krata: reorganize crates

crates/xen/xenstore/Cargo.toml

@@ -0,0 +1,27 @@
+[package]
+name = "xenstore"
+version.workspace = true
+edition = "2021"
+resolver = "2"
+
+[dependencies]
+async-trait = { workspace = true }
+byteorder = { workspace = true }
+libc = { workspace = true }
+log = { workspace = true }
+thiserror = { workspace = true }
+tokio = { workspace = true }
+
+[lib]
+name = "xenstore"
+
+[dev-dependencies]
+env_logger = { workspace = true }
+
+[[example]]
+name = "xenstore-ls"
+path = "examples/list.rs"
+
+[[example]]
+name = "xenstore-watch"
+path = "examples/watch.rs"

crates/xen/xenstore/examples/list.rs

@@ -0,0 +1,35 @@
+use std::env::args;
+
+use xenstore::client::{XsdClient, XsdInterface};
+use xenstore::error::Result;
+
+async fn list_recursive(client: &XsdClient, path: &str) -> Result<()> {
+    let mut pending = vec![path.to_string()];
+
+    while let Some(ref path) = pending.pop() {
+        let children = client.list(path).await?;
+        for child in children {
+            let full = format!("{}/{}", if path == "/" { "" } else { path }, child);
+            let value = client
+                .read_string(full.as_str())
+                .await?
+                .expect("expected value");
+            println!("{} = {:?}", full, value,);
+            pending.push(full);
+        }
+    }
+    Ok(())
+}
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    env_logger::Builder::from_env(env_logger::Env::default().default_filter_or("warn")).init();
+    let client = XsdClient::open().await?;
+    loop {
+        list_recursive(&client, "/").await?;
+        if args().nth(1).unwrap_or("none".to_string()) != "stress" {
+            break;
+        }
+    }
+    Ok(())
+}

crates/xen/xenstore/examples/watch.rs

@@ -0,0 +1,23 @@
+use std::env::args;
+use xenstore::client::XsdClient;
+use xenstore::error::Result;
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    env_logger::Builder::from_env(env_logger::Env::default().default_filter_or("warn")).init();
+    let path = args().nth(1).unwrap_or("/local/domain".to_string());
+    let client = XsdClient::open().await?;
+    let mut handle = client.watch(&path).await?;
+    let mut count = 0;
+    loop {
+        let Some(event) = handle.receiver.recv().await else {
+            break;
+        };
+        println!("{}", event);
+        count += 1;
+        if count >= 3 {
+            break;
+        }
+    }
+    Ok(())
+}

