On 7/28/06, Pavel Machek <pavel@xxxxxxx> wrote:
Event interface suits PC world where BIOS already does the polling...
The BIOS does polling only for its internal tasks. It doesn't generate events when readouts change unless something important happened. So if you want readouts you need to poll the SMBIOS or hardware, like on the Zaurus.
+ perhaps it would not need explicit maintainer, just assign names carefully
We also need to decide on clear convention about units. Are they in the output and/or filename? Filename is best, I think, since it's impossible to miss and works nicely for input attributes too.
- does not suit PC-style batteries which trigger events when data change (can be fixed by /sys/XXX/anything-new, which gives one byte when something changes)
Changed since last poll? That doesn't work with multiple clients. Changed for the last X seconds? That requires everybody to poll that frequenty, and risks missing events due to system load. Wild thought: how about adding a generic "event source" mechanism into sysfs, at the same level as attributes? Maybe even make them textual, in keeping with sysfs philosophy: while read TYPE PARAM < /sys/class/battery/BAT0/criticl_events; do echo "battery 0 generated ctitical event $TYPE with parameters $PARAM" done The simpler solution is to convert events into state (e.g., critical=0/1) and present them as normal attributes which userspace can poll, as Greg KH suggested (did I get that right?). I'm not sure it's always easy, e.g., does ACPI genereate an explicit no-longer-critical event?
- you are not getting atomic snapshot of battery state. For example you could read battery status okay, voltage 9.5V; while real states were (okay, 10.5V), (critical, 9.5V) and update happened between you reading status and voltage. (Is it problem?)
I can't think of a realistic scenario where it's a problem. The latest readout is always the best one to look at.
- hard to handle obscure features (do_not_charge_battery_for_X_minutes)
So where does that go in the /dev scheme? Shem - To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html