pif: Add helpers to get the name of a pif

Future debugging will want to identify a specific passt interface.  We make
a distinction in these helpers between the name of the *type* of pif, and
name of the pif itself.  For the time being these are always the same
thing, since we have at most instance of each type of pif.  However, that
might change in future.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

pif.c

@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright Red Hat
+ * Author: David Gibson <david@gibson.dropbear.id.au>
+ *
+ * Passt/pasta interface types and IDs
+ */
+
+#include <stdint.h>
+#include <assert.h>
+
+#include "util.h"
+#include "pif.h"
+
+const char *pif_type_str[] = {
+	[PIF_NONE]		= "<none>",
+	[PIF_HOST]		= "HOST",
+	[PIF_TAP]		= "TAP",
+	[PIF_SPLICE]		= "SPLICE",
+};
+static_assert(ARRAY_SIZE(pif_type_str) == PIF_NUM_TYPES,
+	      "pif_type_str[] doesn't match enum pif_type");