RedBear-OS/netstack/src/scheme/netcfg/mod.rs

#[macro_use]
mod nodes;
mod notifier;

use redox_scheme::{
    scheme::{register_scheme_inner, SchemeState, SchemeSync},
    CallerCtx, OpenResult, RequestKind, SignalBehavior, Socket,
};
use scheme_utils::HandleMap;
use smoltcp::wire::{EthernetAddress, IpAddress, IpCidr, Ipv4Address, Ipv6Address};
use std::cell::{Cell, RefCell};
use std::collections::BTreeMap;
use std::mem;
use std::rc::Rc;
use std::str;
use std::str::FromStr;
use syscall;
use syscall::data::Stat;
use syscall::flag::{MODE_DIR, MODE_FILE};
use syscall::schemev2::NewFdFlags;
use syscall::{Error as SyscallError, EventFlags as SyscallEventFlags, Result as SyscallResult};

use crate::error::{Error, Result};
use crate::link::DeviceList;
use crate::observer::ObserverRef;
use crate::router::route_table::{RouteTable, Rule};

use self::nodes::*;
use self::notifier::*;
use super::{post_fevent, Interface, SocketSet};

const WRITE_BUFFER_MAX_SIZE: usize = 0xffff;

fn gateway_cidr() -> IpCidr {
    // TODO: const fn
    IpCidr::new(IpAddress::v4(0, 0, 0, 0), 0)
}

fn cidr_network(cidr: IpCidr) -> IpCidr {
    match cidr {
        IpCidr::Ipv4(c) => IpCidr::Ipv4(c.network()),
        IpCidr::Ipv6(c) => {
            let prefix = c.prefix_len();
            let bytes = c.address().octets();
            let mut masked = [0u8; 16];
            let full_bytes = (prefix / 8) as usize;
            let remainder = prefix % 8;
            for i in 0..full_bytes {
                masked[i] = bytes[i];
            }
            if remainder > 0 && full_bytes < 16 {
                masked[full_bytes] = bytes[full_bytes] & (0xff << (8 - remainder));
            }
            let segments: [u16; 8] = core::array::from_fn(|i| {
                u16::from_be_bytes([masked[i * 2], masked[i * 2 + 1]])
            });
            IpCidr::Ipv6(smoltcp::wire::Ipv6Cidr::new(
                Ipv6Address::new(
                    segments[0], segments[1], segments[2], segments[3],
                    segments[4], segments[5], segments[6], segments[7],
                ),
                prefix,
            ))
        }
    }
}

fn parse_route(value: &str, route_table: &RouteTable) -> SyscallResult<Rule> {
    let mut parts = value.split_whitespace();
    let cidr_str = parts.next().ok_or(SyscallError::new(syscall::EINVAL))?;
    let cidr = match cidr_str {
        "default" => gateway_cidr(),
        cidr_str => cidr_str
            .parse()
            .map_err(|_| SyscallError::new(syscall::EINVAL))?,
    };

    let via: IpAddress = match parts.next().ok_or(SyscallError::new(syscall::EINVAL))? {
        "via" => parts
            .next()
            .ok_or(SyscallError::new(syscall::EINVAL))?
            .parse()
            .map_err(|_| SyscallError::new(syscall::EINVAL))?,
        _ => return Err(SyscallError::new(syscall::EINVAL)),
    };

    if !via.is_unicast() {
        return Err(SyscallError::new(syscall::EINVAL));
    }

    let rule = route_table
        .lookup_rule(&via)
        .ok_or(SyscallError::new(syscall::EINVAL))?;

