features/changelog: RPC'fy {libgf}changelog

This patch introduces RPC based communication between the changelog
translator and libgfchangelog. It replaces the old pathetic stream
based interaction that existed earlier (due to time constraints :-/).

Changelog, upon initialization starts a RPC server (rpcsvc) allowing
clients to invoke a probe API as a bootup mechanism to request for
event notifications. During probe, clients can choose an event
filter specifying the type(s) of events they are interested in. As
of now there is no way to change the event notification set once
the probe RPC call is made, but that is easier to implement.

The actual event notifications is done on a separate RPC session.
The client (libgfchangelog) itself starts and RPC server which the
changelog translator "connects back" during probe. Notifications
are dispatched by a bunch of threads from the server (translator)
and the client optionally orders them if ordered notifications
are requried. FOPs fill in their respective event details in a
buffer (rot-buffs to be particular) and a bunch of threads
(consumers) swap the buffers out of roatation and dispatch them
via RPC. To avoid writer starvation, then number of dispatcher
threads is one less than the number of buffer list in rot-buffs.x

libgfchangelog becomes purely callback based -- upon event
notification from the server (and re-ordering them if required)
invoke a callback routine specified by consumer(s).

A major part of the patch is also aimed at providing backward
compatibility for geo-replication, which was one of the main
consumer of the stream based API. Also, this patch does not\
"turn on" event notifications for all fops, just a bunch which
is currently in requirement. Another pain point is that the
server does not filter events before dispatching it to the
clients. That load is taken up by the client itself (although
it's done at the library layer rather than making it hard on
the callback implementor). This needs improvement and care
needs to be taken to not load the server up with expensive
filtering mechanisms.

Change-Id: Ibf60a432b68f2dfa60c6f9add2bcfd37a9c41395
BUG: 1170075
Signed-off-by: Venky Shankar <vshankar@redhat.com>
Reviewed-on: http://review.gluster.org/9708
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>

2 files changed, 35 insertions, 1 deletions

diff --git a/rpc/xdr/src/Makefile.am b/rpc/xdr/src/Makefile.am
index a1c5525c17e..e27528d0e01 100644
--- a/rpc/xdr/src/Makefile.am
+++ b/rpc/xdr/src/Makefile.am
@@ -1,5 +1,6 @@
 XDRSOURCES = glusterfs3-xdr.c cli1-xdr.c nlm4-xdr.c nsm-xdr.c \
-	rpc-common-xdr.c glusterd1-xdr.c acl3-xdr.c portmap-xdr.c mount3udp.c
+	rpc-common-xdr.c glusterd1-xdr.c acl3-xdr.c portmap-xdr.c \
+	mount3udp.c changelog-xdr.c
 XDRHEADERS = $(XDRSOURCES:.c=.h)
 XDRGENFILES = $(XDRSOURCES:.c=.x)
 
@@ -76,3 +77,9 @@ mount3udp.c: mount3udp.x mount3udp.h
 
 mount3udp.h: mount3udp.x
 	$(top_srcdir)/build-aux/xdrgen header $(xdrsrc)/`basename ${@:.h=.x}`
+
+changelog-xdr.c: changelog-xdr.x changelog-xdr.h
+	$(top_srcdir)/build-aux/xdrgen source $(xdrsrc)/`basename ${@:.c=.x}`
+
+changelog-xdr.h: changelog-xdr.x
+	$(top_srcdir)/build-aux/xdrgen header $(xdrsrc)/`basename ${@:.h=.x}`
diff --git a/rpc/xdr/src/changelog-xdr.x b/rpc/xdr/src/changelog-xdr.x
new file mode 100644
index 00000000000..ba1ebd27836
--- /dev/null
+++ b/rpc/xdr/src/changelog-xdr.x
@@ -0,0 +1,27 @@
+/* XDR: libgfchangelog -> changelog */
+
+struct changelog_probe_req {
+       unsigned int filter;
+       char sock[UNIX_PATH_MAX];
+};
+
+struct changelog_probe_rsp {
+       int op_ret;
+};
+
+/* XDR: changelog -> libgfchangelog */
+struct changelog_event_req {
+       /* sequence number for the buffer */
+       unsigned long seq;
+
+       /* time of dispatch */
+       unsigned long tv_sec;
+       unsigned long tv_usec;
+};
+
+struct changelog_event_rsp {
+       int op_ret;
+
+       /* ack'd buffers sequence number */
+       unsigned long seq;
+};