On Fri 2020-10-23 09:33:34, Sergey Senozhatsky wrote: > On (20/10/22 13:42), Petr Mladek wrote: > > +static bool mute_console; > > + > > +static int __init mute_console_setup(char *str) > > +{ > > + mute_console = true; > > + pr_info("All consoles muted.\n"); > > + > > + return 0; > > +} > > First of all, thanks a lot for picking this up and for the patch set! > > I've several thoughts and comments below. > > > static bool suppress_message_printing(int level) > > { > > - return (level >= console_loglevel && !ignore_loglevel); > > + if (unlikely(mute_console)) > > + return true; > > + > > + if (unlikely(ignore_loglevel)) > > + return false; > > + > > + return (level >= console_loglevel); > > } > > This is one way of doing it. Another one is to clear CON_ENABLED bit > from all consoles (upon registration), one upside of this is that we > will signal user-space that consoles are disabled/muted (by removing > the E flag from /proc/consoles).
Hmm, CON_ENABLED is used by suspend/resume code unconditionaly. We would need another flag to define the state after resume. Well, it is true that CON_ENABLED has the same effect. Messages are not printed to the console. So, introducing another variable is likely overkill. > Thinking more about it. We are still relying on the fact that there is > anything registered as console driver, which is not necessarily the case, > we can have NULL console drivers list. So how about having a dummy struct > console in printk, with NOP read/write and NOP tty_driver and NOP > tty_operations. So that when init calls filp_open("/dev/console") and > we can't give tty anything but NULL, we'd just give tty back the dummy > NOP device. Yup, this seems to be the best solution. Best Regards, Petr