Merge tag 'migration-20230206-pull-request' of https://gitlab.com/juan.quintela/qemu...

Migration Pull request

In this try
- rebase to latest upstream
- same than previous patch
- fix compilation on non linux (userfaultfd.h) (me)
- query-migrationthreads (jiang)
- fix race on reading MultiFDPages_t.block (zhenzhong)
- fix flush of zero copy page send reuest  (zhenzhong)

Please apply.

Previous try:
It includes:
- David Hildenbrand fixes for virtio-men
- David Gilbert canary to detect problems
- Fix for rdma return values (Fiona)
- Peter Xu uffd_open fixes
- Peter Xu show right downtime for postcopy
- manish.mishra msg fix fixes
- my vfio changes.

Please apply.

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# gpg: Signature made Tue 07 Feb 2023 00:56:22 GMT
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# gpg: Good signature from "Juan Quintela <quintela@redhat.com>" [full]
# gpg:                 aka "Juan Quintela <quintela@trasno.org>" [full]
# Primary key fingerprint: 1899 FF8E DEBF 58CC EE03  4B82 F487 EF18 5872 D723

* tag 'migration-20230206-pull-request' of https://gitlab.com/juan.quintela/qemu: (30 commits)
  migration: save/delete migration thread info
  migration: Introduce interface query-migrationthreads
  multifd: Fix flush of zero copy page send request
  multifd: Fix a race on reading MultiFDPages_t.block
  migration: check magic value for deciding the mapping of channels
  io: Add support for MSG_PEEK for socket channel
  migration/dirtyrate: Show sample pages only in page-sampling mode
  migration: Perform vmsd structure check during tests
  migration: Add canary to VMSTATE_END_OF_LIST
  migration/rdma: fix return value for qio_channel_rdma_{readv,writev}
  migration: Show downtime during postcopy phase
  virtio-mem: Proper support for preallocation with migration
  virtio-mem: Migrate immutable properties early
  virtio-mem: Fail if a memory backend with "prealloc=on" is specified
  migration/ram: Factor out check for advised postcopy
  migration/vmstate: Introduce VMSTATE_WITH_TMP_TEST() and VMSTATE_BITMAP_TEST()
  migration/savevm: Allow immutable device state to be migrated early (i.e., before RAM)
  migration/savevm: Prepare vmdesc json writer in qemu_savevm_state_setup()
  migration/savevm: Move more savevm handling into vmstate_save()
  migration/ram: Optimize ram_write_tracking_start() for RamDiscardManager
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>