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Hermes SMTP Server) with ESMTPA ID 3921f1432360f11af80326769747f20a; Sun, 18 Aug 2024 00:09:26 +0000 (UTC) From: nerdopolis To: pmladek@suse.com, rostedt@goodmis.org, john.ogness@linutronix.de, senozhatsky@chromium.org, gregkh@linuxfoundation.org, tglx@linutronix.de, tony@atomide.com, linux-kernel@vger.kernel.org Subject: VT-less kernels, and /dev/console on x86 Date: Sat, 17 Aug 2024 20:09:20 -0400 Message-ID: <2669238.7s5MMGUR32@nerdopolis2> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable References: <2669238.7s5MMGUR32.ref@nerdopolis2> X-Mailer: WebService/1.1.22544 mail.backend.jedi.jws.acl:role.jedi.acl.token.atz.jws.hermes.aol Content-Type: text/plain; charset="utf-8" Hi I originally brought this up on linux-serial, but I think it makes more sen= se that it's part of how printk console device selection works. Without VTs, w= hile most software is able to handle the situation, some userspace programs expe= ct /dev/console to still be responsive. Namely systemd. It calls isatty() agai= nst /dev/console, and since /dev/console on VT-less systems currently defaults = to /dev/ttyS0, and when /dev/ttyS0 is disconnected, the ioctl's fail, and it refuses to write log messages to it. There doesn't seem to be a mailing list for printk, so I had to use get_maintainer.pl. Hopefully this is correct After some grepping and guessing and testing, and playing around Something = like diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig index a45d423ad10f..f94a4632aab0 100644 --- a/drivers/tty/Kconfig +++ b/drivers/tty/Kconfig @@ -384,9 +384,12 @@ config NULL_TTY =20 In order to use this driver, you should redirect the console to t= his TTY, or boot the kernel with console=3Dttynull. - If unsure, say N. =20 +config NULL_TTY_CONSOLE + bool "Supports /dev/ttynull as a console automatically" + depends on NULL_TTY && !VT_CONSOLE + config VCC tristate "Sun Virtual Console Concentrator" depends on SUN_LDOMS diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index dddb15f48d59..c1554a789de8 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3712,6 +3712,11 @@ void __init console_init(void) initcall_t call; initcall_entry_t *ce; =20 +#ifdef CONFIG_NULL_TTY_CONSOLE + if (!strstr(boot_command_line, "console=3D")) + add_preferred_console("ttynull", 0, NULL); +#endif + /* Setup the default TTY line discipline. */ n_tty_init(); =20 seems to work, it conflicts with CONFIG_VT_CONSOLE since it is effectively redundant, it is optional, so that it doesn't cause any changes to configurations, that historically had CONFIG_VT_CONSOLE turned off in the p= ast, and for bootloader configs, it won't change any behavior if the kernel comm= and line has a console device specified With ttynull as the console device, isatty() no longer fails on /dev/consol= e, systemd writes the log messages fine to /dev/console, and when Plymouth cal= ls TIOCCONS on its PTY, it is able to get the log messages. Thanks