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    SubjectRe: [PATCH 9/10] sh: Use struct syscore_ops instead of sysdev class and sysdev
    On Tuesday, March 22, 2011, Kay Sievers wrote:
    > On Tue, 2011-03-22 at 23:23 +0100, Rafael J. Wysocki wrote:
    > > On Tuesday, March 22, 2011, Kay Sievers wrote:
    > >
    > > Now, I can easily understand arguments about representing everything under
    > > /sys/devices/ by struct device objects, no question about that. However,
    > > I also think there should be a place for things like those mentioned in the
    > > comment in sys.c, presumably outside of /sys/devices/.
    > No, please. We have all we need. Let's do one example, which you might
    > apply to any other thing, because you never know what's the next big
    > thing in hardware. We need to be a future-proof-as-possible, and that's
    > not some second-class out-of-scope sysfs directory.
    > Lets' take CPUs:
    > - they send events when registered
    > - they want to export device specific properties
    > - userspace wants to take actions when such devices are available
    > That all fits properly into the driver model in theory. Unless you do
    > coldplug and bootup a box.
    > These devices are already there before userspace even starts, hence we
    > find all these devices and "trigger" an fake uevent for all of them at
    > bootup. That will match execute all the rules specified for that device,
    > just as it would be hotplugges in that moment, hence we call it
    > coldplug, which works for all devices with the hotplug code, even when
    > they are never hot-pluggable.
    > What we do for coldplug is that we iterate over all flat lists of
    > subsystems and find the devices lists and trigger the event by poking in
    > the "uevent" sysfs file. Now all the sysdevs do not have a subsystem to
    > find, and do not have a standard "uevent" file.
    > Back to the CPUs, we have all the nice device directories which could
    > have all the CPU features in properties we need to make autoloading of
    > cpufreq, governer, kvm possible (patch exists from Andi Kleen already)
    > But these dumb CPU sysfs device directories are completely invisible for
    > the *usual* logic, and should just join the model and all will just work
    > out-of-the-box.

    That all is cool, but I'm not sure how it is related to things like
    available_clocksource and current_clocksource (which happen to be located
    under /sys/devices/system/clocksource/clocksource0/ being simply a path
    in sysfs).

    > When we started to clean up /sys (again only talking about devices, not
    > other stuff) we had:
    > /block/*
    > /class/<subsys>/*
    > /bus/<subsys>/devices/*
    > /devices/system/<subsys>/*
    > which are 4 different exports of exactly the same thing, a "device".
    > "Block" we converted to "class" already, "class" will be converted to
    > "bus", and "bus" will be renamed to "subsystem". All the current names
    > will be kept as compat symlinks, just as we did for "block". After that,
    > _all_ devices have a "subsystem" and a subsystem global directory where
    > people can add custom stuff shared by all devices-of-the-same-type. Ev

    OK, sounds good.

    > You can also argument from the other side, if a kernel device export is
    > not worth the few bytes of /sys/devices/ and a "subsystem" (struct
    > bus_type) it should not be in /sys at all, especially not hidden
    > somehwere outside of /sys/devices when it is something remotely close to
    > a device.

    Well, Greg apparently thinks that available_clocksource and current_clocksource
    could be located under /sys/bus/clock/. Perhaps other attributes now exported
    through sysdevs could be moved to places like this?


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