Initial commit

I started this project on February 2021, but postponed further
development until now. The only modification introduced since then is
try_trait_v2 (try_trait no longer exists).

1 files changed, 569 insertions, 0 deletions

diff --git a/src/fuse/session.rs b/src/fuse/session.rs
new file mode 100644
index 0000000..35ebb69
--- /dev/null
+++ b/src/fuse/session.rs
@@ -0,0 +1,569 @@
+use std::{
+    collections::{hash_map, HashMap},
+    convert::TryInto,
+    os::unix::io::IntoRawFd,
+    sync::{Arc, Mutex},
+};
+
+use nix::{
+    fcntl::{fcntl, FcntlArg, OFlag},
+    sys::uio::{readv, writev, IoVec},
+    unistd::{sysconf, SysconfVar},
+};
+
+use tokio::{
+    io::unix::AsyncFd,
+    sync::{broadcast, Notify, OwnedSemaphorePermit, Semaphore},
+};
+
+use bytemuck::{bytes_of, try_from_bytes};
+use smallvec::SmallVec;
+
+use crate::{
+    proto::{self, InHeader},
+    util::{display_or, from_nix_error, OutputChain},
+    Errno, FuseError, FuseResult, Ino,
+};
+
+use super::{
+    fs::{Fuse, Inode},
+    Reply, Request, Session, Start,
+};
+
+pub fn ok<Fs: Fuse>(session: &Session<Fs>, unique: u64, output: OutputChain<'_>) -> FuseResult<()> {
+    session.send(unique, 0, output)
+}
+
+pub fn notify<Fs: Fuse>(
+    session: &Session<Fs>,
+    op: proto::NotifyCode,
+    output: OutputChain<'_>,
+) -> FuseResult<()> {
+    session.send(0, op as i32, output)
+}
+
+pub fn fail<Fs: Fuse>(session: &Session<Fs>, unique: u64, mut errno: i32) -> FuseResult<()> {
+    if errno <= 0 {
+        log::warn!(
+            "Attempted to fail req#{} with errno {} <= 0, coercing to ENOMSG",
+            unique,
+            errno
+        );
+
+        errno = Errno::ENOMSG as i32;
+    }
+
+    session.send(unique, -errno, OutputChain::empty())
+}
+
+pub fn unveil<Fs: Fuse>(session: &Session<Fs>, inode: &Fs::Farc) {
+    let ino = <Fs as Fuse>::Inode::ino(inode);
+    let mut known = session.known.lock().unwrap();
+
+    use hash_map::Entry::*;
+    match known.entry(ino) {
+        Occupied(entry) => {
+            let (_, count) = entry.into_mut();
+            *count += 1;
+        }
+
+        Vacant(entry) => {
+            entry.insert((Fs::Farc::clone(inode), 1));
+        }
+    }
+}
+
+pub fn interrupt_rx<Fs: Fuse>(session: &Session<Fs>) -> broadcast::Receiver<u64> {
+    session.interrupt_tx.subscribe()
+}
+
+impl<Fs: Fuse> Session<Fs> {
+    pub fn fs(&self) -> &Fs {
+        &self.fs
+    }
+
+    pub async fn main_loop(self: Arc<Self>) -> FuseResult<()> {
+        let this = Arc::clone(&self);
+        let main_loop = async move {
+            loop {
+                let incoming = this.receive().await;
+                let this = Arc::clone(&this);
+
+                tokio::spawn(async move {
+                    let (result, header): (FuseResult<()>, Option<InHeader>) = match incoming {
+                        Ok(mut incoming) => match this.dispatch(&mut incoming).await {
+                            Ok(()) => (Ok(()), None),
+
+                            Err(error) => {
+                                let data = incoming.buffer.data();
+                                let data = &data[..std::mem::size_of::<InHeader>().max(data.len())];
+                                (Err(error), try_from_bytes(data).ok().copied())
+                            }
+                        },
+
+                        Err(error) => (Err(error.into()), None),
+                    };
+
+                    let header = display_or(header, "(bad)");
+                    if let Err(error) = result {
+                        log::error!("Handling request {}: {}", header, error);
+                    }
+                });
+            }
+        };
+
+        tokio::select! {
+            () = main_loop => unreachable!(),
+            () = self.destroy.notified() => Ok(()),
+        }
+    }
+
+    async fn do_handshake(
+        &mut self,
+        pages_per_buffer: usize,
+        bytes_per_buffer: usize,
+    ) -> FuseResult<Handshake> {
+        use FuseError::*;
+
+        let buffer = {
+            self.session_fd.readable().await?.retain_ready();
+            let large_buffer = self.large_buffers.get_mut().unwrap().first_mut().unwrap();
+
+            let mut data = InputBufferStorage::Sbo(SboStorage([0; SBO_SIZE]));
+            let sbo = match &mut data {
+                InputBufferStorage::Sbo(SboStorage(sbo)) => sbo,
+                _ => unreachable!(),
+            };
+
+            let mut io_vecs = [
+                IoVec::from_mut_slice(sbo),
+                IoVec::from_mut_slice(large_buffer),
+            ];
+
