src/devices/v4l2_device_proxy.rs

// Copyright 2024 The ChromiumOS Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

//! This module uses `v4l2r` to proxy a host V4L2 device into the guest.

use std::collections::BTreeMap;
use std::io::Result as IoResult;
use std::os::fd::AsFd;
use std::os::fd::BorrowedFd;
use std::os::fd::OwnedFd;
use std::path::PathBuf;
use std::sync::Arc;
use std::time::Duration;

use log::error;
use log::warn;
use v4l2r::bindings::v4l2_audio;
use v4l2r::bindings::v4l2_audioout;
use v4l2r::bindings::v4l2_control;
use v4l2r::bindings::v4l2_create_buffers;
use v4l2r::bindings::v4l2_decoder_cmd;
use v4l2r::bindings::v4l2_dv_timings;
use v4l2r::bindings::v4l2_dv_timings_cap;
use v4l2r::bindings::v4l2_enc_idx;
use v4l2r::bindings::v4l2_encoder_cmd;
use v4l2r::bindings::v4l2_event;
use v4l2r::bindings::v4l2_event_subscription;
use v4l2r::bindings::v4l2_ext_control;
use v4l2r::bindings::v4l2_ext_controls;
use v4l2r::bindings::v4l2_fmtdesc;
use v4l2r::bindings::v4l2_format;
use v4l2r::bindings::v4l2_frequency;
use v4l2r::bindings::v4l2_frequency_band;
use v4l2r::bindings::v4l2_frmivalenum;
use v4l2r::bindings::v4l2_frmsizeenum;
use v4l2r::bindings::v4l2_input;
use v4l2r::bindings::v4l2_modulator;
use v4l2r::bindings::v4l2_output;
use v4l2r::bindings::v4l2_query_ext_ctrl;
use v4l2r::bindings::v4l2_queryctrl;
use v4l2r::bindings::v4l2_querymenu;
use v4l2r::bindings::v4l2_rect;
use v4l2r::bindings::v4l2_requestbuffers;
use v4l2r::bindings::v4l2_standard;
use v4l2r::bindings::v4l2_std_id;
use v4l2r::bindings::v4l2_streamparm;
use v4l2r::bindings::v4l2_tuner;
use v4l2r::device::poller::DeviceEvent;
use v4l2r::device::poller::PollEvent;
use v4l2r::device::poller::Poller;
pub use v4l2r::device::Device as V4l2Device;
use v4l2r::device::DeviceConfig;
use v4l2r::device::DeviceOpenError;
use v4l2r::ioctl::AudioMode;
use v4l2r::ioctl::BufferFlags;
use v4l2r::ioctl::CtrlId;
use v4l2r::ioctl::CtrlWhich;
use v4l2r::ioctl::DqBufError;
use v4l2r::ioctl::DqBufIoctlError;
use v4l2r::ioctl::DqEventError;
use v4l2r::ioctl::EventType as V4l2EventType;
use v4l2r::ioctl::ExpbufFlags;
use v4l2r::ioctl::ExtControlError;
use v4l2r::ioctl::IntoErrno;
use v4l2r::ioctl::QueryCapError;
use v4l2r::ioctl::QueryCtrlFlags;
use v4l2r::ioctl::SelectionFlags;
use v4l2r::ioctl::SelectionTarget;
use v4l2r::ioctl::SelectionType;
use v4l2r::ioctl::SubscribeEventFlags;
use v4l2r::ioctl::TunerMode;
use v4l2r::ioctl::TunerTransmissionFlags;
use v4l2r::ioctl::TunerType;
use v4l2r::ioctl::V4l2Buffer;
use v4l2r::ioctl::V4l2PlanesWithBacking;
use v4l2r::ioctl::V4l2PlanesWithBackingMut;
use v4l2r::memory::Memory;
use v4l2r::memory::MemoryType;
use v4l2r::memory::UserPtr;
use v4l2r::QueueDirection;
use v4l2r::QueueType;

use crate::ioctl::virtio_media_dispatch_ioctl;
use crate::ioctl::IoctlResult;
use crate::ioctl::VirtioMediaIoctlHandler;
use crate::mmap::MmapMappingManager;
use crate::protocol::DequeueBufferEvent;
use crate::protocol::SessionEvent;
use crate::protocol::SgEntry;
use crate::protocol::V4l2Event;
use crate::protocol::V4l2Ioctl;
use crate::protocol::VIRTIO_MEDIA_MMAP_FLAG_RW;
use crate::GuestMemoryRange;
use crate::ReadFromDescriptorChain;
use crate::VirtioMediaDevice;
use crate::VirtioMediaDeviceSession;
use crate::VirtioMediaEventQueue;
use crate::VirtioMediaGuestMemoryMapper;
use crate::VirtioMediaHostMemoryMapper;
use crate::WriteToDescriptorChain;

type GuestAddrType = <UserPtr as Memory>::RawBacking;

fn guest_v4l2_buffer_to_host<M: VirtioMediaGuestMemoryMapper>(
    guest_buffer: &V4l2Buffer,
    guest_regions: Vec<Vec<SgEntry>>,
    m: &M,
) -> anyhow::Result<(V4l2Buffer, Vec<M::GuestMemoryMapping>)> {
    let mut resources = vec![];
    // The host buffer is a copy of the guest's with its plane resources updated.
    let mut host_buffer = guest_buffer.clone();
    let writable = host_buffer.queue().direction() == QueueDirection::Capture;

    if let V4l2PlanesWithBackingMut::UserPtr(host_planes) =
        host_buffer.planes_with_backing_iter_mut()
    {
        for (mut host_plane, mem_regions) in
            host_planes.filter(|p| *p.length > 0).zip(guest_regions)
        {
            let mut mapping = m.new_mapping(mem_regions)?;

            host_plane.set_userptr(if writable {
                mapping.as_mut_ptr()
            } else {
                mapping.as_ptr()
            } as GuestAddrType);
            resources.push(mapping);
        }
    };