crates/xen/xenstore/src/bus.rs

@@ -0,0 +1,358 @@
+use std::{collections::HashMap, ffi::CString, io::ErrorKind, sync::Arc, time::Duration};
+
+use libc::O_NONBLOCK;
+use log::warn;
+use tokio::{
+    fs::{metadata, File},
+    io::{unix::AsyncFd, AsyncReadExt, AsyncWriteExt},
+    select,
+    sync::{
+        mpsc::{channel, Receiver, Sender},
+        oneshot::{self, channel as oneshot_channel},
+        Mutex,
+    },
+    task::JoinHandle,
+    time::timeout,
+};
+
+use crate::{
+    error::{Error, Result},
+    sys::{XsdMessageHeader, XSD_ERROR, XSD_UNWATCH, XSD_WATCH_EVENT},
+};
+
+const XEN_BUS_PATHS: &[&str] = &["/dev/xen/xenbus"];
+const XEN_BUS_MAX_PAYLOAD_SIZE: usize = 4096;
+const XEN_BUS_MAX_PACKET_SIZE: usize = XsdMessageHeader::SIZE + XEN_BUS_MAX_PAYLOAD_SIZE;
+
+async fn find_bus_path() -> Option<&'static str> {
+    for path in XEN_BUS_PATHS {
+        match metadata(path).await {
+            Ok(_) => return Some(path),
+            Err(_) => continue,
+        }
+    }
+    None
+}
+
+struct WatchState {
+    sender: Sender<String>,
+}
+
+struct ReplyState {
+    sender: oneshot::Sender<XsdMessage>,
+}
+
+type ReplyMap = Arc<Mutex<HashMap<u32, ReplyState>>>;
+type WatchMap = Arc<Mutex<HashMap<u32, WatchState>>>;
+
+#[derive(Clone)]
+pub struct XsdSocket {
+    tx_sender: Sender<XsdMessage>,
+    replies: ReplyMap,
+    watches: WatchMap,
+    next_request_id: Arc<Mutex<u32>>,
+    next_watch_id: Arc<Mutex<u32>>,
+    processor_task: Arc<JoinHandle<()>>,
+    rx_task: Arc<JoinHandle<()>>,
+    unwatch_sender: Sender<u32>,
+}
+
+impl XsdSocket {
+    pub async fn open() -> Result<XsdSocket> {
+        let path = match find_bus_path().await {
+            Some(path) => path,
+            None => return Err(Error::BusNotFound),
+        };
+
+        let file = File::options()
+            .read(true)
+            .write(true)
+            .custom_flags(O_NONBLOCK)
+            .open(path)
+            .await?;
+        XsdSocket::from_handle(file).await
+    }
+
+    pub async fn from_handle(handle: File) -> Result<XsdSocket> {
+        let replies: ReplyMap = Arc::new(Mutex::new(HashMap::new()));
+        let watches: WatchMap = Arc::new(Mutex::new(HashMap::new()));
+
+        let next_request_id = Arc::new(Mutex::new(0u32));
+
+        let (rx_sender, rx_receiver) = channel::<XsdMessage>(10);
+        let (tx_sender, tx_receiver) = channel::<XsdMessage>(10);
+        let (unwatch_sender, unwatch_receiver) = channel::<u32>(1000);
+        let read: File = handle.try_clone().await?;
+
+        let mut processor = XsdSocketProcessor {
+            handle,
+            replies: replies.clone(),
+            watches: watches.clone(),
+            next_request_id: next_request_id.clone(),
+            tx_receiver,
+            rx_receiver,
+            unwatch_receiver,
+        };
+
+        let processor_task = tokio::task::spawn(async move {
+            if let Err(error) = processor.process().await {
+                warn!("failed to process xen store messages: {}", error);
+            }
+        });
+
+        let rx_task = tokio::task::spawn(async move {
+            if let Err(error) = XsdSocketProcessor::process_rx(read, rx_sender).await {
+                warn!("failed to process xen store responses: {}", error);
+            }
+        });
+
+        Ok(XsdSocket {
+            tx_sender,
+            replies,
+            watches,
+            next_request_id,
+            next_watch_id: Arc::new(Mutex::new(0u32)),
+            processor_task: Arc::new(processor_task),
+            rx_task: Arc::new(rx_task),
+            unwatch_sender,
+        })
+    }
+
+    pub async fn send_buf(&self, tx: u32, typ: u32, payload: &[u8]) -> Result<XsdMessage> {
+        let req = {
+            let mut guard = self.next_request_id.lock().await;
+            let req = *guard;
+            *guard = req + 1;
+            req
+        };
