On 05/12/2017 04:46 PM, Petr Mladek wrote:
On Fri 2017-05-12 14:57:29, Petr Mladek wrote:
On Thu 2017-05-11 17:41:58, Sergey Senozhatsky wrote:
On (05/11/17 17:24), Sergey Senozhatsky wrote:
On (05/09/17 10:29), Sabrina Dubroca wrote:
[..]
That's caused a change of behavior in my qemu setup, with this cmdline
root=/dev/sda1 console=ttyS1 console=ttyS0
Before, the kernel logs appeared on ttyS1, and I logged in with ttyS0
(with my setup, ttyS1 is a file and ttyS0 is unix socket). Now, the
kernel logs go to ttyS0. I need to swap the two console= parameters to
restore behavior.
Do you actually need to define console=ttyS0 on the cmdline?
Exactly. You should specify a console on the command line only
if you want kernel logs on it. It's kernel bug that one of this
consoles does not receive kernel logs, see
Documentation/admin-guide/serial-console.rst
IMHO, if register_console() was called for the unix socket, it
would make logs appear on both ttyS0 and ttyS1. It seems
that register_console() is called only for the console that
stores logs into the file.
It's not quite accurate sentence. It's qemu who deals with file/socket and
it is transparent to kernel.
adding
console=tty0 anywhere on that cmdline makes the logs appear on both
tty0 and one ttyS* (but only one of them, and the ordering of the
ttyS* matters).
I guess that it worked this way before. I mean that the logs appeared
on both tty0 and one of ttyS*. The only difference should be that
the patch changed the selected ttyS*. So this is still the same problem.
Hmm, I have no idea how to fix this. This is the case where
a registered console matches more entries from the command line.
The fix that caused this regression fixed exactly this situation
and we wanted to make the preferred console first.
I am not sure if we broke some backward compatibility or actually made
it more predictable in the long term.
I think that we actually fixed a very old bug. The last mentioned
console= should be the preferred one and the logs are finally
printed there. Or do I miss anything?
Last mentioned 'console=' (preferred console) is the console that
should become /dev/console. Its driver is returned by console_device().
In other respects the last mentioned console is not special,
so I believe it is irrelevant to the report.
Thank you
Aleksey Makarov
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