path: root/devices/src/virtio/block.rs

// 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 file.

use std::cmp;
use std::io::{self, Seek, SeekFrom, Read, Write};
use std::os::unix::io::{AsRawFd, RawFd};
use std::result;
use std::sync::Arc;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::thread;

use sys_util::Result as SysResult;
use sys_util::{EventFd, GuestAddress, GuestMemory, GuestMemoryError, PollContext, PollToken};

use super::{VirtioDevice, Queue, DescriptorChain, INTERRUPT_STATUS_USED_RING, TYPE_BLOCK};

const QUEUE_SIZE: u16 = 256;
const QUEUE_SIZES: &'static [u16] = &[QUEUE_SIZE];
const SECTOR_SHIFT: u8 = 9;
const SECTOR_SIZE: u64 = 0x01 << SECTOR_SHIFT;

const VIRTIO_BLK_T_IN: u32 = 0;
const VIRTIO_BLK_T_OUT: u32 = 1;
const VIRTIO_BLK_T_FLUSH: u32 = 4;

const VIRTIO_BLK_S_OK: u8 = 0;
const VIRTIO_BLK_S_IOERR: u8 = 1;
const VIRTIO_BLK_S_UNSUPP: u8 = 2;

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

#[derive(PartialEq)]
enum RequestType {
    In,
    Out,
    Flush,
    Unsupported(u32),
}

#[derive(Debug)]
enum ParseError {
    /// Guest gave us bad memory addresses
    GuestMemory(GuestMemoryError),
    /// Guest gave us offsets that would have overflowed a usize.
    CheckedOffset(GuestAddress, u64),
    /// 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,
}

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

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

    mem.read_obj_from_addr(addr)
        .map_err(ParseError::GuestMemory)
}

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

impl ExecuteError {
    fn status(&self) -> u8 {
        match self {
            &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,
        }
    }
}

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

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

        let req_type = request_type(&mem, avail_desc.addr)?;
        let sector = sector(&mem, avail_desc.addr)?;
        let data_desc = avail_desc
            .next_descriptor()
            .ok_or(ParseError::DescriptorChainTooShort)?;
        let status_desc = data_desc
            .next_descriptor()
            .ok_or(ParseError::DescriptorChainTooShort)?;

        if data_desc.is_write_only() && req_type == RequestType::Out {
            return Err(ParseError::UnexpectedWriteOnlyDescriptor);
        }

        if !data_desc.is_write_only() && req_type == RequestType::In {
            return Err(ParseError::UnexpectedReadOnlyDescriptor);
        }

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

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

        Ok(Request {
               request_type: req_type,
               sector: sector,
               data_addr: data_desc.addr,
               data_len: data_desc.len,
               status_addr: status_desc.addr,
           })
    }

    fn execute<T: DiskFile>(&self,
                                       disk: &mut T,
                                       mem: &GuestMemory)
                                       -> result::Result<u32, ExecuteError> {
        disk.seek(SeekFrom::Start(self.sector << SECTOR_SHIFT))
            .map_err(ExecuteError::Seek)?;
        match self.request_type {
            RequestType::In => {
                mem.read_to_memory(self.data_addr, disk, self.data_len as usize)
                    .map_err(|e| ExecuteError::Read(self.data_addr, self.data_len, e))?;
                return Ok(self.data_len);
            }
            RequestType::Out => {
                mem.write_from_memory(self.data_addr, disk, self.data_len as usize)
                    .map_err(|e| ExecuteError::Write(self.data_addr, self.data_len, e))?;
            }
            RequestType::Flush => disk.flush().map_err(ExecuteError::Flush)?,
            RequestType::Unsupported(t) => return Err(ExecuteError::Unsupported(t)),
        };
        Ok(0)
    }
}

struct Worker<T: DiskFile> {
    queues: Vec<Queue>,
    mem: GuestMemory,
    disk_image: T,
    interrupt_status: Arc<AtomicUsize>,
    interrupt_evt: EventFd,
}

impl<T: DiskFile> Worker<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;
        for avail_desc in queue.iter(&self.mem) {
            let len;
            match Request::parse(&avail_desc, &self.mem) {
                Ok(request) => {
                    let status = match request.execute(&mut self.disk_image, &self.mem) {
                        Ok(l) => {
                            len = l;
                            VIRTIO_BLK_S_OK
                        }
                        Err(e) => {
                            error!("failed executing disk request: {:?}", e);
                            len = 1; // 1 byte for the status
                            e.status()
                        }
                    };
                    // We use unwrap because the request parsing process already checked that the
                    // status_addr was valid.
                    self.mem
                        .write_obj_at_addr(status, request.status_addr)
                        .unwrap();
                }
                Err(e) => {
                    error!("failed processing 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(&self.mem, desc_index, len);
        }
        used_count > 0
    }

