Do not open an interface if not needed for -d

diff --git a/tcpdump.c b/tcpdump.c
index a63cdcf0bd6ecb83700da1bf0e47a5900c458570..1a15d3c5d8a772cfea8271f5ed326329e7a7878f 100644 (file)
--- a/tcpdump.c
+++ b/tcpdump.c
@@ -2022,6 +2022,29 @@ main(int argc, char **argv)
                if (dlt == DLT_LINUX_SLL2)
                        fprintf(stderr, "Warning: interface names might be incorrect\n");
 #endif
+       } else if (dflag && !device) {
+               int dump_dlt = DLT_EN10MB;
+               /*
+                * We're dumping the compiled code without an explicit
+                * device specification.  (If a device is specified, we
+                * definitely want to open it to use the DLT of that device.)
+                * Either default to DLT_EN10MB with a warning, or use
+                * the user-specified value if supplied.
+                */
+               /*
+                * If no snapshot length was specified, or a length of 0 was
+                * specified, default to 256KB.
+                */
+               if (ndo->ndo_snaplen == 0)
+                       ndo->ndo_snaplen = MAXIMUM_SNAPLEN;
+               /*
+                * If a DLT was specified with the -y flag, use that instead.
+                */
+               if (yflag_dlt != -1)
+                       dump_dlt = yflag_dlt;
+               else
+                       fprintf(stderr, "Warning: assuming Ethernet\n");
+               pd = pcap_open_dead(dump_dlt, ndo->ndo_snaplen);
        } else {
                /*
                 * We're doing a live capture.