* Does sysrq work over USB?
@ 2021-11-16 14:04 Marc SCHAEFER
2021-11-16 21:29 ` Valentin Vidić
0 siblings, 1 reply; 6+ messages in thread
From: Marc SCHAEFER @ 2021-11-16 14:04 UTC (permalink / raw)
To: kernelnewbies
Hello,
I made the following setup work, that is I can send break and '?'
(to get the magic sysrq help) or 's' to do an Emergency sync, and the
kernel logs it:
laptop apu2
USB serial port ------- null modem ------- ttyS0 internal 16550A
(an apu2 is an embedded amd64 computer [4])
As it works, of course MAGIC_SYSRQ is enabled, including for serial
ports, and the correct value is in the /proc pseudo-file.
It works with the getty enabled or disabled.
However, the following does not work to support magic sysrq, although
bidirectionnal communication also works with cu [5], with the correct
speed set:
laptop apu2
USB serial port ------- null modem ------- USB serial port
First, reading documentation, I thought that this would not be possible with
USB and only with the internal serial port [1], but then, reading kernel
source, it looks it should work with my adapter:
Oct 11 14:30:56 apu2-init7 kernel: [ 9.915105] usb 2-2: pl2303 converter now attached to ttyUSB0
since the driver [2] contains code for magic sysrq, see line 993 for
sysrq mode and line 892 for break handling, with implementation in [3]
(lines 589-597).
I am running Debian buster kernel 4.19.0-18-amd64 on the apu2.
Should I abandon all hope to make it work with USB, or should it work?
Thank your for any pointers.
[1] https://www.kernel.org/doc/Documentation/admin-guide/sysrq.rst
"On the serial console (PC style standard serial ports only)"
[2] https://github.com/jplozi/linux-4.19/blob/loadbalancing/drivers/usb/serial/pl2303.c
[3] https://github.com/jplozi/linux-4.19/blob/loadbalancing/drivers/usb/serial/generic.c
[4] https://pcengines.ch/apu2.htm
[5] https://linux.die.net/man/1/cu
from the days before 2003 where I was doing UUCP
cu -l ttyUSB0 -s 9600
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^ permalink raw reply [flat|nested] 6+ messages in thread* Re: Does sysrq work over USB?
2021-11-16 14:04 Does sysrq work over USB? Marc SCHAEFER
@ 2021-11-16 21:29 ` Valentin Vidić
2021-11-21 15:47 ` Marc SCHAEFER
0 siblings, 1 reply; 6+ messages in thread
From: Valentin Vidić @ 2021-11-16 21:29 UTC (permalink / raw)
To: kernelnewbies
On Tue, Nov 16, 2021 at 03:04:56PM +0100, Marc SCHAEFER wrote:
> First, reading documentation, I thought that this would not be possible with
> USB and only with the internal serial port [1], but then, reading kernel
> source, it looks it should work with my adapter:
>
> Oct 11 14:30:56 apu2-init7 kernel: [ 9.915105] usb 2-2: pl2303 converter now attached to ttyUSB0
>
> since the driver [2] contains code for magic sysrq, see line 993 for
> sysrq mode and line 892 for break handling, with implementation in [3]
> (lines 589-597).
>
> I am running Debian buster kernel 4.19.0-18-amd64 on the apu2.
>
> Should I abandon all hope to make it work with USB, or should it work?
>
> Thank your for any pointers.
Do you have console=ttyUSB0,... set? What does /proc/consoles say?
--
Valentin
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Does sysrq work over USB?
2021-11-16 21:29 ` Valentin Vidić
@ 2021-11-21 15:47 ` Marc SCHAEFER
2021-11-21 17:51 ` Valentin Vidić
0 siblings, 1 reply; 6+ messages in thread
From: Marc SCHAEFER @ 2021-11-21 15:47 UTC (permalink / raw)
To: kernelnewbies
On Tue, Nov 16, 2021 at 10:29:00PM +0100, Valentin Vidi?? wrote:
> Do you have console=ttyUSB0,... set? What does /proc/consoles say?
No, I did not.
Now, I have added on a test machine:
console=ttyUSB0,9600 console=tty0
to /etc/default/grub and started upgrade-grub and rebooted.
I had and I still have:
root@gluster-1:~# cat /proc/consoles
tty0 -WU (EC p ) 4:1
However, the command line seems correct and multiple console= are
valid [1]:
root@gluster-1:~# cat /proc/cmdline
BOOT_IMAGE=/vmlinuz-4.19.0-18-amd64 root=/dev/mapper/vg1-root ro console=ttyUSB0,9600 console=tty0 quiet raid0.default_layout=1
It does not seem to be work for some reason.
