From 419d75949c6d2720ef7703b863a060a15a171755 Mon Sep 17 00:00:00 2001
From: Julian Orth <ju.orth@gmail.com>
Date: Thu, 24 Apr 2025 17:44:52 +0200
Subject: [PATCH] reexec: close evdev fds in a separate process

---
 src/backend.rs        |  4 +++
 src/backends/metal.rs | 12 ++++++++
 src/ifs/jay_reexec.rs | 65 +++++++++++++++++++++++++++++++++++++++++--
 3 files changed, 78 insertions(+), 3 deletions(-)

diff --git a/src/backend.rs b/src/backend.rs
index fa3ad5ce..2f555402 100644
--- a/src/backend.rs
+++ b/src/backend.rs
@@ -60,6 +60,10 @@ pub trait Backend: Any {
     fn supports_presentation_feedback(&self) -> bool {
         false
     }
+
+    fn get_input_fds(&self) -> Vec<Rc<OwnedFd>> {
+        vec![]
+    }
 }
 
 #[derive(Copy, Clone, Debug, Default, Eq, PartialEq)]
diff --git a/src/backends/metal.rs b/src/backends/metal.rs
index 48d2ddf2..2ab08d57 100644
--- a/src/backends/metal.rs
+++ b/src/backends/metal.rs
@@ -277,6 +277,18 @@ impl Backend for MetalBackend {
     fn supports_presentation_feedback(&self) -> bool {
         true
     }
+
+    fn get_input_fds(&self) -> Vec<Rc<OwnedFd>> {
+        let mut res = vec![];
+        for dev in &*self.device_holder.input_devices.borrow() {
+            if let Some(dev) = dev {
+                if let Some(fd) = dev.fd.get() {
+                    res.push(fd);
+                }
+            }
+        }
+        res
+    }
 }
 
 fn dup_fd(fd: c::c_int) -> Result<Rc<OwnedFd>, MetalError> {
diff --git a/src/ifs/jay_reexec.rs b/src/ifs/jay_reexec.rs
index 8d7cc465..1c60aa76 100644
--- a/src/ifs/jay_reexec.rs
+++ b/src/ifs/jay_reexec.rs
@@ -3,12 +3,16 @@ use {
         client::{Client, ClientError},
         leaks::Tracker,
         object::{Object, Version},
-        utils::oserror::OsError,
+        utils::{
+            clone3::{Forked, fork_with_pidfd},
+            errorfmt::ErrorFmt,
+            oserror::OsError,
+        },
         wire::{JayReexecId, jay_reexec::*},
     },
-    std::{cell::RefCell, rc::Rc},
+    std::{array::from_mut, cell::RefCell, rc::Rc},
     thiserror::Error,
-    uapi::UstrPtr,
+    uapi::{OwnedFd, UstrPtr, c, close_range, dup2, pipe2},
 };
 
 pub struct JayReexec {
@@ -26,6 +30,60 @@ impl JayReexec {
             msg,
         });
     }
+
+    fn delay_close_input_fd(&self) -> Option<OwnedFd> {
+        // It's 2025 and closing evdev fds is still abysmally slow.
+        let mut fds = self.client.state.backend.get().get_input_fds();
+        if fds.is_empty() {
+            return None;
+        }
+        macro_rules! pipe {
+            () => {
+                match pipe2(c::O_CLOEXEC) {
+                    Ok(p) => p,
+                    Err(e) => {
+                        log::error!("Could not create pipe: {}", ErrorFmt(OsError::from(e)));
+                        return None;
+                    }
+                }
+            };
+        }
+        let (p1, c1) = pipe!();
+        let (c2, p2) = pipe!();
+        if let Ok(f) = fork_with_pidfd(false) {
+            if let Forked::Child { .. } = f {
+                drop(p2);
+                fds.sort_by_key(|fd| fd.raw());
+                let c2_dup = fds.last().unwrap().raw() + 1;
+                let c1_dup = c2_dup + 1;
+                let _ = dup2(c1.raw(), c1_dup);
+                let _ = dup2(c2.raw(), c2_dup);
+                for (idx, fd) in fds.iter().enumerate() {
+                    let _ = dup2(fd.raw(), idx as _);
+                }
+                let c2_dup_dup = fds.len() as _;
+                let _ = dup2(c2_dup, c2_dup_dup);
+                let _ = close_range(c2_dup_dup as c::c_uint + 1, !0, 0);
+                let mut pollfd = c::pollfd {
+                    fd: c2_dup_dup,
+                    events: 0,
+                    revents: 0,
+                };
+                let _ = uapi::poll(from_mut(&mut pollfd), -1);
+                unsafe {
+                    c::_exit(0);
+                }
+            }
+        }
+        drop(c1);
+        let mut pollfd = c::pollfd {
+            fd: p1.raw(),
+            events: 0,
+            revents: 0,
+        };
+        let _ = uapi::poll(from_mut(&mut pollfd), -1);
+        Some(p2)
+    }
 }
 
 impl JayReexecRequestHandler for JayReexec {
@@ -43,6 +101,7 @@ impl JayReexecRequestHandler for JayReexec {
         for arg in &*args {
             args2.push(&**arg);
         }
+        let _drop_after_exec = self.delay_close_input_fd();
         if let Err(e) = uapi::execvp(req.path, &args2) {
             self.send_failed(&OsError(e.0).to_string());
         }