    Ok((host_buffer, resources))
}

/// Restore the user pointers of `host_buffer` using the values in `initial_guest_buffer`, if the buffer's
/// memory type is `USERPTR`. This allows a buffer processed on the host to be passed back to the
/// guest with the correct values.
fn host_v4l2_buffer_to_guest<R>(
    host_buffer: &V4l2Buffer,
    userptr_buffers: &BTreeMap<GuestAddrType, V4l2UserPlaneInfo<R>>,
) -> anyhow::Result<V4l2Buffer> {
    // The guest buffer is a copy of the host's with its plane resources updated.
    let mut guest_buffer = host_buffer.clone();

    if let V4l2PlanesWithBackingMut::UserPtr(host_planes) =
        guest_buffer.planes_with_backing_iter_mut()
    {
        for mut plane in host_planes.filter(|p| p.userptr() != 0) {
            let host_userptr = plane.userptr();
            let guest_userptr = userptr_buffers
                .get(&(host_userptr as GuestAddrType))
                .map(|p| p.guest_addr)
                .ok_or_else(|| {
                    anyhow::anyhow!("host buffer address 0x{:x} not registered!", host_userptr)
                })?;
            plane.set_userptr(guest_userptr as GuestAddrType);
        }
    }

    Ok(guest_buffer)
}

#[derive(Clone, Copy, Debug)]
enum ExtCtrlIoctl {
    Get,
    Set,
    Try,
}

fn perform_ext_ctrls_ioctl<M: VirtioMediaGuestMemoryMapper>(
    ioctl: ExtCtrlIoctl,
    device: &V4l2Device,
    mem: &M,
    which: CtrlWhich,
    ctrls: (
        &mut v4l2_ext_controls,
        &mut Vec<v4l2_ext_control>,
        Vec<Vec<SgEntry>>,
    ),
) -> Result<(), ExtControlError> {
    let (ctrls, ctrl_array, mem_regions) = ctrls;
    // TODO only backup the addresses of controls which size of > 0 for efficiency? Also keep track
    // of the control index so we don't make a mistake if the host changes the control size.
    let ctrl_array_backup = ctrl_array.clone();

    // Read the payloads for all the controls with one.
    let mut payloads = ctrl_array
        .iter()
        .filter(|ctrl| ctrl.size > 0)
        .zip(mem_regions)
        .map(|(_, sgs)| mem.new_mapping(sgs))
        // TODO remove unwrap
        .collect::<anyhow::Result<Vec<_>>>()
        .unwrap();

    // Patch the pointers to the payloads.
    for (ctrl, payload) in ctrl_array
        .iter_mut()
        .filter(|ctrl| ctrl.size > 0)
        .zip(payloads.iter_mut())
    {
        ctrl.__bindgen_anon_1.ptr = payload.as_mut_ptr() as *mut libc::c_void;
    }

    let res = match ioctl {
        ExtCtrlIoctl::Get => v4l2r::ioctl::g_ext_ctrls(device, which, ctrl_array.as_mut_slice()),
        ExtCtrlIoctl::Set => v4l2r::ioctl::s_ext_ctrls(device, which, ctrl_array.as_mut_slice()),
        ExtCtrlIoctl::Try => v4l2r::ioctl::try_ext_ctrls(device, which, ctrl_array.as_mut_slice()),
    };

    // Restore guest addresses in the controls array.
    for (ctrl, ctrl_backup) in ctrl_array
        .iter_mut()
        .zip(ctrl_array_backup.iter())
        .filter(|(_, ctrl)| ctrl.size > 0)
    {
        ctrl.__bindgen_anon_1.ptr = unsafe { ctrl_backup.__bindgen_anon_1.ptr };
    }

    if let Err(e) = &res {
        ctrls.error_idx = e.error_idx;
    }

    res
}

/// Information about a given USERPTR memory plane.
struct V4l2UserPlaneInfo<R> {
    /// Queue the buffer belongs to.
    queue: QueueType,
    /// Buffer index.
    index: u8,

    guest_addr: GuestAddrType,
    _guest_resource: R,
}

pub struct V4l2Session<M: VirtioMediaGuestMemoryMapper> {
    id: u32,
    device: Arc<V4l2Device>,
    /// Proxy epoll for polling `device`. We need to use a proxy here because V4L2 events are
    /// signaled using `EPOLLPRI`, and we sometimes need to stop listening to the `CAPTURE` queue.
    /// `poller`'s FD is what is actually added to the client's session poller.
    poller: Poller,

    /// Type of the capture queue, if one has been set up.
    capture_queue_type: Option<QueueType>,
    /// Type of the output queue, if one has been set up.
    output_queue_type: Option<QueueType>,

    capture_streaming: bool,
    capture_num_queued: usize,

    output_streaming: bool,
    output_num_queued: usize,

    /// Map of host USERPTR addresses to guest USERPTR addresses. Only used for queues which memory
    /// type is USERPTR.
    ///
    /// TODO this is not properly cleared. We should probably record the session ID and queue in
    /// order to remove the records upon REQBUFS or session deletion?
    userptr_buffers: BTreeMap<GuestAddrType, V4l2UserPlaneInfo<M::GuestMemoryMapping>>,
}

impl<M: VirtioMediaGuestMemoryMapper> VirtioMediaDeviceSession for V4l2Session<M> {
    fn poll_fd(&self) -> Option<BorrowedFd> {
        Some(self.poller.as_fd())
    }
}

impl<M> V4l2Session<M>
where
    M: VirtioMediaGuestMemoryMapper,
{
    fn new(id: u32, device: Arc<V4l2Device>) -> Self {
        // Only listen to V4L2 events for now.
        let mut poller = Poller::new(Arc::clone(&device)).unwrap();
        poller.enable_event(DeviceEvent::V4L2Event).unwrap();

        Self {
            id,
            device,
            poller,
            capture_queue_type: None,
            output_queue_type: None,
            capture_streaming: false,
            capture_num_queued: 0,
            output_streaming: false,
            output_num_queued: 0,
            userptr_buffers: Default::default(),
        }
    }

