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cpu: Rename CPUClass vmsd -> legacy_vmsd

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Quoting Peter Maydell [*]:

  There are two ways to handle migration for
  a CPU object:

  (1) like any other device, so it has a dc->vmsd that covers
  migration for the whole object. As usual for objects that are a
  subclass of a parent that has state, the first entry in the
  VMStateDescription field list is VMSTATE_CPU(), which migrates
  the cpu_common fields, followed by whatever the CPU's own migration
  fields are.

  (2) a backwards-compatible mechanism for CPUs that were
  originally migrated using manual "write fields to the migration
  stream structures". The on-the-wire migration format
  for those is based on the 'env' pointer (which isn't a QOM object),
  and the cpu_common part of the migration data is elsewhere.

  cpu_exec_realizefn() handles both possibilities:

  * for type 1, dc->vmsd is set and cc->vmsd is not,
    so cpu_exec_realizefn() does nothing, and the standard
    "register dc->vmsd for a device" code does everything needed

  * for type 2, dc->vmsd is NULL and so we register the
    vmstate_cpu_common directly to handle the cpu-common fields,
    and the cc->vmsd to handle the per-CPU stuff

  You can't change a CPU from one type to the other without breaking
  migration compatibility, which is why some guest architectures
  are stuck on the cc->vmsd form. New targets should use dc->vmsd.

To avoid new targets to start using type (2), rename cc->vmsd as
cc->legacy_vmsd. The correct field to implement is dc->vmsd (the
DeviceClass one).

See also commit b170fce3dd ("cpu: Register VMStateDescription
through CPUState") for historic background.

[*] https://www.mail-archive.com/qemu-devel@nongnu.org/msg800849.html

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Cc: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20210517105140.1062037-13-f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Philippe Mathieu-Daudé 2021-05-17 12:51:29 +02:00 • committed by Richard Henderson
parent 4336073b9b
commit 744c72a837
10 changed files with 17 additions and 17 deletions
Download patch file Download diff file Expand all files Collapse all files

12
cpu.c
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@ -143,13 +143,13 @@ void cpu_exec_realizefn(CPUState *cpu, Error **errp)
#ifdef CONFIG_USER_ONLY
assert(qdev_get_vmsd(DEVICE(cpu)) == NULL ||
qdev_get_vmsd(DEVICE(cpu))->unmigratable);
assert(cc->vmsd == NULL);
assert(cc->legacy_vmsd == NULL);
#else
if (qdev_get_vmsd(DEVICE(cpu)) == NULL) {
vmstate_register(NULL, cpu->cpu_index, &vmstate_cpu_common, cpu);
}
if (cc->vmsd != NULL) {
vmstate_register(NULL, cpu->cpu_index, cc->vmsd, cpu);
if (cc->legacy_vmsd != NULL) {
vmstate_register(NULL, cpu->cpu_index, cc->legacy_vmsd, cpu);
}
#endif /* CONFIG_USER_ONLY */
}
@ -159,10 +159,10 @@ void cpu_exec_unrealizefn(CPUState *cpu)
CPUClass *cc = CPU_GET_CLASS(cpu);
#ifdef CONFIG_USER_ONLY
assert(cc->vmsd == NULL);
assert(cc->legacy_vmsd == NULL);
#else
if (cc->vmsd != NULL) {
vmstate_unregister(NULL, cc->vmsd, cpu);
if (cc->legacy_vmsd != NULL) {
vmstate_unregister(NULL, cc->legacy_vmsd, cpu);
}
if (qdev_get_vmsd(DEVICE(cpu)) == NULL) {
vmstate_unregister(NULL, &vmstate_cpu_common, cpu);