Re: [RFC] tty/sysrq: Add alternative SysRq key

[Andrzej Pietrasiewicz <andrzej.p@xxxxxxxxxxxxx>]

Hi Randy,

W dniu 03.11.2021 o 17:19, Randy Dunlap pisze:
> On 11/3/21 8:54 AM, Andrzej Pietrasiewicz wrote:
> > There exist machines which don't have SysRq key at all, e.g. chromebooks.
> >
> > This patch allows configuring an alternative key to act as SysRq. Devices
> > which declare KEY_SYSRQ in their 'keybit' bitmap continue using KEY_SYSRQ,
> > but other devices use the alternative SysRq key instead, by default F10.
> > Which key is actually used can be modified with sysrq's module parameter.
> >
> > Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@xxxxxxxxxxxxx>
> > ---
> > I'd like to resurrect an old thread regarding supporting alternative SysRq
> > key for machines which don't have a physical SysRq key at all.
> >
> > The old thread:
> >
> > https://www.spinics.net/lists/linux-input/msg67982.html
> >
> > I'm resending this patch, rebased onto v5.15.
> >
> > Any (new) thoughts about it?
>
> Hi,
> Did you test it with this patch?


Thanks... I must have sent an incorrect version (with incomplete
conflict resolution).

Andrzej

> >   drivers/tty/sysrq.c | 28 +++++++++++++++++++++++++---
> >   1 file changed, 25 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> > index c911196ac893..6dd288e53ce9 100644
> > --- a/drivers/tty/sysrq.c
> > +++ b/drivers/tty/sysrq.c
> > @@ -634,6 +634,7 @@ EXPORT_SYMBOL(handle_sysrq);
> >   #ifdef CONFIG_INPUT
> >   static int sysrq_reset_downtime_ms;
> > +static unsigned short alternative_sysrq_key = KEY_F10;
> >   /* Simple translation table for the SysRq keys */
> >   static const unsigned char sysrq_xlate[KEY_CNT] =
> > @@ -653,6 +654,7 @@ struct sysrq_state {
> >       unsigned int alt_use;
> >       unsigned int shift;
> >       unsigned int shift_use;
> > +    unsigned short sys
>
> That line appears to need an ending ';'.
> Or maybe that line was truncated since 'sys' isn't used anywhere in this patch.
>
> >       bool active;
> >       bool need_reinject;
> >       bool reinjecting;
> > @@ -802,10 +804,10 @@ 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->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->sysrq_key, 0);
> >           input_inject_event(handle, EV_KEY, alt_code, 0);
> >           input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
> > @@ -845,6 +847,7 @@ static bool sysrq_handle_keypress(struct sysrq_state *sysrq,
> >               sysrq->shift = code;
> >           break;
> > +key_sysrq:
> >       case KEY_SYSRQ:
> >           if (value == 1 && sysrq->alt != KEY_RESERVED) {
> >               sysrq->active = true;
> > @@ -867,11 +870,15 @@ static bool sysrq_handle_keypress(struct sysrq_state 
> > *sysrq,
> >            * triggering print screen function.
> >            */
> >           if (sysrq->active)
> > -            clear_bit(KEY_SYSRQ, sysrq->handle.dev->key);
> > +            clear_bit(sysrq->sysrq_key, sysrq->handle.dev->key);
> >           break;
> >       default:
> > +        /* handle non-default sysrq key */
> > +        if (code == sysrq->sysrq_key)
> > +            goto key_sysrq;
> > +
> >           if (sysrq->active && value && value != 2) {
> >               unsigned char c = sysrq_xlate[code];
> > @@ -970,6 +977,14 @@ static int sysrq_connect(struct input_handler *handler,
> >       sysrq->handle.private = sysrq;
> >       timer_setup(&sysrq->keyreset_timer, sysrq_do_reset, 0);
> > +    if (test_bit(KEY_SYSRQ, dev->keybit)) {
> > +        sysrq->sysrq_key = KEY_SYSRQ;
> > +        pr_info("%s: using default sysrq key [%x]\n", dev->name, KEY_SYSRQ);
> > +    } else {
> > +        sysrq->sysrq_key = alternative_sysrq_key;
> > +        pr_info("%s: Using alternative sysrq key: [%x]\n", dev->name, 
> > sysrq->sysrq_key);
> > +    }
> > +
> >       error = input_register_handle(&sysrq->handle);
> >       if (error) {
> >           pr_err("Failed to register input sysrq handler, error %d\n",
> > @@ -1078,6 +1093,13 @@ module_param_array_named(reset_seq, sysrq_reset_seq, 
> > sysrq_reset_seq,
> >   module_param_named(sysrq_downtime_ms, sysrq_reset_downtime_ms, int, 0644);
> > +module_param(alternative_sysrq_key, ushort, 0644);
> > +MODULE_PARM_DESC(alternative_sysrq_key,
> > +    "Alternative SysRq key for input devices that don't have SysRq key. F10 
> > by default.\n"
> > +    "Example\n"
> > +    "Using F9 as SysRq:\n"
> > +    "sysrq.alternative_sysrq_key=0x43\n");
> > +
> >   #else
> >   static inline void sysrq_register_handler(void)