From 902f59ecb9fc4fd8c0874b85c50d209398bcdd17 Mon Sep 17 00:00:00 2001
From: Barret Rhoden <brho@google.com>
Date: Thu, 12 Nov 2026 20:41:42 +0000
Subject: [PATCH] os: implement Chtimes on Linux

Implement os.Chtimes on Linux using syscall.UtimesNano, preserving timestamps with UTIME_OMIT when a zero time.Time is passed.
---
 src/os/chtimes_linux.go      | 29 +++++++++++++++++++++++++
 src/os/chtimes_linux_test.go | 42 ++++++++++++++++++++++++++++++++++++
 src/os/chtimes_other.go      | 10 +++++++++
 src/os/file_posix.go         |  5 -----
 4 files changed, 81 insertions(+), 5 deletions(-)
 create mode 100644 src/os/chtimes_linux.go
 create mode 100644 src/os/chtimes_linux_test.go
 create mode 100644 src/os/chtimes_other.go

diff --git a/src/os/chtimes_linux.go b/src/os/chtimes_linux.go
new file mode 100644
index 0000000000..afb0c38fa0
--- /dev/null
+++ b/src/os/chtimes_linux.go
@@ -0,0 +1,29 @@
+//go:build !baremetal && !nintendoswitch && !wasip1 && !wasm_unknown && !wasip2
+
+package os
+
+import (
+	"syscall"
+	"time"
+)
+
+// See https://github.com/torvalds/linux/blob/master/include/linux/stat.h
+const _UTIME_OMIT = (1 << 30) - 2
+
+// Chtimes changes the access and modification times of the named file.
+func Chtimes(name string, atime time.Time, mtime time.Time) error {
+	var utimes [2]syscall.Timespec
+	set := func(i int, t time.Time) {
+		if t.IsZero() {
+			utimes[i] = syscall.Timespec{Sec: _UTIME_OMIT, Nsec: _UTIME_OMIT}
+		} else {
+			utimes[i] = syscall.NsecToTimespec(t.UnixNano())
+		}
+	}
+	set(0, atime)
+	set(1, mtime)
+	if e := syscall.UtimesNano(fixLongPath(name), utimes[0:]); e != nil {
+		return &PathError{Op: "chtimes", Path: name, Err: e}
+	}
+	return nil
+}
diff --git a/src/os/chtimes_linux_test.go b/src/os/chtimes_linux_test.go
new file mode 100644
index 0000000000..72cc8b974c
--- /dev/null
+++ b/src/os/chtimes_linux_test.go
@@ -0,0 +1,42 @@
+//go:build !baremetal && !nintendoswitch && !wasip1 && !wasm_unknown && !wasip2
+
+package os_test
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func TestChtimes(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "file.txt")
+	if err := os.WriteFile(path, []byte("hello"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	wantMtime := time.Date(2025, 3, 15, 12, 30, 45, 0, time.UTC)
+	if err := os.Chtimes(path, wantMtime, wantMtime); err != nil {
+		t.Fatalf("Chtimes failed: %v", err)
+	}
+
+	fi, err := os.Stat(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !fi.ModTime().Equal(wantMtime) {
+		t.Errorf("ModTime() = %v, want %v", fi.ModTime(), wantMtime)
+	}
+
+	// Zero time.Time should leave the modification time unchanged.
+	if err := os.Chtimes(path, time.Time{}, time.Time{}); err != nil {
+		t.Fatalf("Chtimes with zero times failed: %v", err)
+	}
+	fi, err = os.Stat(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !fi.ModTime().Equal(wantMtime) {
+		t.Errorf("ModTime() after zero Chtimes = %v, want %v", fi.ModTime(), wantMtime)
+	}
+}
diff --git a/src/os/chtimes_other.go b/src/os/chtimes_other.go
new file mode 100644
index 0000000000..6b5a226bf2
--- /dev/null
+++ b/src/os/chtimes_other.go
@@ -0,0 +1,10 @@
+//go:build !linux || baremetal || nintendoswitch || wasip1 || wasm_unknown || wasip2
+
+package os
+
+import "time"
+
+// Chtimes is a stub on non-Linux targets.
+func Chtimes(name string, atime time.Time, mtime time.Time) error {
+	return ErrNotImplemented
+}
diff --git a/src/os/file_posix.go b/src/os/file_posix.go
index a10ff49196..ca6004847b 100644
--- a/src/os/file_posix.go
+++ b/src/os/file_posix.go
@@ -6,11 +6,6 @@ import (
 
 //TODO: re-implement the ErrNoDeadline error in the correct code path
 
-// Chtimes is a stub, not yet implemented
-func Chtimes(name string, atime time.Time, mtime time.Time) error {
-	return ErrNotImplemented
-}
-
 // setDeadline sets the read and write deadline.
 func (f *File) setDeadline(t time.Time) error {
 	if t.IsZero() {