On Sun, Jun 30, 2024 at 12:44:02PM -0700, Steve Sistare wrote:
> What?
>
> This patch series adds the live migration cpr-transfer mode, which
> allows the user to transfer a guest to a new QEMU instance on the same
> host. It is identical to cpr-exec in most respects, except as described
> below.
I definitely prefer this one more than the exec solution, thanks for trying
this out. It's a matter of whether we'll need both, my answer would be
no..
>
> The new user-visible interfaces are:
> * cpr-transfer (MigMode migration parameter)
> * cpr-uri (migration parameter)
I wonder whether this parameter can be avoided already, maybe we can let
cpr-transfer depend on unix socket in -incoming, then integrate fd sharing
in the same channel?
> * cpr-uri (command-line argument)
>
> In this mode, the user starts new QEMU on the same host as old QEMU, with
> the same arguments as old QEMU, plus the -incoming and the -cpr-uri options.
> The user issues the migrate command to old QEMU, which stops the VM, saves
> state to the migration channels, and enters the postmigrate state. Execution
> resumes in new QEMU.
>
> This mode requires a second migration channel, specified by the cpr-uri
> migration property on the outgoing side, and by the cpr-uri QEMU command-line
> option on the incoming side. The channel must be a type, such as unix socket,
> that supports SCM_RIGHTS.
>
> This series depends on the series "Live update: cpr-exec mode".
>
> Why?
>
> cpr-transfer offers the same benefits as cpr-exec mode, but with a model
> for launching new QEMU that may be more natural for some management packages.
>
> How?
>
> The file descriptors are kept open by sending them to new QEMU via the
> cpr-uri, which must support SCM_RIGHTS.
>
> Example:
>
> In this example, we simply restart the same version of QEMU, but in
> a real scenario one would use a new QEMU binary path in terminal 2.
>
> Terminal 1: start old QEMU
> # qemu-kvm -monitor stdio -object
> memory-backend-file,id=ram0,size=4G,mem-path=/dev/shm/ram0,share=on
> -m 4G -machine anon-alloc=memfd ...
>
> Terminal 2: start new QEMU
> # qemu-kvm ... -incoming unix:vm.sock -cpr-uri unix:cpr.sock
>
> Terminal 1:
> QEMU 9.1.50 monitor - type 'help' for more information
> (qemu) info status
> VM status: running
> (qemu) migrate_set_parameter mode cpr-transfer
> (qemu) migrate_set_parameter cpr-uri unix:cpr.sock
> (qemu) migrate -d unix:vm.sock
> (qemu) info status
> VM status: paused (postmigrate)
>
> Terminal 2:
> QEMU 9.1.50 monitor - type 'help' for more information
> (qemu) info status
> VM status: running
>
> Steve Sistare (6):
> migration: SCM_RIGHTS for QEMUFile
> migration: VMSTATE_FD
> migration: cpr-transfer save and load
> migration: cpr-uri parameter
> migration: cpr-uri option
> migration: cpr-transfer mode
>
> include/migration/cpr.h | 4 ++
> include/migration/vmstate.h | 9 +++++
> migration/cpr-transfer.c | 81 +++++++++++++++++++++++++++++++++++++++++
> migration/cpr.c | 16 +++++++-
> migration/meson.build | 1 +
> migration/migration-hmp-cmds.c | 10 +++++
> migration/migration.c | 37 +++++++++++++++++++
> migration/options.c | 29 +++++++++++++++
> migration/options.h | 1 +
> migration/qemu-file.c | 83 ++++++++++++++++++++++++++++++++++++++++--
> migration/qemu-file.h | 2 +
> migration/ram.c | 1 +
> migration/trace-events | 2 +
> migration/vmstate-types.c | 33 +++++++++++++++++
> qapi/migration.json | 38 ++++++++++++++++++-
> qemu-options.hx | 8 ++++
> stubs/vmstate.c | 7 ++++
> system/vl.c | 3 ++
> 18 files changed, 359 insertions(+), 6 deletions(-)
> create mode 100644 migration/cpr-transfer.c
>
> --
> 1.8.3.1
>
--
Peter Xu