// Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
//
// Portions Copyright 2017 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE-BSD-3-Clause file.
//
// Copyright © 2019 Intel Corporation
//
// SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause

use super::Error as DeviceError;
use super::{
    ActivateError, ActivateResult, DescriptorChain, DeviceEventT, Queue, VirtioDevice,
    VirtioDeviceType, VirtioInterruptType,
};
use crate::VirtioInterrupt;
use arc_swap::ArcSwap;
use epoll;
use libc::{c_void, EFD_NONBLOCK};
use std::alloc::{alloc_zeroed, dealloc, Layout};
use std::cmp;
use std::convert::TryInto;
use std::fs::{File, Metadata};
use std::io::{self, Read, Seek, SeekFrom, Write};
use std::os::linux::fs::MetadataExt;
use std::os::unix::io::{AsRawFd, RawFd};
use std::path::PathBuf;
use std::result;
use std::slice;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;
use std::thread;
use virtio_bindings::bindings::virtio_blk::*;
use vm_device::{Migratable, MigratableError, Pausable, Snapshotable};
use vm_memory::{Bytes, GuestAddress, GuestMemory, GuestMemoryError, GuestMemoryMmap};
use vmm_sys_util::{eventfd::EventFd, seek_hole::SeekHole, write_zeroes::PunchHole};

const CONFIG_SPACE_SIZE: usize = 8;
const SECTOR_SHIFT: u8 = 9;
pub const SECTOR_SIZE: u64 = (0x01 as u64) << SECTOR_SHIFT;
const QUEUE_SIZE: u16 = 256;
const NUM_QUEUES: usize = 1;
const QUEUE_SIZES: &[u16] = &[QUEUE_SIZE];

// New descriptors are pending on the virtio queue.
const QUEUE_AVAIL_EVENT: DeviceEventT = 0;
// The device has been dropped.
pub const KILL_EVENT: DeviceEventT = 1;
// Number of DeviceEventT events supported by this implementation.
pub const BLOCK_EVENTS_COUNT: usize = 2;
// The device should be paused.
const PAUSE_EVENT: DeviceEventT = 3;

#[derive(Debug)]
pub enum Error {
    /// Guest gave us bad memory addresses.
    GuestMemory(GuestMemoryError),
    /// Guest gave us offsets that would have overflowed a usize.
    CheckedOffset(GuestAddress, usize),
    /// Guest gave us a write only descriptor that protocol says to read from.
    UnexpectedWriteOnlyDescriptor,
    /// Guest gave us a read only descriptor that protocol says to write to.
    UnexpectedReadOnlyDescriptor,
    /// Guest gave us too few descriptors in a descriptor chain.
    DescriptorChainTooShort,
    /// Guest gave us a descriptor that was too short to use.
    DescriptorLengthTooSmall,
    /// Getting a block's metadata fails for any reason.
    GetFileMetadata,
    /// The requested operation would cause a seek beyond disk end.
    InvalidOffset,
}

#[derive(Debug)]
pub enum ExecuteError {
    BadRequest(Error),
    Flush(io::Error),
    Read(GuestMemoryError),
    Seek(io::Error),
    Write(GuestMemoryError),
    Unsupported(u32),
}

impl ExecuteError {
    pub fn status(&self) -> u32 {
        match *self {
            ExecuteError::BadRequest(_) => VIRTIO_BLK_S_IOERR,
            ExecuteError::Flush(_) => VIRTIO_BLK_S_IOERR,
            ExecuteError::Read(_) => VIRTIO_BLK_S_IOERR,
            ExecuteError::Seek(_) => VIRTIO_BLK_S_IOERR,
            ExecuteError::Write(_) => VIRTIO_BLK_S_IOERR,
            ExecuteError::Unsupported(_) => VIRTIO_BLK_S_UNSUPP,
        }
    }
}

pub trait DiskFile: Read + Seek + Write + Clone {}
impl<D: Read + Seek + Write + Clone> DiskFile for D {}

