toml b/vhost_user_backend/Cargo.toml
new file mode 100644
index 000000000..4e49171c9
--- /dev/null
+++ b/vhost_user_backend/Cargo.toml
@@ -0,0 +1,23 @@
+[package]
+name = "vhost_user_backend"
+version = "0.1.0"
+authors = ["The Cloud Hypervisor Authors"]
+edition = "2018"
+
+[features]
+default = []
+pci_support = ["vm-virtio/pci_support"]
+mmio_support = ["vm-virtio/mmio_support"]
+
+[dependencies]
+epoll = "4.1.0"
+libc = "0.2.60"
+vm-memory = { git = "https://github.com/rust-vmm/vm-memory" } 
+vm-virtio = { path = "../vm-virtio" }
+vmm-sys-util = { git = "https://github.com/rust-vmm/vmm-sys-util" }
+
+[dependencies.vhost_rs]
+path = "../vhost_rs"
+features = ["vhost-user-slave"]
+
+[workspace]
diff --git a/vhost_user_backend/src/lib.rs b/vhost_user_backend/src/lib.rs
new file mode 100644
index 000000000..dab81c0ca
--- /dev/null
+++ b/vhost_user_backend/src/lib.rs
@@ -0,0 +1,778 @@
+// Copyright 2019 Intel Corporation. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+//
+// Copyright 2019 Alibaba Cloud Computing. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+use std::fs::File;
+use std::io;
+use std::num::Wrapping;
+use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
+use std::result;
+use std::sync::{Arc, Mutex};
+use std::thread;
+use vhost_rs::vhost_user::message::{
+    VhostUserConfigFlags, VhostUserMemoryRegion, VhostUserProtocolFeatures,
+    VhostUserVirtioFeatures, VhostUserVringAddrFlags, VhostUserVringState,
+    VHOST_USER_CONFIG_OFFSET, VHOST_USER_CONFIG_SIZE,
+};
+use vhost_rs::vhost_user::{
+    Error as VhostUserError, Result as VhostUserResult, SlaveReqHandler, VhostUserSlaveReqHandler,
+};
+use vm_memory::guest_memory::FileOffset;
+use vm_memory::{GuestAddress, GuestMemoryMmap};
+use vm_virtio::{DescriptorChain, Queue};
+use vmm_sys_util::eventfd::EventFd;
+
+#[derive(Debug)]
+/// Errors related to vhost-user daemon.
+pub enum Error {
+    /// Failed creating vhost-user slave handler.
+    CreateSlaveReqHandler(VhostUserError),
+    /// Failed starting daemon thread.
+    StartDaemon(io::Error),
+    /// Failed waiting for daemon thread.
+    WaitDaemon(std::boxed::Box<dyn std::any::Any + std::marker::Send>),
+    /// Failed handling a vhost-user request.
+    HandleRequest(VhostUserError),
+    /// Could not find the mapping from memory regions.
+    MissingMemoryMapping,
+    /// Failed to create epoll file descriptor.
+    EpollCreateFd(io::Error),
+    /// Failed to add a file descriptor to the epoll handler.
+    EpollCtl(io::Error),
+    /// Failed while waiting for events.
+    EpollWait(io::Error),
+    /// Failed to signal used queue.
+    SignalUsedQueue(io::Error),
+}
+
+/// Result of vhost-user daemon operations.
+pub type Result<T> = std::result::Result<T, Error>;
+
+/// This trait must be implemented by the caller in order to provide backend
+/// specific implementation.
+pub trait VhostUserBackend: Send + Sync + 'static {
+    /// Number of queues.
+    fn num_queues(&self) -> usize;
+
+    /// Depth of each queue.
+    fn max_queue_size(&self) -> usize;
+
+    /// Virtio features.
+    fn features(&self) -> u64;
+
+    /// This function gets called if the backend registered some additional
+    /// listeners onto specific file descriptors. The library can handle
+    /// virtqueues on its own, but does not know what to do with events
+    /// happening on custom listeners.
+    fn handle_event(&self, device_event: u16, evset: epoll::Events) -> Result<bool>;
+
+    /// This function is responsible for the actual processing that needs to
+    /// happen when one of the virtqueues is available.
+    fn process_queue(
+        &self,
+        q_idx: u16,
+        avail_desc: &DescriptorChain,
+        mem: &GuestMemoryMmap,
+    ) -> Result<u32>;
+
+    /// Get virtio device configuration.
