[openib-general] Re: [PATCH] CMA: allow/require bind before connect

[Tom Tucker]

On Sun, 2006-03-26 at 17:34 +0200, Michael S. Tsirkin wrote:
> Quoting r. Tom Tucker <tom at opengridcomputing.com>:
> > Subject: Re: [PATCH] CMA: allow/require bind before connect
> > 
> > On Sun, 2006-03-26 at 16:59 +0200, Michael S. Tsirkin wrote:
> > > Sean, CMA currently bails out if I bind to ANY address before connect.
> > > I think in TCP you bind before connect 
> > 
> > It is not typical to use bind on the active side before connect. When it
> > is done, is when the application wants to control which local port
> > and/or interface to use when connecting to a remove peer. bind(2) is
> > typically used on the passive side before listen.
> 
> Tom, I have a connection bind on a local port to control which local port
> to use when connecting to a remove peer.
> 
> Further, I think TCP connections autobind to a local port on connect,
> even if you don't do it explicitly.
> I think a local port is required for the communication to work in TCP.
> 
> At the level I work in SDP, Linux net core calls bind before connect if the
> socket source port is 0. I could override this but I don't think its a good
> idea since the point is to emulate TCP: TCP connections always have a source
> port and so should CMA connections.

Wow. Now I'm really lost. I thought you were trying to specify the local
port. You're not, you're asking the stack to select one for you -- which
is the common case. 

I'm still searching for the actual problem you're having. Are you saying
that the local port number after connect on SDP over IB is 0?  If so,
then something is fundamentally busted. If sin_port is 0, the stack is
supposed to allocate an ephemeral port for you. That's what 0 means. 

The bind in the net/core case is specifically for this purpose, to cause
the stack to allocate a port number. In the CMA, the rdma_resolve_addr
call has everything you need. It is sort of an uber-bind. The port
number in the src_addr should be being used to either confirm that that
the specified local port is available (and you have rights to the
specified port if it is below 1024) and if it is zero, allocating one
for you. I think the only question is 'when' this allocation/checking is
done. It could be done early in the rdma_resolve_addr, or delayed until
rdma_connect time. I think the former is preferred.

> Since bind to port 0 isn't supported in CMA yet, I proposed making an
> explicit bind a requirement before resolve_addr - not a serious
> overhead and it keeps the code simple.
>