    /// Returns whether this session should be polling for CAPTURE buffers in its current state.
    fn should_poll_capture(&self) -> bool {
        self.capture_streaming && self.capture_num_queued > 0
    }

    fn register_userptr_addresses(
        &mut self,
        host_buffer: &V4l2Buffer,
        guest_buffer: &V4l2Buffer,
        guest_resources: Vec<M::GuestMemoryMapping>,
    ) {
        if let V4l2PlanesWithBacking::UserPtr(host_planes) = host_buffer.planes_with_backing_iter()
        {
            if let V4l2PlanesWithBacking::UserPtr(guest_planes) =
                guest_buffer.planes_with_backing_iter()
            {
                for ((host_userptr, guest_plane), guest_resource) in host_planes
                    .map(|p| p.userptr())
                    .zip(guest_planes)
                    .filter(|(h, _)| *h != 0)
                    .zip(guest_resources.into_iter())
                {
                    let plane_info = {
                        V4l2UserPlaneInfo {
                            queue: guest_buffer.queue(),
                            index: guest_buffer.index() as u8,
                            guest_addr: guest_plane.userptr(),
                            _guest_resource: guest_resource,
                        }
                    };
                    self.userptr_buffers.insert(host_userptr, plane_info);
                }
            }
        }
    }
}

/// Information about a given MMAP memory plane.
///
/// We keep these around indexed by the memory offset in order to service MMAP commands. Only used
/// if the memory type of the queue is MMAP.
struct V4l2MmapPlaneInfo {
    /// ID of the session the buffer belongs to.
    session_id: u32,
    /// Queue the buffer belongs to.
    queue: QueueType,
    /// Buffer index.
    index: u8,
    /// Plane index.
    plane: u8,
    /// Guest address at which the buffer has been mapped.
    map_address: u64,
    /// Whether the buffer is still active from the device's point of view.
    active: bool,
}

/// A host V4L2 device that can be proxied into a virtio-media guest.
pub struct V4l2ProxyDevice<
    Q: VirtioMediaEventQueue,
    M: VirtioMediaGuestMemoryMapper,
    HM: VirtioMediaHostMemoryMapper,
> {
    /// `/dev/videoX` host device path.
    device_path: PathBuf,

    mem: M,
    evt_queue: Q,

    /// Map of memory offsets to detailed buffer information. Only used for queues which memory
    /// type is MMAP.
    mmap_buffers: BTreeMap<u32, V4l2MmapPlaneInfo>,

    mmap_manager: MmapMappingManager<HM>,
}

#[derive(Debug)]
pub struct DequeueEventError(pub i32);
#[derive(Debug)]
pub struct DequeueBufferError(pub i32);

impl<Q, M, HM> V4l2ProxyDevice<Q, M, HM>
where
    Q: VirtioMediaEventQueue,
    M: VirtioMediaGuestMemoryMapper,
    HM: VirtioMediaHostMemoryMapper,
{
    pub fn new(device_path: PathBuf, evt_queue: Q, mem: M, mapper: HM) -> Self {
        Self {
            mem,
            evt_queue,
            device_path,
            mmap_buffers: Default::default(),
            mmap_manager: MmapMappingManager::from(mapper),
        }
    }

    fn delete_session(&mut self, session: &V4l2Session<M>) {
        // Mark all buffers from this session as being inactive.
        for (&offset, buffer) in self.mmap_buffers.iter_mut() {
            if buffer.session_id == session.id {
                self.mmap_manager.unregister_buffer(offset);
                buffer.active = false;
            }
        }
        // Garbage-collect buffers that can be deleted.
        self.mmap_buffers.retain(|_, b| b.active);
    }

    /// Clear all the previous buffer information for this queue, and insert new information if the
    /// memory type is MMAP.
    fn update_mmap_offsets(
        &mut self,
        session: &mut V4l2Session<M>,
        queue: QueueType,
        range: std::ops::Range<u32>,
    ) {
        // Remove buffers that have been deallocated.
        self.mmap_buffers
            .iter_mut()
            .filter(|(_, b)| b.session_id == session.id && b.queue == queue)
            .filter(|(_, b)| range.is_empty() || b.index as u32 >= range.start)
            .for_each(|(&offset, b)| {
                self.mmap_manager.unregister_buffer(offset);
                b.active = false;
            });
        // Garbage-collect buffers that can be deleted.
        self.mmap_buffers.retain(|_, b| b.active);

        for i in range {
            let buffer =
                match v4l2r::ioctl::querybuf::<V4l2Buffer>(&session.device, queue, i as usize) {
                    Ok(buffer) => buffer,
                    Err(e) => {
                        warn!("failed to query newly allocated buffer: {:#}", e);
                        continue;
                    }
                };

            if let V4l2PlanesWithBacking::Mmap(planes) = buffer.planes_with_backing_iter() {
                for (j, plane) in planes.enumerate() {
                    let offset = plane.mem_offset();

                    self.mmap_manager
                        .register_buffer(Some(offset), *plane.length)
                        .unwrap();

                    self.mmap_buffers.insert(
                        offset,
                        V4l2MmapPlaneInfo {
                            session_id: session.id,
                            queue,
                            index: buffer.index() as u8,
                            plane: j as u8,
                            map_address: 0,
                            active: true,
                        },
                    );
                }
            };
        }

        // If we allocated on the capture or output queue successfully, remember its type.
        // TODO this should be somewhere else?
        match queue {
            QueueType::VideoCapture | QueueType::VideoCaptureMplane => {
                session.capture_queue_type = Some(queue);
            }
            QueueType::VideoOutput | QueueType::VideoOutputMplane => {
                session.output_queue_type = Some(queue);
            }
            _ => (),
        }
    }

    /// Dequeue all pending events for `session` and send them to the guest.
    ///
    /// In case of error, the session should be considered invalid and destroyed.
    fn dequeue_events(&mut self, session: &mut V4l2Session<M>) -> Result<(), DequeueEventError> {
        loop {
            match v4l2r::ioctl::dqevent::<v4l2_event>(&session.device) {
                Ok(event) => self
                    .evt_queue
                    .send_event(V4l2Event::Event(SessionEvent::new(session.id, event))),
                Err(DqEventError::NotReady) => return Ok(()),
                Err(e) => {
                    let err = e.into_errno();
                    self.evt_queue.send_error(session.id, err);
                    return Err(DequeueEventError(err));
                }
            }
        }
    }