+        let (sender, receiver) = oneshot_channel::<XsdMessage>();
+        self.replies.lock().await.insert(req, ReplyState { sender });
+
+        let header = XsdMessageHeader {
+            typ,
+            req,
+            tx,
+            len: payload.len() as u32,
+        };
+        let message = XsdMessage {
+            header,
+            payload: payload.to_vec(),
+        };
+        if let Err(error) = self.tx_sender.try_send(message) {
+            return Err(error.into());
+        }
+        let reply = receiver.await?;
+        if reply.header.typ == XSD_ERROR {
+            let error = CString::from_vec_with_nul(reply.payload)?;
+            return Err(Error::ResponseError(error.into_string()?));
+        }
+        Ok(reply)
+    }
+
+    pub async fn send(&self, tx: u32, typ: u32, payload: &[&str]) -> Result<XsdMessage> {
+        let mut buf: Vec<u8> = Vec::new();
+        for item in payload {
+            buf.extend_from_slice(item.as_bytes());
+            buf.push(0);
+        }
+        self.send_buf(tx, typ, &buf).await
+    }
+
+    pub async fn add_watch(&self) -> Result<(u32, Receiver<String>, Sender<u32>)> {
+        let id = {
+            let mut guard = self.next_watch_id.lock().await;
+            let req = *guard;
+            *guard = req + 1;
+            req
+        };
+        let (sender, receiver) = channel(10);
+        self.watches.lock().await.insert(id, WatchState { sender });
+        Ok((id, receiver, self.unwatch_sender.clone()))
+    }
+}
+
+struct XsdSocketProcessor {
+    handle: File,
+    replies: ReplyMap,
+    watches: WatchMap,
+    next_request_id: Arc<Mutex<u32>>,
+    tx_receiver: Receiver<XsdMessage>,
+    rx_receiver: Receiver<XsdMessage>,
+    unwatch_receiver: Receiver<u32>,
+}
+
+impl XsdSocketProcessor {
+    async fn process_rx(read: File, rx_sender: Sender<XsdMessage>) -> Result<()> {
+        let mut buffer: Vec<u8> = vec![0u8; XEN_BUS_MAX_PACKET_SIZE];
+        let mut fd = AsyncFd::new(read)?;
+        loop {
+            select! {
+                x = fd.readable_mut() => match x {
+                    Ok(mut guard) => {
+                        let future = XsdSocketProcessor::read_message(&mut buffer, guard.get_inner_mut());
+                        if let Ok(message) = timeout(Duration::from_secs(1), future).await {
+                            rx_sender.send(message?).await?;
+                        }
+                    },
+
+                    Err(error) => {
+                        return Err(error.into());
+                    }
+                },
+
+                _ = rx_sender.closed() => {
+                    break;
+                }
+            };
+        }
+        Ok(())
+    }
+
+    async fn read_message(buffer: &mut [u8], read: &mut File) -> Result<XsdMessage> {
+        let size = loop {
+            match read.read(buffer).await {
+                Ok(size) => break size,
+                Err(error) => {
+                    if error.kind() == ErrorKind::WouldBlock {
+                        tokio::task::yield_now().await;
+                        continue;
+                    }
+                    return Err(error.into());
+                }
+            };
+        };
+
+        if size < XsdMessageHeader::SIZE {
+            return Err(Error::InvalidBusData);
+        }
+
+        let header = XsdMessageHeader::decode(&buffer[0..XsdMessageHeader::SIZE])?;
+        if size < XsdMessageHeader::SIZE + header.len as usize {
+            return Err(Error::InvalidBusData);
+        }
+        let payload =
+            &mut buffer[XsdMessageHeader::SIZE..XsdMessageHeader::SIZE + header.len as usize];
+        Ok(XsdMessage {
+            header,
+            payload: payload.to_vec(),
+        })
+    }
+
+    async fn process(&mut self) -> Result<()> {
+        loop {
+            select! {
+                x = self.tx_receiver.recv() => match x {