    Ok(Rule::new(cidr, Some(via), rule.dev.clone(), rule.src))
}

fn mk_root_node(
    iface: Interface,
    notifier: NotifierRef,
    dns_config: DNSConfigRef,
    route_table: Rc<RefCell<RouteTable>>,
    devices: Rc<RefCell<DeviceList>>,
    socket_set: Rc<RefCell<SocketSet>>,
    ip_forward: Rc<Cell<bool>>,
    observer: ObserverRef,
) -> CfgNodeRef {
    cfg_node! {
        "capture" => {
            "enable" => {
                wo [observer] (Option<()>, None)
                |_cur_value, _line| { Ok(()) }
                |_cur_value| {
                    observer.enable();
                    Ok(())
                }
            },
            "disable" => {
                wo [observer] (Option<()>, None)
                |_cur_value, _line| { Ok(()) }
                |_cur_value| {
                    observer.disable();
                    Ok(())
                }
            },
            "read" => {
                ro [observer] || {
                    if observer.is_enabled() {
                        observer.drain_hex()
                    } else {
                        "capture disabled (echo to /scheme/netcfg/capture/enable to start)\n".to_string()
                    }
                }
            },
            "filter" => {
                rw [observer] (Option<String>, None)
                || {
                    format!("{}\n", observer.filter_str())
                }
                |cur_value, line| {
                    let s = line.trim().to_string();
                    observer.set_filter(&s);
                    *cur_value = Some(s);
                    Ok(())
                }
                |_cur_value| { Ok(()) }
            },
            "count" => {
                ro [observer] || {
                    format!("captured={} buffered={} enabled={}\n",
                        observer.total(), observer.len(), observer.is_enabled())
                }
            },
        },
        "sockets" => {
            "list" => {
                ro [socket_set] || {
                    let set = socket_set.borrow();
                    format!("sockets: {}\n", set.iter().count())
                }
            }
        },
        "resolv" => {
            "nameserver" => {
                rw [dns_config, notifier] (Option<Ipv4Address>, None)
                || {
                    format!("{}\n", dns_config.borrow().name_server)
                }
                |cur_value, line| {
                    if cur_value.is_none() {
                        let ip = Ipv4Address::from_str(line.trim())
                            .map_err(|_| SyscallError::new(syscall::EINVAL))?;
                        if ip.is_broadcast() || ip.is_multicast() || ip.is_unspecified() {
                            return Err(SyscallError::new(syscall::EINVAL));
                        }
                        *cur_value = Some(ip);
                        Ok(())
                    } else {
                        Err(SyscallError::new(syscall::EINVAL))
                    }
                }
                |cur_value| {
                    if let Some(ip) = *cur_value {
                        dns_config.borrow_mut().name_server = ip;
                        notifier.borrow_mut().schedule_notify("resolv/nameserver");
                    }
                    Ok(())
                }
            },
            "nameserver6" => {
                rw [dns_config, notifier] (Option<Ipv6Address>, None)
                || {
                    match dns_config.borrow().name_server6 {
                        Some(ip) => format!("{}\n", ip),
                        None => "Not configured\n".into(),
                    }
                }
                |cur_value, line| {
                    if cur_value.is_none() {
                        let ip = Ipv6Address::from_str(line.trim())
                            .map_err(|_| SyscallError::new(syscall::EINVAL))?;
                        if ip.is_multicast() || ip.is_unspecified() {
                            return Err(SyscallError::new(syscall::EINVAL));
                        }
                        *cur_value = Some(ip);
                        Ok(())
                    } else {
                        Err(SyscallError::new(syscall::EINVAL))
                    }
                }
                |cur_value| {
                    if let Some(ip) = *cur_value {
                        dns_config.borrow_mut().name_server6 = Some(ip);
                        notifier.borrow_mut().schedule_notify("resolv/nameserver6");
                    }
                    Ok(())
                }
            }
        },
        "route" => {
            "list" => {
                ro [route_table] || {
                    format!("{}", route_table.borrow())
                }
            },
            "add" => {
                wo [iface, notifier, route_table] (Option<Rule>, None)
                |cur_value, line| {
                    if cur_value.is_none() {
                        let route = parse_route(line, &route_table.borrow())?;
                        *cur_value = Some(route);
                        Ok(())
                    } else {
                        Err(SyscallError::new(syscall::EINVAL))
                    }
                }
                |cur_value| {
                    if let Some(route) = cur_value.take() {
                        route_table.borrow_mut().insert_rule(route);
                        notifier.borrow_mut().schedule_notify("route/list");
                        Ok(())
                    } else {
                        Err(SyscallError::new(syscall::EINVAL))
                    }
                }