    /// Attempt to dequeue all processed OUTPUT buffers and send the corresponding events to
    /// `evt_queue`.
    ///
    /// In case of error, the session should be considered invalid and destroyed.
    fn dequeue_output_buffers(
        &mut self,
        session: &mut V4l2Session<M>,
    ) -> Result<(), DequeueBufferError> {
        let output_queue_type = match session.output_queue_type {
            Some(queue_type) => queue_type,
            None => return Ok(()),
        };

        if !session.output_streaming || session.output_num_queued == 0 {
            return Ok(());
        }

        loop {
            match v4l2r::ioctl::dqbuf::<V4l2Buffer>(&session.device, output_queue_type) {
                Ok(buffer) => {
                    // Drop buffer information. This also syncs the buffer content if it has been shadowed.
                    session.userptr_buffers.retain(|_, v| {
                        Some(v.queue) != session.output_queue_type
                            || v.index != buffer.index() as u8
                    });
                    self.evt_queue
                        .send_event(V4l2Event::DequeueBuffer(DequeueBufferEvent::new(
                            session.id, buffer,
                        )))
                }
                Err(DqBufError::IoctlError(DqBufIoctlError::Eos))
                | Err(DqBufError::IoctlError(DqBufIoctlError::NotReady)) => return Ok(()),
                Err(e) => {
                    let err = e.into_errno();
                    self.evt_queue.send_error(session.id, err);
                    return Err(DequeueBufferError(err));
                }
            };
        }
    }

    /// Attempt to dequeue a single CAPTURE buffer and send the corresponding event to `evt_queue`.
    ///
    /// In case of error, the session should be considered invalid and destroyed.
    fn dequeue_capture_buffer(
        &mut self,
        session: &mut V4l2Session<M>,
    ) -> Result<(), DequeueBufferError> {
        let capture_queue_type = match session.capture_queue_type {
            Some(queue_type) => queue_type,
            None => return Ok(()),
        };

        let v4l2_buffer =
            match v4l2r::ioctl::dqbuf::<V4l2Buffer>(&session.device, capture_queue_type) {
                Ok(buffer) => buffer,
                Err(DqBufError::IoctlError(DqBufIoctlError::Eos)) => return Ok(()),
                Err(DqBufError::IoctlError(DqBufIoctlError::NotReady)) => return Ok(()),
                Err(e) => {
                    let err = e.into_errno();
                    self.evt_queue.send_error(session.id, err);
                    return Err(DequeueBufferError(err));
                }
            };

        // Drop buffer information. This also syncs the buffer content if it has been shadowed.
        session.userptr_buffers.retain(|_, v| {
            Some(v.queue) != session.capture_queue_type || v.index != v4l2_buffer.index() as u8
        });

        let capture_polling_active = session.should_poll_capture();
        session.capture_num_queued -= 1;
        if (capture_polling_active && session.capture_num_queued == 0) ||
            // This may or may not be needed...
            v4l2_buffer.flags().contains(BufferFlags::LAST)
        {
            if let Err(e) = session.poller.disable_event(DeviceEvent::CaptureReady) {
                error!("cannot disable CAPTURE polling after last buffer: {}", e);
            }
        }

        self.evt_queue
            .send_event(V4l2Event::DequeueBuffer(DequeueBufferEvent::new(
                session.id,
                v4l2_buffer,
            )));

        Ok(())
    }
}

impl<Q, M, HM> VirtioMediaIoctlHandler for V4l2ProxyDevice<Q, M, HM>
where
    Q: VirtioMediaEventQueue,
    M: VirtioMediaGuestMemoryMapper,
    HM: VirtioMediaHostMemoryMapper,
{
    type Session = V4l2Session<M>;

    fn enum_fmt(
        &mut self,
        session: &Self::Session,
        queue: QueueType,
        index: u32,
    ) -> IoctlResult<v4l2_fmtdesc> {
        v4l2r::ioctl::enum_fmt(&session.device, queue, index).map_err(IntoErrno::into_errno)
    }

    fn g_fmt(&mut self, session: &Self::Session, queue: QueueType) -> IoctlResult<v4l2_format> {
        v4l2r::ioctl::g_fmt(&session.device, queue).map_err(IntoErrno::into_errno)
    }

    fn s_fmt(
        &mut self,
        session: &mut Self::Session,
        _queue: QueueType,
        format: v4l2_format,
    ) -> IoctlResult<v4l2_format> {
        v4l2r::ioctl::s_fmt(&mut session.device, format).map_err(IntoErrno::into_errno)
    }

    fn reqbufs(
        &mut self,
        session: &mut Self::Session,
        queue: QueueType,
        memory: MemoryType,
        count: u32,
    ) -> IoctlResult<v4l2_requestbuffers> {
        let mut reqbufs: v4l2_requestbuffers =
            v4l2r::ioctl::reqbufs(&session.device, queue, memory, count)
                .map_err(IntoErrno::into_errno)?;

        // We do not support requests at the moment, so do not advertize them.
        reqbufs.capabilities &= !v4l2r::bindings::V4L2_BUF_CAP_SUPPORTS_REQUESTS;

        self.update_mmap_offsets(session, queue, 0..reqbufs.count);

        match queue {
            QueueType::VideoCapture | QueueType::VideoCaptureMplane => {
                // REQBUFS(0) is an implicit STREAMOFF.
                if reqbufs.count == 0 {
                    let was_polling_capture = session.should_poll_capture();
                    session.capture_streaming = false;
                    session.capture_num_queued = 0;
                    if was_polling_capture {
                        if let Err(e) = session.poller.disable_event(DeviceEvent::CaptureReady) {
                            error!(
                                "cannot disable CAPTURE polling after REQBUFS(0) ioctl: {}",
                                e
                            );
                        }
                    }
                }
            }
            QueueType::VideoOutput | QueueType::VideoOutputMplane => {
                // REQBUFS(0) is an implicit STREAMOFF.
                if reqbufs.count == 0 {
                    session.output_streaming = false;
                    session.output_num_queued = 0;
                }
            }
            _ => (),
        }

