13 messages in org.freebsd.freebsd-archnewbus flaw| From | Sent On | Attachments |
|---|---|---|
| Dag-Erling Smørgrav | May 11, 2004 7:39 am | |
| Doug Rabson | May 11, 2004 8:08 am | |
| Poul-Henning Kamp | May 11, 2004 8:12 am | |
| John-Mark Gurney | May 11, 2004 6:02 pm | |
| Dag-Erling Smørgrav | May 12, 2004 6:27 am | |
| John-Mark Gurney | May 12, 2004 10:41 am | |
| Dag-Erling Smørgrav | May 12, 2004 10:48 am | |
| John-Mark Gurney | May 12, 2004 10:53 am | |
| Dag-Erling Smørgrav | May 12, 2004 1:30 pm | |
| Doug Rabson | May 13, 2004 1:27 am | |
| Dag-Erling Smørgrav | May 13, 2004 3:46 am | |
| Doug Rabson | May 13, 2004 5:34 am | |
| M. Warner Losh | May 13, 2004 9:06 am |
| Subject: | newbus flaw | |
|---|---|---|
| From: | Doug Rabson (df...@nlsystems.com) | |
| Date: | May 11, 2004 8:08:03 am | |
| List: | org.freebsd.freebsd-arch | |
On Tue, 2004-05-11 at 15:39, Dag-Erling Sm?rgrav 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);