From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Thu, 18 Aug 2011 14:58:17 -0400
From: Andrew Tannenbaum <trb@domain.hid>
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Subject: [Xenomai-help] odd code for loopback option in
	/src/utils/can/rtcansend.c
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To: xenomai@xenomai.org

In xenomai-2.5.5.2/src/utils/can/rtcansend.c, the code that handles 
local loopback mode looks like this:

static void print_usage(char *prg)
{
...
             " -L, --loopback=0|1    switch local loopback off or on\n"
...
}

static int loopback=-1;

         switch (opt) {
	...
         case 'L':
             loopback = strtoul(optarg, NULL, 0);
             break;
	...
	}

...
     if (loopback >= 0) {
         ret = rt_dev_setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK,
                                 &loopback, sizeof(loopback));
         if (ret < 0) {
             fprintf(stderr, "rt_dev_setsockopt: %s\n", strerror(-ret));
             goto failure;
         }
         if (verbose)
             printf("Using loopback=%d\n", loopback);
     }

It looks like the default value for loopback is -1, and if you set it to 
0 or 1, it turns loopback on, which seems strange.  I don't understand 
rt_dev_setsockopt() fully, so I'm not sure if it's a bug - I don't know 
if -1 and 0 and 1 are three separate loopback states, but I think it 
merits attention.  I think either the code is wrong or the help string 
and man page are not clear.

-Andy