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.
Couldn't you specify the local port when calling rdma_resolve_addr()? TCP
doesn't require calling bind before connect, so I'd like to avoid requiring that
here.
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.
The purpose behind the CMA is to establish connections using TCP/IP addressing,
versus trying to emulate TCP. On the passive side, this means that the CMA
supports listening on a 16-bit port number on a single IP address, or across all
IP addresses. On the active side, there's no need to even use a port number
(when running over IB). The CMA doesn't need it to establish a connection or
use it to match received data with the correct connection.
CMA does not allocate ephemeral ports currently.
This actually makes some sense since address families/port spaces expect
different semantics wrt which port numbers are legal.
It's correct that the CMA currently does not do this. I guess I'm still unsure
of why it needs to when running over IB. The CMA should work fine if it
assigned every active connection the same port number. As long as the CMA
manages its own port spaces, does it matter if its semantics are defined this way?
- Sean
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