+                    Some(message) => {
+                        let mut composed: Vec<u8> = Vec::new();
+                        message.header.encode_to(&mut composed)?;
+                        composed.extend_from_slice(&message.payload);
+                        self.handle.write_all(&composed).await?;
+                    }
+
+                    None => {
+                        break;
+                    }
+                },
+
+                x = self.rx_receiver.recv() => match x {
+                    Some(message) => {
+                        if message.header.typ == XSD_WATCH_EVENT && message.header.req == 0 && message.header.tx == 0 {
+                            let strings = message.parse_string_vec()?;
+                            let Some(path) = strings.first() else {
+                                return Ok(());
+                            };
+                            let Some(token) = strings.get(1) else {
+                                return Ok(());
+                            };
+
+                            let Ok(id) = token.parse::<u32>() else {
+                                return Ok(());
+                            };
+
+                            if let Some(state) = self.watches.lock().await.get(&id) {
+                                let _ = state.sender.try_send(path.clone());
+                            }
+                        } else if let Some(state) = self.replies.lock().await.remove(&message.header.req) {
+                            let _ = state.sender.send(message);
+                        }
+                    }
+
+                    None => {
+                        break;
+                    }
+                },
+
+                x = self.unwatch_receiver.recv() => match x {
+                    Some(id) => {
+                        let req = {
+                            let mut guard = self.next_request_id.lock().await;
+                            let req = *guard;
+                            *guard = req + 1;
+                            req
+                        };
+
+                        let mut payload = id.to_string().as_bytes().to_vec();
+                        payload.push(0);
+                        let header = XsdMessageHeader {
+                            typ: XSD_UNWATCH,
+                            req,
+                            tx: 0,
+                            len: payload.len() as u32,
+                        };
+                        let mut data = header.encode()?;
+                        data.extend_from_slice(&payload);
+                        self.handle.write_all(&data).await?;
+                    },
+
+                    None => {
+                        break;
+                    }
+                }
+            };
+        }
+        Ok(())
+    }
+}
+
+#[derive(Debug)]
+pub struct XsdMessage {
+    pub header: XsdMessageHeader,
+    pub payload: Vec<u8>,
+}
+
+impl XsdMessage {
+    pub fn parse_string(&self) -> Result<String> {
+        Ok(CString::from_vec_with_nul(self.payload.clone())?.into_string()?)
+    }
+
+    pub fn parse_string_vec(&self) -> Result<Vec<String>> {
+        let mut strings: Vec<String> = Vec::new();
+        let mut buffer: Vec<u8> = Vec::new();
+        for b in &self.payload {
+            if *b == 0 {
+                let string = String::from_utf8(buffer.clone())?;
+                strings.push(string);
+                buffer.clear();
+                continue;
+            }
+            buffer.push(*b);
+        }
+        Ok(strings)
+    }
+
+    pub fn parse_bool(&self) -> Result<bool> {
+        Ok(true)
+    }
+}
+
+impl Drop for XsdSocket {
+    fn drop(&mut self) {
+        if Arc::strong_count(&self.rx_task) <= 1 {
+            self.rx_task.abort();
+        }
+
+        if Arc::strong_count(&self.processor_task) <= 1 {
+            self.processor_task.abort();
+        }
+    }
+}

