add os.Link

Signed-off-by: leongross <[email protected]>

src/os/file_unix.go

@@ -74,6 +74,19 @@ func tempDir() string {
 	return dir
 }
 
+// Link creates newname as a hard link to the oldname file.
+// If there is an error, it will be of type *LinkError.
+func Link(oldname, newname string) error {
+	e := ignoringEINTR(func() error {
+		return syscall.Link(oldname, newname)
+	})
+
+	if e != nil {
+		return &LinkError{"link", oldname, newname, e}
+	}
+	return nil
+}
+
 // Symlink creates newname as a symbolic link to oldname.
 // On Windows, a symlink to a non-existent oldname creates a file symlink;
 // if oldname is later created as a directory the symlink will not work.

src/os/os_hardlink_test.go

@@ -0,0 +1,53 @@
+//go:build !windows && !baremetal && !js && !wasi && !wasip1 && !wasm_unknown
+
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os_test
+
+import (
+	. "os"
+	"syscall"
+	"testing"
+)
+
+func TestHardlink(t *testing.T) {
+	defer chtmpdir(t)()
+	from, to := "hardlinktestfrom", "hardlinktestto"
+
+	file, err := Create(to)
+	if err != nil {
+		t.Fatalf("Create(%q) failed: %v", to, err)
+	}
+	if err = file.Close(); err != nil {
+		t.Errorf("Close(%q) failed: %v", to, err)
+	}
+	err = Link(to, from)
+	if err != nil {
+		t.Fatalf("Link(%q, %q) failed: %v", to, from, err)
+	}
+
+	tostat, err := Lstat(to)
+	if err != nil {
+		t.Fatalf("Lstat(%q) failed: %v", to, err)
+	}
+	fromstat, err := Stat(from)
+	if err != nil {
+		t.Fatalf("Stat(%q) failed: %v", from, err)
+	}
+	if !SameFile(tostat, fromstat) {
+		t.Errorf("Symlink(%q, %q) did not create symlink", to, from)
+	}
+
+	fromstat, err = Lstat(from)
+	if err != nil {
+		t.Fatalf("Lstat(%q) failed: %v", from, err)
+	}
+	// if they have the same inode, they are hard links
+	if fromstat.Sys().(*syscall.Stat_t).Ino != tostat.Sys().(*syscall.Stat_t).Ino {
+		t.Fatalf("Lstat(%q).Sys().Ino = %v, Lstat(%q).Sys().Ino = %v, want the same", to, tostat.Sys().(*syscall.Stat_t).Ino, from, fromstat.Sys().(*syscall.Stat_t).Ino)
+	}
+
+	file.Close()
+}

src/syscall/syscall_libc.go

@@ -134,6 +134,16 @@ func Rename(from, to string) (err error) {
 	return
 }
 
+func Link(oldname, newname string) (err error) {
+	fromdata := cstring(oldname)
+	todata := cstring(newname)
+	fail := int(libc_link(&fromdata[0], &todata[0]))
+	if fail < 0 {
+		err = getErrno()
+	}
+	return
+}
+
 func Symlink(from, to string) (err error) {
 	fromdata := cstring(from)
 	todata := cstring(to)
@@ -416,6 +426,11 @@ func libc_rename(from, to *byte) int32
 //export symlink
 func libc_symlink(from, to *byte) int32
 
+// int link(const char *oldname, *newname);
+//
+//export link
+func libc_link(oldname, newname *byte) int32
+
 // int fsync(int fd);
 //
 //export fsync