#[derive(Debug)]
pub struct RawFile {
    file: File,
    alignment: usize,
    position: u64,
}

const BLK_ALIGNMENTS: [usize; 2] = [512, 4096];

fn is_valid_alignment(fd: RawFd, alignment: usize) -> bool {
    let layout = Layout::from_size_align(alignment, alignment).unwrap();
    let ptr = unsafe { alloc_zeroed(layout) };

    let ret = unsafe {
        ::libc::pread(
            fd,
            ptr as *mut c_void,
            alignment,
            alignment.try_into().unwrap(),
        )
    };

    unsafe { dealloc(ptr, layout) };

    ret >= 0
}

impl RawFile {
    pub fn new(file: File, direct_io: bool) -> Self {
        // Assume no alignment restrictions if we aren't using O_DIRECT.
        let mut alignment = 0;
        if direct_io {
            for align in &BLK_ALIGNMENTS {
                if is_valid_alignment(file.as_raw_fd(), *align) {
                    alignment = *align;
                    break;
                }
            }
        }
        RawFile {
            file,
            alignment: alignment.try_into().unwrap(),
            position: 0,
        }
    }

    fn round_up(&self, offset: u64) -> u64 {
        let align: u64 = self.alignment.try_into().unwrap();
        ((offset / (align + 1)) + 1) * align
    }

    fn round_down(&self, offset: u64) -> u64 {
        let align: u64 = self.alignment.try_into().unwrap();
        (offset / align) * align
    }

    fn is_aligned(&self, buf: &[u8]) -> bool {
        if self.alignment == 0 {
            return true;
        }

        let align64: u64 = self.alignment.try_into().unwrap();

        (self.position % align64 == 0)
            && ((buf.as_ptr() as usize) % self.alignment == 0)
            && (buf.len() % self.alignment == 0)
    }

    pub fn set_len(&self, size: u64) -> std::io::Result<()> {
        self.file.set_len(size)
    }

    pub fn metadata(&self) -> std::io::Result<Metadata> {
        self.file.metadata()
    }

    pub fn try_clone(&self) -> std::io::Result<RawFile> {
        Ok(RawFile {
            file: self.file.try_clone().expect("RawFile cloning failed"),
            alignment: self.alignment,
            position: self.position,
        })
    }

    pub fn sync_all(&self) -> std::io::Result<()> {
        self.file.sync_all()
    }

    pub fn sync_data(&self) -> std::io::Result<()> {
        self.file.sync_data()
    }
}

impl Read for RawFile {
    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
        if self.is_aligned(buf) {
            match self.file.read(buf) {
                Ok(r) => {
                    self.position = self.position.checked_add(r.try_into().unwrap()).unwrap();
                    Ok(r)
                }
                Err(e) => Err(e),
            }
        } else {
            let rounded_pos: u64 = self.round_down(self.position);
            let file_offset: usize = self
                .position
                .checked_sub(rounded_pos)
                .unwrap()
                .try_into()
                .unwrap();
            let buf_len: usize = buf.len();
            let rounded_len: usize = self
                .round_up(
                    file_offset
                        .checked_add(buf_len)
                        .unwrap()
                        .try_into()
                        .unwrap(),
                )
                .try_into()
                .unwrap();

            let layout = Layout::from_size_align(rounded_len, self.alignment).unwrap();
            let tmp_ptr = unsafe { alloc_zeroed(layout) };
            let tmp_buf = unsafe { slice::from_raw_parts_mut(tmp_ptr, rounded_len) };

            // This can eventually replaced with read_at once its interface
            // has been stabilized.
            let ret = unsafe {
                ::libc::pread64(
                    self.file.as_raw_fd(),
                    tmp_buf.as_mut_ptr() as *mut c_void,
                    tmp_buf.len(),
                    rounded_pos.try_into().unwrap(),
                )
            };
            if ret < 0 {
                unsafe { dealloc(tmp_ptr, layout) };
                return Err(io::Error::last_os_error());
            }

            let read: usize = ret.try_into().unwrap();
            if read < file_offset {
                unsafe { dealloc(tmp_ptr, layout) };
                return Ok(0);
            }

            let mut to_copy = read - file_offset;
            if to_copy > buf_len {
                to_copy = buf_len;
            }

