rust: time: introduce time module

It only contains the bare minimum to implement inode timestamps.

Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>

Author: wedsonaf

rust/kernel/lib.rs

@@ -46,6 +46,7 @@ pub mod std_vendor;
 pub mod str;
 pub mod sync;
 pub mod task;
+pub mod time;
 pub mod types;
 
 #[doc(hidden)]

rust/kernel/time.rs

@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Time representation in the kernel.
+//!
+//! C headers: [`include/linux/time64.h`](../../include/linux/time64.h)
+
+use crate::{bindings, error::code::*, error::Result};
+
+/// A [`Timespec`] instance at the Unix epoch.
+pub const UNIX_EPOCH: Timespec = Timespec {
+    t: bindings::timespec64 {
+        tv_sec: 0,
+        tv_nsec: 0,
+    },
+};
+
+/// A timestamp.
+#[derive(Copy, Clone)]
+#[repr(transparent)]
+pub struct Timespec {
+    t: bindings::timespec64,
+}
+
+impl Timespec {
+    /// Creates a new timestamp.
+    ///
+    /// `sec` is the number of seconds since the Unix epoch. `nsec` is the number of nanoseconds
+    /// within that second.
+    pub fn new(sec: u64, nsec: u32) -> Result<Self> {
+        if nsec >= 1000000000 {
+            return Err(EDOM);
+        }
+
+        Ok(Self {
+            t: bindings::timespec64 {
+                tv_sec: sec.try_into()?,
+                tv_nsec: nsec.try_into()?,
+            },
+        })
+    }
+}
+
+impl From<Timespec> for bindings::timespec64 {
+    fn from(v: Timespec) -> Self {
+        v.t
+    }
+}