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Date: Thu, 7 Jan 2021 20:16:39 +0100 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: Petr Mladek <pmladek@...e.com> Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Steven Rostedt <rostedt@...dmis.org>, John Ogness <john.ogness@...utronix.de>, Linus Torvalds <torvalds@...ux-foundation.org>, Guenter Roeck <linux@...ck-us.net>, Shreyas Joshi <shreyas.joshi@...mp.com>, shreyasjoshi15@...il.com, Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>, Greg Ungerer <gerg@...ux-m68k.org>, Vineet Gupta <vgupta@...opsys.com>, Thomas Meyer <thomas@...3r.de>, David Gow <davidgow@...gle.com>, Brendan Higgins <brendanhiggins@...gle.com>, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Shuah Khan <skhan@...uxfoundation.org>, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/1] Revert "init/console: Use ttynull as a fallback when there is no console" On Thu, Jan 07, 2021 at 05:44:00PM +0100, Petr Mladek wrote: > This reverts commit 757055ae8dedf5333af17b3b5b4b70ba9bc9da4e. > > The commit caused that ttynull was used as the default console > on many systems. It happened when there was no console configured > on the command line and ttynull_init() was the first initcall > calling register_console(). > > The commit fixed a historical problem that have been there for ages. > The primary motivation was the commit 3cffa06aeef7ece30f6 > ("printk/console: Allow to disable console output by using console="" > or console=null"). It provided a clean solution > for a workaround that was widely used and worked only by chance. > > This revert causes that the console="" or console=null command line > options will again work only by chance. These options will cause that > a particular console will be preferred and the default (tty) ones > will not get enabled. There will be no console registered at > all. As a result there won't be stdin, stdout, and stderr for > the init process. But it worked exactly this way even before. > > The proper solution has to fulfill many conditions: > > + Register ttynull only when explicitly required or as > the ultimate fallback. > > + ttynull must get associated with /dev/console but it must > not become preferred console when used as a fallback. > Especially, it must still be possible to replace it > by a better console later. > > Such a change requires clean up of the register_console() code. > Otherwise, it would be even harder to follow. Especially, the use > of has_preferred_console and CON_CONSDEV flag is tricky. The clean > up is risky. The ordering of consoles is not well defined. And > any changes tend to break existing user settings. > > Do the revert at the least risky solution for now. > > Signed-off-by: Petr Mladek <pmladek@...e.com> Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Linus, can you take this directly, or is this going through some other tree? thanks, greg k-h
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