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    SubjectRe: split kobject creation and hotplug event generation
    On Mon, Feb 28, 2005 at 11:46:42AM -0800, Greg KH wrote:
    > On Sat, Feb 26, 2005 at 06:53:16AM +0100, Kay Sievers wrote:
    > > This splits the implicit generation of a hotplug events from
    > > kobject_add() and kobject_del(), to give the user of of these
    > > functions control over the time the event is created.
    > >
    > > The kobject_register() and unregister functions still have the same
    > > behavior and emit the events by themselves.
    > >
    > > The class, block and device core is changed now to emit the hotplug
    > > event _after_ the "dev" file, the "device" symlink and the default
    > > attributes are created. This will save udev from spinning in a stat() loop
    > > to wait for the files to appear, which is expensive if we have a lot of
    > > concurrent events.
    >
    > So, does this solve the issue that everyone has been complaining about
    > for years with the hotplug event happening before the sysfs files are
    > present?

    I expect most of them, yes. It is not a guarantee, cause drivers can and will
    create attributes at any time. :) But the most interesting default ones, that
    people tend to expect at event time will be there _before_ the event happens.

    To get this for the whole system and not only the class+block core, a few remainig
    places that use kobject_register() need to be changed to use kobject_add(), but
    that is a trivial change and nice too, cause it cleans up some error pathes, where
    a device needs to be unregistered in the same function and it emits two completely
    useless events for that.

    > And if we add this, can we pretty much get rid of all of the
    > wait_for_sysfs like logic in udev?

    Yes, that was the motivation to do this. With all the hotplug env vars
    we have now, we can throw out all the compiled-in lists and if some crazy
    devices still need to wait, we can add something to udev's rule logic, that a
    configured rule will wait for that file to show up.

    Thanks,
    Kay
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