    fn signal_used_queue(&self) {
        self.interrupt_status
            .fetch_or(INTERRUPT_STATUS_USED_RING as usize, Ordering::SeqCst);
        self.interrupt_evt.write(1).unwrap();
    }

    fn run(&mut self, queue_evt: EventFd, kill_evt: EventFd) {
        #[derive(PollToken)]
        enum Token {
            QueueAvailable,
            Kill,
        }

        let poll_ctx: PollContext<Token> =
            match PollContext::new()
                      .and_then(|pc| pc.add(&queue_evt, Token::QueueAvailable).and(Ok(pc)))
                      .and_then(|pc| pc.add(&kill_evt, Token::Kill).and(Ok(pc))) {
                Ok(pc) => pc,
                Err(e) => {
                    error!("failed creating PollContext: {:?}", e);
                    return;
                }
            };

        'poll: loop {
            let events = match poll_ctx.wait() {
                Ok(v) => v,
                Err(e) => {
                    error!("failed polling for events: {:?}", e);
                    break;
                }
            };

            let mut needs_interrupt = false;
            for event in events.iter_readable() {
                match event.token() {
                    Token::QueueAvailable => {
                        if let Err(e) = queue_evt.read() {
                            error!("failed reading queue EventFd: {:?}", e);
                            break 'poll;
                        }
                        needs_interrupt |= self.process_queue(0);
                    }
                    Token::Kill => break 'poll,
                }
            }
            if needs_interrupt {
                self.signal_used_queue();
            }
        }
    }
}

/// 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>,
    config_space: Vec<u8>,
}

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(8);
    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) -> SysResult<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);
        }
        Ok(Block {
               kill_evt: None,
               disk_image: Some(disk_image),
               config_space: build_config_space(disk_size),
           })
    }
}

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 + AsRawFd + DiskFile + Send> VirtioDevice for Block<T> {
    fn keep_fds(&self) -> Vec<RawFd> {
        let mut keep_fds = Vec::new();

        if let Some(ref disk_image) = self.disk_image {
            keep_fds.push(disk_image.as_raw_fd());
        }

        keep_fds
    }

    fn device_type(&self) -> u32 {
        TYPE_BLOCK
    }

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

    fn read_config(&self, offset: u64, mut data: &mut [u8]) {
        let config_len = self.config_space.len() as u64;
        if offset >= config_len {
            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 activate(&mut self,
                mem: GuestMemory,
                interrupt_evt: EventFd,
                status: Arc<AtomicUsize>,
                queues: Vec<Queue>,
                mut queue_evts: Vec<EventFd>) {
        if queues.len() != 1 || queue_evts.len() != 1 {
            return;
        }

        let (self_kill_evt, kill_evt) =
            match EventFd::new().and_then(|e| Ok((e.try_clone()?, e))) {
                Ok(v) => v,
                Err(e) => {
                    error!("failed creating kill EventFd pair: {:?}", e);
                    return;
                }
            };
        self.kill_evt = Some(self_kill_evt);

        if let Some(disk_image) = self.disk_image.take() {
            let worker_result = thread::Builder::new()
                .name("virtio_blk".to_string())
                .spawn(move || {
                    let mut worker = Worker {
                        queues: queues,
                        mem: mem,
                        disk_image: disk_image,
                        interrupt_status: status,
                        interrupt_evt: interrupt_evt,
                    };
                    worker.run(queue_evts.remove(0), kill_evt);
                });

            if let Err(e) = worker_result {
                error!("failed to spawn virtio_blk worker: {}", e);
                return;
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use std::fs::File;
    use std::path::PathBuf;
    use sys_util::TempDir;

    use super::*;

    #[test]
    fn read_size() {
        let tempdir = TempDir::new("/tmp/block_read_test").unwrap();
        let mut path = PathBuf::from(tempdir.as_path().unwrap());
        path.push("disk_image");
        let f = File::create(&path).unwrap();
        f.set_len(0x1000).unwrap();

        let b = Block::new(f).unwrap();
        let mut num_sectors = [0u8; 4];
        b.read_config(0, &mut num_sectors);
        // size is 0x1000, so num_sectors is 8 (4096/512).
        assert_eq!([0x08, 0x00, 0x00, 0x00], num_sectors);
        let mut msw_sectors = [0u8; 4];
        b.read_config(4, &mut msw_sectors);
        // size is 0x1000, so msw_sectors is 0.
        assert_eq!([0x00, 0x00, 0x00, 0x00], msw_sectors);
    }
}