Let's try with one ttyUSB console specification only: does not
boot anymore. Does not print anything on ttyUSB0. Had to recover
using a grub kernel command line edition at boot time.
Any idea?
NB: the USB serial port works with cu bidirectionnally once the
system is booted, but %break has no effect.
[1] https://www.kernel.org/doc/html/latest/admin-guide/serial-console.html
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Does sysrq work over USB?
2021-11-21 15:47 ` Marc SCHAEFER
@ 2021-11-21 17:51 ` Valentin Vidić
2021-11-21 18:07 ` Valentin Vidić
0 siblings, 1 reply; 6+ messages in thread
From: Valentin Vidić @ 2021-11-21 17:51 UTC (permalink / raw)
To: kernelnewbies
On Sun, Nov 21, 2021 at 04:47:57PM +0100, Marc SCHAEFER wrote:
> On Tue, Nov 16, 2021 at 10:29:00PM +0100, Valentin Vidi?? wrote:
> > Do you have console=ttyUSB0,... set? What does /proc/consoles say?
>
> No, I did not.
>
> Now, I have added on a test machine:
>
> console=ttyUSB0,9600 console=tty0
>
> to /etc/default/grub and started upgrade-grub and rebooted.
>
> I had and I still have:
>
> root@gluster-1:~# cat /proc/consoles
> tty0 -WU (EC p ) 4:1
>
> However, the command line seems correct and multiple console= are
> valid [1]:
>
> root@gluster-1:~# cat /proc/cmdline
> BOOT_IMAGE=/vmlinuz-4.19.0-18-amd64 root=/dev/mapper/vg1-root ro console=ttyUSB0,9600 console=tty0 quiet raid0.default_layout=1
Seems like it was not picked up for some reason. You can try with this:
console=tty0 console=ttyUSB0,9600n8
--
Valentin
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Does sysrq work over USB?
2021-11-21 17:51 ` Valentin Vidić
@ 2021-11-21 18:07 ` Valentin Vidić
2021-11-21 20:49 ` Marc SCHAEFER
0 siblings, 1 reply; 6+ messages in thread
From: Valentin Vidić @ 2021-11-21 18:07 UTC (permalink / raw)
To: kernelnewbies
On Sun, Nov 21, 2021 at 06:51:54PM +0100, Valentin Vidić wrote:
> Seems like it was not picked up for some reason. You can try with this:
>
> console=tty0 console=ttyUSB0,9600n8
I tried and it doesn't work for me either, but the problem is most
likely missing CONFIG_USB_SERIAL_CONSOLE=y option in the kernel build:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=868352
--
Valentin
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Does sysrq work over USB?
2021-11-21 18:07 ` Valentin Vidić
@ 2021-11-21 20:49 ` Marc SCHAEFER
0 siblings, 0 replies; 6+ messages in thread
From: Marc SCHAEFER @ 2021-11-21 20:49 UTC (permalink / raw)
To: kernelnewbies
Hello,
On Sun, Nov 21, 2021 at 07:07:33PM +0100, Valentin Vidi?? wrote:
> I tried and it doesn't work for me either, but the problem is most
> likely missing CONFIG_USB_SERIAL_CONSOLE=y option in the kernel build:
>
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=868352
Yes,
with a kernel recompiled with those options and grub configured,
I get:
CONFIG_USB=y
CONFIG_USB_SERIAL=y
CONFIG_USB_SERIAL_CONSOLE=y
CONFIG_U_SERIAL_CONSOLE=y
I get:
root@gluster-1:~# cat /proc/consoles
tty0 -WU (EC p ) 4:1
ttyUSB0 -W- (E p ) 188:0
and I can then do sysrq from USB:
schaefer@acer-1:~$ cu -l ttyUSB0 -s 9600
Connected.
~%break
[ 1633.701624] sysrq: HELP : loglevel(0-9) reboot(b) crash(c)
terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i)
thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l)
show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p)
show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u)
force-fb(V) show-blocked-tasks(w) dump-ftrace-buffer(z)
Thank you for your help: I have now a way to make it work.
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^ permalink raw reply [flat|nested] 6+ messages in thread
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2021-11-16 14:04 Does sysrq work over USB? Marc SCHAEFER
2021-11-16 21:29 ` Valentin Vidić
2021-11-21 15:47 ` Marc SCHAEFER
2021-11-21 17:51 ` Valentin Vidić
2021-11-21 18:07 ` Valentin Vidić
2021-11-21 20:49 ` Marc SCHAEFER
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