crates/xen/xenstore/src/client.rs

@@ -0,0 +1,302 @@
+use crate::bus::XsdSocket;
+use crate::error::{Error, Result};
+use crate::sys::{
+    XSD_DIRECTORY, XSD_GET_DOMAIN_PATH, XSD_INTRODUCE, XSD_MKDIR, XSD_READ, XSD_RM, XSD_SET_PERMS,
+    XSD_TRANSACTION_END, XSD_TRANSACTION_START, XSD_WATCH, XSD_WRITE,
+};
+use log::trace;
+use std::ffi::CString;
+use tokio::sync::mpsc::Receiver;
+use tokio::sync::mpsc::Sender;
+
+pub const XS_PERM_NONE: u32 = 0x00;
+pub const XS_PERM_READ: u32 = 0x01;
+pub const XS_PERM_WRITE: u32 = 0x02;
+pub const XS_PERM_READ_WRITE: u32 = XS_PERM_READ | XS_PERM_WRITE;
+
+#[derive(Debug, Copy, Clone)]
+pub struct XsPermission {
+    pub id: u32,
+    pub perms: u32,
+}
+
+#[derive(Clone)]
+pub struct XsdClient {
+    pub socket: XsdSocket,
+}
+
+impl XsPermission {
+    pub fn encode(&self) -> Result<String> {
+        let c = match self.perms {
+            XS_PERM_READ_WRITE => 'b',
+            XS_PERM_WRITE => 'w',
+            XS_PERM_READ => 'r',
+            XS_PERM_NONE => 'n',
+            _ => return Err(Error::InvalidPermissions),
+        };
+        Ok(format!("{}{}", c, self.id))
+    }
+}
+
+pub struct XsdWatchHandle {
+    id: u32,
+    unwatch_sender: Sender<u32>,
+    pub receiver: Receiver<String>,
+}
+
+impl Drop for XsdWatchHandle {
+    fn drop(&mut self) {
+        let _ = self.unwatch_sender.try_send(self.id);
+    }
+}
+
+#[allow(async_fn_in_trait)]
+pub trait XsdInterface {
+    async fn list(&self, path: &str) -> Result<Vec<String>>;
+    async fn read(&self, path: &str) -> Result<Option<Vec<u8>>>;
+    async fn read_string(&self, path: &str) -> Result<Option<String>>;
+    async fn write(&self, path: &str, data: Vec<u8>) -> Result<bool>;
+    async fn write_string(&self, path: &str, data: &str) -> Result<bool>;
+    async fn mkdir(&self, path: &str) -> Result<bool>;
+    async fn rm(&self, path: &str) -> Result<bool>;
+    async fn set_perms(&self, path: &str, perms: &[XsPermission]) -> Result<bool>;
+
+    async fn mknod(&self, path: &str, perms: &[XsPermission]) -> Result<bool> {
+        let result1 = self.write_string(path, "").await?;
+        let result2 = self.set_perms(path, perms).await?;
+        Ok(result1 && result2)
+    }
+}
+
+impl XsdClient {
+    pub async fn open() -> Result<XsdClient> {
+        let socket = XsdSocket::open().await?;
+        Ok(XsdClient { socket })
+    }
+
+    async fn list(&self, tx: u32, path: &str) -> Result<Vec<String>> {
+        trace!("list tx={tx} path={path}");
+        let response = match self.socket.send(tx, XSD_DIRECTORY, &[path]).await {
+            Ok(response) => response,
+            Err(error) => {
+                if error.is_noent_response() {
+                    return Ok(vec![]);
+                }
+                return Err(error);
+            }
+        };
+        response.parse_string_vec()
+    }
+
+    async fn read(&self, tx: u32, path: &str) -> Result<Option<Vec<u8>>> {
+        trace!("read tx={tx} path={path}");
+        match self.socket.send(tx, XSD_READ, &[path]).await {
+            Ok(response) => Ok(Some(response.payload)),
+            Err(error) => {
+                if error.is_noent_response() {
+                    Ok(None)
+                } else {
+                    Err(error)
+                }
+            }
+        }
+    }
+
+    async fn write(&self, tx: u32, path: &str, data: Vec<u8>) -> Result<bool> {
+        trace!("write tx={tx} path={path} data={:?}", data);
+        let mut buffer = Vec::new();
+        let path = CString::new(path)?;
+        buffer.extend_from_slice(path.as_bytes_with_nul());
+        buffer.extend_from_slice(data.as_slice());
+        let response = self
+            .socket
+            .send_buf(tx, XSD_WRITE, buffer.as_slice())
+            .await?;
+        response.parse_bool()
+    }
+
+    async fn mkdir(&self, tx: u32, path: &str) -> Result<bool> {
+        trace!("mkdir tx={tx} path={path}");
+        self.socket.send(tx, XSD_MKDIR, &[path]).await?.parse_bool()
+    }
+
+    async fn rm(&self, tx: u32, path: &str) -> Result<bool> {
+        trace!("rm tx={tx} path={path}");
+        let result = self.socket.send(tx, XSD_RM, &[path]).await;
+        if let Err(error) = result {
+            if error.is_noent_response() {
+                return Ok(true);
+            }
+            return Err(error);
+        }
+        result.unwrap().parse_bool()
+    }
+
+    async fn set_perms(&self, tx: u32, path: &str, perms: &[XsPermission]) -> Result<bool> {
+        trace!("set_perms tx={tx} path={path} perms={:?}", perms);
+        let mut items: Vec<String> = Vec::new();
+        items.push(path.to_string());
+        for perm in perms {
+            items.push(perm.encode()?);
+        }
+        let items_str: Vec<&str> = items.iter().map(|x| x.as_str()).collect();