+            let bytes = readv(*self.session_fd.get_ref(), &mut io_vecs).map_err(from_nix_error)?;
+            InputBuffer { bytes, data }
+        };
+
+        let request: proto::Request<'_> = buffer.data().try_into()?;
+
+        let unique = request.header().unique;
+        let init = match request.body() {
+            proto::RequestBody::Init(body) => body,
+            _ => return Err(ProtocolInit),
+        };
+
+        use std::cmp::Ordering;
+        let supported = match init.major.cmp(&proto::MAJOR_VERSION) {
+            Ordering::Less => false,
+
+            Ordering::Equal => {
+                self.proto_minor = init.minor;
+                self.proto_minor >= proto::REQUIRED_MINOR_VERSION
+            }
+
+            Ordering::Greater => {
+                let tail = [bytes_of(&proto::MAJOR_VERSION)];
+                ok(&self, unique, OutputChain::tail(&tail))?;
+
+                return Ok(Handshake::Restart);
+            }
+        };
+
+        //TODO: fake some decency by supporting a few older minor versions
+        if !supported {
+            log::error!(
+                "Unsupported protocol {}.{}; this build requires \
+                 {major}.{}..={major}.{} (or a greater version \
+                 through compatibility)",
+                init.major,
+                init.minor,
+                proto::REQUIRED_MINOR_VERSION,
+                proto::TARGET_MINOR_VERSION,
+                major = proto::MAJOR_VERSION
+            );
+
+            fail(&self, unique, Errno::EPROTONOSUPPORT as i32)?;
+            return Err(ProtocolInit);
+        }
+
+        let root = {
+            let mut init_result = Err(0);
+            let reply = Reply {
+                session: &self,
+                unique,
+                tail: &mut init_result,
+            };
+
+            self.fs.init(reply).await.into_result()?;
+
+            match init_result {
+                Ok(root) => root,
+                Err(errno) => {
+                    log::error!("init() handler failed: {}", Errno::from_i32(errno));
+                    return Err(FuseError::Io(std::io::Error::from_raw_os_error(errno)));
+                }
+            }
+        };
+
+        self.known.get_mut().unwrap().insert(Ino::ROOT, (root, 1));
+
+        use proto::InitFlags;
+        let flags = InitFlags::from_bits_truncate(init.flags);
+        let supported = InitFlags::PARALLEL_DIROPS
+            | InitFlags::ABORT_ERROR
+            | InitFlags::MAX_PAGES
+            | InitFlags::CACHE_SYMLINKS;
+
+        let flags = flags & supported;
+        let max_write = bytes_per_buffer - std::mem::size_of::<(InHeader, proto::WriteIn)>();
+        let init_out = proto::InitOut {
+            major: proto::MAJOR_VERSION,
+            minor: proto::TARGET_MINOR_VERSION,
+            max_readahead: 0, //TODO
+            flags: flags.bits(),
+            max_background: 0,       //TODO
+            congestion_threshold: 0, //TODO
+            max_write: max_write.try_into().unwrap(),
+            time_gran: 1, //TODO
+            max_pages: pages_per_buffer.try_into().unwrap(),
+            padding: Default::default(),
+            unused: Default::default(),
+        };
+
+        let tail = [bytes_of(&init_out)];
+        ok(&self, unique, OutputChain::tail(&tail))?;
+
+        Ok(Handshake::Done)
+    }
+
+    async fn dispatch(self: &Arc<Self>, request: &mut Incoming<Fs>) -> FuseResult<()> {
+        let request: proto::Request<'_> = request.buffer.data().try_into()?;
+        let header = request.header();
+        let InHeader { unique, ino, .. } = *header;
+        let ino = Ino(ino);
+
+        use proto::RequestBody::*;
+
+        macro_rules! op {
+            () => {
+                op!(())
+            };
+
+            ($body:expr) => {
+                op!($body, ())
+            };
+
+            ($body:expr, $tail:expr) => {{
+                let request = Request {
+                    header,
+                    body: $body,
+                };
+                let reply = Reply {
+                    session: &self,
+                    unique,
+                    tail: $tail,
+                };
+
+                (request, reply, self)
+            }};
+        }
+
+        // These operations don't involve locking and searching self.known
+        match request.body() {
+            Forget(body) => {
+                self.forget(std::iter::once((ino, body.nlookup))).await;
+                return Ok(());
+            }
+
+            Statfs => return self.fs.statfs(op!()).await.into_result(),
+
+            Interrupt(body) => {
+                //TODO: Don't reply with EAGAIN if the interrupt is successful
