kern/124223: [acpi] [patch] acpi_battery.c -- Notify user-defined critical level via devd(8)

[Nate Lawson]

Pietro Cerutti wrote:
> Nate Lawson wrote:
> | There are a few problems with your approach.
> |
> | Critical status is already reported with a flag when usermode polls for
> | the battery status:
> |> if (sc->bst.state & ACPI_BATT_STAT_CRITICAL) {
> |>     if ((sc->flags & ACPI_BATT_STAT_CRITICAL) == 0) {
> |>         sc->flags |= ACPI_BATT_STAT_CRITICAL;
> |>         device_printf(dev, "critically low charge!\n");
> |>     }
> |> }
> 
> I agree. Critical level is already checked for in the cmbat module.
> However, reporting is not done in a "standardized" way. My patch would
> just like to add notification through devd.

But it doesn't just add notification through devd.  It adds a thread,
that separately polls for battery state and sends a notify through devd.
 If the user is running any battery app, there's a double poll for the
same info.

I subscribe to the design approach that where it makes sense to do
something in usermode, don't do it in kernel mode.  In this case, the IO
interface is poll-only, and any user app that is running can set its own
policy for how to deal with the information it gets from polling.

> I agree that userlevel utilities can e.g., retrieve the remaining
> percent and set the critical level arbitrarily, but I anyway think that
> a configurable level to be seen as critical by the OS could be a useful
> addition.
> 
> I'm open to discussions about the best way to implement it (cmbat,
> battery, ...?), if we get to an agreement that this could be a useful
> feature :) Otherwise feel free to close the PR, as I can accept your
> arguments.

I think it would be better to work with the third-party apps to support
configurable levels.  In xbatt:

    /* If battery life is short, ring a bell */
    if ((life != APM_STAT_UNKNOWN) && (life < 5) && ((life % 5) == 0)) {

... and ...

      /* set gage color */
        if (displayType == Color) {
            if (life < 3) {
                gage_color = "red";
            } else if (life < 5) {
                gage_color = "yellow";
            }
        }

These thresholds could easily be a command-line var or X resource.
Let's keep this in usermode, where policy belongs.

-- 
Nate