Re: [PATCH 3/6] tty/sysrq: Allow configurable SysRq key

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Hi Dmitry,

W dniu 11.05.2020 o 20:01, Dmitry Torokhov pisze:
Hi Andrzej,

On Mon, May 11, 2020 at 03:59:15PM +0200, Andrzej Pietrasiewicz wrote:
There are existing machines which don't have SysRq key, e.g. chromebooks.
This patch allows configuring which key acts as SysRq. The value is passed
with sysrq's module parameter.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@xxxxxxxxxxxxx>
---
  drivers/tty/sysrq.c | 14 +++++++++++---
  1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 93202fc24308..ebad9799fdc0 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -604,6 +604,7 @@ EXPORT_SYMBOL(handle_sysrq);
#ifdef CONFIG_INPUT
  static int sysrq_reset_downtime_ms;
+static unsigned short sysrq_key = KEY_SYSRQ;
/* Simple translation table for the SysRq keys */
  static const unsigned char sysrq_xlate[KEY_CNT] =
@@ -735,10 +736,10 @@ static void sysrq_reinject_alt_sysrq(struct work_struct *work)
/* Simulate press and release of Alt + SysRq */
  		input_inject_event(handle, EV_KEY, alt_code, 1);
-		input_inject_event(handle, EV_KEY, KEY_SYSRQ, 1);
+		input_inject_event(handle, EV_KEY, sysrq_key, 1);
  		input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
- input_inject_event(handle, EV_KEY, KEY_SYSRQ, 0);
+		input_inject_event(handle, EV_KEY, sysrq_key, 0);
  		input_inject_event(handle, EV_KEY, alt_code, 0);
  		input_inject_event(handle, EV_SYN, SYN_REPORT, 1);

Unfortunately this means that if I connect my external keyboard to
chromebook SysRq there will stop working, which is not great. If we want
to support this we need to figure out how to make this handling
per-device.

I see your point.

So what you envision is SysRq key being configured for each input device
separately. I can see these problems:

- How to attach such a configuration information to each specific
device instance? It is easy if done framework-wise, but gets messy
if done per-device. And we are talking per-device rather than per-driver.

- If a user has multiple USB keyboards connected (possibly through a cascade
of hubs), how would they know which key is valid for which keyboard?

Wouldn't it be better if such a piece of configuration were valid for the
whole system instead of per-device?

Andrzej



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