+                let _ = self.interrupt_tx.send(body.unique);
+                return fail(&self, unique, Errno::EAGAIN as i32);
+            }
+
+            Destroy => {
+                self.destroy.notify_one();
+                return Ok(());
+            }
+
+            BatchForget { forgets, .. } => {
+                let forgets = forgets
+                    .iter()
+                    .map(|target| (Ino(target.ino), target.nlookup));
+
+                self.forget(forgets).await;
+                return Ok(());
+            }
+
+            _ => (),
+        }
+
+        // Some operations are handled while self.known is locked
+        let inode = {
+            let known = self.known.lock().unwrap();
+            let inode = match known.get(&ino) {
+                Some((farc, _)) => farc,
+                None => {
+                    log::error!(
+                        "Lookup count for ino {} reached zero while still \
+                         known to the kernel, this is a bug",
+                        ino
+                    );
+
+                    return fail(&self, unique, Errno::ENOANO as i32);
+                }
+            };
+
+            match request.body() {
+                Getattr(_) => {
+                    //TODO: Getattr flags
+                    let (attrs, ttl) = <Fs as Fuse>::Inode::attrs(inode);
+                    let attrs = attrs.finish::<Fs>(inode);
+                    drop(known);
+
+                    let out = proto::AttrOut {
+                        attr_valid: ttl.seconds,
+                        attr_valid_nsec: ttl.nanoseconds,
+                        dummy: Default::default(),
+                        attr: attrs,
+                    };
+
+                    return ok(&self, unique, OutputChain::tail(&[bytes_of(&out)]));
+                }
+
+                Access(body) => {
+                    return <Fs as Fuse>::Inode::access(inode, op!(*body)).into_result()
+                }
+
+                _ => inode.clone(),
+            }
+        };
+
+        macro_rules! inode_op {
+            ($op:ident, $($exprs:expr),+) => {
+                <Fs as Fuse>::Inode::$op(inode, op!($($exprs),+)).await
+            };
+        }
+
+        // These operations involve a Farc cloned from self.known
+        let done = match request.body() {
+            Lookup { name } => inode_op!(lookup, *name),
+            Readlink => inode_op!(readlink, ()),
+            Open(body) => {
+                let mut flags = proto::OpenOutFlags::empty();
+                if <Fs as Fuse>::Inode::direct_io(&inode) {
+                    flags |= proto::OpenOutFlags::DIRECT_IO;
+                }
+
+                inode_op!(open, *body, (ino, flags))
+            }
+            Opendir(body) => inode_op!(opendir, *body),
+            Readdir(body) => inode_op!(readdir, *body),
+
+            _ => return fail(&self, unique, Errno::ENOSYS as i32),
+        };
+
+        done.into_result()
+    }
+
+    async fn forget<I>(&self, targets: I)
+    where
+        I: Iterator<Item = (Ino, u64)>,
+    {
+        let mut known = self.known.lock().unwrap();
+
+        for (ino, subtracted) in targets {
+            use hash_map::Entry::*;
+
+            match known.entry(ino) {
+                Occupied(mut entry) => {
+                    let (_, count) = entry.get_mut();
+
+                    *count = count.saturating_sub(subtracted);
+                    if *count > 0 {
+                        continue;
+                    }
+
+                    entry.remove();
+                }
+
+                Vacant(_) => {
+                    log::warn!("Kernel attempted to forget {:?} (bad refcount?)", ino);
+                    continue;
+                }
+            }
+        }
+    }
+
+    async fn receive(self: &Arc<Self>) -> std::io::Result<Incoming<Fs>> {
+        use InputBufferStorage::*;
+
+        let permit = Arc::clone(&self.input_semaphore)
+            .acquire_owned()
+            .await
+            .unwrap();
+
+        let mut incoming = Incoming {
+            session: Arc::clone(self),
+            buffer: InputBuffer {
+                bytes: 0,
+                data: Sbo(SboStorage([0; SBO_SIZE])),
+            },
+        };
+
+        let sbo = match &mut incoming.buffer.data {
+            Sbo(SboStorage(sbo)) => sbo,
+            _ => unreachable!(),
+        };
+
+        loop {
+            let mut readable = self.session_fd.readable().await?;
+
+            let mut large_buffers = self.large_buffers.lock().unwrap();
