= 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.

`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. ||