+        let response = self.socket.send(tx, XSD_SET_PERMS, &items_str).await?;
+        response.parse_bool()
+    }
+
+    pub async fn transaction(&self) -> Result<XsdTransaction> {
+        trace!("transaction start");
+        let response = self.socket.send(0, XSD_TRANSACTION_START, &[""]).await?;
+        let str = response.parse_string()?;
+        let tx = str.parse::<u32>()?;
+        Ok(XsdTransaction {
+            client: self.clone(),
+            tx,
+        })
+    }
+
+    pub async fn get_domain_path(&mut self, domid: u32) -> Result<String> {
+        let response = self
+            .socket
+            .send(0, XSD_GET_DOMAIN_PATH, &[&domid.to_string()])
+            .await?;
+        response.parse_string()
+    }
+
+    pub async fn introduce_domain(&mut self, domid: u32, mfn: u64, evtchn: u32) -> Result<bool> {
+        trace!("introduce domain domid={domid} mfn={mfn} evtchn={evtchn}");
+        let response = self
+            .socket
+            .send(
+                0,
+                XSD_INTRODUCE,
+                &[
+                    domid.to_string().as_str(),
+                    mfn.to_string().as_str(),
+                    evtchn.to_string().as_str(),
+                ],
+            )
+            .await?;
+        response.parse_bool()
+    }
+
+    pub async fn watch(&self, path: &str) -> Result<XsdWatchHandle> {
+        let (id, receiver, unwatch_sender) = self.socket.add_watch().await?;
+        let id_string = id.to_string();
+        let _ = self.socket.send(0, XSD_WATCH, &[path, &id_string]).await?;
+        Ok(XsdWatchHandle {
+            id,
+            receiver,
+            unwatch_sender,
+        })
+    }
+}
+
+#[derive(Clone)]
+pub struct XsdTransaction {
+    client: XsdClient,
+    tx: u32,
+}
+
+impl XsdInterface for XsdClient {
+    async fn list(&self, path: &str) -> Result<Vec<String>> {
+        self.list(0, path).await
+    }
+
+    async fn read(&self, path: &str) -> Result<Option<Vec<u8>>> {
+        self.read(0, path).await
+    }
+
+    async fn read_string(&self, path: &str) -> Result<Option<String>> {
+        match self.read(0, path).await {
+            Ok(value) => match value {
+                Some(value) => Ok(Some(String::from_utf8(value)?)),
+                None => Ok(None),
+            },
+            Err(error) => Err(error),
+        }
+    }
+
+    async fn write(&self, path: &str, data: Vec<u8>) -> Result<bool> {
+        self.write(0, path, data).await
+    }
+
+    async fn write_string(&self, path: &str, data: &str) -> Result<bool> {
+        self.write(0, path, data.as_bytes().to_vec()).await
+    }
+
+    async fn mkdir(&self, path: &str) -> Result<bool> {
+        self.mkdir(0, path).await
+    }
+
+    async fn rm(&self, path: &str) -> Result<bool> {
+        self.rm(0, path).await
+    }
+
+    async fn set_perms(&self, path: &str, perms: &[XsPermission]) -> Result<bool> {
+        self.set_perms(0, path, perms).await
+    }
+}
+
+impl XsdInterface for XsdTransaction {
+    async fn list(&self, path: &str) -> Result<Vec<String>> {
+        self.client.list(self.tx, path).await
+    }
+
+    async fn read(&self, path: &str) -> Result<Option<Vec<u8>>> {
+        self.client.read(self.tx, path).await
+    }
+
+    async fn read_string(&self, path: &str) -> Result<Option<String>> {
+        match self.client.read(self.tx, path).await {
+            Ok(value) => match value {
+                Some(value) => Ok(Some(String::from_utf8(value)?)),
+                None => Ok(None),
+            },
+            Err(error) => Err(error),
+        }
+    }
+
+    async fn write(&self, path: &str, data: Vec<u8>) -> Result<bool> {
+        self.client.write(self.tx, path, data).await
+    }
+
+    async fn write_string(&self, path: &str, data: &str) -> Result<bool> {
+        self.client
+            .write(self.tx, path, data.as_bytes().to_vec())
+            .await
+    }
+
+    async fn mkdir(&self, path: &str) -> Result<bool> {
+        self.client.mkdir(self.tx, path).await
+    }
+
+    async fn rm(&self, path: &str) -> Result<bool> {
+        self.client.rm(self.tx, path).await
+    }
+
+    async fn set_perms(&self, path: &str, perms: &[XsPermission]) -> Result<bool> {
+        self.client.set_perms(self.tx, path, perms).await
+    }
+}
+
+impl XsdTransaction {
+    pub async fn end(&self, abort: bool) -> Result<bool> {
+        let abort_str = if abort { "F" } else { "T" };
+
+        trace!("transaction end abort={}", abort);
+        self.client
+            .socket
+            .send(self.tx, XSD_TRANSACTION_END, &[abort_str])
+            .await?
+            .parse_bool()
+    }
+
+    pub async fn commit(&self) -> Result<bool> {
+        self.end(false).await
+    }
+
+    pub async fn abort(&self) -> Result<bool> {
+        self.end(true).await
+    }
+}