+            let large_buffer = large_buffers.last_mut().unwrap();
+
+            let mut io_vecs = [
+                IoVec::from_mut_slice(sbo),
+                IoVec::from_mut_slice(&mut large_buffer[SBO_SIZE..]),
+            ];
+
+            match readable.try_io(|fd| readv(*fd.get_ref(), &mut io_vecs).map_err(from_nix_error)) {
+                Ok(Ok(bytes)) => {
+                    if bytes > SBO_SIZE {
+                        (&mut large_buffer[..SBO_SIZE]).copy_from_slice(sbo);
+                        incoming.buffer.data = Spilled(large_buffers.pop().unwrap(), permit);
+                    }
+
+                    incoming.buffer.bytes = bytes;
+                    return Ok(incoming);
+                }
+
+                // Interrupted
+                Ok(Err(error)) if error.kind() == std::io::ErrorKind::NotFound => continue,
+
+                Ok(Err(error)) => return Err(error),
+                Err(_) => continue,
+            }
+        }
+    }
+
+    fn send(&self, unique: u64, error: i32, output: OutputChain<'_>) -> FuseResult<()> {
+        let length = std::mem::size_of::<proto::OutHeader>();
+        let length = length
+            + output
+                .iter()
+                .map(<[_]>::iter)
+                .flatten()
+                .copied()
+                .map(<[_]>::len)
+                .sum::<usize>();
+
+        let length = length.try_into().unwrap();
+        let header = proto::OutHeader {
+            len: length,
+            error,
+            unique,
+        };
+
+        //TODO: Full const generics any time now? Fs::EXPECTED_REQUEST_SEGMENTS
+        let header = [bytes_of(&header)];
+        let output = output.preceded(&header);
+        let buffers: SmallVec<[_; 8]> = output
+            .iter()
+            .map(<[_]>::iter)
+            .flatten()
+            .copied()
+            .filter(|slice| !slice.is_empty())
+            .map(IoVec::from_slice)
+            .collect();
+
+        let written = writev(*self.session_fd.get_ref(), &buffers).map_err(from_nix_error)?;
+        if written == length as usize {
+            Ok(())
+        } else {
+            Err(FuseError::ShortWrite)
+        }
+    }
+}
+
+impl Start {
+    pub async fn start<Fs: Fuse>(self, fs: Fs) -> FuseResult<Arc<Session<Fs>>> {
+        let session_fd = self.session_fd.into_raw_fd();
+
+        let flags = OFlag::O_NONBLOCK | OFlag::O_LARGEFILE;
+        fcntl(session_fd, FcntlArg::F_SETFL(flags)).unwrap();
+
+        let page_size = sysconf(SysconfVar::PAGE_SIZE).unwrap().unwrap() as usize;
+        let pages_per_buffer = fs.request_buffer_pages().get();
+        let bytes_per_buffer = pages_per_buffer.checked_mul(page_size).unwrap();
+        assert!(bytes_per_buffer >= proto::MIN_READ_SIZE);
+
+        let mut large_buffers = Vec::with_capacity(fs.request_buffers().get());
+        for _ in 0..large_buffers.capacity() {
+            large_buffers.push(vec![0; bytes_per_buffer].into_boxed_slice());
+        }
+
+        let (interrupt_tx, _) = broadcast::channel(INTERRUPT_BROADCAST_CAPACITY);
+        let mut session = Session {
+            _fusermount_fd: self.fusermount_fd,
+            session_fd: AsyncFd::with_interest(session_fd, tokio::io::Interest::READABLE)?,
+            proto_minor: 0, // Set by Session::do_handshake()
+            fs,
+            input_semaphore: Arc::new(Semaphore::new(large_buffers.len())),
+            large_buffers: Mutex::new(large_buffers),
+            known: Mutex::new(HashMap::new()),
+            destroy: Notify::new(),
+            interrupt_tx,
+        };
+
+        loop {
+            let state = session
+                .do_handshake(pages_per_buffer, bytes_per_buffer)
+                .await?;
+
+            if let Handshake::Done = state {
+                break Ok(Arc::new(session));
+            }
+        }
+    }
+}
+
+enum Handshake {
+    Done,
+    Restart,
+}
+
+struct Incoming<Fs: Fuse> {
+    session: Arc<Session<Fs>>,
+    buffer: InputBuffer,
+}
+
+struct InputBuffer {
+    pub bytes: usize,
+    pub data: InputBufferStorage,
+}
+
+enum InputBufferStorage {
+    Sbo(SboStorage),
+    Spilled(Box<[u8]>, OwnedSemaphorePermit),
+}
+
+#[repr(align(8))]
+struct SboStorage(pub [u8; 4 * std::mem::size_of::<InHeader>()]);
+
+const SBO_SIZE: usize = std::mem::size_of::<SboStorage>();
+const INTERRUPT_BROADCAST_CAPACITY: usize = 32;
+
+impl InputBuffer {
+    fn data(&self) -> &[u8] {
+        use InputBufferStorage::*;
+        let storage = match &self.data {
+            Sbo(sbo) => &sbo.0,
+            Spilled(buffer, _) => &buffer[..],
+        };
+
+        &storage[..self.bytes]
+    }
+}