            buf.copy_from_slice(&tmp_buf[file_offset..(file_offset + buf_len)]);
            unsafe { dealloc(tmp_ptr, layout) };

            self.seek(SeekFrom::Current(to_copy.try_into().unwrap()))
                .unwrap();
            Ok(to_copy.try_into().unwrap())
        }
    }
}

impl Write for RawFile {
    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
        if self.is_aligned(buf) {
            match self.file.write(buf) {
                Ok(r) => {
                    self.position = self.position.checked_add(r.try_into().unwrap()).unwrap();
                    Ok(r)
                }
                Err(e) => Err(e),
            }
        } else {
            let rounded_pos: u64 = self.round_down(self.position);
            let file_offset: usize = self
                .position
                .checked_sub(rounded_pos)
                .unwrap()
                .try_into()
                .unwrap();
            let buf_len: usize = buf.len();
            let rounded_len: usize = self
                .round_up(
                    file_offset
                        .checked_add(buf_len)
                        .unwrap()
                        .try_into()
                        .unwrap(),
                )
                .try_into()
                .unwrap();

            let layout = Layout::from_size_align(rounded_len, self.alignment).unwrap();
            let tmp_ptr = unsafe { alloc_zeroed(layout) };
            let tmp_buf = unsafe { slice::from_raw_parts_mut(tmp_ptr, rounded_len) };

            // This can eventually replaced with read_at once its interface
            // has been stabilized.
            let ret = unsafe {
                ::libc::pread64(
                    self.file.as_raw_fd(),
                    tmp_buf.as_mut_ptr() as *mut c_void,
                    tmp_buf.len(),
                    rounded_pos.try_into().unwrap(),
                )
            };
            if ret < 0 {
                unsafe { dealloc(tmp_ptr, layout) };
                return Err(io::Error::last_os_error());
            };

            tmp_buf[file_offset..(file_offset + buf_len)].copy_from_slice(buf);

            // This can eventually replaced with write_at once its interface
            // has been stabilized.
            let ret = unsafe {
                ::libc::pwrite64(
                    self.file.as_raw_fd(),
                    tmp_buf.as_ptr() as *const c_void,
                    tmp_buf.len(),
                    rounded_pos.try_into().unwrap(),
                )
            };

            unsafe { dealloc(tmp_ptr, layout) };

            if ret < 0 {
                return Err(io::Error::last_os_error());
            }

            let written: usize = ret.try_into().unwrap();
            if written < file_offset {
                Ok(0)
            } else {
                let mut to_seek = written - file_offset;
                if to_seek > buf_len {
                    to_seek = buf_len;
                }

                self.seek(SeekFrom::Current(to_seek.try_into().unwrap()))
                    .unwrap();
                Ok(to_seek.try_into().unwrap())
            }
        }
    }

    fn flush(&mut self) -> std::io::Result<()> {
        self.file.flush()
    }
}

impl Seek for RawFile {
    fn seek(&mut self, newpos: SeekFrom) -> std::io::Result<u64> {
        match self.file.seek(newpos) {
            Ok(pos) => {
                self.position = pos;
                Ok(pos)
            }
            Err(e) => Err(e),
        }
    }
}

impl PunchHole for RawFile {
    fn punch_hole(&mut self, offset: u64, length: u64) -> std::io::Result<()> {
        self.file.punch_hole(offset, length)
    }
}

impl SeekHole for RawFile {
    fn seek_hole(&mut self, offset: u64) -> std::io::Result<Option<u64>> {
        match self.file.seek_hole(offset) {
            Ok(pos) => {
                if let Some(p) = pos {
                    self.position = p;
                }
                Ok(pos)
            }
            Err(e) => Err(e),
        }
    }

    fn seek_data(&mut self, offset: u64) -> std::io::Result<Option<u64>> {
        match self.file.seek_data(offset) {
            Ok(pos) => {
                if let Some(p) = pos {
                    self.position = p;
                }
                Ok(pos)
            }
            Err(e) => Err(e),
        }
    }
}

impl Clone for RawFile {
    fn clone(&self) -> Self {
        RawFile {
            file: self.file.try_clone().expect("RawFile cloning failed"),
            alignment: self.alignment,
            position: self.position,
        }
    }
}