        Ok(reqbufs)
    }

    fn querybuf(
        &mut self,
        session: &Self::Session,
        queue: QueueType,
        index: u32,
    ) -> IoctlResult<V4l2Buffer> {
        v4l2r::ioctl::querybuf(&session.device, queue, index as usize)
            .map_err(IntoErrno::into_errno)
            .and_then(|host_buffer| {
                host_v4l2_buffer_to_guest(&host_buffer, &session.userptr_buffers).map_err(|e| {
                    error!("{:#}", e.context("while performing QUERYBUF ioctl"));
                    libc::EINVAL
                })
            })
    }

    fn streamon(&mut self, session: &mut Self::Session, queue: QueueType) -> IoctlResult<()> {
        v4l2r::ioctl::streamon(&session.device, queue).map_err(IntoErrno::into_errno)?;

        match queue {
            QueueType::VideoCapture | QueueType::VideoCaptureMplane
                if !session.capture_streaming =>
            {
                session.capture_streaming = true;
                if session.should_poll_capture() {
                    if let Err(e) = session.poller.enable_event(DeviceEvent::CaptureReady) {
                        error!("cannot enable CAPTURE polling after STREAMON ioctl: {}", e);
                    }
                }
            }
            QueueType::VideoOutput | QueueType::VideoOutputMplane if !session.output_streaming => {
                session.output_streaming = true;
            }
            _ => (),
        }

        Ok(())
    }

    fn streamoff(&mut self, session: &mut Self::Session, queue: QueueType) -> IoctlResult<()> {
        v4l2r::ioctl::streamoff(&session.device, queue).map_err(IntoErrno::into_errno)?;

        match queue {
            QueueType::VideoCapture | QueueType::VideoCaptureMplane => {
                let was_polling_capture = session.should_poll_capture();
                session.capture_streaming = false;
                session.capture_num_queued = 0;
                if was_polling_capture {
                    if let Err(e) = session.poller.disable_event(DeviceEvent::CaptureReady) {
                        error!(
                            "cannot disable CAPTURE polling after STREAMOFF ioctl: {}",
                            e
                        );
                    }
                }
            }
            QueueType::VideoOutput | QueueType::VideoOutputMplane => {
                session.output_streaming = false;
                session.output_num_queued = 0;
            }
            _ => (),
        }

        Ok(())
    }

    fn qbuf(
        &mut self,
        session: &mut Self::Session,
        guest_buffer: V4l2Buffer,
        guest_regions: Vec<Vec<SgEntry>>,
    ) -> IoctlResult<V4l2Buffer> {
        // Proactively dequeue output buffers we are done with. Errors can be ignored in
        // this context.
        let _ = self.dequeue_output_buffers(session);

        let (host_buffer, guest_resources) =
            guest_v4l2_buffer_to_host(&guest_buffer, guest_regions, &self.mem)
                .map_err(|_| libc::EINVAL)?;
        session.register_userptr_addresses(&host_buffer, &guest_buffer, guest_resources);
        let queue = host_buffer.queue();
        let out_buffer = v4l2r::ioctl::qbuf(&session.device, host_buffer)
            .map_err(|e| e.into_errno())
            .and_then(|host_out_buffer| {
                // TODO if we had a PREPARE_BUF before, do we need to patch the addresses
                // from the buffer given at that time?
                host_v4l2_buffer_to_guest(&host_out_buffer, &session.userptr_buffers).map_err(|e| {
                    error!("{:#}", e.context("while processing QBUF"));
                    libc::EINVAL
                })
            })?;

        match queue {
            QueueType::VideoCapture | QueueType::VideoCaptureMplane => {
                let was_polling_capture = session.should_poll_capture();
                session.capture_num_queued += 1;
                if !was_polling_capture && session.should_poll_capture() {
                    if let Err(e) = session.poller.enable_event(DeviceEvent::CaptureReady) {
                        error!("cannot enable CAPTURE polling after QBUF ioctl: {}", e);
                    }
                }
            }
            QueueType::VideoOutput | QueueType::VideoOutputMplane => {
                session.output_num_queued += 1;
            }
            _ => (),
        }

        Ok(out_buffer)
    }

    fn g_parm(
        &mut self,
        session: &Self::Session,
        queue: QueueType,
    ) -> IoctlResult<v4l2_streamparm> {
        v4l2r::ioctl::g_parm(&session.device, queue).map_err(|e| e.into_errno())
    }

    fn s_parm(
        &mut self,
        session: &mut Self::Session,
        parm: v4l2_streamparm,
    ) -> IoctlResult<v4l2_streamparm> {
        v4l2r::ioctl::s_parm(&session.device, parm).map_err(|e| e.into_errno())
    }

    fn g_std(&mut self, session: &Self::Session) -> IoctlResult<v4l2_std_id> {
        v4l2r::ioctl::g_std(&session.device).map_err(|e| e.into_errno())
    }

    fn s_std(&mut self, session: &mut Self::Session, std: v4l2_std_id) -> IoctlResult<()> {
        v4l2r::ioctl::s_std(&session.device, std).map_err(|e| e.into_errno())
    }

    fn enumstd(&mut self, session: &Self::Session, index: u32) -> IoctlResult<v4l2_standard> {
        v4l2r::ioctl::enumstd(&session.device, index).map_err(|e| e.into_errno())
    }

    fn enuminput(&mut self, session: &Self::Session, index: u32) -> IoctlResult<v4l2_input> {
        v4l2r::ioctl::enuminput(&session.device, index as usize).map_err(|e| e.into_errno())
    }

    fn g_ctrl(&mut self, session: &Self::Session, id: u32) -> IoctlResult<v4l2_control> {
        v4l2r::ioctl::g_ctrl(&session.device, id)
            .map(|value| v4l2_control { id, value })
            .map_err(|e| e.into_errno())
    }

    fn s_ctrl(
        &mut self,
        session: &mut Self::Session,
        id: u32,
        value: i32,
    ) -> IoctlResult<v4l2_control> {
        v4l2r::ioctl::s_ctrl(&session.device, id, value)
            .map(|value| v4l2_control { id, value })
            .map_err(|e| e.into_errno())
    }