            },
            "rm" => {
                wo [iface, notifier, route_table] (Option<IpCidr>, None)
                |cur_value, line| {
                    if cur_value.is_none() {
                        match line.parse() {
                            Ok(cidr) => {
                                *cur_value = Some(cidr);
                                Ok(())
                            }
                            Err(_) => Err(SyscallError::new(syscall::EINVAL))
                        }
                    } else {
                        Err(SyscallError::new(syscall::EINVAL))
                    }
                }
                |cur_value| {
                    if let Some(cidr) = *cur_value {
                        route_table.borrow_mut().remove_rule(cidr);
                        notifier.borrow_mut().schedule_notify("route/list");
                        Ok(())
                    } else {
                        Err(SyscallError::new(syscall::EINVAL))
                    }
                }
            },
        },
        "sysctl" => {
            "net" => {
                "ipv4" => {
                    "ip_forward" => {
                        rw [ip_forward] (Option<bool>, None)
                        || {
                            let val: u8 = if ip_forward.get() { 1 } else { 0 };
                            format!("{}\n", val)
                        }
                        |cur_value, line| {
                            let val = line.trim().parse::<u8>()
                                .map_err(|_| SyscallError::new(syscall::EINVAL))?;
                            match val {
                                0 => { ip_forward.set(false); }
                                1 => { ip_forward.set(true); }
                                _ => return Err(SyscallError::new(syscall::EINVAL)),
                            }
                            *cur_value = Some(val == 1);
                            Ok(())
                        }
                        |_cur_value| {
                            Ok(())
                        }
                    }
                }
            }
        },
        "ifaces" => {
            "eth0" => {
                "mac" => {
                    rw [iface, notifier, devices] (Option<EthernetAddress>, None)
                    || {
                        match devices.borrow().get("eth0") {
                            Some(dev) => {
                                match dev.mac_address() {
                                    Some(addr) => format!("{addr}\n"),
                                    None => "Not configured\n".into(),
                                }
                            }
                            None => "Device not found\n".into(),
                        }
                    }
                    |cur_value, line| {
                        if cur_value.is_none() {
                            let mac = EthernetAddress::from_str(line).
                                map_err(|_| SyscallError::new(syscall::EINVAL))?;
                            if !mac.is_unicast() {
                                return Err(SyscallError::new(syscall::EINVAL));
                            }
                            *cur_value = Some(mac);
                            Ok(())
                        } else {
                            Err(SyscallError::new(syscall::EINVAL))
                        }
                    }
                    |cur_value| {
                        if let Some(mac) = *cur_value {
                            if let Some(dev) = devices.borrow_mut().get_mut("eth0") {
                                dev.set_mac_address(mac);
                                notifier.borrow_mut().schedule_notify("ifaces/eth0/mac");
                            }
                        }
                        Ok(())
                    }
                },
                "addr" => {
                    "list" => {
                        ro [devices]
                        || {
                            let res = match devices.borrow().get("eth0") {
                                Some(dev) => {
                                    match dev.ip_address() {
                                        Some(addr) => format!("{addr}\n"),
                                        None => "Not configured\n".into(),
                                    }
                                }
                                None => "Device not found\n".into(),
                            };
                            res
                        }
                    },
                    "set" => {
                        wo [iface, notifier, devices, route_table] (Option<IpCidr>, None)
                        |cur_value, line| {
                            if cur_value.is_none() {
                                let cidr = IpCidr::from_str(line)
                                    .map_err(|_| SyscallError::new(syscall::EINVAL))?;
                                if !cidr.address().is_unicast() {
                                    return Err(SyscallError::new(syscall::EINVAL));
                                }
                                *cur_value = Some(cidr);
                                Ok(())
                            } else {
                                Err(SyscallError::new(syscall::EINVAL))
                            }
                        }
                        |cur_value| {
                            // TODO: Multiple IPs
                            if let Some(cidr) = cur_value.take() {
                                if let Some(dev) = devices.borrow_mut().get_mut("eth0") {

