contrib/rdmacm-mux: Add implementation of RDMA User MAD multiplexer

RDMA MAD kernel module (ibcm) disallow more than one MAD-agent for a
given MAD class.
This does not go hand-by-hand with qemu pvrdma device's requirements
where each VM is MAD agent.
Fix it by adding implementation of RDMA MAD multiplexer service which on
one hand register as a sole MAD agent with the kernel module and on the
other hand gives service to more than one VM.

Design Overview:
Reviewed-by: Shamir Rabinovitch <shamir.rabinovitch@oracle.com>
----------------
A server process is registered to UMAD framework (for this to work the
rdma_cm kernel module needs to be unloaded) and creates a unix socket to
listen to incoming request from clients.
A client process (such as QEMU) connects to this unix socket and
registers with its own GID.

TX:
----
When client needs to send rdma_cm MAD message it construct it the same
way as without this multiplexer, i.e. creates a umad packet but this
time it writes its content to the socket instead of calling umad_send().
The server, upon receiving such a message fetch local_comm_id from it so
a context for this session can be maintain and relay the message to UMAD
layer by calling umad_send().

RX:
----
The server creates a worker thread to process incoming rdma_cm MAD
messages. When an incoming message arrived (umad_recv()) the server,
depending on the message type (attr_id) looks for target client by
either searching in gid->fd table or in local_comm_id->fd table. With
the extracted fd the server relays to incoming message to the client.

Signed-off-by: Yuval Shaia <yuval.shaia@oracle.com>
Reviewed-by: Shamir Rabinovitch <shamir.rabinovitch@oracle.com>
Signed-off-by: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index 038780c6d0..dd53965f77 100644
--- a/Makefile
+++ b/Makefile
@@ -362,6 +362,7 @@ dummy := $(call unnest-vars,, \
                 elf2dmp-obj-y \
                 ivshmem-client-obj-y \
                 ivshmem-server-obj-y \
+                rdmacm-mux-obj-y \
                 libvhost-user-obj-y \
                 vhost-user-scsi-obj-y \
                 vhost-user-blk-obj-y \
@@ -579,6 +580,8 @@ vhost-user-scsi$(EXESUF): $(vhost-user-scsi-obj-y) libvhost-user.a
 	$(call LINK, $^)
 vhost-user-blk$(EXESUF): $(vhost-user-blk-obj-y) libvhost-user.a
 	$(call LINK, $^)
+rdmacm-mux$(EXESUF): $(rdmacm-mux-obj-y) $(COMMON_LDADDS)
+	$(call LINK, $^)
 
 module_block.h: $(SRC_PATH)/scripts/modules/module_block.py config-host.mak
 	$(call quiet-command,$(PYTHON) $< $@ \