    fn g_tuner(&mut self, session: &Self::Session, index: u32) -> IoctlResult<v4l2_tuner> {
        v4l2r::ioctl::g_tuner(&session.device, index).map_err(|e| e.into_errno())
    }

    fn s_tuner(
        &mut self,
        session: &mut Self::Session,
        index: u32,
        mode: TunerMode,
    ) -> IoctlResult<()> {
        v4l2r::ioctl::s_tuner(&session.device, index, mode).map_err(|e| e.into_errno())
    }

    fn g_audio(&mut self, session: &Self::Session) -> IoctlResult<v4l2_audio> {
        v4l2r::ioctl::g_audio(&session.device).map_err(|e| e.into_errno())
    }

    fn s_audio(
        &mut self,
        session: &mut Self::Session,
        index: u32,
        mode: Option<AudioMode>,
    ) -> IoctlResult<()> {
        v4l2r::ioctl::s_audio(&session.device, index, mode).map_err(|e| e.into_errno())
    }

    fn queryctrl(
        &mut self,
        session: &Self::Session,
        id: v4l2r::ioctl::CtrlId,
        flags: v4l2r::ioctl::QueryCtrlFlags,
    ) -> IoctlResult<v4l2_queryctrl> {
        v4l2r::ioctl::queryctrl(&session.device, id, flags).map_err(|e| e.into_errno())
    }

    fn querymenu(
        &mut self,
        session: &Self::Session,
        id: u32,
        index: u32,
    ) -> IoctlResult<v4l2_querymenu> {
        v4l2r::ioctl::querymenu(&session.device, id, index).map_err(|e| e.into_errno())
    }

    fn g_input(&mut self, session: &Self::Session) -> IoctlResult<i32> {
        v4l2r::ioctl::g_input(&session.device)
            .map(|i| i as i32)
            .map_err(|e| e.into_errno())
    }

    fn s_input(&mut self, session: &mut Self::Session, input: i32) -> IoctlResult<i32> {
        v4l2r::ioctl::s_input(&session.device, input as usize)
            .map(|i| i as i32)
            .map_err(|e| e.into_errno())
    }

    fn g_output(&mut self, session: &Self::Session) -> IoctlResult<i32> {
        v4l2r::ioctl::g_output(&session.device)
            .map(|o| o as i32)
            .map_err(|e| e.into_errno())
    }

    fn s_output(&mut self, session: &mut Self::Session, output: i32) -> IoctlResult<i32> {
        v4l2r::ioctl::s_output(&session.device, output as usize)
            .map(|()| output)
            .map_err(|e| e.into_errno())
    }

    fn enumoutput(&mut self, session: &Self::Session, index: u32) -> IoctlResult<v4l2_output> {
        v4l2r::ioctl::enumoutput(&session.device, index as usize).map_err(|e| e.into_errno())
    }

    fn g_audout(&mut self, session: &Self::Session) -> IoctlResult<v4l2_audioout> {
        v4l2r::ioctl::g_audout(&session.device).map_err(|e| e.into_errno())
    }

    fn s_audout(&mut self, session: &mut Self::Session, index: u32) -> IoctlResult<()> {
        v4l2r::ioctl::s_audout(&session.device, index).map_err(|e| e.into_errno())
    }

    fn g_modulator(&mut self, session: &Self::Session, index: u32) -> IoctlResult<v4l2_modulator> {
        v4l2r::ioctl::g_modulator(&session.device, index).map_err(|e| e.into_errno())
    }

    fn s_modulator(
        &mut self,
        session: &mut Self::Session,
        index: u32,
        flags: TunerTransmissionFlags,
    ) -> IoctlResult<()> {
        v4l2r::ioctl::s_modulator(&session.device, index, flags).map_err(|e| e.into_errno())
    }

    fn g_frequency(&mut self, session: &Self::Session, tuner: u32) -> IoctlResult<v4l2_frequency> {
        v4l2r::ioctl::g_frequency(&session.device, tuner).map_err(|e| e.into_errno())
    }

    fn s_frequency(
        &mut self,
        session: &mut Self::Session,
        tuner: u32,
        type_: TunerType,
        frequency: u32,
    ) -> IoctlResult<()> {
        v4l2r::ioctl::s_frequency(&session.device, tuner, type_, frequency)
            .map_err(|e| e.into_errno())
    }

    fn querystd(&mut self, session: &Self::Session) -> IoctlResult<v4l2_std_id> {
        v4l2r::ioctl::querystd::<v4l2_std_id>(&session.device).map_err(|e| e.into_errno())
    }

    fn try_fmt(
        &mut self,
        session: &Self::Session,
        _queue: QueueType,
        format: v4l2_format,
    ) -> IoctlResult<v4l2_format> {
        v4l2r::ioctl::try_fmt::<_, v4l2_format>(&session.device, format).map_err(|e| e.into_errno())
    }

    fn enumaudio(&mut self, session: &Self::Session, index: u32) -> IoctlResult<v4l2_audio> {
        v4l2r::ioctl::enumaudio::<v4l2_audio>(&session.device, index).map_err(|e| e.into_errno())
    }

    fn enumaudout(&mut self, session: &Self::Session, index: u32) -> IoctlResult<v4l2_audioout> {
        v4l2r::ioctl::enumaudout::<v4l2_audioout>(&session.device, index)
            .map_err(|e| e.into_errno())
    }

    fn g_ext_ctrls(
        &mut self,
        session: &Self::Session,
        which: CtrlWhich,
        ctrls: &mut v4l2_ext_controls,
        ctrl_array: &mut Vec<v4l2_ext_control>,
        user_regions: Vec<Vec<SgEntry>>,
    ) -> IoctlResult<()> {
        perform_ext_ctrls_ioctl(
            ExtCtrlIoctl::Get,
            &session.device,
            &self.mem,
            which,
            (ctrls, ctrl_array, user_regions),
        )
        .map_err(|e| e.into_errno())
    }

    fn s_ext_ctrls(
        &mut self,
        session: &mut Self::Session,
        which: CtrlWhich,
        ctrls: &mut v4l2_ext_controls,
        ctrl_array: &mut Vec<v4l2_ext_control>,
        user_regions: Vec<Vec<SgEntry>>,
    ) -> IoctlResult<()> {
        perform_ext_ctrls_ioctl(
            ExtCtrlIoctl::Set,
            &session.device,
            &self.mem,
            which,
            (ctrls, ctrl_array, user_regions),
        )
        .map_err(|e| e.into_errno())
    }