+    fn get_config(&self, offset: u32, size: u32) -> Vec<u8>;
+
+    /// Set virtio device configuration.
+    fn set_config(&self, offset: u32, buf: &[u8]);
+}
+
+/// This structure is the public API the backend is allowed to interact with
+/// in order to run a fully functional vhost-user daemon.
+pub struct VhostUserDaemon<S: VhostUserBackend> {
+    name: String,
+    sock_path: String,
+    handler: Arc<Mutex<VhostUserHandler<S>>>,
+    vring_handler: Arc<Mutex<VringEpollHandler<S>>>,
+    main_thread: Option<thread::JoinHandle<Result<()>>>,
+}
+
+impl<S: VhostUserBackend> VhostUserDaemon<S> {
+    /// Create the daemon instance, providing the backend implementation of
+    /// VhostUserBackend.
+    /// Under the hood, this will start a dedicated thread responsible for
+    /// listening onto registered event. Those events can be vring events or
+    /// custom events from the backend, but they get to be registered later
+    /// during the sequence.
+    pub fn new(name: String, sock_path: String, backend: S) -> Result<Self> {
+        let handler = Arc::new(Mutex::new(VhostUserHandler::new(backend)));
+        let vring_handler = handler.lock().unwrap().get_vring_handler();
+
+        Ok(VhostUserDaemon {
+            name,
+            sock_path,
+            handler,
+            vring_handler,
+            main_thread: None,
+        })
+    }
+
+    /// Connect to the vhost-user socket and run a dedicated thread handling
+    /// all requests coming through this socket. This runs in an infinite loop
+    /// that should be terminating once the other end of the socket (the VMM)
+    /// disconnects.
+    pub fn start(&mut self) -> Result<()> {
+        let mut slave_handler =
+            SlaveReqHandler::connect(self.sock_path.as_str(), self.handler.clone())
+                .map_err(Error::CreateSlaveReqHandler)?;
+        let handle = thread::Builder::new()
+            .name(self.name.clone())
+            .spawn(move || loop {
+                slave_handler
+                    .handle_request()
+                    .map_err(Error::HandleRequest)?;
+            })
+            .map_err(Error::StartDaemon)?;
+
+        self.main_thread = Some(handle);
+
+        Ok(())
+    }
+
+    /// Wait for the thread handling the vhost-user socket connection to
+    /// terminate.
+    pub fn wait(&mut self) -> Result<()> {
+        if let Some(handle) = self.main_thread.take() {
+            let _ = handle.join().map_err(Error::WaitDaemon)?;
+        }
+        Ok(())
+    }
+
+    /// Register a custom event only meaningful to the caller. When this event
+    /// is later triggered, and because only the caller knows what to do about
+    /// it, the backend implementation of `handle_event` will be called.
+    /// This lets entire control to the caller about what needs to be done for
+    /// this special event, without forcing it to run its own dedicated epoll
+    /// loop for it.
+    pub fn register_listener(
+        &self,
+        fd: RawFd,
+        ev_type: epoll::Events,
+        data: u64,
+    ) -> result::Result<(), io::Error> {
+        self.vring_handler
+            .lock()
+            .unwrap()
+            .register_listener(fd, ev_type, data)
+    }
+
+    /// Unregister a custom event. If the custom event is triggered after this
+    /// function has been called, nothing will happen as it will be removed
+    /// from the list of file descriptors the epoll loop is listening to.
+    pub fn unregister_listener(
+        &self,
+        fd: RawFd,
+        ev_type: epoll::Events,
+        data: u64,
+    ) -> result::Result<(), io::Error> {
+        self.vring_handler
+            .lock()
+            .unwrap()
+            .unregister_listener(fd, ev_type, data)
+    }
+
+    /// Trigger the processing of a virtqueue. This function is meant to be
+    /// used by the caller whenever it might need some available queues to
+    /// send data back to the guest.
+    /// A concrete example is a backend registering one extra listener for
+    /// data that needs to be sent to the guest. When the associated event
+    /// is triggered, the backend will be invoked through its `handle_event`
+    /// implementation. And in this case, the way to handle the event is to
+    /// call into `process_queue` to let it invoke the backend implementation
+    /// of `process_queue`. With this twisted trick, all common parts related
+    /// to the virtqueues can remain part of the library.