#[derive(Clone, Copy, Debug, PartialEq)]
pub enum RequestType {
    In,
    Out,
    Flush,
    GetDeviceID,
    Unsupported(u32),
}

pub fn request_type(
    mem: &GuestMemoryMmap,
    desc_addr: GuestAddress,
) -> result::Result<RequestType, Error> {
    let type_ = mem.read_obj(desc_addr).map_err(Error::GuestMemory)?;
    match type_ {
        VIRTIO_BLK_T_IN => Ok(RequestType::In),
        VIRTIO_BLK_T_OUT => Ok(RequestType::Out),
        VIRTIO_BLK_T_FLUSH => Ok(RequestType::Flush),
        VIRTIO_BLK_T_GET_ID => Ok(RequestType::GetDeviceID),
        t => Ok(RequestType::Unsupported(t)),
    }
}

fn sector(mem: &GuestMemoryMmap, desc_addr: GuestAddress) -> result::Result<u64, Error> {
    const SECTOR_OFFSET: usize = 8;
    let addr = match mem.checked_offset(desc_addr, SECTOR_OFFSET) {
        Some(v) => v,
        None => return Err(Error::CheckedOffset(desc_addr, SECTOR_OFFSET)),
    };

    mem.read_obj(addr).map_err(Error::GuestMemory)
}

fn build_device_id(disk_path: &PathBuf) -> result::Result<String, Error> {
    let blk_metadata = match disk_path.metadata() {
        Err(_) => return Err(Error::GetFileMetadata),
        Ok(m) => m,
    };
    // This is how kvmtool does it.
    let device_id = format!(
        "{}{}{}",
        blk_metadata.st_dev(),
        blk_metadata.st_rdev(),
        blk_metadata.st_ino()
    );
    Ok(device_id)
}

pub fn build_disk_image_id(disk_path: &PathBuf) -> Vec<u8> {
    let mut default_disk_image_id = vec![0; VIRTIO_BLK_ID_BYTES as usize];
    match build_device_id(disk_path) {
        Err(_) => {
            warn!("Could not generate device id. We'll use a default.");
        }
        Ok(m) => {
            // The kernel only knows to read a maximum of VIRTIO_BLK_ID_BYTES.
            // This will also zero out any leftover bytes.
            let disk_id = m.as_bytes();
            let bytes_to_copy = cmp::min(disk_id.len(), VIRTIO_BLK_ID_BYTES as usize);
            default_disk_image_id[..bytes_to_copy].clone_from_slice(&disk_id[..bytes_to_copy])
        }
    }
    default_disk_image_id
}

pub struct Request {
    request_type: RequestType,
    sector: u64,
    data_addr: GuestAddress,
    data_len: u32,
    pub status_addr: GuestAddress,
}

impl Request {
    pub fn parse(
        avail_desc: &DescriptorChain,
        mem: &GuestMemoryMmap,
    ) -> result::Result<Request, Error> {
        // The head contains the request type which MUST be readable.
        if avail_desc.is_write_only() {
            return Err(Error::UnexpectedWriteOnlyDescriptor);
        }

        let mut req = Request {
            request_type: request_type(&mem, avail_desc.addr)?,
            sector: sector(&mem, avail_desc.addr)?,
            data_addr: GuestAddress(0),
            data_len: 0,
            status_addr: GuestAddress(0),
        };

        let data_desc;
        let status_desc;
        let desc = avail_desc
            .next_descriptor()
            .ok_or(Error::DescriptorChainTooShort)?;

        if !desc.has_next() {
            status_desc = desc;
            // Only flush requests are allowed to skip the data descriptor.
            if req.request_type != RequestType::Flush {
                return Err(Error::DescriptorChainTooShort);
            }
        } else {
            data_desc = desc;
            status_desc = data_desc
                .next_descriptor()
                .ok_or(Error::DescriptorChainTooShort)?;

            if data_desc.is_write_only() && req.request_type == RequestType::Out {
                return Err(Error::UnexpectedWriteOnlyDescriptor);
            }
            if !data_desc.is_write_only() && req.request_type == RequestType::In {
                return Err(Error::UnexpectedReadOnlyDescriptor);
            }
            if !data_desc.is_write_only() && req.request_type == RequestType::GetDeviceID {
                return Err(Error::UnexpectedReadOnlyDescriptor);
            }

            req.data_addr = data_desc.addr;
            req.data_len = data_desc.len;
        }