crates/xen/xenstore/src/error.rs

@@ -0,0 +1,53 @@
+use std::ffi::{FromVecWithNulError, IntoStringError, NulError};
+use std::io;
+use std::num::ParseIntError;
+use std::str::Utf8Error;
+use std::string::FromUtf8Error;
+
+use tokio::sync::mpsc::error::{SendError, TrySendError};
+use tokio::sync::oneshot::error::RecvError;
+
+use crate::bus::XsdMessage;
+
+#[derive(thiserror::Error, Debug)]
+pub enum Error {
+    #[error("io issue encountered: {0}")]
+    Io(#[from] io::Error),
+    #[error("invalid data received on bus")]
+    InvalidBusData,
+    #[error("utf8 string decode failed: {0}")]
+    Utf8DecodeString(#[from] FromUtf8Error),
+    #[error("utf8 str decode failed: {0}")]
+    Utf8DecodeStr(#[from] Utf8Error),
+    #[error("unable to decode cstring as utf8: {0}")]
+    Utf8DecodeCstring(#[from] IntoStringError),
+    #[error("nul byte found in string: {0}")]
+    NulByteFoundString(#[from] NulError),
+    #[error("unable to find nul byte in vec: {0}")]
+    VecNulByteNotFound(#[from] FromVecWithNulError),
+    #[error("unable to parse integer: {0}")]
+    ParseInt(#[from] ParseIntError),
+    #[error("bus was not found on any available path")]
+    BusNotFound,
+    #[error("store responded with error: `{0}`")]
+    ResponseError(String),
+    #[error("invalid permissions provided")]
+    InvalidPermissions,
+    #[error("failed to receive reply: {0}")]
+    ReceiverError(#[from] RecvError),
+    #[error("failed to send request: {0}")]
+    SendError(#[from] SendError<XsdMessage>),
+    #[error("failed to send request: {0}")]
+    TrySendError(#[from] TrySendError<XsdMessage>),
+}
+
+impl Error {
+    pub fn is_noent_response(&self) -> bool {
+        match self {
+            Error::ResponseError(message) => message == "ENOENT",
+            _ => false,
+        }
+    }
+}
+
+pub type Result<T> = std::result::Result<T, Error>;

crates/xen/xenstore/src/lib.rs

@@ -0,0 +1,4 @@
+pub mod bus;
+pub mod client;
+pub mod error;
+pub mod sys;

