[PATCH net-next v2 5/6] rust: Add read_poll_timeout function

[FUJITA Tomonori]

Add read_poll_timeout function which polls periodically until a
condition is met or a timeout is reached.

C's read_poll_timeout (include/linux/iopoll.h) is a complicated macro
and a simple wrapper for Rust doesn't work. So this implements the
same functionality in Rust.

The C version uses usleep_range() while the Rust version uses
fsleep(), which uses the best sleep method so it works with spans that
usleep_range() doesn't work nicely with.

might_sleep() is called via a wrapper so the __FILE__ and __LINE__
debug info with CONFIG_DEBUG_ATOMIC_SLEEP enabled isn't what we
expect; the wrapper instead of the caller.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxx>
---
 rust/helpers/helpers.c |  1 +
 rust/helpers/kernel.c  | 13 ++++++++
 rust/kernel/error.rs   |  1 +
 rust/kernel/io.rs      |  5 +++
 rust/kernel/io/poll.rs | 70 ++++++++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs     |  1 +
 6 files changed, 91 insertions(+)
 create mode 100644 rust/helpers/kernel.c
 create mode 100644 rust/kernel/io.rs
 create mode 100644 rust/kernel/io/poll.rs

diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index c274546bcf78..f9569ff1717e 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -12,6 +12,7 @@
 #include "build_assert.c"
 #include "build_bug.c"
 #include "err.c"
+#include "kernel.c"
 #include "kunit.c"
 #include "mutex.c"
 #include "page.c"
diff --git a/rust/helpers/kernel.c b/rust/helpers/kernel.c
new file mode 100644
index 000000000000..5b9614974c76
--- /dev/null
+++ b/rust/helpers/kernel.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(void)
+{
+	might_sleep();
+}
diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
index 6f1587a2524e..d571b9587ed6 100644
--- a/rust/kernel/error.rs
+++ b/rust/kernel/error.rs
@@ -58,6 +58,7 @@ 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.");
diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
new file mode 100644
index 000000000000..033f3c4e4adf
--- /dev/null
+++ b/rust/kernel/io.rs
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Input and Output.
+
+pub mod poll;
diff --git a/rust/kernel/io/poll.rs b/rust/kernel/io/poll.rs
new file mode 100644
index 000000000000..d248a16a7158
--- /dev/null
+++ b/rust/kernel/io/poll.rs
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! IO polling.
+//!
+//! C header: [`include/linux/iopoll.h`](srctree/include/linux/iopoll.h).
+
+use crate::{
+    bindings,
+    error::{code::*, Result},
+    time::{fsleep, Delta, Ktime},
+};
+
+/// Polls periodically until a condition is met or a timeout is reached.
+///
+/// `op` is called repeatedly until `cond` returns `true` or the timeout is
+///  reached. The return value of `op` is passed to `cond`.
+///
+/// `sleep_delta` is the duration to sleep between calls to `op`.
+/// If `sleep_delta` is less than one microsecond, the function will busy-wait.
+///
+/// `timeout_delta` is the maximum time to wait for `cond` to return `true`.
+///
+/// If `sleep_before_read` is `true`, the function will sleep for `sleep_delta`
+/// first.
+///
+/// This function can only be used in a nonatomic context.
+pub fn read_poll_timeout<Op, Cond, T: Copy>(
+    mut op: Op,
+    cond: Cond,
+    sleep_delta: Delta,
+    timeout_delta: Delta,
+    sleep_before_read: bool,
+) -> Result<T>
+where
+    Op: FnMut() -> Result<T>,
+    Cond: Fn(T) -> bool,
+{
+    let timeout = Ktime::ktime_get() + timeout_delta;
+    let sleep = sleep_delta.as_micros() != 0;
+
+    if sleep {
+        // SAFETY: FFI call.
+        unsafe { bindings::might_sleep() }
+    }
+
+    if sleep_before_read && sleep {
+        fsleep(sleep_delta);
+    }
+
+    let val = loop {
+        let val = op()?;
+        if cond(val) {
+            break val;
+        }
+        if !timeout_delta.is_zero() && Ktime::ktime_get() > timeout {
+            break op()?;
+        }
+        if sleep {
+            fsleep(sleep_delta);
+        }
+        // SAFETY: FFI call.
+        unsafe { bindings::cpu_relax() }
+    };
+
+    if cond(val) {
+        Ok(val)
+    } else {
+        Err(ETIMEDOUT)
+    }
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 22a3bfa5a9e9..7b6888723fc4 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -35,6 +35,7 @@
 #[cfg(CONFIG_RUST_FW_LOADER_ABSTRACTIONS)]
 pub mod firmware;
 pub mod init;
+pub mod io;
 pub mod ioctl;
 #[cfg(CONFIG_KUNIT)]
 pub mod kunit;
-- 
2.34.1