= Logging functions in HelenOS =

If you want to add logging to your application, you can use already existing functions in `libc`. Currently, the implementation is trivial as the messages are only printed to the screen but using single API allows for further improvements (logging to file/over network etc.).

To use logging functions, include `io/log.h` and initialize the logging subsystem. After that, you can use the `log_msg` to do the logging.

{{{
#!c
...
#include <io/log.h>

#define NAME "myapp"
...

int main(int argc, char *argv[])
{
    log_init(NAME, LVL_NOTE);
    ...
    if (rc != EOK) {
        log_msg(LVL_ERROR, "Something failed (rc=%d), trying fallback...", rc);
        ...
    }
}
}}}

The first argument to `log_init` is application name, the second is the default logging level. Messages with higher level won't be printed at all. Normally the (when an application is not being debugged) the logging level should be set to LVL_NOTE. That is, messages with level LVL_NOTE or higher are printed.

`log_msg` is a `printf`-like function where first argument is level of the message (its seriousness).

Currently, following levels are recognised.

||= Name =||= Typical usage =||
|| `LVL_FATAL` || Fatal error, program is not able to recover at all. ||
|| `LVL_ERROR` || Serious error but the program can recover from it.[[BR]]E.g. driver cannot control one device but otherwise is healthy. ||
|| `LVL_WARN` || Easily recoverable problem, such as one corrupted packet that can be skipped. ||
|| `LVL_NOTE` || Message that does not indicate a problem, but should be printed at the default logging level. ||
|| `LVL_DEBUG` || Debugging-purpose message. Not printed at the default logging level. Increasing logging level to LVL_DEBUG should not swamp the log. ||
|| `LVL_DEBUG2` || More detailed debugging message. ||