xwayland: core infrastructure

Cargo.toml

@@ -7,15 +7,15 @@ description = "Smithay is a library for writing wayland compositors."
 repository = "https://github.com/Smithay/smithay"
 
 [dependencies]
-wayland-server = "0.20.1"
-wayland-sys = "0.20.1"
+wayland-server = "0.20.2"
+wayland-sys = "0.20.2"
 nix = "0.10.0"
 xkbcommon = "0.2.1"
 tempfile = "2.1.5"
 slog = { version = "2.1.1" }
 slog-stdlog = "3.0.2"
 libloading = "0.4.0"
-wayland-client = { version = "0.20.1", optional = true }
+wayland-client = { version = "0.20.2", optional = true }
 winit = { version = "0.10.0", optional = true }
 drm = { version = "^0.3.1", optional = true }
 gbm = { version = "^0.4.0", optional = true, default-features = false, features = ["drm-support"] }
@@ -24,7 +24,7 @@ input = { version = "0.4.0", optional = true }
 udev = { version = "0.2.0", optional = true }
 dbus = { version = "0.6.1", optional = true }
 systemd = { version = "^0.2.0", optional = true }
-wayland-protocols = { version = "0.20.1", features = ["unstable_protocols", "server"] }
+wayland-protocols = { version = "0.20.2", features = ["unstable_protocols", "server"] }
 image = "0.17.0"
 error-chain = "0.11.0"
 lazy_static = "1.0.0"
@@ -38,7 +38,7 @@ slog-async = "2.2"
 rand = "0.3"
 
 [features]
-default = ["backend_winit", "backend_drm", "backend_libinput", "backend_udev", "renderer_glium"]
+default = ["backend_winit", "backend_drm", "backend_libinput", "backend_udev", "renderer_glium", "xwayland"]
 backend_winit = ["winit", "wayland-server/dlopen", "wayland-client/dlopen"]
 backend_drm = ["drm", "gbm"]
 backend_libinput = ["input"]
@@ -47,4 +47,4 @@ backend_session_udev = ["udev", "backend_session"]
 backend_session_logind = ["dbus", "systemd", "backend_session"]
 backend_udev = ["udev", "backend_drm", "backend_session_udev"]
 renderer_glium = ["glium"]
-
+xwayland = []

src/lib.rs

@@ -52,6 +52,9 @@ pub mod backend;
 pub mod wayland;
 pub mod utils;
 
+#[cfg(feature = "xwayland")]
+pub mod xwayland;
+
 fn slog_or_stdlog<L>(logger: L) -> ::slog::Logger
 where
     L: Into<Option<::slog::Logger>>,

src/xwayland/mod.rs

@@ -0,0 +1,4 @@
+mod xserver;
+mod x11_sockets;
+
+pub use self::xserver::{XWayland, XWindowManager};

