io: use io_uring for all io

There should no longer be any

- read
- write
- connect
- sendmsg
- recvmsg
- accept

calls in the codebase. Previously we were using a mix of io_uring and
these calls which had some negative effects: Since we were using the old
system calls, we had to set the file descriptors to non-blocking. But
our io_uring code did not handle EAGAIN. This lead to programs sometimes
being killed when the wayland IO was actually blocking.

Now all file descriptors are set to blocking, but io_uring makes it
non-blocking from our perspective. The one exception are evdev files
because they are read via libinput and libinput uses the old system
calls.

src/io_uring/ops/accept.rs

@@ -0,0 +1,67 @@
+use {
+    crate::io_uring::{
+        pending_result::PendingResult,
+        sys::{io_uring_sqe, IORING_OP_ACCEPT},
+        IoUring, IoUringData, IoUringError, Task, TaskResultExt,
+    },
+    std::rc::Rc,
+    uapi::{c, OwnedFd},
+};
+
+impl IoUring {
+    pub async fn accept(
+        &self,
+        fd: &Rc<OwnedFd>,
+        flags: c::c_int,
+    ) -> Result<Rc<OwnedFd>, IoUringError> {
+        self.ring.check_destroyed()?;
+        let id = self.ring.id();
+        let pr = self.ring.pending_results.acquire();
+        {
+            let mut pw = self.ring.cached_accepts.pop().unwrap_or_default();
+            pw.id = id.id;
+            pw.fd = fd.raw() as _;
+            pw.flags = flags as _;
+            pw.data = Some(Data {
+                pr: pr.clone(),
+                _fd: fd.clone(),
+            });
+            self.ring.schedule(pw);
+        }
+        Ok(pr.await.map(OwnedFd::new).map(Rc::new)).merge()
+    }
+}
+
+struct Data {
+    pr: PendingResult,
+    _fd: Rc<OwnedFd>,
+}
+
+#[derive(Default)]
+pub struct AcceptTask {
+    id: u64,
+    fd: i32,
+    flags: u32,
+    data: Option<Data>,
+}
+
+unsafe impl Task for AcceptTask {
+    fn id(&self) -> u64 {
+        self.id
+    }
+
+    fn complete(mut self: Box<Self>, ring: &IoUringData, res: i32) {
+        if let Some(data) = self.data.take() {
+            data.pr.complete(res);
+        }
+        ring.cached_accepts.push(self);
+    }
+
+    fn encode(&self, sqe: &mut io_uring_sqe) {
+        sqe.opcode = IORING_OP_ACCEPT;
+        sqe.fd = self.fd;
+        sqe.u2.addr = 0;
+        sqe.u1.addr2 = 0;
+        sqe.u3.accept_flags = self.flags;
+    }
+}