start TPM support

client/internal/tpm/open_linux.go

@@ -0,0 +1,29 @@
+package tpm
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/google/go-tpm/tpmutil"
+)
+
+// The kernel resource manager multiplexes clients and flushes what they leave behind,
+// so it is tried before the raw device.
+var devicePaths = []string{"/dev/tpmrm0", "/dev/tpm0"}
+
+func open() (io.ReadWriteCloser, error) {
+	if path := os.Getenv(DeviceEnv); path != "" {
+		return tpmutil.OpenTPM(path)
+	}
+	var errs error
+	for _, path := range devicePaths {
+		rwc, err := tpmutil.OpenTPM(path)
+		if err == nil {
+			return rwc, nil
+		}
+		errs = errors.Join(errs, err)
+	}
+	return nil, fmt.Errorf("open TPM: %w", errs)
+}