src/xwayland/x11_sockets.rs

@@ -0,0 +1,136 @@
+use std::io::{Read, Write};
+use std::os::unix::io::RawFd;
+
+use nix::{Error as NixError, Result as NixResult};
+use nix::errno::Errno;
+use nix::sys::socket;
+
+pub(crate) fn make_pair() -> Result<(RawFd, RawFd), ()> {
+    socket::socketpair(
+        socket::AddressFamily::Unix,
+        socket::SockType::Stream,
+        None,
+        socket::SockFlag::SOCK_CLOEXEC,
+    ).map_err(|_| ())
+}
+
+/// Find a free X11 display slot and setup
+pub(crate) fn prepare_x11_sockets() -> Result<(u32, [RawFd; 2]), ()> {
+    for d in 0..33 {
+        // if fails, try the next one
+        if let Err(()) = grab_lockfile(d) {
+            continue;
+        }
+        // we got a lockfile, try and create the socket
+        if let Ok(fds) = open_x11_sockets_for_display(d) {
+            return Ok((d, fds));
+        }
+        // creating the sockets failed, for some readon ?
+        // release the lockfile and try with the next
+        release_lockfile(d);
+    }
+    // If we reach here, all values from 0 to 32 failed
+    // we need to stop trying at some point
+    return Err(());
+}
+
+/// Remove the X11 sockets for a given display number
+pub(crate) fn cleanup_x11_sockets(display: u32) {
+    let _ = ::std::fs::remove_file(format!("/tmp/.X11-unix/X{}", display));
+    let _ = ::std::fs::remove_file(format!("/tmp/.X{}-lock", display));
+}
+
+/// Try to grab a lockfile for given X display number
+fn grab_lockfile(display: u32) -> Result<(), ()> {
+    let filename = format!("/tmp/.X{}-lock", display);
+    let lockfile = ::std::fs::OpenOptions::new()
+        .write(true)
+        .create_new(true)
+        .open(&filename);
+    match lockfile {
+        Ok(mut file) => {
+            // we got it, write our PID in it and we're good
+            let ret = file.write_fmt(format_args!("{:>10}", ::nix::unistd::Pid::this()));
+            if let Err(_) = ret {
+                // write to the file failed ? we abandon
+                ::std::mem::drop(file);
+                let _ = ::std::fs::remove_file(&filename);
+                return Err(());
+            } else {
+                // we got the lockfile and wrote our pid to it, all is good
+                return Ok(());
+            }
+        }
+        Err(_) => {
+            // we could not open the file, now we try to read it
+            // and if it contains the pid of a process that no longer
+            // exist (so if a previous x server claimed it and did not
+            // exit gracefully and remove it), we claim it
+            // if we can't open it, give up
+            let mut file = ::std::fs::File::open(&filename).map_err(|_| ())?;
+            let mut spid = [0u8; 11];
+            file.read_exact(&mut spid).map_err(|_| ())?;
+            ::std::mem::drop(file);
+            let pid = ::nix::unistd::Pid::from_raw(::std::str::from_utf8(&spid)
+                .map_err(|_| ())?
+                .trim()
+                .parse::<i32>()
+                .map_err(|_| ())?);
+            if let Err(NixError::Sys(Errno::ESRCH)) = ::nix::sys::signal::kill(pid, None) {
+                // no process whose pid equals the contents of the lockfile exists
+                // remove the lockfile and try grabbing it again
+                let _ = ::std::fs::remove_file(filename);
+                return grab_lockfile(display);
+            }
+            // if we reach here, this lockfile exists and is probably in use, give up
+            return Err(());
+        }
+    }
+}
+
+/// Release an X11 lockfile
+fn release_lockfile(display: u32) {
+    let filename = format!("/tmp/.X{}-lock", display);
+    let _ = ::std::fs::remove_file(filename);
+}
+
+/// Open the two unix sockets an X server listens on
+///
+/// SHould only be done after the associated lockfile is aquired!
+fn open_x11_sockets_for_display(display: u32) -> NixResult<[RawFd; 2]> {
+    let fs_socket = open_socket(
+        socket::UnixAddr::new(format!("/tmp/.X11-unix/X{}", display).as_bytes()).unwrap(), // We know this path is not to long, this unwrap cannot fail
+    )?;
+    let ret = open_socket(
+        socket::UnixAddr::new_abstract(format!("/tmp/.X11-unix/X{}", display).as_bytes()).unwrap(), // We know this path is not to long, this unwrap cannot fail
+    );
+    match ret {
+        Ok(abstract_socket) => Ok([fs_socket, abstract_socket]),
+        Err(e) => {
+            // close the first socket and return the error
+            let _ = ::nix::unistd::close(fs_socket);
+            Err(e)
+        }
+    }
+}
+
+/// Open an unix socket for listening and bind it to given path
+fn open_socket(addr: socket::UnixAddr) -> NixResult<RawFd> {
+    // create an unix stream socket
+    let fd = socket::socket(
+        socket::AddressFamily::Unix,
+        socket::SockType::Stream,
+        socket::SockFlag::SOCK_CLOEXEC,
+        None,
+    )?;
+    // bind it to requested address
+    if let Err(e) = socket::bind(fd, &socket::SockAddr::Unix(addr)) {
+        let _ = ::nix::unistd::close(fd);
+        return Err(e);
+    }
+    if let Err(e) = socket::listen(fd, 1) {
+        let _ = ::nix::unistd::close(fd);
+        return Err(e);
+    }
+    Ok(fd)
+}