+    pub fn process_queue(&self, q_idx: u16) -> Result<()> {
+        self.vring_handler.lock().unwrap().process_queue(q_idx)
+    }
+}
+
+struct AddrMapping {
+    vmm_addr: u64,
+    size: u64,
+}
+
+struct Memory {
+    mappings: Vec<AddrMapping>,
+}
+
+struct Vring {
+    queue: Queue,
+    kick: Option<EventFd>,
+    call: Option<EventFd>,
+    err: Option<EventFd>,
+    started: bool,
+    enabled: bool,
+}
+
+impl Clone for Vring {
+    fn clone(&self) -> Self {
+        let kick = if let Some(c) = &self.kick {
+            Some(c.try_clone().unwrap())
+        } else {
+            None
+        };
+
+        let call = if let Some(c) = &self.call {
+            Some(c.try_clone().unwrap())
+        } else {
+            None
+        };
+
+        let err = if let Some(e) = &self.err {
+            Some(e.try_clone().unwrap())
+        } else {
+            None
+        };
+
+        Vring {
+            queue: self.queue.clone(),
+            kick,
+            call,
+            err,
+            started: self.started,
+            enabled: self.enabled,
+        }
+    }
+}
+
+impl Vring {
+    fn new(max_queue_size: u16) -> Self {
+        Vring {
+            queue: Queue::new(max_queue_size),
+            kick: None,
+            call: None,
+            err: None,
+            started: false,
+            enabled: false,
+        }
+    }
+}
+
+struct VringEpollHandler<S: VhostUserBackend> {
+    backend: Arc<S>,
+    vrings: Arc<Mutex<Vec<Vring>>>,
+    mem: Option<GuestMemoryMmap>,
+    epoll_fd: RawFd,
+}
+
+impl<S: VhostUserBackend> VringEpollHandler<S> {
+    fn update_memory(&mut self, mem: Option<GuestMemoryMmap>) {
+        self.mem = mem;
+    }
+
+    fn process_queue(&self, q_idx: u16) -> Result<()> {
+        let vring = &mut self.vrings.lock().unwrap()[q_idx as usize];
+        let mut used_desc_heads = vec![(0, 0); vring.queue.size as usize];
+        let mut used_count = 0;
+        if let Some(mem) = &self.mem {
+            for avail_desc in vring.queue.iter(&mem) {
+                let used_len = self
+                    .backend
+                    .process_queue(q_idx, &avail_desc, &mem)
+                    .unwrap();
+
+                used_desc_heads[used_count] = (avail_desc.index, used_len);
+                used_count += 1;
+            }
+
+            for &(desc_index, len) in &used_desc_heads[..used_count] {
+                vring.queue.add_used(&mem, desc_index, len);
+            }
+        }
+
+        if used_count > 0 {
+            if let Some(call) = &vring.call {
+                return call.write(1).map_err(Error::SignalUsedQueue);
+            }
+        }
+
+        Ok(())
+    }
+
+    fn handle_event(&mut self, device_event: u16, evset: epoll::Events) -> Result<bool> {
+        let num_queues = self.vrings.lock().unwrap().len();
+        match device_event as usize {
+            x if x < num_queues => {
+                if let Some(kick) = &self.vrings.lock().unwrap()[device_event as usize].kick {
+                    kick.read().unwrap();
+                }
+
+                self.process_queue(device_event).unwrap();
+
+                Ok(false)
+            }
+            _ => self.backend.handle_event(device_event, evset),
+        }
+    }
+
+    fn register_vring_listener(&self, q_idx: usize) -> result::Result<(), io::Error> {
+        if let Some(fd) = &self.vrings.lock().unwrap()[q_idx].kick {
+            self.register_listener(fd.as_raw_fd(), epoll::Events::EPOLLIN, q_idx as u64)
+        } else {
+            Ok(())
+        }
+    }
+
+    fn unregister_vring_listener(&self, q_idx: usize) -> result::Result<(), io::Error> {
+        if let Some(fd) = &self.vrings.lock().unwrap()[q_idx].kick {