crates/xen/xenstore/src/sys.rs

@@ -0,0 +1,171 @@
+/// Handwritten protocol definitions for XenStore.
+/// Used xen/include/public/io/xs_wire.h as a reference.
+use libc;
+
+use crate::error::Result;
+use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
+use std::io::Cursor;
+
+#[derive(Copy, Clone, Debug)]
+pub struct XsdMessageHeader {
+    pub typ: u32,
+    pub req: u32,
+    pub tx: u32,
+    pub len: u32,
+}
+
+impl XsdMessageHeader {
+    pub const SIZE: usize = 16;
+
+    pub fn decode(bytes: &[u8]) -> Result<XsdMessageHeader> {
+        let mut cursor = Cursor::new(bytes);
+        Ok(XsdMessageHeader {
+            typ: cursor.read_u32::<LittleEndian>()?,
+            req: cursor.read_u32::<LittleEndian>()?,
+            tx: cursor.read_u32::<LittleEndian>()?,
+            len: cursor.read_u32::<LittleEndian>()?,
+        })
+    }
+
+    pub fn encode_to(&self, buffer: &mut Vec<u8>) -> Result<()> {
+        buffer.write_u32::<LittleEndian>(self.typ)?;
+        buffer.write_u32::<LittleEndian>(self.req)?;
+        buffer.write_u32::<LittleEndian>(self.tx)?;
+        buffer.write_u32::<LittleEndian>(self.len)?;
+        Ok(())
+    }
+
+    pub fn encode(&self) -> Result<Vec<u8>> {
+        let mut buffer = Vec::with_capacity(XsdMessageHeader::SIZE);
+        self.encode_to(&mut buffer)?;
+        Ok(buffer)
+    }
+}
+
+pub const XSD_CONTROL: u32 = 0;
+pub const XSD_DIRECTORY: u32 = 1;
+pub const XSD_READ: u32 = 2;
+pub const XSD_GET_PERMS: u32 = 3;
+pub const XSD_WATCH: u32 = 4;
+pub const XSD_UNWATCH: u32 = 5;
+pub const XSD_TRANSACTION_START: u32 = 6;
+pub const XSD_TRANSACTION_END: u32 = 7;
+pub const XSD_INTRODUCE: u32 = 8;
+pub const XSD_RELEASE: u32 = 9;
+pub const XSD_GET_DOMAIN_PATH: u32 = 10;
+pub const XSD_WRITE: u32 = 11;
+pub const XSD_MKDIR: u32 = 12;
+pub const XSD_RM: u32 = 13;
+pub const XSD_SET_PERMS: u32 = 14;
+pub const XSD_WATCH_EVENT: u32 = 15;
+pub const XSD_ERROR: u32 = 16;
+pub const XSD_IS_DOMAIN_INTRODUCED: u32 = 17;
+pub const XSD_RESUME: u32 = 18;
+pub const XSD_SET_TARGET: u32 = 19;
+pub const XSD_RESET_WATCHES: u32 = XSD_SET_TARGET + 2;
+pub const XSD_DIRECTORY_PART: u32 = 20;
+pub const XSD_TYPE_COUNT: u32 = 21;
+pub const XSD_INVALID: u32 = 0xffff;
+
+pub const XSD_WRITE_NONE: &str = "NONE";
+pub const XSD_WRITE_CREATE: &str = "CREATE";
+pub const XSD_WRITE_CREATE_EXCL: &str = "CREATE|EXCL";
+
+#[repr(C)]
+pub struct XsdError<'a> {
+    pub num: i32,
+    pub error: &'a str,
+}
+
+pub const XSD_ERROR_EINVAL: XsdError = XsdError {
+    num: libc::EINVAL,
+    error: "EINVAL",
+};
+pub const XSD_ERROR_EACCES: XsdError = XsdError {
+    num: libc::EACCES,
+    error: "EACCES",
+};
+pub const XSD_ERROR_EEXIST: XsdError = XsdError {
+    num: libc::EEXIST,
+    error: "EEXIST",
+};
+pub const XSD_ERROR_EISDIR: XsdError = XsdError {
+    num: libc::EISDIR,
+    error: "EISDIR",
+};
+pub const XSD_ERROR_ENOENT: XsdError = XsdError {
+    num: libc::ENOENT,
+    error: "ENOENT",
+};
+pub const XSD_ERROR_ENOMEM: XsdError = XsdError {
+    num: libc::ENOMEM,
+    error: "ENOMEM",
+};
+pub const XSD_ERROR_ENOSPC: XsdError = XsdError {
+    num: libc::ENOSPC,
+    error: "ENOSPC",
+};
+pub const XSD_ERROR_EIO: XsdError = XsdError {
+    num: libc::EIO,
+    error: "EIO",
+};
+pub const XSD_ERROR_ENOTEMPTY: XsdError = XsdError {
+    num: libc::ENOTEMPTY,
+    error: "ENOTEMPTY",
+};
+pub const XSD_ERROR_ENOSYS: XsdError = XsdError {
+    num: libc::ENOSYS,
+    error: "ENOSYS",
+};
+pub const XSD_ERROR_EROFS: XsdError = XsdError {
+    num: libc::EROFS,
+    error: "EROFS",
+};
+pub const XSD_ERROR_EBUSY: XsdError = XsdError {
+    num: libc::EBUSY,
+    error: "EBUSY",
+};
+pub const XSD_ERROR_EAGAIN: XsdError = XsdError {
+    num: libc::EAGAIN,
+    error: "EAGAIN",
+};
+pub const XSD_ERROR_EISCONN: XsdError = XsdError {
+    num: libc::EISCONN,
+    error: "EISCONN",
+};
+pub const XSD_ERROR_E2BIG: XsdError = XsdError {
+    num: libc::E2BIG,
+    error: "E2BIG",
+};
+pub const XSD_ERROR_EPERM: XsdError = XsdError {
+    num: libc::EPERM,
+    error: "EPERM",
+};
+
+pub const XSD_WATCH_PATH: u32 = 0;
+pub const XSD_WATCH_TOKEN: u32 = 1;
+
+#[repr(C)]
+pub struct XenDomainInterface {
+    req: [i8; 1024],
+    rsp: [i8; 1024],
+    req_cons: u32,
+    req_prod: u32,
+    rsp_cons: u32,
+    rsp_prod: u32,
+    server_features: u32,
+    connection: u32,
+    error: u32,
+}
+
+pub const XS_PAYLOAD_MAX: u32 = 4096;
+pub const XS_ABS_PATH_MAX: u32 = 3072;
+pub const XS_REL_PATH_MAX: u32 = 2048;
+pub const XS_SERVER_FEATURE_RECONNECTION: u32 = 1;
+pub const XS_SERVER_FEATURE_ERROR: u32 = 2;
+pub const XS_CONNECTED: u32 = 0;
+pub const XS_RECONNECT: u32 = 1;
+pub const XS_ERROR_NONE: u32 = 0;
+pub const XS_ERROR_COMM: u32 = 1;
+pub const XS_ERROR_RINGIDX: u32 = 2;
+pub const XS_ERROR_PROTO: u32 = 3;