This series allows live migration to work with image formats. This series has two parts. The first part adds a new error infrastructure to migration which allows for different subsystems (other than qdev) to block migration when specific features are in use.
The second part adds block interfaces to flush metadata with image formats. The migration error infrastructure is a no brainer for 1.0. It significantly improves the user experience and prevents a user from doing things that will cause a VM to crash during migration. I'm less comfortable with the block interface for flushing metadata for 1.0. The code is completely isolated to the image formats and live migration. It should have no impact on normal use of an image format or live migration with raw images. That makes the risk for this very, very low. Moreover, I'm sympathetic to the argument that this is a required feature for a 1.0 release. Image formats are a fairly normal way to use QEMU and not supporting live migration in this scenario means that live migration won't work for a large portion of QEMU's users.