+            self.unregister_listener(fd.as_raw_fd(), epoll::Events::EPOLLIN, q_idx as u64)
+        } else {
+            Ok(())
+        }
+    }
+
+    fn register_listener(
+        &self,
+        fd: RawFd,
+        ev_type: epoll::Events,
+        data: u64,
+    ) -> result::Result<(), io::Error> {
+        epoll::ctl(
+            self.epoll_fd,
+            epoll::ControlOptions::EPOLL_CTL_ADD,
+            fd,
+            epoll::Event::new(ev_type, data),
+        )
+    }
+
+    fn unregister_listener(
+        &self,
+        fd: RawFd,
+        ev_type: epoll::Events,
+        data: u64,
+    ) -> result::Result<(), io::Error> {
+        epoll::ctl(
+            self.epoll_fd,
+            epoll::ControlOptions::EPOLL_CTL_DEL,
+            fd,
+            epoll::Event::new(ev_type, data),
+        )
+    }
+}
+
+struct VringWorker<S: VhostUserBackend> {
+    handler: Arc<Mutex<VringEpollHandler<S>>>,
+}
+
+impl<S: VhostUserBackend> VringWorker<S> {
+    fn run(&self, epoll_fd: RawFd) -> Result<()> {
+        const EPOLL_EVENTS_LEN: usize = 100;
+        let mut events = vec![epoll::Event::new(epoll::Events::empty(), 0); EPOLL_EVENTS_LEN];
+
+        'epoll: loop {
+            let num_events = match epoll::wait(epoll_fd, -1, &mut events[..]) {
+                Ok(res) => res,
+                Err(e) => {
+                    if e.kind() == io::ErrorKind::Interrupted {
+                        // It's well defined from the epoll_wait() syscall
+                        // documentation that the epoll loop can be interrupted
+                        // before any of the requested events occurred or the
+                        // timeout expired. In both those cases, epoll_wait()
+                        // returns an error of type EINTR, but this should not
+                        // be considered as a regular error. Instead it is more
+                        // appropriate to retry, by calling into epoll_wait().
+                        continue;
+                    }
+                    return Err(Error::EpollWait(e));
+                }
+            };
+
+            for event in events.iter().take(num_events) {
+                let evset = match epoll::Events::from_bits(event.events) {
+                    Some(evset) => evset,
+                    None => {
+                        let evbits = event.events;
+                        println!("epoll: ignoring unknown event set: 0x{:x}", evbits);
+                        continue;
+                    }
+                };
+
+                let ev_type = event.data as u16;
+
+                if self.handler.lock().unwrap().handle_event(ev_type, evset)? {
+                    break 'epoll;
+                }
+            }
+        }
+
+        Ok(())
+    }
+}
+
+struct VhostUserHandler<S: VhostUserBackend> {
+    backend: Arc<S>,
+    vring_handler: Arc<Mutex<VringEpollHandler<S>>>,
+    owned: bool,
+    features_acked: bool,
+    acked_features: u64,
+    acked_protocol_features: u64,
+    num_queues: usize,
+    max_queue_size: usize,
+    memory: Option<Memory>,
+    vrings: Arc<Mutex<Vec<Vring>>>,
+}
+
+impl<S: VhostUserBackend> VhostUserHandler<S> {
+    fn new(backend: S) -> Self {
+        let num_queues = backend.num_queues();
+        let max_queue_size = backend.max_queue_size();
+
+        let arc_backend = Arc::new(backend);
+        let vrings = Arc::new(Mutex::new(vec![
+            Vring::new(max_queue_size as u16);
+            num_queues
+        ]));
+        // Create the epoll file descriptor
+        let epoll_fd = epoll::create(true).unwrap();
+
+        let vring_handler = Arc::new(Mutex::new(VringEpollHandler {
+            backend: arc_backend.clone(),
