From: Adam Simonelli <adamsimonelli@xxxxxxxxx>
When switching to a CONFIG_VT=n world, at least on x86 systems,
/dev/console becomes /dev/ttyS0. This can cause some undesired effects.
/dev/console's behavior is now tied to the physical /dev/ttyS0, which when
disconnected can cause isatty() to fail when /dev/ttyS0 is disconnected,
and users who upgrade to a theoretical vt-less kernel from their
distribution who have a device such as a science instrument connected to
their /dev/ttyS0 port will suddenly see it receive kernel log messages.
When the new CONFIG_NULL_TTY_DEFAULT_CONSOLE option is turned on, this will
allow the ttynull device to be leveraged as the default console. Distributions
that had CONFIG_VT turned on before will be able to leverage this option
to where /dev/console is still backed by a psuedo device, avoiding these
issues, without needing to enable the entire VT subsystem.
v2:
rebase
v3:
Clarify commit messages.
Guard the all the register_console()s in ttynull to prevent it from being
registered twice.
Only change the link order if CONFIG_NULL_TTY_CONSOLE is enabled, otherwise
use the existing order for ttynull if only CONFIG_NULL_TTY is enabled.
Document why the link order changes in the drivers/tty/Makefile file.
Replace #ifdefs
v4:
Remember to actually include the changes to v3 in the cover letter.
v5:
Correct code formatting in Makefile comment.
v6:
Change to CONFIG_NULL_TTY_DEFAULT_CONSOLE
Set the index to -1, and don't set the flags
Use add_preferred_console() instead of register_console() in ttynull's
console_initcall when CONFIG_NULL_TTY_DEFAULT_CONSOLE is enabled
v7
Add a commit message to the first commit, and the Suggested-by
Correct Kconfig tabs/spaces formatting
Invert the console_set_on_cmdline check
v8
Update Documentation.
Remove the "CONFIG_" in the help text when mentioning other configuration
options.
Update commit message
Adam Simonelli (4):
ttynull: Always initialize console index to -1
ttynull: Add an option to allow ttynull to be used as a console device
tty: Change order of ttynull to be linked sooner if enabled as a
console.
Documentation/serial-console: Document
CONFIG_NULL_TTY_DEFAULT_CONSOLE.
Documentation/admin-guide/serial-console.rst | 4 +++-
drivers/tty/Kconfig | 15 ++++++++++++++-
drivers/tty/Makefile | 12 ++++++++++++
drivers/tty/ttynull.c | 14 ++++++++++++++
4 files changed, 43 insertions(+), 2 deletions(-)
--
2.45.2
