what is the best way to display the different modes of a protocol in a custom c dissector

asked 2021-03-04 08:43:04 +0000

Robin26689 gravatar image

updated 2021-03-04 11:27:35 +0000

grahamb gravatar image

Hi,

i'm still working on my plugin c dissector for the iolink protocol. In the specification there are several operation modes of a iolink device. I want to display the mode on the GUI.

Until now i figured this out. The variable "iolink_mode" is static. The mode/status should be displayed for everyframe. The first incoming frame gives the first mode which stays until one of the following frames has a different mode. If i dont use the static variable i just have the one frame marked, where the mode changes. I'm sure there are better solutions out there but i couldn't finde one yet. Thanks in advance

greetings

Robin

The code:

static void determine_iolink_mode(packet_info *pinfo, guint32 iolink_mode) 
{   
    switch (iolink_mode)
        {
        case 0x5A: // Fallback
            col_append_fstr(pinfo->cinfo, COL_EXPERT,"%s", val_to_str(iolink_mode, values_for_mastercommand, "Unknown (0x%02x)"));
            break;
        case 0x95: // MasterIdent
            col_append_fstr(pinfo->cinfo, COL_EXPERT,"%s", val_to_str(iolink_mode, values_for_mastercommand, "Unknown (0x%02x)"));
            break;
        case 0x96: // DeviceIdent
            col_append_fstr(pinfo->cinfo, COL_EXPERT,"%s", val_to_str(iolink_mode, values_for_mastercommand, "Unknown (0x%02x)"));
            break;
        case 0x97: // DeviceStartUp
            col_append_fstr(pinfo->cinfo, COL_EXPERT,"%s", val_to_str(iolink_mode, values_for_mastercommand, "Unknown (0x%02x)"));
            break;
        case 0x98: // ProcessDataOutputOperate
            col_append_fstr(pinfo->cinfo, COL_EXPERT,"%s", val_to_str(iolink_mode, values_for_mastercommand, "Unknown (0x%02x)"));
            break;
        case 0x99: // DeviceOperate
            col_append_fstr(pinfo->cinfo, COL_EXPERT,"%s", val_to_str(iolink_mode, values_for_mastercommand, "Unknown (0x%02x)"));
            break;
        case 0x9A: // Preoperate
            col_append_fstr(pinfo->cinfo, COL_EXPERT,"%s", val_to_str(iolink_mode, values_for_mastercommand, "Unknown (0x%02x)"));
            break;
        }
}
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Comments

To clarify, is it the case that the "mode" is set by a packet and remains constant for that conversation until modified by a subsequent packet which sets the "mode" until possibly changed later on by another packet?

It seems to me that the "mode" is a property of the state of the conversation between the end points and not in the state of the dissector itself, so should be held in per-conversation info. See README.dissector section 2.2.

grahamb gravatar imagegrahamb ( 2021-03-04 11:36:33 +0000 )edit

Yes i think so. In one frame there can be three different data kinds (output, on-request and input data). The output always belongs to the bytes sent by the master and the input always belongs to the data sent by the device. The on-request data can belong to both. The state can just be changed, if the on-request data is sent by the master to the device. The first byte of the on-request data is then the mode, if on of the cases of my function fits. The mode won't change until the next frame with on-request data sent by the master follows and is one of the cases. Is this how you understood my question? I dont have implemented conversations yet. I wasn't sure if i need it and didn't understand the whole part of the conversations to be honest. Will look at this chapter again ...(more)

Robin26689 gravatar imageRobin26689 ( 2021-03-04 11:47:31 +0000 )edit
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