+            vrings: vrings.clone(),
+            mem: None,
+            epoll_fd,
+        }));
+        let worker = VringWorker {
+            handler: vring_handler.clone(),
+        };
+
+        thread::Builder::new()
+            .name("vring_epoll_handler".to_string())
+            .spawn(move || worker.run(epoll_fd))
+            .unwrap();
+
+        VhostUserHandler {
+            backend: arc_backend,
+            vring_handler,
+            owned: false,
+            features_acked: false,
+            acked_features: 0,
+            acked_protocol_features: 0,
+            num_queues,
+            max_queue_size,
+            memory: None,
+            vrings,
+        }
+    }
+
+    fn get_vring_handler(&self) -> Arc<Mutex<VringEpollHandler<S>>> {
+        self.vring_handler.clone()
+    }
+
+    fn vmm_va_to_gpa(&self, vmm_va: u64) -> Result<u64> {
+        if let Some(memory) = &self.memory {
+            for mapping in memory.mappings.iter() {
+                if vmm_va >= mapping.vmm_addr && vmm_va < mapping.vmm_addr + mapping.size {
+                    return Ok(vmm_va - mapping.vmm_addr);
+                }
+            }
+        }
+
+        Err(Error::MissingMemoryMapping)
+    }
+}
+
+impl<S: VhostUserBackend> VhostUserSlaveReqHandler for VhostUserHandler<S> {
+    fn set_owner(&mut self) -> VhostUserResult<()> {
+        if self.owned {
+            return Err(VhostUserError::InvalidOperation);
+        }
+        self.owned = true;
+        Ok(())
+    }
+
+    fn reset_owner(&mut self) -> VhostUserResult<()> {
+        self.owned = false;
+        self.features_acked = false;
+        self.acked_features = 0;
+        self.acked_protocol_features = 0;
+        Ok(())
+    }
+
+    fn get_features(&mut self) -> VhostUserResult<u64> {
+        Ok(self.backend.features())
+    }
+
+    fn set_features(&mut self, features: u64) -> VhostUserResult<()> {
+        if !self.owned || self.features_acked {
+            return Err(VhostUserError::InvalidOperation);
+        } else if (features & !self.backend.features()) != 0 {
+            return Err(VhostUserError::InvalidParam);
+        }
+
+        self.acked_features = features;
+        self.features_acked = true;
+
+        // If VHOST_USER_F_PROTOCOL_FEATURES has not been negotiated,
+        // the ring is initialized in an enabled state.
+        // If VHOST_USER_F_PROTOCOL_FEATURES has been negotiated,
+        // the ring is initialized in a disabled state. Client must not
+        // pass data to/from the backend until ring is enabled by
+        // VHOST_USER_SET_VRING_ENABLE with parameter 1, or after it has
+        // been disabled by VHOST_USER_SET_VRING_ENABLE with parameter 0.
+        let vring_enabled =
+            self.acked_features & VhostUserVirtioFeatures::PROTOCOL_FEATURES.bits() == 0;
+        for vring in self.vrings.lock().unwrap().iter_mut() {
+            vring.enabled = vring_enabled;
+        }
+
+        Ok(())
+    }
+
+    fn get_protocol_features(&mut self) -> VhostUserResult<VhostUserProtocolFeatures> {
+        Ok(VhostUserProtocolFeatures::all())
+    }
+
+    fn set_protocol_features(&mut self, features: u64) -> VhostUserResult<()> {
+        // Note: slave that reported VHOST_USER_F_PROTOCOL_FEATURES must
+        // support this message even before VHOST_USER_SET_FEATURES was
+        // called.
+        self.acked_protocol_features = features;
+        Ok(())
+    }
+
+    fn set_mem_table(
+        &mut self,
+        ctx: &[VhostUserMemoryRegion],
+        fds: &[RawFd],
+    ) -> VhostUserResult<()> {
+        // We need to create tuple of ranges from the list of VhostUserMemoryRegion
+        // that we get from the caller.
