Migration is a black hole to most people. One of the biggest reasons for this is that its protocol is a secret, undocumented sauce of code rolling around random parts of the QEMU code base.
But what if we simply exposed the description of how the format looks like alongside the actual migration stream? This is what this patch set does. It adds a new section that comes after the end of stream marker (so that it doesn't slow down migration) that contains a JSON description of the device state description. Along with this patch set also comes a python script that can read said JSON from a migration dump and decipher the device state contents of the migration dump using it. With this, you can now fully examine all glorious details that go over the wire when virtual machine state gets dumped, such as during live migration. We discussed the approach taken here during KVM Forum 2013. Originally, my idea was to include a special device that contains the JSON data which can be enabled on demand. Anthony suggested however to just always include the description data after the end marker which I think is a great idea. Example decoded migration: http://csgraf.de/mig/mig.txt Example migration description: http://csgraf.de/mig/mig.desc.txt Presentation: https://www.youtube.com/watch?v=iq1x40Qsrew Slides: https://www.dropbox.com/s/otp2pk2n3g087zp/Live%20Migration.pdf (If you received this email twice, I'm sorry about this. I forgot to send it to qemu-devel in the first round. Sigh. Merry Christmas! ) Alexander Graf (4): QJSON: Add JSON writer qemu-file: Add fast ftell code path migration: Append JSON description of migration stream Add migration stream analyzation script Makefile.objs | 1 + hw/pci/pci.c | 2 +- hw/scsi/spapr_vscsi.c | 2 +- hw/virtio/virtio.c | 2 +- include/migration/migration.h | 1 + include/migration/qemu-file.h | 1 + include/migration/vmstate.h | 3 +- include/qjson.h | 28 +++ migration/qemu-file.c | 5 + migration/vmstate.c | 181 ++++++++++++++- qjson.c | 97 ++++++++ savevm.c | 53 ++++- scripts/analyze-migration.py | 529 ++++++++++++++++++++++++++++++++++++++++++ tests/test-vmstate.c | 6 +- 14 files changed, 892 insertions(+), 19 deletions(-) create mode 100644 include/qjson.h create mode 100644 qjson.c create mode 100755 scripts/analyze-migration.py -- 1.7.12.4
