path: root/init
diff options
authorPetr Mladek <pmladek@suse.com>2021-01-08 12:48:47 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2021-01-08 11:02:18 -0800
commita91bd6223ecd46addc71ee6fcd432206d39365d2 (patch)
tree1358320c4be9be264fe87ea6e014343e715b3580 /init
parentc4cc3b1de31b76f425ce92854783709386f9e1b7 (diff)
Revert "init/console: Use ttynull as a fallback when there is no console"
This reverts commit 757055ae8dedf5333af17b3b5b4b70ba9bc9da4e. The commit caused that ttynull was used as the default console on several systems[1][2][3]. As a result, the console was blank even when a better alternative existed. It happened when there was no console configured on the command line and ttynull_init() was the first initcall calling register_console(). Or it happened when /dev/ did not exist when console_on_rootfs() was called. It was not able to open /dev/console even though a console driver was registered. It tried to add ttynull console but it obviously did not help. But ttynull became the preferred console and was used by /dev/console when it was available later. The commit tried to fix 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 should 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. [1] https://lore.kernel.org/linux-kselftest/20201221144302.GR4077@smile.fi.intel.com/ [2] https://lore.kernel.org/lkml/d2a3b3c0-e548-7dd1-730f-59bc5c04e191@synopsys.com/ [3] https://patchwork.ozlabs.org/project/linux-um/patch/20210105120128.10854-1-thomas@m3y3r.de/ Reported-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Reported-by: Vineet Gupta <vgupta@synopsys.com> Reported-by: Thomas Meyer <thomas@m3y3r.de> Signed-off-by: Petr Mladek <pmladek@suse.com> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'init')
1 files changed, 2 insertions, 8 deletions
diff --git a/init/main.c b/init/main.c
index 421640fca375..c68d784376ca 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1480,14 +1480,8 @@ void __init console_on_rootfs(void)
struct file *file = filp_open("/dev/console", O_RDWR, 0);
if (IS_ERR(file)) {
- pr_err("Warning: unable to open an initial console. Fallback to ttynull.\n");
- register_ttynull_console();
- file = filp_open("/dev/console", O_RDWR, 0);
- if (IS_ERR(file)) {
- pr_err("Warning: Failed to add ttynull console. No stdin, stdout, and stderr for the init process!\n");
- return;
- }
+ pr_err("Warning: unable to open an initial console.\n");
+ return;

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