On Tue 2021-04-13 17:22:46, Samo Pogačnik wrote: > Dne 13.04.2021 (tor) ob 16:32 +0200 je Petr Mladek napisal(a): > > On Tue 2021-04-13 13:10:50, Samo Pogačnik wrote: > > > Dne 13.04.2021 (tor) ob 11:41 +0200 je Petr Mladek napisal(a): > > > > On Mon 2021-04-12 14:41:27, Samo Pogačnik wrote: > > > > > Dne 12.04.2021 (pon) ob 19:39 +0900 je Tetsuo Handa napisal(a): > > > > > > What is the intended usage of /dev/ttyprintk ? > > > > > > > > > > > > > > > > The intended use of 'ttyprintk' is to redirect console to > > > > > /dev/ttyprintk > > > > > via the TIOCCONS ioctl. After successfull redirection, all console > > > > > messages get "merged" with kernel messages and as such automatically > > > > > processed > > > > > (stored/transferred) by the syslog service for example. > > > > > > > > The same can be achieved by /dev/kmsg that was created by systemd > > > > developers. > > > > > > > > > > 'kmsg' and 'ttyprintk' are different types of drivers and as such rather > > > complementary than exclusive. The 'ttyprintk' being a tty driver allows > > > for a system wide automatic redirection of anything written to the > > > console. > > > > I might miss something. But how can one setup ttyprintk as the system > > wide console? I do not see any code that would use ttyprintk > > in struct console. > > > > You can compile this simple code below and call: > > # ./tioccons /dev/ttyprintk
Thanks a lot for the example. My head is still spinning around it. I have troubles to update my mental model around /dev/console with this use case. My original model is that kernel or processes write into /dev/console so that a human could see and read it on the device attached to the console. kernel is calling console->write() callback when showing new messages on consoles. The write to the redirected /dev/console makes the messages appear in the kernel log. It feels like it should create an infinite loop. Except that it doesn't work this way. Sigh. Best Regards, Petr