    fn try_ext_ctrls(
        &mut self,
        session: &Self::Session,
        which: CtrlWhich,
        ctrls: &mut v4l2_ext_controls,
        ctrl_array: &mut Vec<v4l2_ext_control>,
        user_regions: Vec<Vec<SgEntry>>,
    ) -> IoctlResult<()> {
        perform_ext_ctrls_ioctl(
            ExtCtrlIoctl::Try,
            &session.device,
            &self.mem,
            which,
            (ctrls, ctrl_array, user_regions),
        )
        .map_err(|e| e.into_errno())
    }

    fn enum_framesizes(
        &mut self,
        session: &Self::Session,
        index: u32,
        pixel_format: u32,
    ) -> IoctlResult<v4l2_frmsizeenum> {
        v4l2r::ioctl::enum_frame_sizes(&session.device, index, pixel_format.into())
            .map_err(|e| e.into_errno())
    }

    fn enum_frameintervals(
        &mut self,
        session: &Self::Session,
        index: u32,
        pixel_format: u32,
        width: u32,
        height: u32,
    ) -> IoctlResult<v4l2_frmivalenum> {
        v4l2r::ioctl::enum_frame_intervals(
            &session.device,
            index,
            pixel_format.into(),
            width,
            height,
        )
        .map_err(|e| e.into_errno())
    }

    fn g_enc_index(&mut self, session: &Self::Session) -> IoctlResult<v4l2_enc_idx> {
        v4l2r::ioctl::g_enc_index(&session.device).map_err(|e| e.into_errno())
    }

    fn encoder_cmd(
        &mut self,
        session: &mut Self::Session,
        cmd: v4l2_encoder_cmd,
    ) -> IoctlResult<v4l2_encoder_cmd> {
        v4l2r::ioctl::encoder_cmd(&session.device, cmd).map_err(|e| e.into_errno())
    }

    fn try_encoder_cmd(
        &mut self,
        session: &Self::Session,
        cmd: v4l2_encoder_cmd,
    ) -> IoctlResult<v4l2_encoder_cmd> {
        v4l2r::ioctl::try_encoder_cmd(&session.device, cmd).map_err(|e| e.into_errno())
    }

    fn s_dv_timings(
        &mut self,
        session: &mut Self::Session,
        timings: v4l2_dv_timings,
    ) -> IoctlResult<v4l2_dv_timings> {
        v4l2r::ioctl::s_dv_timings(&session.device, timings).map_err(|e| e.into_errno())
    }

    fn g_dv_timings(&mut self, session: &Self::Session) -> IoctlResult<v4l2_dv_timings> {
        v4l2r::ioctl::g_dv_timings(&session.device).map_err(|e| e.into_errno())
    }

    fn subscribe_event(
        &mut self,
        session: &mut Self::Session,
        event: V4l2EventType,
        flags: SubscribeEventFlags,
    ) -> IoctlResult<()> {
        v4l2r::ioctl::subscribe_event(&session.device, event, flags).map_err(|e| e.into_errno())?;

        // Make sure the initial event it put into the eventq before we return.
        if flags.contains(SubscribeEventFlags::SEND_INITIAL) {
            // This sends the potential events before the command response,
            // ensuring the guest will be able to see them alongside the response.
            let _ = self.dequeue_events(session).err();
        }

        Ok(())
    }

    fn unsubscribe_event(
        &mut self,
        session: &mut Self::Session,
        event: v4l2_event_subscription,
    ) -> IoctlResult<()> {
        if event.type_ == v4l2r::bindings::V4L2_EVENT_ALL {
            v4l2r::ioctl::unsubscribe_all_events(&session.device)
        } else {
            let event = V4l2EventType::try_from(&event).map_err(|_| libc::EINVAL)?;

            v4l2r::ioctl::unsubscribe_event(&session.device, event)
        }
        .map_err(|e| e.into_errno())
    }

    fn create_bufs(
        &mut self,
        session: &mut Self::Session,
        count: u32,
        queue: QueueType,
        memory: MemoryType,
        format: v4l2_format,
    ) -> IoctlResult<v4l2_create_buffers> {
        let create_bufs = v4l2r::ioctl::create_bufs::<_, v4l2_create_buffers>(
            &session.device,
            count,
            memory,
            format,
        )
        .map_err(|e| (e.into_errno()))?;

        let bufs_range = create_bufs.index..(create_bufs.index + create_bufs.count);
        self.update_mmap_offsets(session, queue, bufs_range);

        Ok(create_bufs)
    }

    fn prepare_buf(
        &mut self,
        session: &mut Self::Session,
        guest_buffer: V4l2Buffer,
        guest_regions: Vec<Vec<SgEntry>>,
    ) -> IoctlResult<V4l2Buffer> {
        let (host_buffer, guest_resources) =
            guest_v4l2_buffer_to_host(&guest_buffer, guest_regions, &self.mem)
                .map_err(|_| libc::EINVAL)?;
        session.register_userptr_addresses(&host_buffer, &guest_buffer, guest_resources);
        v4l2r::ioctl::prepare_buf(&session.device, host_buffer)
            .map_err(|e| e.into_errno())
            .and_then(|host_out_buffer| {
                host_v4l2_buffer_to_guest(&host_out_buffer, &session.userptr_buffers).map_err(|e| {
                    error!("{:#}", e.context("while processing PREPARE_BUF"));
                    libc::EINVAL
                })
            })
    }

    fn g_selection(
        &mut self,
        session: &Self::Session,
        sel_type: SelectionType,
        sel_target: SelectionTarget,
    ) -> IoctlResult<v4l2_rect> {
        v4l2r::ioctl::g_selection(&session.device, sel_type, sel_target).map_err(|e| e.into_errno())
    }