                                    let mut route_table = route_table.borrow_mut();
                                    if let Some(old_addr) = dev.ip_address() {
                                        let old_network = cidr_network(old_addr);

                                        route_table.remove_rule(old_network);
                                        route_table.change_src(old_addr.address(), cidr.address());
                                        iface.borrow_mut().update_ip_addrs(|addrs| addrs.retain(|addr| *addr != old_addr))
                                    }

                                    dev.set_ip_address(cidr);
                                    // FIXME: Here, the insert 0 is a workaround to let UDP sockets
                                    // work with this interface only.
                                    // Smoltcp takes the first ip address when looking for a source
                                    // ip address when sending UDP packets.
                                    // This behavior will have to be fixed as it's our route table
                                    // job to find give this source.
                                    iface.borrow_mut().update_ip_addrs(|addrs| addrs.insert(0, cidr).unwrap());

                                    let network_cidr = cidr_network(cidr);
                                    route_table.insert_rule(Rule::new(network_cidr, None, dev.name().clone(), cidr.address()))
                                }
                                notifier.borrow_mut().schedule_notify("ifaces/eth0/addr/list");
                                notifier.borrow_mut().schedule_notify("route/list");
                            }
                            Ok(())
                        }
                    },
                },
                "arp" => {
                    "list" => {
                        ro [devices] || {
                            match devices.borrow().get("eth0") {
                                Some(dev) => dev.arp_table(),
                                None => "Device not found\n".into(),
                            }
                        }
                    },
                    "stats" => {
                        ro [devices] || {
                            match devices.borrow().get("eth0") {
                                Some(dev) => dev.arp_stats(),
                                None => "Device not found\n".into(),
                            }
                        }
                    },
                    "flush" => {
                        wo [devices] (Option<()>, None)
                        |_cur_value, _line| {
                            Ok(())
                        }
                        |cur_value| {
                            *cur_value = None;
                            if let Some(dev) = devices.borrow_mut().get_mut("eth0") {
                                dev.flush_arp();
                            }
                            Ok(())
                        }
                    },
                },
                "stats" => {
                    ro [devices] || {
                        match devices.borrow().get("eth0") {
                            Some(dev) => {
                                let s = dev.statistics();
                                format!("rx_bytes={} rx_packets={} tx_bytes={} tx_packets={} mtu={} link={}\n",
                                    s.rx_bytes, s.rx_packets, s.tx_bytes, s.tx_packets,
                                    dev.mtu(), dev.link_state())
                            }
                            None => "Device not found\n".into(),
                        }
                    }
                },
                "link" => {
                    ro [devices] || {
                        match devices.borrow().get("eth0") {
                            Some(dev) => format!("{}\n", dev.link_state()),
                            None => "Device not found\n".into(),
                        }
                    }
                },
                "mtu" => {
                    rw [devices] (Option<usize>, None)
                    || {
                        match devices.borrow().get("eth0") {
                            Some(dev) => format!("{}\n", dev.mtu()),
                            None => "Device not found\n".into(),
                        }
                    }
                    |cur_value, line| {
                        let mtu = line.trim().parse::<usize>()
                            .map_err(|_| SyscallError::new(syscall::EINVAL))?;
                        if let Some(dev) = devices.borrow_mut().get_mut("eth0") {
                            dev.set_mtu(mtu);
                            *cur_value = Some(mtu);
                            Ok(())
                        } else {
                            Err(SyscallError::new(syscall::ENODEV))
                        }
                    }
                    |_cur_value| { Ok(()) }
                },
                "qdisc" => {
                    ro [devices] || {
                        match devices.borrow().get("eth0") {
                            Some(dev) => dev.qdisc_info(),
                            None => "Device not found\n".into(),
                        }
                    }
                }
            },
            "lo" => {
                "addr" => {
                    "list" => {
                        ro [devices] || {
                            match devices.borrow().get("loopback") {
                                Some(dev) => match dev.ip_address() {
                                    Some(addr) => format!("{addr}\n"),
                                    None => "Not configured\n".into(),
                                },
                                None => "Device not found\n".into(),
                            }
                        }
                    }
                },
                "stats" => {
                    ro [devices] || {
                        match devices.borrow().get("loopback") {
                            Some(dev) => {
                                let s = dev.statistics();
                                format!("rx_bytes={} rx_packets={} tx_bytes={} tx_packets={} mtu={} link={}\n",
                                    s.rx_bytes, s.rx_packets, s.tx_bytes, s.tx_packets,
                                    dev.mtu(), dev.link_state())
                            }
                            None => "Device not found\n".into(),
                        }
                    }
                },
            }
        }
    }
}