+        let mut regions: Vec<(GuestAddress, usize, Option<FileOffset>)> = Vec::new();
+        let mut mappings: Vec<AddrMapping> = Vec::new();
+
+        for (idx, region) in ctx.iter().enumerate() {
+            let g_addr = GuestAddress(region.guest_phys_addr);
+            let len = (region.memory_size + region.mmap_offset) as usize;
+            let file = unsafe { File::from_raw_fd(fds[idx]) };
+            let f_off = FileOffset::new(file, 0);
+
+            regions.push((g_addr, len, Some(f_off)));
+            mappings.push(AddrMapping {
+                vmm_addr: region.user_addr,
+                size: region.memory_size + region.mmap_offset,
+            });
+        }
+
+        let mem = GuestMemoryMmap::with_files(regions).unwrap();
+        self.vring_handler.lock().unwrap().update_memory(Some(mem));
+        self.memory = Some(Memory { mappings });
+
+        Ok(())
+    }
+
+    fn get_queue_num(&mut self) -> VhostUserResult<u64> {
+        Ok(self.num_queues as u64)
+    }
+
+    fn set_vring_num(&mut self, index: u32, num: u32) -> VhostUserResult<()> {
+        if index as usize >= self.num_queues || num == 0 || num as usize > self.max_queue_size {
+            return Err(VhostUserError::InvalidParam);
+        }
+        self.vrings.lock().unwrap()[index as usize].queue.size = num as u16;
+        Ok(())
+    }
+
+    fn set_vring_addr(
+        &mut self,
+        index: u32,
+        _flags: VhostUserVringAddrFlags,
+        descriptor: u64,
+        used: u64,
+        available: u64,
+        _log: u64,
+    ) -> VhostUserResult<()> {
+        if index as usize >= self.num_queues {
+            return Err(VhostUserError::InvalidParam);
+        }
+
+        if self.memory.is_some() {
+            let desc_table = self.vmm_va_to_gpa(descriptor).unwrap();
+            let avail_ring = self.vmm_va_to_gpa(available).unwrap();
+            let used_ring = self.vmm_va_to_gpa(used).unwrap();
+            self.vrings.lock().unwrap()[index as usize].queue.desc_table = GuestAddress(desc_table);
+            self.vrings.lock().unwrap()[index as usize].queue.avail_ring = GuestAddress(avail_ring);
+            self.vrings.lock().unwrap()[index as usize].queue.used_ring = GuestAddress(used_ring);
+            Ok(())
+        } else {
+            Err(VhostUserError::InvalidParam)
+        }
+    }
+
+    fn set_vring_base(&mut self, index: u32, base: u32) -> VhostUserResult<()> {
+        self.vrings.lock().unwrap()[index as usize].queue.next_avail = Wrapping(base as u16);
+        self.vrings.lock().unwrap()[index as usize].queue.next_used = Wrapping(base as u16);
+        Ok(())
+    }
+
+    fn get_vring_base(&mut self, index: u32) -> VhostUserResult<VhostUserVringState> {
+        if index as usize >= self.num_queues {
+            return Err(VhostUserError::InvalidParam);
+        }
+        // Quotation from vhost-user spec:
+        // Client must start ring upon receiving a kick (that is, detecting
+        // that file descriptor is readable) on the descriptor specified by
+        // VHOST_USER_SET_VRING_KICK, and stop ring upon receiving
+        // VHOST_USER_GET_VRING_BASE.
+        self.vrings.lock().unwrap()[index as usize].started = false;
+        self.vring_handler
+            .lock()
+            .unwrap()
+            .unregister_vring_listener(index as usize)
+            .unwrap();
+
+        let next_avail = self.vrings.lock().unwrap()[index as usize]
+            .queue
+            .next_avail
+            .0 as u16;
+
+        Ok(VhostUserVringState::new(index, u32::from(next_avail)))
+    }
+
+    fn set_vring_kick(&mut self, index: u8, fd: Option<RawFd>) -> VhostUserResult<()> {
+        if index as usize >= self.num_queues {
+            return Err(VhostUserError::InvalidParam);
+        }
+
+        if self.vrings.lock().unwrap()[index as usize].kick.is_some() {
+            // Close file descriptor set by previous operations.
+            let _ = unsafe {
+                libc::close(
+                    self.vrings.lock().unwrap()[index as usize]
+                        .kick
+                        .take()
+                        .unwrap()
+                        .as_raw_fd(),
+                )
+            };
+        }
+        self.vrings.lock().unwrap()[index as usize].kick =
+            Some(unsafe { EventFd::from_raw_fd(fd.unwrap()) });;
+
+        // Quotation from vhost-user spec:
+        // Client must start ring upon receiving a kick (that is, detecting
+        // that file descriptor is readable) on the descriptor specified by
+        // VHOST_USER_SET_VRING_KICK, and stop ring upon receiving
+        // VHOST_USER_GET_VRING_BASE.
+        //
+        // So we should add fd to event monitor(select, poll, epoll) here.
+        self.vrings.lock().unwrap()[index as usize].started = true;
+        self.vring_handler
+            .lock()
+            .unwrap()
+            .register_vring_listener(index as usize)
+            .unwrap();
+
+        Ok(())
+    }
+
+    fn set_vring_call(&mut self, index: u8, fd: Option<RawFd>) -> VhostUserResult<()> {
+        if index as usize >= self.num_queues {
+            return Err(VhostUserError::InvalidParam);
+        }
+
+        if self.vrings.lock().unwrap()[index as usize].call.is_some() {
+            // Close file descriptor set by previous operations.