    fn s_selection(
        &mut self,
        session: &mut Self::Session,
        sel_type: SelectionType,
        sel_target: SelectionTarget,
        sel_rect: v4l2_rect,
        sel_flags: SelectionFlags,
    ) -> IoctlResult<v4l2_rect> {
        v4l2r::ioctl::s_selection(&session.device, sel_type, sel_target, sel_rect, sel_flags)
            .map_err(|e| e.into_errno())
    }

    fn decoder_cmd(
        &mut self,
        session: &mut Self::Session,
        cmd: v4l2_decoder_cmd,
    ) -> IoctlResult<v4l2_decoder_cmd> {
        v4l2r::ioctl::decoder_cmd(&session.device, cmd).map_err(|e| e.into_errno())
    }

    fn try_decoder_cmd(
        &mut self,
        session: &Self::Session,
        cmd: v4l2_decoder_cmd,
    ) -> IoctlResult<v4l2_decoder_cmd> {
        v4l2r::ioctl::try_decoder_cmd(&session.device, cmd).map_err(|e| e.into_errno())
    }

    fn enum_dv_timings(
        &mut self,
        session: &Self::Session,
        index: u32,
    ) -> IoctlResult<v4l2_dv_timings> {
        v4l2r::ioctl::enum_dv_timings(&session.device, index).map_err(|e| e.into_errno())
    }

    fn query_dv_timings(&mut self, session: &Self::Session) -> IoctlResult<v4l2_dv_timings> {
        v4l2r::ioctl::query_dv_timings(&session.device).map_err(|e| e.into_errno())
    }

    fn dv_timings_cap(&self, session: &Self::Session) -> IoctlResult<v4l2_dv_timings_cap> {
        v4l2r::ioctl::dv_timings_cap(&session.device).map_err(|e| e.into_errno())
    }

    fn enum_freq_bands(
        &self,
        session: &Self::Session,
        tuner: u32,
        type_: TunerType,
        index: u32,
    ) -> IoctlResult<v4l2_frequency_band> {
        v4l2r::ioctl::enum_freq_bands(&session.device, tuner, type_, index)
            .map_err(|e| e.into_errno())
    }

    fn query_ext_ctrl(
        &mut self,
        session: &Self::Session,
        id: CtrlId,
        flags: QueryCtrlFlags,
    ) -> IoctlResult<v4l2_query_ext_ctrl> {
        v4l2r::ioctl::query_ext_ctrl::<v4l2_query_ext_ctrl>(&session.device, id, flags)
            .map_err(|e| e.into_errno())
    }
}

impl<Q, M, HM, Reader, Writer> VirtioMediaDevice<Reader, Writer> for V4l2ProxyDevice<Q, M, HM>
where
    Q: VirtioMediaEventQueue,
    M: VirtioMediaGuestMemoryMapper,
    HM: VirtioMediaHostMemoryMapper,
    Reader: ReadFromDescriptorChain,
    Writer: WriteToDescriptorChain,
{
    type Session = V4l2Session<M>;

    fn new_session(&mut self, session_id: u32) -> Result<Self::Session, i32> {
        match V4l2Device::open(&self.device_path, DeviceConfig::new().non_blocking_dqbuf()) {
            Ok(device) => Ok(V4l2Session::new(session_id, Arc::new(device))),
            Err(DeviceOpenError::OpenError(e)) => Err(e as i32),
            Err(DeviceOpenError::QueryCapError(QueryCapError::IoctlError(e))) => Err(e as i32),
        }
    }

    fn close_session(&mut self, session: Self::Session) {
        self.delete_session(&session)
    }

    fn do_mmap(
        &mut self,
        session: &mut Self::Session,
        flags: u32,
        offset: u32,
    ) -> Result<(u64, u64), i32> {
        let rw = (flags & VIRTIO_MEDIA_MMAP_FLAG_RW) != 0;

        let plane_info = self.mmap_buffers.get_mut(&offset).ok_or(libc::EINVAL)?;

        // Export the FD for the plane and cache it if needed.
        //
        // We must NOT cache this result to reuse in case of multiple MMAP requests. If we do, then
        // there is the risk that a session requests a buffer belonging to another one. The call
        // the `expbuf` also serves as a permission check that the requesting session indeed has
        // access to the buffer.
        let exported_fd = v4l2r::ioctl::expbuf::<OwnedFd>(
            &session.device,
            plane_info.queue,
            plane_info.index as usize,
            plane_info.plane as usize,
            if rw {
                ExpbufFlags::RDWR
            } else {
                ExpbufFlags::RDONLY
            },
        )
        .map_err(|e| e.into_errno())?;

        let (mapping_addr, mapping_size) = self
            .mmap_manager
            .create_mapping(offset, exported_fd.as_fd(), rw)
            // TODO: better error mapping?
            .map_err(|_| libc::EINVAL)?;

        plane_info.map_address = mapping_addr;
        Ok((mapping_addr, mapping_size))
    }

    fn do_munmap(&mut self, guest_addr: u64) -> Result<(), i32> {
        self.mmap_manager
            .remove_mapping(guest_addr)
            .map(|_| ())
            .map_err(|_| libc::EINVAL)
    }

    fn do_ioctl(
        &mut self,
        session: &mut Self::Session,
        ioctl: V4l2Ioctl,
        reader: &mut Reader,
        writer: &mut Writer,
    ) -> IoResult<()> {
        virtio_media_dispatch_ioctl(self, session, ioctl, reader, writer)
    }

    fn process_events(&mut self, session: &mut Self::Session) -> Result<(), i32> {
        let events = session
            .poller
            .poll(Some(Duration::ZERO))
            .map_err(|_| libc::EIO)?;

        let mut has_event = false;

        for event in events {
            has_event = true;

            match event {
                PollEvent::Device(DeviceEvent::CaptureReady) => {
                    self.dequeue_capture_buffer(session).map_err(|e| e.0)?;
                    // Try to release OUTPUT buffers while we are at it.
                    self.dequeue_output_buffers(session).map_err(|e| e.0)?;
                }
                PollEvent::Device(DeviceEvent::V4L2Event) => {
                    self.dequeue_events(session).map_err(|e| e.0)?
                }
                _ => panic!(),
            }
        }

        if !has_event {
            log::warn!("process_events called but no event was pending");
        }

        Ok(())
    }
}