img-streamer: introduction of criu-image-streamer

This adds the ability to stream images with criu-image-streamer

The workflow is the following:
1) criu-image-streamer is started, and starts listening on a UNIX
   socket.
2) CRIU is started. img_streamer_init() is invoked, which connects to the
   socket. During dump/restore operations, instead of using local disk to
   open an image file, img_streamer_open() is called to provide a UNIX pipe
   that is sent over the UNIX socket.
3) Once the operation is done, img_streamer_finish() is called, and the
   UNIX socket is disconnected.

criu-image-streamer can be found at:
https://github.com/checkpoint-restore/criu-image-streamer

Signed-off-by: Nicolas Viennot <Nicolas.Viennot@twosigma.com>

2 files changed, 17 insertions, 0 deletions

diff --git a/images/Makefile b/images/Makefile
index 5ddd37664..bc67278e6 100644
--- a/images/Makefile
+++ b/images/Makefile
@@ -65,6 +65,7 @@ proto-obj-y	+= macvlan.o
 proto-obj-y	+= sit.o
 proto-obj-y	+= memfd.o
 proto-obj-y	+= timens.o
+proto-obj-y	+= img-streamer.o
 
 CFLAGS		+= -iquote $(obj)/
 
diff --git a/images/img-streamer.proto b/images/img-streamer.proto
new file mode 100644
index 000000000..d1bd4cc19
--- /dev/null
+++ b/images/img-streamer.proto
@@ -0,0 +1,16 @@
+syntax = "proto2";
+
+// This message is sent from CRIU to the streamer.
+// * During dump, it communicates the name of the file that is about to be sent
+//   to the streamer.
+// * During restore, CRIU requests image files from the streamer. The message is
+//   used to communicate the name of the desired file.
+message img_streamer_request_entry {
+	required string filename = 1;
+}
+
+// This message is sent from the streamer to CRIU. It is only used during
+// restore to report whether the requested file exists.
+message img_streamer_reply_entry {
+	required bool exists = 1;
+}