        // The status MUST always be writable.
        if !status_desc.is_write_only() {
            return Err(Error::UnexpectedReadOnlyDescriptor);
        }

        if status_desc.len < 1 {
            return Err(Error::DescriptorLengthTooSmall);
        }

        req.status_addr = status_desc.addr;

        Ok(req)
    }

    #[allow(clippy::ptr_arg)]
    pub fn execute<T: Seek + Read + Write>(
        &self,
        disk: &mut T,
        disk_nsectors: u64,
        mem: &GuestMemoryMmap,
        disk_id: &Vec<u8>,
    ) -> result::Result<u32, ExecuteError> {
        let mut top: u64 = u64::from(self.data_len) / SECTOR_SIZE;
        if u64::from(self.data_len) % SECTOR_SIZE != 0 {
            top += 1;
        }
        top = top
            .checked_add(self.sector)
            .ok_or(ExecuteError::BadRequest(Error::InvalidOffset))?;
        if top > disk_nsectors {
            return Err(ExecuteError::BadRequest(Error::InvalidOffset));
        }

        disk.seek(SeekFrom::Start(self.sector << SECTOR_SHIFT))
            .map_err(ExecuteError::Seek)?;

        match self.request_type {
            RequestType::In => {
                mem.read_exact_from(self.data_addr, disk, self.data_len as usize)
                    .map_err(ExecuteError::Read)?;
                return Ok(self.data_len);
            }
            RequestType::Out => {
                mem.write_all_to(self.data_addr, disk, self.data_len as usize)
                    .map_err(ExecuteError::Write)?;
            }
            RequestType::Flush => match disk.flush() {
                Ok(_) => {
                    return Ok(0);
                }
                Err(e) => return Err(ExecuteError::Flush(e)),
            },
            RequestType::GetDeviceID => {
                if (self.data_len as usize) < disk_id.len() {
                    return Err(ExecuteError::BadRequest(Error::InvalidOffset));
                }
                mem.write_slice(&disk_id.as_slice(), self.data_addr)
                    .map_err(ExecuteError::Write)?;
            }
            RequestType::Unsupported(t) => return Err(ExecuteError::Unsupported(t)),
        };
        Ok(0)
    }
}

struct BlockEpollHandler<T: DiskFile> {
    queues: Vec<Queue>,
    mem: Arc<ArcSwap<GuestMemoryMmap>>,
    disk_image: T,
    disk_nsectors: u64,
    interrupt_cb: Arc<dyn VirtioInterrupt>,
    disk_image_id: Vec<u8>,
    kill_evt: EventFd,
    pause_evt: EventFd,
}

impl<T: DiskFile> BlockEpollHandler<T> {
    fn process_queue(&mut self, queue_index: usize) -> bool {
        let queue = &mut self.queues[queue_index];

        let mut used_desc_heads = [(0, 0); QUEUE_SIZE as usize];
        let mut used_count = 0;
        let mem = self.mem.load();
        for avail_desc in queue.iter(&mem) {
            let len;
            match Request::parse(&avail_desc, &mem) {
                Ok(request) => {
                    let status = match request.execute(
                        &mut self.disk_image,
                        self.disk_nsectors,
                        &mem,
                        &self.disk_image_id,
                    ) {
                        Ok(l) => {
                            len = l;
                            VIRTIO_BLK_S_OK
                        }
                        Err(e) => {
                            error!("Failed to execute request: {:?}", e);
                            len = 1; // We need at least 1 byte for the status.
                            e.status()
                        }
                    };
                    // We use unwrap because the request parsing process already checked that the
                    // status_addr was valid.
                    mem.write_obj(status, request.status_addr).unwrap();
                }
                Err(e) => {
                    error!("Failed to parse available descriptor chain: {:?}", e);
                    len = 0;
                }
            }
            used_desc_heads[used_count] = (avail_desc.index, len);
            used_count += 1;
        }

