Troubleshooting Embedded Linux Pt1

Using Dynamic Debug (debugfs)

Check dynamic debug option is enabled in the kernel build

grep CONFIG_DYNAMIC_DEBUG= /boot/config-uname -r

If this is not enabled then you will need to set this option inmake menuconfigand rebuild the kernel

Working with module names

If you want to work with a single module use themodulequery and the module name . Note, replacewith the module name)

1. Find the module name from list of installed modules: lsmod | sort
2. Check the module flags grep -i /sys/kernel/debug/dynamic-debug/control
3. Find any options that are enabled for that module awk '$3 != "=_"' control | grep -i
4. Disable all options for module: echo "module -p" > control
5. Enable all options for module: echo "module +p" > control

Working with multiple modules

If you want to enable/disable multiple modules at once you can use the file query and wildcard combination:

1. Disable all USB debug message in kernel log
   • Disable USB debug echo "file drivers/usb/* -p" > control
   • confirm all debug is disabled for USB (should output '0') awk '$3 != "=_"' control | grep -i usb | wc -l
   • Clear the kernel log dmesg -C
   • plugin in your USB device (Here I plug in an ESP32 devkit)
   • check the kernel log dmesg
2. Enable all USB debug messages in kernel log
   • Enable USB debug with all flags (file, line, module, thread) echo "file drivers/usb/* +pflmt" > control
   • confirm all debug is enabled for USB (should output non-zero value) awk '$3 != "=_"' control | grep -i usb | wc -l
   • Clear the kernel log dmesg -C
   • plugin in your USB device (Here I plug in an ESP32 devkit)
   • check the kernel log dmesg