zos: share implementation with unix (less DRY)

console_unix.go

@@ -1,5 +1,5 @@
-//go:build darwin || freebsd || linux || netbsd || openbsd
-// +build darwin freebsd linux netbsd openbsd
+//go:build darwin || freebsd || linux || netbsd || openbsd || zos
+// +build darwin freebsd linux netbsd openbsd zos
 
 /*
    Copyright The containerd Authors.

pty_zos.go

@@ -0,0 +1,43 @@
+//go:build zos
+// +build zos
+
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package console
+
+import (
+	"fmt"
+	"os"
+)
+
+// openpt allocates a new pseudo-terminal by opening the first available /dev/ptypXX device
+func openpt() (*os.File, error) {
+	var f *os.File
+	var err error
+	for i := 0; ; i++ {
+		ptyp := fmt.Sprintf("/dev/ptyp%04d", i)
+		f, err = os.OpenFile(ptyp, os.O_RDWR, 0600)
+		if err == nil {
+			break
+		}
+		if os.IsNotExist(err) {
+			return nil, err
+		}
+		// else probably Resource Busy
+	}
+	return f, nil
+}

tc_zos.go

@@ -17,10 +17,23 @@
 package console
 
 import (
+	"os"
+	"strings"
+
 	"golang.org/x/sys/unix"
 )
 
 const (
 	cmdTcGet = unix.TCGETS
 	cmdTcSet = unix.TCSETS
 )
+
+// unlockpt is a no-op on zos.
+func unlockpt(_ *os.File) error {
+	return nil
+}
+
+// ptsname retrieves the name of the first available pts for the given master.
+func ptsname(f *os.File) (string, error) {
+	return "/dev/ttyp" + strings.TrimPrefix(f.Name(), "/dev/ptyp"), nil
+}