        for &(desc_index, len) in &used_desc_heads[..used_count] {
            queue.add_used(&mem, desc_index, len);
        }
        used_count > 0
    }

    fn signal_used_queue(&self, queue_index: usize) -> result::Result<(), DeviceError> {
        self.interrupt_cb
            .trigger(&VirtioInterruptType::Queue, Some(&self.queues[queue_index]))
            .map_err(|e| {
                error!("Failed to signal used queue: {:?}", e);
                DeviceError::FailedSignalingUsedQueue(e)
            })
    }

    #[allow(dead_code)]
    fn update_disk_image(
        &mut self,
        disk_image: T,
        disk_path: &PathBuf,
    ) -> result::Result<(), DeviceError> {
        self.disk_image = disk_image;
        self.disk_nsectors = self
            .disk_image
            .seek(SeekFrom::End(0))
            .map_err(DeviceError::IoError)?
            / SECTOR_SIZE;
        self.disk_image_id = build_disk_image_id(disk_path);
        Ok(())
    }

    fn run(
        &mut self,
        queue_evt: EventFd,
        paused: Arc<AtomicBool>,
    ) -> result::Result<(), DeviceError> {
        // Create the epoll file descriptor
        let epoll_fd = epoll::create(true).map_err(DeviceError::EpollCreateFd)?;

        // Add events
        epoll::ctl(
            epoll_fd,
            epoll::ControlOptions::EPOLL_CTL_ADD,
            queue_evt.as_raw_fd(),
            epoll::Event::new(epoll::Events::EPOLLIN, u64::from(QUEUE_AVAIL_EVENT)),
        )
        .map_err(DeviceError::EpollCtl)?;
        epoll::ctl(
            epoll_fd,
            epoll::ControlOptions::EPOLL_CTL_ADD,
            self.kill_evt.as_raw_fd(),
            epoll::Event::new(epoll::Events::EPOLLIN, u64::from(KILL_EVENT)),
        )
        .map_err(DeviceError::EpollCtl)?;
        epoll::ctl(
            epoll_fd,
            epoll::ControlOptions::EPOLL_CTL_ADD,
            self.pause_evt.as_raw_fd(),
            epoll::Event::new(epoll::Events::EPOLLIN, u64::from(PAUSE_EVENT)),
        )
        .map_err(DeviceError::EpollCtl)?;

        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(DeviceError::EpollWait(e));
                }
            };

            for event in events.iter().take(num_events) {
                let ev_type = event.data as u16;

                match ev_type {
                    QUEUE_AVAIL_EVENT => {
                        if let Err(e) = queue_evt.read() {
                            error!("Failed to get queue event: {:?}", e);
                            break 'epoll;
                        } else if self.process_queue(0) {
                            if let Err(e) = self.signal_used_queue(0) {
                                error!("Failed to signal used queue: {:?}", e);
                                break 'epoll;
                            }
                        }
                    }
                    KILL_EVENT => {
                        debug!("KILL_EVENT received, stopping epoll loop");
                        break 'epoll;
                    }
                    PAUSE_EVENT => {
                        debug!("PAUSE_EVENT received, pausing virtio-block epoll loop");
                        // We loop here to handle spurious park() returns.
                        // Until we have not resumed, the paused boolean will
                        // be true.
                        while paused.load(Ordering::SeqCst) {
                            thread::park();
                        }
                    }
                    _ => {
                        error!("Unknown event for virtio-block");
                    }
                }
            }
        }