src/xwayland/xserver.rs

@@ -0,0 +1,401 @@
+/*
+ * Steps of Xwayland server creation
+ *
+ * Sockets to create:
+ * - a pair for Xwayland to connect to smithay as a wayland client, we use our
+ *   end to insert the Xwayland client in the display
+ * - a pair for smithay to connect to Xwayland as a WM, we give our end to the
+ *   WM and it deals with it
+ * - 2 listening sockets on which the Xwayland server will listen. We need to
+ *   bind them ouserlves so we know what value put in the $DISPLAY env variable.
+ *   This involves some dance with a lockfile to ensure there is no collision with
+ *   an other starting xserver
+ *   if we listen on display $D, their paths are respectly:
+ *   - /tmp/.X11-unix/X$D
+ *   - @/tmp/.X11-unix/X$D (abstract socket)
+ *
+ * The XWayland server is spawned via fork+exec.
+ * -> wlroot does a double-fork while weston a single one, why ??
+ *    -> https://stackoverflow.com/questions/881388/
+ * -> once it is started, it sends us a SIGUSR1, we need to setup a listener
+ *    for it and when we receive it we can launch the WM
+ * -> we need to track if the Xwayland crashes, to restart it
+ *
+ * cf https://github.com/swaywm/wlroots/blob/master/xwayland/xwayland.c
+ *
+ */
+use std::cell::RefCell;
+use std::rc::Rc;
+use std::env;
+use std::ffi::CString;
+use std::os::unix::io::RawFd;
+
+use nix::{Error as NixError, Result as NixResult};
+use nix::errno::Errno;
+use nix::unistd::{close, fork, ForkResult, Pid};
+use nix::sys::signal;
+
+use wayland_server::{Client, Display, LoopToken};
+use wayland_server::sources::{SignalEvent, Source};
+
+use super::x11_sockets::{make_pair, cleanup_x11_sockets, prepare_x11_sockets};
+
+/// The XWayland handle
+pub struct XWayland<WM: XWindowManager> {
+    inner: Rc<RefCell<Inner<WM>>>,
+}
+
+/// Trait to be implemented by you WM for Xwayland
+///
+/// This is a very low-level trait, only notifying you
+/// when the connection with XWayland is up, or when
+/// it terminates.
+///
+/// You WM must be able handle the XWayland server connecting
+/// then disconnecting several time in a row, but only a single
+/// connection will be active at any given time.
+pub trait XWindowManager {
+    /// The XWayland server is ready
+    ///
+    /// Your previlegied connection to it is this `RawFd`
+    fn xwayland_ready(&mut self, fd: RawFd, client: Client);
+    /// The XWayland server has exited
+    fn xwayland_exited(&mut self);
+}
+
+impl<WM: XWindowManager + 'static> XWayland<WM> {
+    /// Start the XWayland server
+    pub fn init(wm: WM, token: LoopToken, display: Rc<RefCell<Display>>) -> Result<XWayland<WM>, ()> {
+        let inner = Rc::new(RefCell::new(Inner {
+            wm,
+            token,
+            wayland_display: display,
+            instance: None,
+        }));
+        launch(&inner)?;
+        Ok(XWayland { inner })
+    }
+}
+
+impl<WM: XWindowManager> Drop for XWayland<WM> {
+    fn drop(&mut self) {
+        self.inner.borrow_mut().shutdown();
+    }
+}
+
+struct XWaylandInstance {
+    display: u32,
+    wayland_client: Client,
+    sigusr1_handler: Option<Source<SignalEvent>>,
+    wm_fd: RawFd,
+    started_at: ::std::time::Instant,
+    child_pid: Option<Pid>,
+}
+
+// Inner implementation of the XWayland manager
+struct Inner<WM: XWindowManager> {
+    wm: WM,
+    token: LoopToken,
+    wayland_display: Rc<RefCell<Display>>,
+    instance: Option<XWaylandInstance>,
+}
+
+// Launch an XWayland server
+//
+// Does nothing if there is already a launched instance
+fn launch<WM: XWindowManager + 'static>(inner: &Rc<RefCell<Inner<WM>>>) -> Result<(), ()> {
+    let mut guard = inner.borrow_mut();
+    if guard.instance.is_some() {
+        return Ok(());
+    }
+
+    let (display, x_fds) = prepare_x11_sockets()?;
+
+    let (x_wm_x11, x_wm_me) = match make_pair() {
+        Ok(v) => v,
+        Err(()) => {
+            // cleanup
+            for &f in &x_fds {
+                let _ = close(f);
+            }
+            cleanup_x11_sockets(display);
+            return Err(());
+        }
+    };
+    let (wl_x11, wl_me) = match make_pair() {
+        Ok(v) => v,
+        Err(()) => {
+            // cleanup
+            for &f in &x_fds {
+                let _ = close(f);
+            }
+            let _ = close(x_wm_x11);
+            let _ = close(x_wm_me);
+            cleanup_x11_sockets(display);
+            return Err(());
+        }
+    };
+
+    // we have now created all the required sockets
+
+    // record launch time
+    let creation_time = ::std::time::Instant::now();
+
