contrib/vhost-user-blk: introduce a vhost-user-blk sample application

This commit introduces a vhost-user-blk backend device, it uses UNIX
domain socket to communicate with QEMU. The vhost-user-blk sample
application should be used with QEMU vhost-user-blk-pci device.

To use it, complie with:
make vhost-user-blk

and start like this:
vhost-user-blk -b /dev/sdb -s /path/vhost.socket

Signed-off-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

.gitignore

@@ -54,6 +54,7 @@
 /module_block.h
 /scsi/qemu-pr-helper
 /vhost-user-scsi
+/vhost-user-blk
 /fsdev/virtfs-proxy-helper
 *.tmp
 *.[1-9]

Makefile

@@ -334,6 +334,7 @@ dummy := $(call unnest-vars,, \
                 ivshmem-server-obj-y \
                 libvhost-user-obj-y \
                 vhost-user-scsi-obj-y \
+                vhost-user-blk-obj-y \
                 qga-vss-dll-obj-y \
                 block-obj-y \
                 block-obj-m \
@@ -565,6 +566,8 @@ ivshmem-server$(EXESUF): $(ivshmem-server-obj-y) $(COMMON_LDADDS)
 endif
 vhost-user-scsi$(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, $^)
 
 module_block.h: $(SRC_PATH)/scripts/modules/module_block.py config-host.mak
 	$(call quiet-command,$(PYTHON) $< $@ \

Makefile.objs

@@ -115,6 +115,7 @@ libvhost-user-obj-y = contrib/libvhost-user/
 vhost-user-scsi.o-cflags := $(LIBISCSI_CFLAGS)
 vhost-user-scsi.o-libs := $(LIBISCSI_LIBS)
 vhost-user-scsi-obj-y = contrib/vhost-user-scsi/
+vhost-user-blk-obj-y = contrib/vhost-user-blk/
 
 ######################################################################
 trace-events-subdirs =

contrib/vhost-user-blk/Makefile.objs

@@ -0,0 +1 @@
+vhost-user-blk-obj-y = vhost-user-blk.o