| Message ID | 20250311033133.1859963-1-adamsimonelli@gmail.com |
|---|---|
| Headers | show |
| Series | Optionally allow ttynull to be selected as a default console | expand |
On Mon 2025-03-10 23:31:30, adamsimonelli@gmail.com wrote: > From: Adam Simonelli <adamsimonelli@gmail.com> > > This allows ttynull to be considered in console selection. This is not true. It should be possible to register ttynull even when .index == 0. The .index is important only for drivers which support more devices, e.g. the serial port or virtual terminal. > > Suggested-by: Petr Mladek <pmladek@suse.com> > Signed-off-by: Adam Simonelli <adamsimonelli@gmail.com> > --- > drivers/tty/ttynull.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/tty/ttynull.c b/drivers/tty/ttynull.c > index 6b2f7208b564..d8b51edde628 100644 > --- a/drivers/tty/ttynull.c > +++ b/drivers/tty/ttynull.c > @@ -57,6 +57,7 @@ static struct tty_driver *ttynull_device(struct console *c, int *index) > static struct console ttynull_console = { > .name = "ttynull", > .device = ttynull_device, > + .index = -1, There is only one "/dev/ttynull". And its index is initialized to "0". At least it seems to be the last parameter in: static int __init ttynull_init(void) { [...] tty_port_link_device(&ttynull_port, driver, 0); [...] } So, I believe this it should be perfectly fine to keep the default "0" here. Note that it is special for ttynull because it is only one... IMHO, this patch adds more harm than good :-) Best Regards, Petr
On Wednesday, March 12, 2025 10:38:59 AM EDT Petr Mladek wrote: > On Mon 2025-03-10 23:31:30, adamsimonelli@gmail.com wrote: > > From: Adam Simonelli <adamsimonelli@gmail.com> > > > > This allows ttynull to be considered in console selection. > > This is not true. It should be possible to register ttynull even > when .index == 0. > > The .index is important only for drivers which support more devices, > e.g. the serial port or virtual terminal. > > > > > Suggested-by: Petr Mladek <pmladek@suse.com> > > Signed-off-by: Adam Simonelli <adamsimonelli@gmail.com> > > --- > > drivers/tty/ttynull.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/drivers/tty/ttynull.c b/drivers/tty/ttynull.c > > index 6b2f7208b564..d8b51edde628 100644 > > --- a/drivers/tty/ttynull.c > > +++ b/drivers/tty/ttynull.c > > @@ -57,6 +57,7 @@ static struct tty_driver *ttynull_device(struct console *c, int *index) > > static struct console ttynull_console = { > > .name = "ttynull", > > .device = ttynull_device, > > + .index = -1, > > There is only one "/dev/ttynull". And its index is initialized to "0". > At least it seems to be the last parameter in: > > static int __init ttynull_init(void) > { > [...] > tty_port_link_device(&ttynull_port, driver, 0); > [...] > } > > So, I believe this it should be perfectly fine to keep the default "0" > here. Note that it is special for ttynull because it is only one... > > IMHO, this patch adds more harm than good :-) > > Best Regards, > Petr > Understood, thanks for the explanation about that.
From: Adam Simonelli <adamsimonelli@gmail.com> 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(-)