+    // create the wayland client for XWayland
+    let client = unsafe { guard.wayland_display.borrow_mut().create_client(wl_me) };
+    client.set_user_data(Rc::into_raw(inner.clone()) as *const () as *mut ());
+    client.set_destructor(client_destroy::<WM>);
+
+    // setup the SIGUSR1 handler
+    let my_inner = inner.clone();
+    let sigusr1_handler = match guard
+        .token
+        .add_signal_event_source(signal::Signal::SIGUSR1, move |_, ()| {
+            xwayland_ready(&my_inner)
+        }) {
+        Ok(v) => v,
+        Err(_) => {
+            // If that fails (can it even fail ?), cleanup
+            for &f in &x_fds {
+                let _ = close(f);
+            }
+            let _ = close(x_wm_x11);
+            let _ = close(x_wm_me);
+            let _ = close(wl_x11);
+            let _ = close(wl_me);
+            cleanup_x11_sockets(display);
+            return Err(());
+        }
+    };
+
+    // all is ready, we can do the fork dance
+    let child_pid = match fork() {
+        Ok(ForkResult::Parent { child }) => {
+            // we are the main smithay process
+            child
+        }
+        Ok(ForkResult::Child) => {
+            // we are the first child
+            let ppid = Pid::parent();
+            let mut set = signal::SigSet::empty();
+            set.add(signal::Signal::SIGUSR1);
+            set.add(signal::Signal::SIGCHLD);
+            // we can't handle errors here anyway
+            let _ = signal::sigprocmask(signal::SigmaskHow::SIG_BLOCK, Some(&set), None);
+            match fork() {
+                Ok(ForkResult::Parent { child }) => {
+                    // we are still the first child
+                    let sig = set.wait();
+                    // send USR1 to parent
+                    let _ = signal::kill(ppid, signal::Signal::SIGUSR1);
+                    // Parent will wait for us and know from out
+                    // exit status if XWayland launch was a success or not =)
+                    if let Ok(signal::Signal::SIGCHLD) = sig {
+                        // Xwayland has exited before being ready
+                        let _ = ::nix::sys::wait::waitpid(child, None);
+                        unsafe { ::nix::libc::exit(1) };
+                    }
+                    unsafe { ::nix::libc::exit(0) };
+                }
+                Ok(ForkResult::Child) => {
+                    // we are the second child, we exec xwayland
+                    match exec_xwayland(display, wl_x11, x_wm_x11, &x_fds) {
+                        Ok(x) => match x {},
+                        Err(e) => {
+                            // well, what can we do ?
+                            eprintln!("[smithay] exec XWayland failed: {:?}", e);
+                            unsafe { ::nix::libc::exit(1) };
+                        }
+                    }
+                }
+                Err(e) => {
+                    // well, what can we do ?
+                    eprintln!("[smithay] XWayland second fork failed: {:?}", e);
+                    unsafe { ::nix::libc::exit(1) };
+                }
+            }
+        }
+        Err(e) => {
+            eprintln!("[smithay] XWayland first fork failed: {:?}", e);
+            // fork failed ? cleanup
+            for &f in &x_fds {
+                let _ = close(f);
+            }
+            let _ = close(x_wm_x11);
+            let _ = close(x_wm_me);
+            let _ = close(wl_x11);
+            let _ = close(wl_me);
+            cleanup_x11_sockets(display);
+            return Err(());
+        }
+    };
+
+    // now, close the FDs that were given to XWayland
+    for &f in &x_fds {
+        let _ = close(f);
+    }
+    let _ = close(x_wm_x11);
+    let _ = close(wl_x11);
+
+    guard.instance = Some(XWaylandInstance {
+        display,
+        wayland_client: client,
+        sigusr1_handler: Some(sigusr1_handler),
+        wm_fd: x_wm_me,
+        started_at: creation_time,
+        child_pid: Some(child_pid),
+    });
+
+    Ok(())
+}
+
+impl<WM: XWindowManager> Inner<WM> {
+    // Shutdown the XWayland server and cleanup everything
+    fn shutdown(&mut self) {
+        // don't do anything if not running
+        if let Some(mut instance) = self.instance.take() {
+            self.wm.xwayland_exited();
+            // kill the client
+            instance.wayland_client.kill();
+            // remove the event source
+            if let Some(s) = instance.sigusr1_handler.take() {
+                s.remove();
+            }
+            // close the WM fd
+            let _ = close(instance.wm_fd);
