From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 750984414; Mon, 24 Feb 2025 07:23:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740381792; cv=none; b=Ef4O1N4MyHiBGzKL0gQrHHOhmhqxH2F7zHviTHSIMBM65+lBnqn68ex4uUWQC+rcw9CPBm2YlqlYCDKry6ajNGeDaZ8FqU6g6Dd2GOLvozarR5DaJHzIuNZp+nXrQsmCvlXAPsWxUfHcISpojIe5QXxh0nOFTTK4OxAw0ARRPZA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740381792; c=relaxed/simple; bh=+EWaupg0d1Pte3v7FOuZSIlbDDH5RojNM3LDm1F5cMU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=WuJ8K//qEkcMjeYyp5uONaczlX0vHuxaYlXVey9F6F1lm45scIEb9BXl8RMJDQPcLVMDjVImJeZeFWgqvD7rnWmJ7XMhYmJs48BTkbygk2IU49jhLSXksVS1+nb4A218pp9ZvuMQDlA9OZSo7LGzT8yygu3i4KKXpNjE9/INpTY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=fBl8Jj6L; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="fBl8Jj6L" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A97D8C4CED6; Mon, 24 Feb 2025 07:23:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1740381792; bh=+EWaupg0d1Pte3v7FOuZSIlbDDH5RojNM3LDm1F5cMU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fBl8Jj6LUFwHqvw6djbWYuWfXWPw3yQ90Su9J2HvUOINU7Ao6JzFW58lfFB+94NO9 3KUN5hUPiwZobdKfVBKWZvihnfSpJjOAnBGRWc5HU7ykQKiBIQ08mHcDsm6f4EhLYQ VPcfHxOrXgHnhQVL99+Gfa5taiGDWDAYcqtMvBkQ= Date: Mon, 24 Feb 2025 08:23:09 +0100 From: Greg Kroah-Hartman To: adamsimonelli@gmail.com Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Jiri Slaby Subject: Re: [PATCH v4 2/2] tty: Change order of ttynull to be linked sooner if enabled as a console. Message-ID: <2025022421-refract-defame-94db@gregkh> References: <20250223204456.1913392-1-adamsimonelli@gmail.com> <20250223204456.1913392-3-adamsimonelli@gmail.com> Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250223204456.1913392-3-adamsimonelli@gmail.com> On Sun, Feb 23, 2025 at 03:44:56PM -0500, adamsimonelli@gmail.com wrote: > 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 link order. > > Many distributions ship with CONFIG_VT enabled. On tested desktop hardware > if CONFIG_VT is disabled, the default console device falls back to > /dev/ttyS0 instead of /dev/tty. > > This could cause issues in user space, and hardware problems: > > 1. The user space issues include the case where /dev/ttyS0 is > disconnected, and the TCGETS ioctl, which some user space libraries use > as a probe to determine if a file is a tty, is called on /dev/console and > fails. Programs that call isatty() on /dev/console and get an incorrect > false value may skip expected logging to /dev/console > > 2. The hardware issues include the case if a user has a science instrument > or other device connected to the /dev/ttyS0 port, and they were to upgrade > to a kernel that is disabling the CONFIG_VT option, kernel logs will then be > sent to the device connected to /dev/ttyS0 unless they edit their kernel > command line manually. > > The new CONFIG_NULL_TTY_CONSOLE option will give users and distribution > maintainers an option to avoid this. Disabling CONFIG_VT and enabling > CONFIG_NULL_TTY_CONSOLE will ensure the default kernel console behavior > is not dependant on hardware configuration by default, and avoid > unexpected new behavior on devices connected to the /dev/ttyS0 serial > port. > > Signed-off-by: Adam Simonelli > --- > drivers/tty/Makefile | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile > index 07aca5184a55..1a1051ecb1af 100644 > --- a/drivers/tty/Makefile > +++ b/drivers/tty/Makefile > @@ -11,6 +11,10 @@ obj-$(CONFIG_N_HDLC) += n_hdlc.o > obj-$(CONFIG_N_GSM) += n_gsm.o > > obj-y += vt/ > +#If ttynull is configured to be a console by default, ensure that it is linked > +#earlier before a real one is selected. > +obj-$(CONFIG_NULL_TTY_CONSOLE) += ttynull.o > + > obj-$(CONFIG_HVC_DRIVER) += hvc/ > obj-y += serial/ > obj-$(CONFIG_SERIAL_DEV_BUS) += serdev/ > @@ -20,7 +24,13 @@ obj-$(CONFIG_AMIGA_BUILTIN_SERIAL) += amiserial.o > obj-$(CONFIG_MOXA_INTELLIO) += moxa.o > obj-$(CONFIG_MOXA_SMARTIO) += mxser.o > obj-$(CONFIG_NOZOMI) += nozomi.o > + > +#If ttynull is enabled, but not as a boot console, it is linked and used later > +#after the real ones. > +ifneq ($(CONFIG_NULL_TTY_CONSOLE),y) > obj-$(CONFIG_NULL_TTY) += ttynull.o > +endif Nit, a " " needs to be after the "#" character, right? And ick, this is going to be tricky, changing the link order depending on the configuration option setting? This feels wrong, and messy, and very fragile. thanks, greg k-h