migrate: Skeleton of live migration logic

Introduce facilities for guest migration on top of vhost-user
infrastructure.  Add migration facilities based on top of the current
vhost-user infrastructure, moving vu_migrate() and related functions
to migrate.c.

Versioned migration stages define function pointers to be called on
source or target, or data sections that need to be transferred.

The migration header consists of a magic number, a version number for the
encoding, and a "compat_version" which represents the oldest version which
is compatible with the current one.  We don't use it yet, but that allows
for the future possibility of backwards compatible protocol extensions.

Co-authored-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 2 insertions, 47 deletions

diff --git a/vu_common.c b/vu_common.c
index ab04d31..48826b1 100644
--- a/vu_common.c
+++ b/vu_common.c
@@ -5,6 +5,7 @@
  * common_vu.c - vhost-user common UDP and TCP functions
  */
 
+#include <errno.h>
 #include <unistd.h>
 #include <sys/uio.h>
 #include <sys/eventfd.h>
@@ -17,6 +18,7 @@
 #include "vhost_user.h"
 #include "pcap.h"
 #include "vu_common.h"
+#include "migrate.h"
 
 #define VU_MAX_TX_BUFFER_NB	2
 
@@ -303,50 +305,3 @@ err:
 
 	return -1;
 }
-
-/**
- * vu_migrate() - Send/receive passt insternal state to/from QEMU
- * @vdev:	vhost-user device
- * @events:	epoll events
- */
-void vu_migrate(struct vu_dev *vdev, uint32_t events)
-{
-	int ret;
-
-	/* TODO: collect/set passt internal state
-	 * and use vdev->device_state_fd to send/receive it
-	 */
-	debug("vu_migrate fd %d events %x", vdev->device_state_fd, events);
-	if (events & EPOLLOUT) {
-		debug("Saving backend state");
-
-		/* send some stuff */
-		ret = write(vdev->device_state_fd, "PASST", 6);
-		/* value to be returned by VHOST_USER_CHECK_DEVICE_STATE */
-		vdev->device_state_result = ret == -1 ? -1 : 0;
-		/* Closing the file descriptor signals the end of transfer */
-		epoll_del(vdev->context, vdev->device_state_fd);
-		close(vdev->device_state_fd);
-		vdev->device_state_fd = -1;
-	} else if (events & EPOLLIN) {
-		char buf[6];
-
-		debug("Loading backend state");
-		/* read some stuff */
-		ret = read(vdev->device_state_fd, buf, sizeof(buf));
-		/* value to be returned by VHOST_USER_CHECK_DEVICE_STATE */
-		if (ret != sizeof(buf)) {
-			vdev->device_state_result = -1;
-		} else {
-			ret = strncmp(buf, "PASST", sizeof(buf));
-			vdev->device_state_result = ret == 0 ? 0 : -1;
-		}
-	} else if (events & EPOLLHUP) {
-		debug("Closing migration channel");
-
-		/* The end of file signals the end of the transfer. */
-		epoll_del(vdev->context, vdev->device_state_fd);
-		close(vdev->device_state_fd);
-		vdev->device_state_fd = -1;
-	}
-}