+            let _ = unsafe {
+                libc::close(
+                    self.vrings.lock().unwrap()[index as usize]
+                        .call
+                        .take()
+                        .unwrap()
+                        .as_raw_fd(),
+                )
+            };
+        }
+        self.vrings.lock().unwrap()[index as usize].call =
+            Some(unsafe { EventFd::from_raw_fd(fd.unwrap()) });
+
+        Ok(())
+    }
+
+    fn set_vring_err(&mut self, index: u8, fd: Option<RawFd>) -> VhostUserResult<()> {
+        if index as usize >= self.num_queues {
+            return Err(VhostUserError::InvalidParam);
+        }
+
+        if self.vrings.lock().unwrap()[index as usize].err.is_some() {
+            // Close file descriptor set by previous operations.
+            let _ = unsafe {
+                libc::close(
+                    self.vrings.lock().unwrap()[index as usize]
+                        .err
+                        .take()
+                        .unwrap()
+                        .as_raw_fd(),
+                )
+            };
+        }
+        self.vrings.lock().unwrap()[index as usize].err =
+            Some(unsafe { EventFd::from_raw_fd(fd.unwrap()) });
+
+        Ok(())
+    }
+
+    fn set_vring_enable(&mut self, index: u32, enable: bool) -> VhostUserResult<()> {
+        // This request should be handled only when VHOST_USER_F_PROTOCOL_FEATURES
+        // has been negotiated.
+        if self.acked_features & VhostUserVirtioFeatures::PROTOCOL_FEATURES.bits() == 0 {
+            return Err(VhostUserError::InvalidOperation);
+        } else if index as usize >= self.num_queues {
+            return Err(VhostUserError::InvalidParam);
+        }
+
+        // Slave must not pass data to/from the backend until ring is
+        // enabled by VHOST_USER_SET_VRING_ENABLE with parameter 1,
+        // or after it has been disabled by VHOST_USER_SET_VRING_ENABLE
+        // with parameter 0.
+        self.vrings.lock().unwrap()[index as usize].enabled = enable;
+
+        Ok(())
+    }
+
+    fn get_config(
+        &mut self,
+        offset: u32,
+        size: u32,
+        _flags: VhostUserConfigFlags,
+    ) -> VhostUserResult<Vec<u8>> {
+        if self.acked_features & VhostUserProtocolFeatures::CONFIG.bits() == 0 {
+            return Err(VhostUserError::InvalidOperation);
+        } else if offset < VHOST_USER_CONFIG_OFFSET
+            || offset >= VHOST_USER_CONFIG_SIZE
+            || size > VHOST_USER_CONFIG_SIZE - VHOST_USER_CONFIG_OFFSET
+            || size + offset > VHOST_USER_CONFIG_SIZE
+        {
+            return Err(VhostUserError::InvalidParam);
+        }
+
+        Ok(self.backend.get_config(offset, size))
+    }
+
+    fn set_config(
+        &mut self,
+        offset: u32,
+        buf: &[u8],
+        _flags: VhostUserConfigFlags,
+    ) -> VhostUserResult<()> {
+        let size = buf.len() as u32;
+        if self.acked_features & VhostUserProtocolFeatures::CONFIG.bits() == 0 {
+            return Err(VhostUserError::InvalidOperation);
+        } else if offset < VHOST_USER_CONFIG_OFFSET
+            || offset >= VHOST_USER_CONFIG_SIZE
+            || size > VHOST_USER_CONFIG_SIZE - VHOST_USER_CONFIG_OFFSET
+            || size + offset > VHOST_USER_CONFIG_SIZE
+        {
+            return Err(VhostUserError::InvalidParam);
+        }
+
+        self.backend.set_config(offset, buf);
+        Ok(())
+    }
+}
diff --git a/vm-virtio/src/queue.rs b/vm-virtio/src/queue.rs
index 7037ebfda..ffe122c2d 100644
--- a/vm-virtio/src/queue.rs
+++ b/vm-virtio/src/queue.rs
@@ -232,8 +232,8 @@ pub struct Queue {
     /// Guest physical address of the used ring
     pub used_ring: GuestAddress,
 
-    next_avail: Wrapping<u16>,
-    next_used: Wrapping<u16>,
+    pub next_avail: Wrapping<u16>,
+    pub next_used: Wrapping<u16>,
 }
 
 impl Queue {