struct DNSConfig {
    name_server: Ipv4Address,
    name_server6: Option<Ipv6Address>,
}

type DNSConfigRef = Rc<RefCell<DNSConfig>>;

struct NetCfgFile {
    path: String,
    is_dir: bool,
    is_writable: bool,
    is_readable: bool,
    node_writer: Option<Box<dyn NodeWriter>>,
    read_buf: Vec<u8>,
    write_buf: Vec<u8>,
    pos: usize,
    uid: u32,
    done: bool,
}

impl NetCfgFile {
    fn commit(&mut self) -> SyscallResult<()> {
        if let Some(ref mut node_writer) = self.node_writer {
            if !self.write_buf.is_empty() {
                let line = str::from_utf8(&self.write_buf)
                    .or_else(|_| Err(SyscallError::new(syscall::EINVAL)))?;
                node_writer.write_line(line)?;
            }
            node_writer.commit()?;
            self.write_buf.clear();
        }
        Ok(())
    }

    fn consume_lines(&mut self) -> SyscallResult<()> {
        if let Some(ref mut node_writer) = self.node_writer {
            let mut swap_with = None;
            {
                let mut lines = self.write_buf.split(|&c| c == b'\n');
                if let Some(mut cur_line) = lines.next() {
                    let mut consumed = false;
                    for next_line in lines {
                        let line = str::from_utf8(cur_line)
                            .or_else(|_| Err(SyscallError::new(syscall::EINVAL)))?;
                        trace!("writing line {}", line);
                        node_writer.write_line(line)?;
                        cur_line = next_line;
                        consumed = true;
                    }
                    if consumed {
                        swap_with = Some(From::from(cur_line))
                    }
                }
            }
            if let Some(ref mut new_vec) = swap_with {
                mem::swap(&mut self.write_buf, new_vec);
            }
            Ok(())
        } else {
            Err(SyscallError::new(syscall::EBADF))
        }
    }
}

pub struct NetCfgScheme {
    inner: NetCfgSchemeInner,
    state: SchemeState,
}

impl NetCfgScheme {
    pub fn new(
        iface: Interface,
        scheme_file: Socket,
        route_table: Rc<RefCell<RouteTable>>,
        devices: Rc<RefCell<DeviceList>>,
        socket_set: Rc<RefCell<SocketSet>>,
        ip_forward: Rc<Cell<bool>>,
        observer: ObserverRef,
    ) -> Result<NetCfgScheme> {
        let notifier = Notifier::new_ref();
        let dns_config = Rc::new(RefCell::new(DNSConfig {
            name_server: Ipv4Address::new(8, 8, 8, 8),
            name_server6: None,
        }));
        let mut inner = NetCfgSchemeInner {
            scheme_file,
            handles: HandleMap::new(),
            root_node: mk_root_node(
                iface,
                Rc::clone(&notifier),
                dns_config,
                route_table,
                devices,
                socket_set,
                ip_forward,
                observer,
            ),
            notifier,
        };
        let cap_id = inner
            .scheme_root()
            .map_err(|e| Error::from_syscall_error(e, "failed to get scheme root id"))?;
        register_scheme_inner(&inner.scheme_file, "netcfg", cap_id).map_err(|e| {
            Error::from_syscall_error(e, "failed to register netcfg scheme to namespace")
        })?;
        Ok(Self {
            inner,
            state: SchemeState::new(),
        })
    }