+            // cleanup the X11 sockets
+            cleanup_x11_sockets(instance.display);
+            ::std::env::remove_var("DISPLAY");
+            // We do like wlroots:
+            // > We do not kill the Xwayland process, it dies to broken pipe
+            // > after we close our side of the wm/wl fds. This is more reliable
+            // > than trying to kill something that might no longer be Xwayland.
+        }
+    }
+}
+
+fn client_destroy<WM: XWindowManager + 'static>(data: *mut ()) {
+    let inner = unsafe { Rc::from_raw(data as *const () as *const RefCell<Inner<WM>>) };
+
+    // shutdown the server
+    let started_at = inner.borrow().instance.as_ref().map(|i| i.started_at);
+    inner.borrow_mut().shutdown();
+
+    // restart it, unless we really just started it, if it crashes right
+    // at startup there is no point
+    if started_at.map(|t| t.elapsed().as_secs()).unwrap_or(10) > 5 {
+        let _ = launch(&inner);
+    }
+}
+
+fn xwayland_ready<WM: XWindowManager>(inner: &Rc<RefCell<Inner<WM>>>) {
+    use nix::sys::wait;
+    let mut guard = inner.borrow_mut();
+    let inner = &mut *guard;
+    // instance should never be None at this point
+    let instance = inner.instance.as_mut().unwrap();
+    let wm = &mut inner.wm;
+    // neither the pid
+    let pid = instance.child_pid.unwrap();
+
+    // find out if the launch was a success by waiting on the intermediate child
+    let mut success: bool;
+    loop {
+        match wait::waitpid(pid, None) {
+            Ok(wait::WaitStatus::Exited(_, 0)) => {
+                // XWayland was correctly started :)
+                success = true;
+                break;
+            }
+            Err(NixError::Sys(Errno::EINTR)) => {
+                // interupted, retry
+                continue;
+            }
+            _ => {
+                // something went wrong :(
+                success = false;
+                break;
+            }
+        }
+    }
+
+    if success {
+        // signal the WM
+        wm.xwayland_ready(instance.wm_fd, instance.wayland_client.clone());
+
+        // setup the environemnt
+        ::std::env::set_var("DISPLAY", format!(":{}", instance.display));
+    }
+
+    // in all cases, cleanup
+    if let Some(s) = instance.sigusr1_handler.take() {
+        s.remove();
+    }
+}
+
+enum Void {}
+
+/// Exec xwayland with given sockets on given display
+///
+/// If this returns, that means that something failed
+fn exec_xwayland(
+    display: u32,
+    wayland_socket: RawFd,
+    wm_socket: RawFd,
+    listen_sockets: &[RawFd],
+) -> NixResult<Void> {
+    // uset the CLOEXEC flag from the sockets we need to pass
+    // to xwayland
+    unset_cloexec(wayland_socket)?;
+    unset_cloexec(wm_socket)?;
+    for &socket in listen_sockets {
+        unset_cloexec(socket)?;
+    }
+    // prepare the arguments to Xwayland
+    let mut args = vec![
+        CString::new("Xwayland").unwrap(),
+        CString::new(format!(":{}", display)).unwrap(),
+        CString::new("-rootless").unwrap(),
+        CString::new("-terminate").unwrap(),
+        CString::new("-wm").unwrap(),
+        CString::new(format!("{}", wm_socket)).unwrap(),
+    ];
+    for &socket in listen_sockets {
+        args.push(CString::new("-listen").unwrap());
+        args.push(CString::new(format!("{}", socket)).unwrap());
+    }
+    // setup the environment: clear everything except PATH and XDG_RUNTIME_DIR
+    for (key, _) in env::vars_os() {
+        if key.to_str() == Some("PATH") || key.to_str() == Some("XDG_RUNTIME_DIR") {
+            continue;
+        }
+        env::remove_var(key);
+    }
+    // the WAYLAND_SOCKET var tells Xwayland where to connect as a wayland client
+    env::set_var("WAYLAND_SOCKET", format!("{}", wayland_socket));
+
+    // ignore SIGUSR1, this will make the Xwayland server send us this
+    // signal when it is ready apparently
+    unsafe {
+        use nix::sys::signal::*;
+        sigaction(
+            Signal::SIGUSR1,
+            &SigAction::new(SigHandler::SigIgn, SaFlags::empty(), SigSet::empty()),
+        )?;
+    }
+
+    // run it
+    let ret = ::nix::unistd::execvp(&CString::new("Xwayland").unwrap(), &args)?;
+    // small dance to actually return Void
+    match ret {}
+}
+
+/// Remove the O_CLOEXEC flag from this Fd
+///
+/// This means that the Fd will *not* be automatically
+/// closed when we exec() into Xwayland
+fn unset_cloexec(fd: RawFd) -> NixResult<()> {
+    use nix::fcntl::{fcntl, FcntlArg, FdFlag};
+    fcntl(fd, FcntlArg::F_SETFD(FdFlag::empty()))?;
+    Ok(())
+}