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Sun, 16 Feb 2025 20:08:02 -0800 (PST) From: adamsimonelli@gmail.com To: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Jiri Slaby , Greg Kroah-Hartman Cc: Adam Simonelli Subject: [PATCH v2 1/2] ttynull: Add an option to allow ttynull to be used as a console device Date: Sun, 16 Feb 2025 23:07:47 -0500 Message-ID: <20250217040748.2017975-2-adamsimonelli@gmail.com> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20250217040748.2017975-1-adamsimonelli@gmail.com> References: <20250217040748.2017975-1-adamsimonelli@gmail.com> Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Adam Simonelli Add a config option CONFIG_NULL_TTY_CONSOLE that will have ttynull be initialized by console_initcall() and selected as a possible console device. Signed-off-by: Adam Simonelli --- drivers/tty/Kconfig | 18 +++++++++++++++++- drivers/tty/ttynull.c | 16 +++++++++++++++- 2 files changed, 32 insertions(+), 2 deletions(-) diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig index 63a494d36a1f..afe4e7722d4c 100644 --- a/drivers/tty/Kconfig +++ b/drivers/tty/Kconfig @@ -383,7 +383,23 @@ config NULL_TTY available or desired. In order to use this driver, you should redirect the console to this - TTY, or boot the kernel with console=ttynull. + TTY, boot the kernel with console=ttynull, or enable + CONFIG_NULL_TTY_CONSOLE. + + If unsure, say N. + +config NULL_TTY_CONSOLE + bool "Supports /dev/ttynull as a console automatically" + depends on NULL_TTY=y && !VT_CONSOLE + help + Say Y here if you want the NULL TTY to be used as a /dev/console + device. + + This is useful for userspace applications that expect a working + console device, without changing the kernel boot options, such as a + distribuition or environment that historically had CONFIG_VT_CONSOLE + enabled, and have now disabled it, but still need /dev/console to be + working for userspace applications. If unsure, say N. diff --git a/drivers/tty/ttynull.c b/drivers/tty/ttynull.c index 6b2f7208b564..8ba629ae426b 100644 --- a/drivers/tty/ttynull.c +++ b/drivers/tty/ttynull.c @@ -57,6 +57,10 @@ static struct tty_driver *ttynull_device(struct console *c, int *index) static struct console ttynull_console = { .name = "ttynull", .device = ttynull_device, +#ifdef CONFIG_NULL_TTY_CONSOLE + .index = -1, + .flags = CON_PRINTBUFFER, +#endif }; static int __init ttynull_init(void) @@ -90,10 +94,20 @@ static int __init ttynull_init(void) } ttynull_driver = driver; - register_console(&ttynull_console); + if (!console_is_registered(&ttynull_console)) + register_console(&ttynull_console); + + return 0; +} +#ifdef CONFIG_NULL_TTY_CONSOLE +static int __init ttynull_register(void) +{ + register_console(&ttynull_console); return 0; } +console_initcall(ttynull_register); +#endif static void __exit ttynull_exit(void) { From patchwork Mon Feb 17 04:07:48 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: adamsimonelli@gmail.com X-Patchwork-Id: 866052 Received: from mail-qk1-f172.google.com (mail-qk1-f172.google.com [209.85.222.172]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 174BB183CBB; 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Sun, 16 Feb 2025 20:08:06 -0800 (PST) Received: from nerdopolis2.mynetworksettings.com ([2600:4040:5e66:a800:3bda:f60d:1567:d3d0]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c07c861537sm488465085a.67.2025.02.16.20.08.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 16 Feb 2025 20:08:05 -0800 (PST) From: adamsimonelli@gmail.com To: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Jiri Slaby , Greg Kroah-Hartman Cc: Adam Simonelli Subject: [PATCH v2 2/2] tty: Change order of ttynull to be loaded sooner. Date: Sun, 16 Feb 2025 23:07:48 -0500 Message-ID: <20250217040748.2017975-3-adamsimonelli@gmail.com> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20250217040748.2017975-1-adamsimonelli@gmail.com> References: <20250217040748.2017975-1-adamsimonelli@gmail.com> Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Adam Simonelli If CONFIG_NULL_TTY_CONSOLE is enabled, and CONFIG_VT is disabled, ttynull will become the default primary console device, based on the load order. Users and distributions that are migrating away from CONFIG_VT will benefit from this as /dev/console would not suddenly become /dev/ttyS0 which could otherwise cause some user space behavior changes, namely the TCGETS ioctl failing, which causes libc's isatty() to incorrectly return false when /dev/ttyS0 is disabled, and will prevent a device that is connected to a user's /dev/ttyS0 to suddenly start getting kernel log messages. Signed-off-by: Adam Simonelli --- drivers/tty/Makefile | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile index 07aca5184a55..03bb47e11e1c 100644 --- a/drivers/tty/Makefile +++ b/drivers/tty/Makefile @@ -11,6 +11,8 @@ obj-$(CONFIG_N_HDLC) += n_hdlc.o obj-$(CONFIG_N_GSM) += n_gsm.o obj-y += vt/ +obj-$(CONFIG_NULL_TTY) += ttynull.o + obj-$(CONFIG_HVC_DRIVER) += hvc/ obj-y += serial/ obj-$(CONFIG_SERIAL_DEV_BUS) += serdev/ @@ -20,7 +22,6 @@ obj-$(CONFIG_AMIGA_BUILTIN_SERIAL) += amiserial.o obj-$(CONFIG_MOXA_INTELLIO) += moxa.o obj-$(CONFIG_MOXA_SMARTIO) += mxser.o obj-$(CONFIG_NOZOMI) += nozomi.o -obj-$(CONFIG_NULL_TTY) += ttynull.o obj-$(CONFIG_SYNCLINK_GT) += synclink_gt.o obj-$(CONFIG_PPC_EPAPR_HV_BYTECHAN) += ehv_bytechan.o obj-$(CONFIG_GOLDFISH_TTY) += goldfish.o