add pre-copy phase in live migration example (#247)

This patch adds a simplistic pre-copy phase in the live migration
sample. The end goal is have a separate thread in the client to
modify device state while the device is in the pre-copy phase. This will
be done in later patches.

BAR1 is saved during the pre-copy phase and BAR0 is saved during the
stop-and-copy phase. This is purely for convenience. There are quite a
few assumptions and FIXMEs, even in the client code. We plan to address
them in future patches.

Signed-off-by: Thanos Makatos <thanos.makatos@nutanix.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/lib/migration.c b/lib/migration.c
index 31a8d9d..c4eb6f6 100644
--- a/lib/migration.c
+++ b/lib/migration.c
@@ -450,6 +450,12 @@ migration_region_access(vfu_ctx_t *vfu_ctx, char *buf, size_t count,
     assert(migr != NULL);
     assert(buf != NULL);
 
+    /*
+     * FIXME don't call the device callback if the migration state is in not in
+     * pre-copy/stop-and-copy/resuming state, since the behavior is undefined
+     * in that case.
+     */
+
     if (pos + count <= sizeof(struct vfio_device_migration_info)) {
         ret = migration_region_access_registers(vfu_ctx, buf, count,
                                                 pos, is_write);