Toward more reliable logging

The kernel sees "%[subsys]s" and adds the argument as the value of the "subsys" key, using the same format (or alternatively, just prints the unformatted format string, and userspace does the work).

This would make the API easy to use, compared to the patch which requires horrible code like this:

char* buf = kmalloc(64 + strlen(subsys_name) + strlen(dev_name));
sprintf(buf, "SUBSYS=%s\nDEVICE=%s\n", subsys_name, dev_name);
printk_emit(buf, strlen(buf), KERN_EMERG "%s: %s: device caught fire", subsys_name, dev_name);
kfree(buf);

Compare that to just:
printk(KERN_EMERG "%[subsys]s: %[device]s: device caught fire", subsys_name, dev_name);

It's clear that the API in the patch is totally inferior and that almost nobody will use it except dev_printk.