        Ok(())
    }
}

/// Virtio device for exposing block level read/write operations on a host file.
pub struct Block<T: DiskFile> {
    kill_evt: Option<EventFd>,
    disk_image: Option<T>,
    disk_path: PathBuf,
    disk_nsectors: u64,
    avail_features: u64,
    acked_features: u64,
    config_space: Vec<u8>,
    queue_evt: Option<EventFd>,
    interrupt_cb: Option<Arc<dyn VirtioInterrupt>>,
    epoll_thread: Option<Vec<thread::JoinHandle<result::Result<(), DeviceError>>>>,
    pause_evt: Option<EventFd>,
    paused: Arc<AtomicBool>,
}

pub fn build_config_space(disk_size: u64) -> Vec<u8> {
    // We only support disk size, which uses the first two words of the configuration space.
    // If the image is not a multiple of the sector size, the tail bits are not exposed.
    // The config space is little endian.
    let mut config = Vec::with_capacity(CONFIG_SPACE_SIZE);
    let num_sectors = disk_size >> SECTOR_SHIFT;
    for i in 0..8 {
        config.push((num_sectors >> (8 * i)) as u8);
    }
    config
}

impl<T: DiskFile> Block<T> {
    /// Create a new virtio block device that operates on the given file.
    ///
    /// The given file must be seekable and sizable.
    pub fn new(
        mut disk_image: T,
        disk_path: PathBuf,
        is_disk_read_only: bool,
        iommu: bool,
    ) -> io::Result<Block<T>> {
        let disk_size = disk_image.seek(SeekFrom::End(0))? as u64;
        if disk_size % SECTOR_SIZE != 0 {
            warn!(
                "Disk size {} is not a multiple of sector size {}; \
                 the remainder will not be visible to the guest.",
                disk_size, SECTOR_SIZE
            );
        }

        let mut avail_features = (1u64 << VIRTIO_F_VERSION_1) | (1u64 << VIRTIO_BLK_F_FLUSH);

        if iommu {
            avail_features |= 1u64 << VIRTIO_F_IOMMU_PLATFORM;
        }

        if is_disk_read_only {
            avail_features |= 1u64 << VIRTIO_BLK_F_RO;
        };

        Ok(Block {
            kill_evt: None,
            disk_image: Some(disk_image),
            disk_path,
            disk_nsectors: disk_size / SECTOR_SIZE,
            avail_features,
            acked_features: 0u64,
            config_space: build_config_space(disk_size),
            queue_evt: None,
            interrupt_cb: None,
            epoll_thread: None,
            pause_evt: None,
            paused: Arc::new(AtomicBool::new(false)),
        })
    }
}

impl<T: DiskFile> Drop for Block<T> {
    fn drop(&mut self) {
        if let Some(kill_evt) = self.kill_evt.take() {
            // Ignore the result because there is nothing we can do about it.
            let _ = kill_evt.write(1);
        }
    }
}

impl<T: 'static + DiskFile + Send> VirtioDevice for Block<T> {
    fn device_type(&self) -> u32 {
        VirtioDeviceType::TYPE_BLOCK as u32
    }

    fn queue_max_sizes(&self) -> &[u16] {
        QUEUE_SIZES
    }

    fn features(&self, page: u32) -> u32 {
        match page {
            // Get the lower 32-bits of the features bitfield.
            0 => self.avail_features as u32,
            // Get the upper 32-bits of the features bitfield.
            1 => (self.avail_features >> 32) as u32,
            _ => {
                warn!("Received request for unknown features page.");
                0u32
            }
        }
    }

    fn ack_features(&mut self, page: u32, value: u32) {
        let mut v = match page {
            0 => u64::from(value),
            1 => u64::from(value) << 32,
            _ => {
                warn!("Cannot acknowledge unknown features page.");
                0u64
            }
        };

        // Check if the guest is ACK'ing a feature that we didn't claim to have.
        let unrequested_features = v & !self.avail_features;
        if unrequested_features != 0 {
            warn!("Received acknowledge request for unknown feature.");