    pub fn on_scheme_event(&mut self) -> Result<Option<()>> {
        let result = loop {
            let request = match self.inner.scheme_file.next_request(SignalBehavior::Restart) {
                Ok(Some(req)) => req,
                Ok(None) => {
                    break Some(());
                }
                Err(error)
                    if error.errno == syscall::EWOULDBLOCK || error.errno == syscall::EAGAIN =>
                {
                    break None;
                }
                Err(other) => {
                    return Err(Error::from_syscall_error(
                        other,
                        "failed to receive new request",
                    ))
                }
            };

            match request.kind() {
                RequestKind::Call(c) => {
                    let resp = c.handle_sync(&mut self.inner, &mut self.state);
                    let _ = self
                        .inner
                        .scheme_file
                        .write_response(resp, SignalBehavior::Restart)
                        .map_err(|e| {
                            Error::from_syscall_error(e.into(), "failed to write response")
                        })?;
                }
                RequestKind::OnClose { id } => {
                    self.inner.on_close(id);
                }
                _ => {}
            }
        };
        self.inner.notify_scheduled_fds();
        Ok(result)
    }
}

enum Handle {
    SchemeRoot,
    File(NetCfgFile),
}

struct NetCfgSchemeInner {
    scheme_file: Socket,
    handles: HandleMap<Handle>,
    root_node: CfgNodeRef,
    notifier: NotifierRef,
}

impl NetCfgSchemeInner {
    fn notify_scheduled_fds(&mut self) {
        let fds_to_notify = self.notifier.borrow_mut().get_notified_fds();
        for fd in fds_to_notify {
            let _ = post_fevent(&self.scheme_file, fd, syscall::EVENT_READ.bits());
        }
    }
}

impl SchemeSync for NetCfgSchemeInner {
    fn scheme_root(&mut self) -> SyscallResult<usize> {
        Ok(self.handles.insert(Handle::SchemeRoot))
    }

    fn openat(
        &mut self,
        dirfd: usize,
        path: &str,
        _flags: usize,
        _fcntl_flags: u32,
        ctx: &CallerCtx,
    ) -> SyscallResult<OpenResult> {
        {
            let handle = self.handles.get(dirfd)?;

            if !matches!(handle, Handle::SchemeRoot) {
                return Err(SyscallError::new(syscall::EACCES));
            }
        }

        let mut current_node = Rc::clone(&self.root_node);
        for part in path.split('/') {
            if part.is_empty() {
                continue;
            }
            let next_node = current_node
                .borrow_mut()
                .open(part)
                .ok_or_else(|| SyscallError::new(syscall::EINVAL))?;
            current_node = next_node;
        }
        let current_node = current_node.borrow();
        let read_buf = Vec::from(current_node.read());
        let fd = self.handles.insert(Handle::File(NetCfgFile {
            path: path.to_owned(),
            is_dir: current_node.is_dir(),
            is_writable: current_node.is_writable(),
            is_readable: current_node.is_readable(),
            node_writer: if current_node.is_writable() {
                current_node.new_writer()
            } else {
                None
            },
            uid: ctx.uid,
            pos: 0,
            read_buf,
            write_buf: vec![],
            done: false,
        }));
        trace!("open {} {}", fd, path);
        Ok(OpenResult::ThisScheme {
            number: fd,
            flags: NewFdFlags::empty(),
        })
    }

