[openib-general] Proposed device enumeration & async event APIs

[Fab Tillier]

> From: Roland Dreier [mailto:roland at topspin.com]
> Sent: Friday, September 10, 2004 2:29 PM
> 
>     Fab> This sounds sane.  Are existing device notifications invoked
>     Fab> from the thread context of the ib_register_client function?
>     Fab> In other words, does the ib_register_client function return
>     Fab> before or after the client has receive notifications of
>     Fab> existing events?  Does ib_unregister_client synchronize with
>     Fab> callback delivery?  Does ib_unregister_client send "pretend"
>     Fab> removal events?
> 
> Yes to all of these questions.
...
> 
> So everything is synchronized by the lock and all fake events are
> generated.

Great!  I didn't see a way for a client to associate a context or some such
thing with a device when the device is added.  I would think this would be
beneficial in order to avoid requiring clients to search a list for a
matching device.  I'm suggesting something like this:

struct ib_device_reg {
		void (*remove)(struct ib_device_reg *);

		struct list_head reg_list;
		struct list_head dev_list;
	};

struct ib_client {
		struct ib_device_reg * (*add)   (struct ib_device *);

		struct list_head list;
		struct list_head reg_list;
	};

Adding a device does
 
     	lock device list
     	add device to device list
     	generate add callbacks for existing clients
	insert returned value into device's reg_list
	insert returned value into client's reg_list
     	unlock device list
 
and removing a device does
 
    	lock device list
	for each entry in device's reg_list	{
		generate remove callback
		remove device_reg.dev_list and device_reg.reg_list from
lists }
     	unlock device list

and unregister does

    	lock device list
	remove client from client list
	for each entry in client's reg_list {
		generate remove callbacks
		remove device_reg.dev_list and device_reg.reg_list from
lists }
	unlock device list

This does two things: it provides a way for clients to get some sort of
context back for removal, allowing them to embed a struct ib_device_reg in
whatever they allocate for the device; it allows clients to suppress a
remove event for a device for which they failed to allocate stuff or don't
care about.

Thoughts?

- Fab