            // Don't count these features as acked.
            v &= !unrequested_features;
        }
        self.acked_features |= v;
    }

    fn read_config(&self, offset: u64, mut data: &mut [u8]) {
        let config_len = self.config_space.len() as u64;
        if offset >= config_len {
            error!("Failed to read config space");
            return;
        }
        if let Some(end) = offset.checked_add(data.len() as u64) {
            // This write can't fail, offset and end are checked against config_len.
            data.write_all(&self.config_space[offset as usize..cmp::min(end, config_len) as usize])
                .unwrap();
        }
    }

    fn write_config(&mut self, offset: u64, data: &[u8]) {
        let data_len = data.len() as u64;
        let config_len = self.config_space.len() as u64;
        if offset + data_len > config_len {
            error!("Failed to write config space");
            return;
        }
        let (_, right) = self.config_space.split_at_mut(offset as usize);
        right.copy_from_slice(&data[..]);
    }

    fn activate(
        &mut self,
        mem: Arc<ArcSwap<GuestMemoryMmap>>,
        interrupt_cb: Arc<dyn VirtioInterrupt>,
        queues: Vec<Queue>,
        mut queue_evts: Vec<EventFd>,
    ) -> ActivateResult {
        if queues.len() != NUM_QUEUES || queue_evts.len() != NUM_QUEUES {
            error!(
                "Cannot perform activate. Expected {} queue(s), got {}",
                NUM_QUEUES,
                queues.len()
            );
            return Err(ActivateError::BadActivate);
        }

        let (self_kill_evt, kill_evt) = EventFd::new(EFD_NONBLOCK)
            .and_then(|e| Ok((e.try_clone()?, e)))
            .map_err(|e| {
                error!("failed creating kill EventFd pair: {}", e);
                ActivateError::BadActivate
            })?;

        self.kill_evt = Some(self_kill_evt);

        let (self_pause_evt, pause_evt) = EventFd::new(EFD_NONBLOCK)
            .and_then(|e| Ok((e.try_clone()?, e)))
            .map_err(|e| {
                error!("failed creating pause EventFd pair: {}", e);
                ActivateError::BadActivate
            })?;
        self.pause_evt = Some(self_pause_evt);

        if let Some(disk_image) = self.disk_image.clone() {
            let disk_image_id = build_disk_image_id(&self.disk_path);

            // Save the interrupt EventFD as we need to return it on reset
            // but clone it to pass into the thread.
            self.interrupt_cb = Some(interrupt_cb);
            let interrupt_cb = self.interrupt_cb.as_ref().unwrap().clone();

            // Save the queue EventFD as we need to return it on reset
            // but clone it to pass into the thread.
            self.queue_evt = Some(queue_evts.remove(0));
            let queue_evt = self.queue_evt.as_ref().unwrap().try_clone().map_err(|e| {
                error!("failed to clone queue EventFd: {}", e);
                ActivateError::BadActivate
            })?;

            let mut handler = BlockEpollHandler {
                queues,
                mem,
                disk_image,
                disk_nsectors: self.disk_nsectors,
                interrupt_cb,
                disk_image_id,
                kill_evt,
                pause_evt,
            };

            let paused = self.paused.clone();
            let mut epoll_threads = Vec::new();
            thread::Builder::new()
                .name("virtio_blk".to_string())
                .spawn(move || handler.run(queue_evt, paused))
                .map(|thread| epoll_threads.push(thread))
                .map_err(|e| {
                    error!("failed to clone the virtio-blk epoll thread: {}", e);
                    ActivateError::BadActivate
                })?;

            self.epoll_thread = Some(epoll_threads);

            return Ok(());
        }
        Err(ActivateError::BadActivate)
    }

    fn reset(&mut self) -> Option<(Arc<dyn VirtioInterrupt>, Vec<EventFd>)> {
        // We first must resume the virtio thread if it was paused.
        if self.pause_evt.take().is_some() {
            self.resume().ok()?;
        }

        if let Some(kill_evt) = self.kill_evt.take() {
            // Ignore the result because there is nothing we can do about it.
            let _ = kill_evt.write(1);
        }

        // Return the interrupt and queue EventFDs
        Some((
            self.interrupt_cb.take().unwrap(),
            vec![self.queue_evt.take().unwrap()],
        ))
    }
}

impl<T: 'static + DiskFile + Send> Pausable for Block<T> {
    virtio_pausable_inner!();
}

impl<T: 'static + DiskFile + Send> Snapshotable for Block<T> {}
impl<T: 'static + DiskFile + Send> Migratable for Block<T> {}