    fn on_close(&mut self, fd: usize) {
        trace!("close {}", fd);
        if let Some(handle) = self.handles.remove(fd) {
            match handle {
                Handle::SchemeRoot => {
                    // SchemeRoot closed, nothing specific to clean up
                }
                Handle::File(mut file) => {
                    self.notifier.borrow_mut().unsubscribe(&file.path, fd);
                    if !file.done {
                        let _ = file.commit().map(|_| 0);
                    }
                }
            }
        }
    }

    fn write(
        &mut self,
        fd: usize,
        buf: &[u8],
        _offset: u64,
        _fcntl_flags: u32,
        _ctx: &CallerCtx,
    ) -> SyscallResult<usize> {
        let handle = self.handles.get_mut(fd)?;

        let file = match handle {
            Handle::File(file) => file,
            Handle::SchemeRoot => return Err(SyscallError::new(syscall::EBADF)),
        };

        if file.done {
            return Err(SyscallError::new(syscall::EBADF));
        }

        if file.uid != 0 {
            return Err(SyscallError::new(syscall::EACCES));
        }

        if (WRITE_BUFFER_MAX_SIZE - file.write_buf.len()) < buf.len() {
            return Err(SyscallError::new(syscall::EMSGSIZE));
        }

        file.write_buf.extend_from_slice(buf);

        if let Err(e) = file.consume_lines() {
            trace!("Failed write {} {}", fd, e);
            file.done = true;
            return Err(e);
        }

        Ok(buf.len())
    }

    fn read(
        &mut self,
        fd: usize,
        buf: &mut [u8],
        _offset: u64,
        _fcntl_flags: u32,
        _ctx: &CallerCtx,
    ) -> SyscallResult<usize> {
        let handle = self.handles.get_mut(fd)?;

        let file = match handle {
            Handle::File(file) => file,
            Handle::SchemeRoot => return Err(SyscallError::new(syscall::EBADF)),
        };

        let mut i = 0;
        while i < buf.len() && file.pos < file.read_buf.len() {
            buf[i] = file.read_buf[file.pos];
            i += 1;
            file.pos += 1;
        }
        Ok(i)
    }

    fn fstat(&mut self, fd: usize, stat: &mut Stat, _ctx: &CallerCtx) -> SyscallResult<()> {
        let handle = self.handles.get_mut(fd)?;

        match handle {
            Handle::SchemeRoot => return Err(SyscallError::new(syscall::EBADF)),
            Handle::File(file) => {
                stat.st_mode = if file.is_dir { MODE_DIR } else { MODE_FILE };
                if file.is_writable {
                    stat.st_mode |= 0o222;
                }
                if file.is_readable {
                    stat.st_mode |= 0o444;
                }
                stat.st_uid = 0;
                stat.st_gid = 0;
                stat.st_size = file.read_buf.len() as u64;
            }
        }

        Ok(())
    }

    fn fevent(
        &mut self,
        fd: usize,
        events: SyscallEventFlags,
        _ctx: &CallerCtx,
    ) -> SyscallResult<SyscallEventFlags> {
        let handle = self.handles.get_mut(fd)?;

        match handle {
            Handle::SchemeRoot => return Err(SyscallError::new(syscall::EBADF)),
            Handle::File(file) => {
                if events.contains(syscall::EVENT_READ) {
                    self.notifier.borrow_mut().subscribe(&file.path, fd);
                } else {
                    self.notifier.borrow_mut().unsubscribe(&file.path, fd);
                }
            }
        }
        Ok(SyscallEventFlags::empty())
    }

    fn fsync(&mut self, fd: usize, _ctx: &CallerCtx) -> SyscallResult<()> {
        let handle = self.handles.get_mut(fd)?;

        let file = match handle {
            Handle::File(file) => file,
            Handle::SchemeRoot => return Err(SyscallError::new(syscall::EBADF)),
        };

        if !file.done {
            let res = file.commit();
            file.done = true;
            res
        } else {
            Err(SyscallError::new(syscall::EBADF))
        }
    }
}