"dbus-top" tool update: sensor associations and I2C stats

[Sui Chen]

Hello, OpenBMC,

This is an update to the work-in-progress "dbus-top" tool:

In the screenshot below, the bottom-left window shows sensor objects
as well association edges they're involved in; the bottom-right window
shows I2C transactions (the user can choose to show different columns
too) performed by each of the processes sending DBus messages.

This tool is in progress so some improvement still needs to be done.
If interested, you can try it by cloning this change (or the latest
change in its chain) and adding the BitBake recipes in there:
https://gerrit.openbmc-project.xyz/c/openbmc/openbmc-tools/+/50856/

(The screenshot is manually squashed to fit into a 70-character column
width. A console window is recommended when actually running the tool
on a BMC.)

+-----------------------------------------------------------------+
|Message Type  msg/s |Method Call (us) Hist|History  (Total msg/s)|
|Method Call   11.26 |  7553-:             |                 -900 |
|Method Return 11.26 |   810-::.  .        |      :      .   -675 |
|Signal        69.05 |    86-:::::::..::...|      :      :   -450 |
|Error          0.00 |     9-::::::::::::::|. ::  :.  :.::.  -225 |
|Total         91.58 |1%-99% 56.00  85321.0|:::::::::::::::::-0   |
+----------------------------------+------------------------------|
| Details of fan0_tach Sensor 3/123| Sender CMD           I2C Tx/s|
|                                  | /usr/bin/externals...        |
| There are 1 sensors with the name| /usr/bin/fansensor    470.13 |
|                                  | /usr/bin/cpusensor           |
| DBus Service    : xyz.openbmc_pr | phosphor-watchd --...        |
| DBus Connection : :1.238         | /usr/bin/hwmontemp...        |
| DBus Object Path: /xyz/openbmc_p | /usr/bin/psusensor    13584.3|
| fanX_tach                        | ipmid                        |
|                                  | ipmid                        |
|                                  | ipmid                        |
| Association status:              | /usr/libexec/kcsbr...        |
| Used as Forward vertex 1 times:  |                              |
| 1. /chassis (1)                  |                              |
|   /xyz/openbmc_project/invent... |                              |
|   chassis                        |                              |
|                                  |                              |
| Used as reverse vertex 1 times:  |                              |
| 1. /all_sensors (1)              |                              |
|   /xyz/openbmc_project/invent... |                              |
|   all_sensors                    |                              |
|                                  |                              |
|                                  |                              |
+----------------------------------+------------------------------+
 Wed Jan  7 06:34:47 1970        Press [Tab] to cycle through views


Personally, I didn't have much background in embedded development in
general, and this tool helped me climb OpenBMC's learning curve a bit.
Hopefully it might be useful for others to learn OpenBMC and for
debugging too.
Any comments are greatly welcome and appreciated.

Thanks!