![]() The %p format specifier (used for printing pointers in printf) is extended to add additional formatting modes, for example, requesting to print a struct sockaddr * using %pISpc would print an IPv4/v6 address and port in a human-friendly format (e.g. Which log levels are printed is configured using the sysctl file /proc/sys/kernel/printk. When a log level is not specified, the default log level is KERN_WARNING, unless a different default has been set in the kernel itself. 0Īn emergency condition the system is probably deadĪ problem that requires immediate attentionĪ normal, but perhaps noteworthy, condition The following log levels, along with their interpretations, are given below. The string specifying the log level consists of the ASCII start of header character followed by a digit describing the log level or the character 'c' to indicate the message is a continuation of the previous message. If the CONFIG_DYNAMIC_DEBUG option is not set, then dev_dbg/pr_debug can be turned into normal printk() statements with KERN_DEBUG level.īut for that you need to add #define DEBUG at beginning of file.Printk ( KERN_INFO "Message: %s \n ", arg ) If you still do not see your message then enable prink level echo "8 4 1 7" > /proc/sys/kernel/printk Some more commands to play with dynamic_debug/control are at echo 'file +p'>/sys/kernel/debug/dynamic_debug/control Mostly it get mounted in /sys/kernel/debug if not then you can manually mount it anywhere like below mount -t debugfs none /sys/kernel/debugģ) Now enable the file name for which you need dev_dbg() logs. If not then recompile your kernel with CONFIG_DYNAMIC_DEBUG=yĢ) After boot up check that debugfs is mounted somewhere or not. Make sure that your kernel is complied with CONFIG_DYNAMIC_DEBUG=y cat /proc/config.gz | gunzip | grep CONFIG_DYNAMIC_DEBUG if the driver is loaded but remain silent with no trace messages means the probe has never been executed because of some kernel expected service structures information were missing or faultyġ. ![]() The kernel drivers trace mechanism will not help on debugging internal driver improper configured or missing service structures. In case if the driver has been already assigned by DTS and there is no way to exclude it temporary from the tree source - it's useful to detach and reattach it once again after the debug (trace) level messages activatedįor the i2c subsystem it would require to execute a command: If the DTS will have a driver record assignment, manually repeated driver assignment will cause the error - in case of i2c subsystem - error EBUSY (-16), the driver will be assigned way before the command prompt and the dmesg messages will be limited to the default level (usually dev_info only) Load the driver if the module with the command either insmod or modprobe or if the driver is integrated into the kernel the insertion commands may vary.Įxample on how to assign the kernel integrated driver for the i2c bus subsystem:Įcho > /sys/bus/i2c/devices/i2c-0/new_device Upon the kernel booted and the prompt appear to enable debug level messages by executing either dmesg -n 8 or echo 8 > /proc/sys/kernel/printk Provide debug key into bootargs kernel parametersĪppend #define DEBUG at the first line of the driver file - if the driver is a single file and is using a common Makefile, or append -DDEBUG inside the CC build options if the driver contains of multiple source files and as usually has it's own Makefile The simplest way to receive dev_dbg messages without installing/configuring syslog/etc, appeared necessary to do following steps: The outputs like dev_info are getting into the dmesg with no issue so it's definitely something close. Some posts already suggested to add debug keyword for the bootargs kernel parameters unfortunately wasn't enough. the target system is very slow and is very compact so there is NO WAY to add syslog/etc, there is nothing but dmesg where exactly would be good to see the output of the lines like: there is NO network interface and only single serial port is available. There is NO syslog/daemonlog/system log running at all. Is there a simplest possible way to enable linux kernel driver dev_dbg debug messages (actually it's a trace style messages) hopefully without messing up with the kernel patching/recompiling or the driver implementing something extra like debugfs? perhaps there is a way to enable something SIMPLE in the kernel (like one flag?) triggering particular driver or all drivers dev_dbg (it can be filtered with the `dmesg|grep "driverName") output?
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