bhyve/snapshot: provide a way to send other messages/data to bhyve

This is a step towards sending messages (other than suspend/checkpoint)
from bhyvectl to bhyve.

Introduce a new struct, ipc_message - this struct stores the type of
message and a union containing message specific structures for the type
of message being sent.

Reviewed by:    grehan
Differential Revision: https://reviews.freebsd.org/D30221

3 files changed, 35 insertions, 17 deletions

diff --git a/usr.sbin/bhyve/snapshot.c b/usr.sbin/bhyve/snapshot.c
index 221558b6f205..019f4fdd6cb0 100644
--- a/usr.sbin/bhyve/snapshot.c
+++ b/usr.sbin/bhyve/snapshot.c
@@ -1441,16 +1441,16 @@ done:
 }
 
 int
-handle_message(struct checkpoint_op *checkpoint_op, struct vmctx *ctx)
+handle_message(struct ipc_message *imsg, struct vmctx *ctx)
 {
 	int err;
 
-	switch (checkpoint_op->op) {
+	switch (imsg->code) {
 		case START_CHECKPOINT:
-			err = vm_checkpoint(ctx, checkpoint_op->snapshot_filename, false);
+			err = vm_checkpoint(ctx, imsg->data.op.snapshot_filename, false);
 			break;
 		case START_SUSPEND:
-			err = vm_checkpoint(ctx, checkpoint_op->snapshot_filename, true);
+			err = vm_checkpoint(ctx, imsg->data.op.snapshot_filename, true);
 			break;
 		default:
 			EPRINTLN("Unrecognized checkpoint operation\n");
@@ -1469,7 +1469,7 @@ handle_message(struct checkpoint_op *checkpoint_op, struct vmctx *ctx)
 void *
 checkpoint_thread(void *param)
 {
-	struct checkpoint_op op;
+	struct ipc_message imsg;
 	struct checkpoint_thread_info *thread_info;
 	ssize_t n;
 
@@ -1477,14 +1477,14 @@ checkpoint_thread(void *param)
 	thread_info = (struct checkpoint_thread_info *)param;
 
 	for (;;) {
-		n = recvfrom(thread_info->socket_fd, &op, sizeof(op), 0, NULL, 0);
+		n = recvfrom(thread_info->socket_fd, &imsg, sizeof(imsg), 0, NULL, 0);
 
 		/*
 		 * slight sanity check: see if there's enough data to at
 		 * least determine the type of message.
 		 */
-		if (n >= sizeof(op.op))
-			handle_message(&op, thread_info->ctx);
+		if (n >= sizeof(imsg.code))
+			handle_message(&imsg, thread_info->ctx);
 		else
 			EPRINTLN("Failed to receive message: %s\n",
 			    n == -1 ? strerror(errno) : "unknown error");
diff --git a/usr.sbin/bhyve/snapshot.h b/usr.sbin/bhyve/snapshot.h
index 8a6ee67ef19d..f28b56cf0a7f 100644
--- a/usr.sbin/bhyve/snapshot.h
+++ b/usr.sbin/bhyve/snapshot.h
@@ -60,14 +60,29 @@ struct restore_state {
 	ucl_object_t *meta_root_obj;
 };
 
+/* Filename that will be used for save/restore */
+struct checkpoint_op {
+	char snapshot_filename[MAX_SNAPSHOT_FILENAME];
+};
+
+/* Messages that a bhyve process understands. */
 enum ipc_opcode {
 	START_CHECKPOINT,
 	START_SUSPEND,
 };
 
-struct checkpoint_op {
-	unsigned int op;
-	char snapshot_filename[MAX_SNAPSHOT_FILENAME];
+/*
+ * The type of message and associated data to
+ * send to a bhyve process.
+ */
+struct ipc_message {
+        enum ipc_opcode code;
+        union {
+                /*
+                 * message specific structures
+                 */
+                struct checkpoint_op op;
+        } data;
 };
 
 struct checkpoint_thread_info {
diff --git a/usr.sbin/bhyvectl/bhyvectl.c b/usr.sbin/bhyvectl/bhyvectl.c
index df02f7caf345..017427db4d4f 100644
--- a/usr.sbin/bhyvectl/bhyvectl.c
+++ b/usr.sbin/bhyvectl/bhyvectl.c
@@ -1684,7 +1684,7 @@ show_memseg(struct vmctx *ctx)
 
 #ifdef BHYVE_SNAPSHOT
 static int
-send_checkpoint_op_req(struct vmctx *ctx, struct checkpoint_op *op)
+send_message(struct vmctx *ctx, void *data, size_t len)
 {
 	struct sockaddr_un addr;
 	ssize_t len_sent;
@@ -1709,7 +1709,7 @@ send_checkpoint_op_req(struct vmctx *ctx, struct checkpoint_op *op)
 
 	snprintf(addr.sun_path, sizeof(addr.sun_path), "%s%s", BHYVE_RUN_DIR, vmname_buf);
 
-	len_sent = sendto(socket_fd, op, sizeof(*op), 0,
+	len_sent = sendto(socket_fd, data, len, 0,
 	    (struct sockaddr *)&addr, sizeof(struct sockaddr_un));
 
 	if (len_sent < 0) {
@@ -1726,12 +1726,15 @@ done:
 static int
 snapshot_request(struct vmctx *ctx, const char *file, enum ipc_opcode code)
 {
-	struct checkpoint_op op;
+	struct ipc_message imsg;
+	size_t length;
 
-	op.op = code;
-	strlcpy(op.snapshot_filename, file, MAX_SNAPSHOT_FILENAME);
+	imsg.code = code;
+	strlcpy(imsg.data.op.snapshot_filename, file, MAX_SNAPSHOT_FILENAME);
 
-	return (send_checkpoint_op_req(ctx, &op));
+	length = offsetof(struct ipc_message, data) + sizeof(imsg.data.op);
+
+	return (send_message(ctx, (void *)&imsg, length));
 }
 #endif