[Qemu-devel] [PATCH v3 0/5] Add ignore-external migration capability

[Yury Kotov]

Hi,

The series adds a migration capability, which allows to skip shared RAM blocks
during the migration. It's useful for fast local migration. E.g. to update QEMU
for the running guests.

Usage example:
1. Start source VM:
   qemu-system-x86 \
     -m 4G \
     -object 
memory-backend-file,id=mem0,size=4G,share=on,mem-path=/dev/shm/mem0 \
     -numa node,memdev=mem0 \
     -qmp unix:/tmp/qemu-qmp-1.sock,server,nowait \

2. Start target VM:
   qemu-system-x86 \
     -m 4G \
     -object 
memory-backend-file,id=mem0,size=4G,share=on,mem-path=/dev/shm/mem0 \
     -numa node,memdev=mem0 \
     -qmp unix:/tmp/qemu-qmp-2.sock,server,nowait \
     -incoming defer

3. Enable ignore-shared capability on both VMs:
   { "execute": "migrate-set-capabilities" , "arguments":
     { "capabilities": [ { "capability": "x-ignore-shared", "state": true } ] } 
}

4. Start migration.

Another use case I keep in mind is to migrate to file. Usage is very similar.

V2 to V3:
* Split "migration: Introduce ignore-shared capability"
* Serialize the capabilities as strings rather than as indexes
* Don't allow to enable postcopy and ignore-shared together
* Skip the test for OSs which don't have /dev/shm
* Add a check whether shared RAM has been really skipped

V1 to V2:
* Keep migration stream compatibility
* Reuse the existing code to ignore unwanted RAMBlocks
* Add capability validation feature
* ignore-external -> ignore-shared

Regards,
Yury

Yury Kotov (5):
  exec: Change RAMBlockIterFunc definition
  migration: Introduce ignore-shared capability
  migration: Add an ability to ignore shared RAM blocks
  tests/migration-test: Add a test for ignore-shared capability
  migration: Add capabilities validation

 exec.c                    |  38 +++++------
 include/exec/cpu-common.h |   7 +-
 migration/migration.c     |  14 ++++
 migration/migration.h     |   5 +-
 migration/postcopy-ram.c  |  48 +++++++------
 migration/ram.c           | 110 ++++++++++++++++++++++--------
 migration/rdma.c          |   9 ++-
 migration/savevm.c        | 137 ++++++++++++++++++++++++++++++++++++++
 qapi/migration.json       |   5 +-
 stubs/ram-block.c         |  15 +++++
 tests/migration-test.c    | 131 +++++++++++++++++++++++++++++-------
 util/vfio-helpers.c       |   6 +-
 12 files changed, 420 insertions(+), 105 deletions(-)

-- 
2.20.1