Re: newbus flaw

From: Doug Rabson (dfr_at_nlsystems.com)
Date: 05/11/04

  • Next message: Poul-Henning Kamp: "Re: newbus flaw" 
    To: Dag-Erling Smørgrav <des@des.no>
Date: Tue, 11 May 2004 16:07:50 +0100

    On Tue, 2004-05-11 at 15:39, Dag-Erling Smørgrav wrote:
    > I've found what I believe is a serious flaw in newbus.
    >
    > When a driver that has a DEVICE_IDENTIFY method is loaded, the
    > identify method is called. If it finds supported hardware, it uses
    > BUS_ADD_CHILD to notify the parent bus of the presence of that
    > hardware. At some later point, during a bus rescan, the attach
    > routine is called for each device that was identified in this manner.
    >
    > When the driver is unloaded, the device is detached, but it remains on
    > the bus's list of child devices. The next time the module is loaded,
    > its DEVICE_IDENTIFY method is called again, and incorrectly adds a
    > second child device to the bus, because it does not know that one
    > already exists.
    >
    > There is no way for DEVICE_IDENTIFY to check if a matching child
    > already exists on the bus, or for the module's event handler to unlist
    > the child when unloading.
    >
    > The first time you load the module, you get foo0; the second time, you
    > get foo0 *and* foo1 referencing the same physical device; the third
    > time, you get foo0, foo1, and foo2, etc.
    >
    > I've also seen something similar happen when multiple ndis drivers are
    > loaded; the first one re-attaches to the hardware when the second one
    > is loaded.

    This is a known problem. The 'right' solution is to add a new static
    method to the device interface which is the opposite of IDENTIFY (e.g.
    UNIDENTIFY). One way to get around the problem is to do something like:

    void foo_identify(driver_t *driver, device_t parent)
    {
            device_t child;
            child = device_find_child(parent, "foo", 0);
            if (!child)
                    BUS_ADD_CHILD(parent, 0, "foo", 0);
    }

    Alternatively, you can add a module handler:

    static device_t foo;

    void foo_identify(driver_t *driver, device_t parent)
    {
            foo = BUS_ADD_CHILD(parent, 0, "foo", -1);
    }

    ...

    int foo_module_handler(struct module *mod, int what, void *arg)
    {
            if (what == MOD_UNLOAD && foo)
                    device_delete_child(device_get_parent(foo), foo);
    }

    ...

    DRIVER_MODULE(foo, bar, foo_driver, foo_devclass, foo_module_handler,
    0);

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