dmesg: support ctime & notime time-format.

src/uu/dmesg/Cargo.toml

@@ -16,3 +16,8 @@ uucore = { workspace = true }
 regex = { workspace = true }
 serde_json = { workspace = true }
 serde = { workspace = true }
+chrono = "0.4.38"
+procfs = "0.17"
+
+[features]
+fixed-boot-time = []

src/uu/dmesg/src/dmesg.rs

@@ -155,9 +155,13 @@ impl Dmesg<'_> {
         if let Some(records) = &self.records {
             for record in records {
                 match self.time_format {
+                    TimeFormat::Ctime => {
+                        print!("[{}] ", time_formatter::ctime(record.timestamp_us))
+                    }
                     TimeFormat::Raw => {
                         print!("[{}] ", time_formatter::raw(record.timestamp_us))
                     }
+                    TimeFormat::Notime => (),
                     _ => unimplemented!(),
                 }
                 println!("{}", record.message);

src/uu/dmesg/src/time_formatter.rs

@@ -1,5 +1,40 @@
+use chrono::{DateTime, FixedOffset, TimeDelta, Timelike};
+#[cfg(feature = "fixed-boot-time")]
+use chrono::{NaiveDate, NaiveTime};
+use std::sync::OnceLock;
+
 pub fn raw(timestamp_us: u64) -> String {
     let seconds = timestamp_us / 1000000;
     let sub_seconds = timestamp_us % 1000000;
     format!("{:>5}.{:0>6}", seconds, sub_seconds)
 }
+
+pub fn ctime(timestamp_us: u64) -> String {
+    let mut date_time = boot_time()
+        .checked_add_signed(TimeDelta::microseconds(timestamp_us as i64))
+        .unwrap();
+    // dmesg always round up sub seconds.
+    if date_time.time().nanosecond() > 0 {
+        date_time = date_time.checked_add_signed(TimeDelta::seconds(1)).unwrap();
+    }
+    date_time.format("%a %b %d %H:%M:%S %Y").to_string()
+}
+
+static BOOT_TIME: OnceLock<DateTime<FixedOffset>> = OnceLock::new();
+
+#[cfg(feature = "fixed-boot-time")]
+fn boot_time() -> DateTime<FixedOffset> {
+    *BOOT_TIME.get_or_init(|| {
+        let date = NaiveDate::from_ymd_opt(2024, 11, 18).unwrap();
+        let time = NaiveTime::from_hms_opt(19, 34, 12).unwrap();
+        let tz = FixedOffset::east_opt(7 * 3600).unwrap();
+        chrono::NaiveDateTime::new(date, time)
+            .and_local_timezone(tz)
+            .unwrap()
+    })
+}
+
+#[cfg(not(feature = "fixed-boot-time"))]
+fn boot_time() -> DateTime<FixedOffset> {
+    *BOOT_TIME.get_or_init(|| procfs::boot_time().unwrap().into())
+}