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Hermes SMTP Server) with ESMTPA ID a897091e1f8a4ddc26c454231bb7095b; Sun, 18 Aug 2024 14:30:22 +0000 (UTC) From: nerdopolis To: Greg KH Cc: pmladek@suse.com, rostedt@goodmis.org, john.ogness@linutronix.de, senozhatsky@chromium.org, tglx@linutronix.de, tony@atomide.com, linux-kernel@vger.kernel.org Subject: Re: VT-less kernels, and /dev/console on x86 Date: Sun, 18 Aug 2024 10:30:22 -0400 Message-ID: <1947584.IobQ9Gjlxr@nerdopolis2> In-Reply-To: <3669532.hdfAi7Kttb@nerdopolis2> References: <2669238.7s5MMGUR32.ref@nerdopolis2> <2024081824-leggings-omission-562a@gregkh> <3669532.hdfAi7Kttb@nerdopolis2> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Mailer: WebService/1.1.22544 mail.backend.jedi.jws.acl:role.jedi.acl.token.atz.jws.hermes.aol On Sunday, August 18, 2024 8:33:25 AM EDT nerdopolis wrote: > On Sunday, August 18, 2024 1:12:14 AM EDT Greg KH wrote: > > On Sat, Aug 17, 2024 at 08:09:20PM -0400, nerdopolis wrote: > > > Hi > > > > > > I originally brought this up on linux-serial, but I think it makes more sense > > > that it's part of how printk console device selection works. Without VTs, while > > > most software is able to handle the situation, some userspace programs expect > > > /dev/console to still be responsive. Namely systemd. It calls isatty() against > > > /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 > > > > > > In order to use this driver, you should redirect the console to this > > > TTY, or boot the kernel with console=ttynull. > > > - > > > If unsure, say N. > > > > > > +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; > > > > > > +#ifdef CONFIG_NULL_TTY_CONSOLE > > > + if (!strstr(boot_command_line, "console=")) > > > + add_preferred_console("ttynull", 0, NULL); > > > +#endif > > > + > > > /* Setup the default TTY line discipline. */ > > > n_tty_init(); > > > > > > > > > > > > > > > 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 past, > > > and for bootloader configs, it won't change any behavior if the kernel command > > > line has a console device specified > > > > What is wrong with just setting the kernel command line for this > > instead? > > > When they eventually start shipping kernels without VTs, they will then have to > include a script in their upgrade process that runs > > sed -i "s/GRUB_CMDLINE_LINUX_DEFAULT=\"/GRUB_CMDLINE_LINUX_DEFAULT=\"nomodeset /g" /etc/default/grub Ugh, I meant sed -i "s/GRUB_CMDLINE_LINUX_DEFAULT=\"/GRUB_CMDLINE_LINUX_DEFAULT=\"console=ttynull /g" /etc/default/grub sorry > > (Assuming they are using Grub) > > thanks, > > > > greg k-h > > > > > > >