[Patch] Bandwidth Utilization Patch.

[guyharris]

Converted from SourceForge issue 1037376, submitted by ellzey

A very simple patch that add's a -M flag to see the
current bandwidth in bps/Kbps/Mbps.

[guyharris]

Submitted by guy_harris

Logged In: YES
user_id=541179

"-M", in the current top-of-tree CVS version of tcpdump, is used to
specify a shared secret for validating digests for TCP segments with the
TCP-MD5 option (RFC 2385). You'll have to pick a different flag.

[infrastation]

Contents of the original patch is below:

*** tcpdump-3.8.3/tcpdump.c 2004-03-17 14:47:48.000000000 -0500
--- tcpdump-3.8.3-mark/tcpdump.c    2004-09-29 19:34:18.000000000 -0400
***************
*** 74,79 ****
--- 74,80 ----
  int fflag;            /* don't translate "foreign" IP address */
  int Lflag;            /* list available data link types and exit */
  int nflag;            /* leave addresses as numbers */
+ int Mflag;            /* see bandwidth stats */
  int Nflag;            /* remove domains from printed host names */
  int Oflag = 1;            /* run filter code optimizer */
  int pflag;            /* don't go promiscuous */
***************
*** 104,109 ****
--- 105,111 ----

  int32_t thiszone;     /* seconds offset from gmt to local time */

+ time_t bw_gtime;      /* global time for bandwidth stats */
  /* Forwards */
  static RETSIGTYPE cleanup(int);
  static void usage(void) __attribute__((noreturn));
***************
*** 119,124 ****
--- 121,127 ----

  static void info(int);
  static u_int packets_captured;
+ static u_int bytes_captured;

  /* Length of saved portion of packet. */
  int snaplen = DEFAULT_SNAPLEN;
***************
*** 346,352 ****

    opterr = 0;
    while (
!       (op = getopt(argc, argv, "aA" B_FLAG "c:C:d" D_FLAG "eE:fF:i:lLm:nNOpqr:Rs:StT:u" U_FLAG "vw:xXy:Y")) != -1)
        switch (op) {

        case 'a':
--- 349,355 ----

    opterr = 0;
    while (
!       (op = getopt(argc, argv, "aA" B_FLAG "c:C:d" D_FLAG "eE:fF:i:lLMm:nNOpqr:Rs:StT:u" U_FLAG "vw:xXy:Y")) != -1)
        switch (op) {

        case 'a':
***************
*** 499,504 ****
--- 502,511 ----
  #endif
            break;

+       case 'M':
+           Mflag = 1;
+           time(&bw_gtime);
+           break;
        case 'O':
            Oflag = 0;
            break;
***************
*** 1000,1005 ****
--- 1007,1032 ----
    ++packets_captured;

    ++infodelay;
+ 
+   if(Mflag)
+   {
+       time_t bw_curtime;
+ 
+       bytes_captured += h->len;
+ 
+       time(&bw_curtime);
+       if((bw_curtime-bw_gtime) >= 1)
+       {
+           int Kbps = bytes_captured*8/1024;
+           int Mbps = Kbps/1048576;
+           ts_print(&h->ts);
+           printf("Bandwidth: %10dBytes/s | %8dKbps | %6dMbps\n",bytes_captured,Kbps,Mbps);
+               time(&bw_gtime);
+               packets_captured=0;
+       }
+       return;
+   }
+ 
    ts_print(&h->ts);

    print_info = (struct print_info *)user;

[infrastation]

I had briefly looked into this and could note the following:

1. Since getopt_long() is now guaranteed to be available, it is possible to use just the long option --bwonly[=seconds] with the default period of 1 second.
2. The man page should explain the new option.
3. The time calculation should remain correct when the measured period is much shorter or much longer than 1 second, this involves respective time units and makes the option depend on compile-time checks for clock_gettime() and CLOCK_MONOTONIC.

[mcr]

So I understand that this calculates bandwidth based upon pcap time stamps and packet sizes. That's kinda interesting.

[infrastation]

This feature is very close to what iftop does.