Report the DLT description in error messages

Introduce pcap_datalink_val_to_description_or_dlt, and
use that when reporting an error.  This was inspired by
seeing "tcpdump: no VLAN support for data link type 113".
The new equivalent message is
"tcpdump: no VLAN support for Linux cooked".

1 files changed, 15 insertions, 0 deletions

diff --git a/pcap.c b/pcap.c
index 36a118bc..d25e569c 100644
--- a/pcap.c
+++ b/pcap.c
@@ -3152,6 +3152,21 @@ pcap_datalink_val_to_description(int dlt)
 	return (NULL);
 }
 
+const char *
+pcap_datalink_val_to_description_or_dlt(int dlt)
+{
+        static char unkbuf[40];
+        const char *description;
+
+        description = pcap_datalink_val_to_description(dlt);
+        if (description != NULL) {
+                return description;
+        } else {
+                (void)pcap_snprintf(unkbuf, sizeof(unkbuf), "DLT %u", dlt);
+                return unkbuf;
+        }
+}
+
 struct tstamp_type_choice {
 	const char *name;
 	const char *description;