Re: [RFC PATCH] device-core: sysfs open - close notify

[Alan Cox <alan@linux.intel.com>]

> Your patch may cause many unnecessary memory waste because
> most of drivers does not need attribute file .open/.close notifier.

Firstly there are not that many driver objects in a small system so it
wouldn't take that much to shift the balance the other way. Secondly
its becoming clear that every time a driver goes to runtime pm these
issues come up - even with things like configuration values for drivers
that need to wake the hardware and then silence it.

So the whole sysfs/open thing is going to keep haunting us with runtime
pm, the question is where to put the callbacks so we don't bloat stuff.
Clearly not per attribute or per sysfs node. One possibility would be
with the runtime pm stuff, but that would need a clean reliable way to
go sysfs->device->runtime_pm

There are also obvious hackish ways to handle it like passing a 0
length read to indicate close etc - they save memory but they are
asking for problems in future.