[Pvfs2-developers] Re: pointer aliasing and interface->set_info semantics

[Scott Atchley]

On Mar 5, 2008, at 10:59 AM, Phil Carns wrote:

> I don't know if IB or MX need to use the  
> bmi_method_addr_forget_callback() function.  That function makes a  
> little more sense in the context of a particular tcp problem:
>
> - each time a client opens a new tcp socket to a server, the server  
> creates a bmi_addr corresponding to that socket (so it can send  
> responses, etc.).
> - if that client exits, then reconnects, the server just thinks of  
> that as an entirely new bmi_addr; it doesn't have any way to  
> realize that it is the same client connecting again using a  
> different socket.
>
> bmi_tcp therefore has to garbage collect old bmi_addr's when  
> sockets close, otherwise the number of addresses can grow  
> indefinitely for a long running tcp pvfs2-server (a problem Sam  
> found a while back).
>
> Ideally, when bmi_tcp figures out that a socket is closed, it would  
> garbage collect immediately and get rid of the addr.  However, the  
> server could still have pending operations for that bmi_addr.   
> So... we we mark that addr as in an error state and try to hang  
> onto it until the reference count hits zero before garbage  
> collecting.  That let's us report a more meaningful error on the  
> server side for pending operations than "addr doesn't exist".
>
> The bmi_method_addr_foget_callback() in this case is a way to poke  
> the upper level bmi code to say "keep an eye on this addr, and when  
> the refcount hits zero clean it up for me".
>
> I don't know if that description helps any, but that's my  
> interpretation of what it does :)  The address management (in  
> general) in bmi has ended up being pretty wacky.
>
> The DROP_ADDR function is how the bmi.c layer explicitly tells a  
> bmi method to get rid of an address (if that action makes any sense  
> for the method in question).  So that part needs to really get rid  
> of the address if necessary rather than handing it back to bmi.c  
> with the bmi_method_addr_forget_callback().
>
> -Phil

Thanks Phil,

I will remove the callback from bmi_mx.

I think that I also need to look at sending a BYE message when a  
client goes away to let the server know when to clean up.

Scott