os: add Root.Link

For #67002

Change-Id: I223f3f2dbc8b02726f4ce5a017c628c4a20f109a
Reviewed-on: https://go-review.googlesource.com/c/go/+/659757
Reviewed-by: Quim Muntal <quimmuntal@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Damien Neil <dneil@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/os/root_openat.go b/src/os/root_openat.go
index 2cb867459b..6591825648 100644
--- a/src/os/root_openat.go
+++ b/src/os/root_openat.go
@@ -151,6 +151,19 @@ func rootRename(r *Root, oldname, newname string) error {
 	return err
 }
 
+func rootLink(r *Root, oldname, newname string) error {
+	_, err := doInRoot(r, oldname, func(oldparent sysfdType, oldname string) (struct{}, error) {
+		_, err := doInRoot(r, newname, func(newparent sysfdType, newname string) (struct{}, error) {
+			return struct{}{}, linkat(oldparent, oldname, newparent, newname)
+		})
+		return struct{}{}, err
+	})
+	if err != nil {
+		return &LinkError{"linkat", oldname, newname, err}
+	}
+	return err
+}
+
 // doInRoot performs an operation on a path in a Root.
 //
 // It opens the directory containing the final element of the path,