@@ -13,6 +13,7 @@
 #include "build_bug.c"
 #include "cred.c"
 #include "err.c"
+#include "kernel.c"
 #include "fs.c"
 #include "jump_label.c"
 #include "kunit.c"

@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/kernel.h>
+
+void rust_helper_cpu_relax(void)
+{
+	cpu_relax();
+}
+
+void rust_helper___might_sleep_precision(const char *file, int len, int line)
+{
+	__might_sleep_precision(file, len, line);
+}

@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Processor related primitives.
+//!
+//! C header: [`include/linux/processor.h`](srctree/include/linux/processor.h).
+
+/// Lower CPU power consumption or yield to a hyperthreaded twin processor.
+///
+/// It also happens to serve as a compiler barrier.
+pub fn cpu_relax() {
+    // SAFETY: FFI call.
+    unsafe { bindings::cpu_relax() }
+}

@@ -64,6 +64,7 @@ macro_rules! declare_err {
     declare_err!(EPIPE, "Broken pipe.");
     declare_err!(EDOM, "Math argument out of domain of func.");
     declare_err!(ERANGE, "Math result not representable.");
+    declare_err!(ETIMEDOUT, "Connection timed out.");
     declare_err!(ERESTARTSYS, "Restart the system call.");
     declare_err!(ERESTARTNOINTR, "System call was interrupted by a signal and will be restarted.");
     declare_err!(ERESTARTNOHAND, "Restart if no handler.");

@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Input and Output.
+
+pub mod poll;

@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! IO polling.
+//!
+//! C header: [`include/linux/iopoll.h`](srctree/include/linux/iopoll.h).
+
+use crate::{
+    cpu::cpu_relax,
+    error::{code::*, Result},
+    time::{delay::fsleep, Delta, Instant},
+};
+
+use core::panic::Location;
+
+/// Polls periodically until a condition is met or a timeout is reached.
+///
+/// Public but hidden since it should only be used from public macros.
+///
+/// ```rust
+/// use kernel::io::poll::read_poll_timeout;
+/// use kernel::time::Delta;
+/// use kernel::sync::{SpinLock, new_spinlock};
+///
+/// let lock = KBox::pin_init(new_spinlock!(()), kernel::alloc::flags::GFP_KERNEL)?;
+/// let g = lock.lock();
+/// read_poll_timeout(|| Ok(()), |()| true, Delta::from_micros(42), Delta::from_micros(42));
+/// drop(g);
+///
+/// # Ok::<(), Error>(())
+/// ```
+#[track_caller]
+pub fn read_poll_timeout<Op, Cond, T: Copy>(
+    mut op: Op,
+    mut cond: Cond,
+    sleep_delta: Delta,
+    timeout_delta: Delta,
+) -> Result<T>
+where
+    Op: FnMut() -> Result<T>,
+    Cond: FnMut(&T) -> bool,
+{
+    let start = Instant::now();
+    let sleep = !sleep_delta.is_zero();
+    let timeout = !timeout_delta.is_zero();
+
+    if sleep {
+        might_sleep(Location::caller());
+    }
+
+    loop {
+        let val = op()?;
+        if cond(&val) {
+            // Unlike the C version, we immediately return.
+            // We know the condition is met so we don't need to check again.
+            return Ok(val);
+        }
+        if timeout && start.elapsed() > timeout_delta {
+            // Unlike the C version, we immediately return.
+            // We have just called `op()` so we don't need to call it again.
+            return Err(ETIMEDOUT);
+        }
+        if sleep {
+            fsleep(sleep_delta);
+        }
+        // fsleep() could be busy-wait loop so we always call cpu_relax().
+        cpu_relax();
+    }
+}
+
+fn might_sleep(loc: &Location<'_>) {
+    // SAFETY: FFI call.
+    unsafe {
+        crate::bindings::__might_sleep_precision(
+            loc.file().as_ptr().cast(),
+            loc.file().len() as i32,
+            loc.line() as i32,
+        )
+    }
+}

@@ -35,6 +35,7 @@
 pub mod block;
 #[doc(hidden)]
 pub mod build_assert;
+pub mod cpu;
 pub mod cred;
 pub mod device;
 pub mod error;

@@ -42,6 +43,7 @@
 pub mod firmware;
 pub mod fs;
 pub mod init;
+pub mod io;
 pub mod ioctl;
 pub mod jump_label;
 #[cfg(CONFIG_KUNIT)]