[PATCH RFC 00/11] migration/block: disk activation rewrite

[Peter Xu <peterx@redhat.com>]

I started looking at this problem as a whole when reviewing Fabiano's
series, especially the patch (for a QEMU crash [1]):

https://lore.kernel.org/r/20241125144612.16194-5-farosas@suse.de

The proposed patch could work, but it's unwanted to add such side effect to
migration.  So I start to think about whether we can provide a cleaner
approach, at least remove that "we must active the disk for migration"
dependency, because migration really don't need the disks to be active..

It's also a pure wish that, if bdrv_inactivate_all() could be benign to be
called even if all disks are already inactive.  Then problem also gone.
After all, similar call on bdrv_activate_all() upon all-active disks is all
fine.  I hope that wish could still be fair.

And when I was looking at that, I found more things spread all over the
place on disk activation.  I decided to clean all of them up, while
hopefully fixing the QEMU crash [1] too.

So this is what I came up with as of today.  Marking RFC as of now, just to
collect some feedbacks first.  At least I'd like to go with one more patch
to deprecate late-block-active - not deprecating its function, but make it
always happen (which is the default as of now for Libvirt), which should
hopefully be migration-ABI-safe.

With the help of Fabiano's test cases, I at least am sure this series works
for the ping pong migrations, and all existing qtests.

Let me know, thanks.

[1] https://gitlab.com/qemu-project/qemu/-/issues/2395

Fabiano Rosas (4):
  tests/qtest/migration: Move more code under only_target
  tests/qtest/migration: Don't use hardcoded strings for -serial
  tests/qtest/migration: Support cleaning up only one side of migration
  tests/qtest/migration: Test successive migrations

Peter Xu (7):
  migration: Add helper to get target runstate
  migration/block: Make late-block-active the default
  migration/block: Apply late-block-active behavior to postcopy
  migration/block: Fix possible race with block_inactive
  migration/block: Merge block reactivations for fail/cancel
  migration/block: Extend the migration_block_* API to dest side
  migration/block: Apply the migration_block_* API to postcopy

 migration/migration.h           |  33 ++++-
 tests/qtest/migration-helpers.h |   2 +
 migration/migration.c           | 177 +++++++++++-----------
 migration/savevm.c              |  32 ++--
 tests/qtest/migration-helpers.c |   8 +
 tests/qtest/migration-test.c    | 252 +++++++++++++++++++++++++-------
 6 files changed, 344 insertions(+), 160 deletions(-)

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2.47.0