Date: Thu, 21 Jul 2016 07:26:20 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> To: Bruce Evans <brde@optusnet.com.au> Cc: freebsd-i386@freebsd.org Subject: Re: [Bug 211246] [syscons] console and ttyv0 competing for keystrokes Message-ID: <20160721041213.W1931@besplex.bde.org> In-Reply-To: <20160721013907.T957@besplex.bde.org> References: <bug-211246-10@https.bugs.freebsd.org/bugzilla/> <20160721013907.T957@besplex.bde.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Thu, 21 Jul 2016, Bruce Evans wrote: > On Wed, 20 Jul 2016 bugzilla-noreply@freebsd.org wrote: > >> ... >> As an aside, things written to /dev/console invariably appear on the >> ttyv0-screen on my system, but are never passed on to xconsole. > > This seems to be the expected behaviour. You asked for foot-shooting and > got it. This is not a security hole since it requires root privilege. > > xconsole without -f should use the correct file. If not, try /dev/tty or > $(tty). It uses the correct file, but still doesn't work... > xconsole under FreeBSD-11 with a FreeBSD-~5.2 userland and a FreeBSD-4 > ports version of X fails due to permissions problems here, but I saw > exactly the same behaviour in the simpler setup of logins on ttyv0 > and ttyv1 and a program on ttyv1 grabbing the console using > > int c = 1; ioctl(0, TIOCCONS, &c);". I forgot to redirect fd 0 from ttyv1 to /dev/console, so this was testing something different. Apparently I had /dev/console open somewhere to get the same symptoms. But it is not necessary to use TIOCCONS to see problems. Simply run "cat /dev/console" on 1 terminal. This competes for input with a shell on the device behing the console. On an SMP system with 8 CPUs, the sharing of the input was very fair with 3 processes reading it (1 normal, 1 TIOCCONS and 1 /dev/console). > > xconsole with no args works correctly under FreeBSD-~5.2. The permissions problems were just root not being able to read .Xauthority owned by non-root over nfs (nfs maps root somewhere unusable by default). The ~5.2 system is UP, so working correctly might have been UP magic instead of syscons magic. With 1 cat of /sys/console, the sharing was very unfair -- the shell on ttyv0 got it all. So using ttyv0 and console with getty and xconsole is much the same foot shooting as using them with 2 getty's. So you must not use ttyv0 if you want to use xconsole! Not using ttyv0 means not running any program that opens it, starting with getty (init uses only /dev/console). There are further complications for low-level consoles, but using TIOCCONS reduces complications together with features and bugs in the low-level consoles by mostly not using them. Bruce
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20160721041213.W1931>