Add an OSD stub to compare sync socket I/O with io_uring + skip multiple fsyncs that fio issues

Makefile

@@ -1,7 +1,7 @@
 BLOCKSTORE_OBJS := allocator.o blockstore.o blockstore_impl.o blockstore_init.o blockstore_open.o blockstore_journal.o blockstore_read.o \
 	blockstore_write.o blockstore_sync.o blockstore_stable.o blockstore_flush.o crc32c.o ringloop.o timerfd_interval.o
 CXXFLAGS := -g -O3 -Wall -Wno-sign-compare -Wno-comment -Wno-parentheses -Wno-pointer-arith -fPIC -fdiagnostics-color=always
-all: $(BLOCKSTORE_OBJS) libfio_blockstore.so osd libfio_sec_osd.so test_blockstore
+all: $(BLOCKSTORE_OBJS) libfio_blockstore.so osd libfio_sec_osd.so test_blockstore stub_osd
 clean:
 	rm -f *.o
 
@@ -34,6 +34,8 @@ osd.o: osd.cpp osd.h osd_ops.h
 	g++ $(CXXFLAGS) -c -o $@ $<
 osd: ./libblockstore.so osd_main.cpp osd.h osd_ops.h osd.o osd_exec_secondary.o osd_read.o osd_send.o json11.o
 	g++ $(CXXFLAGS) -o osd osd_main.cpp osd.o osd_exec_secondary.o osd_read.o osd_send.o json11.o ./libblockstore.so -ltcmalloc_minimal -luring
+stub_osd: stub_osd.cpp osd_ops.h
+	g++ $(CXXFLAGS) -o stub_osd stub_osd.cpp -ltcmalloc_minimal
 
 libfio_sec_osd.so: fio_sec_osd.cpp osd_ops.h
 	g++ $(CXXFLAGS) -ltcmalloc_minimal -shared -o libfio_sec_osd.so fio_sec_osd.cpp -luring