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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
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5
include/hw/core/cpu.h
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@ -122,7 +122,8 @@ struct AccelCPUClass;
* 32-bit VM coredump.
* @write_elf32_qemunote: Callback for writing a CPU- and QEMU-specific ELF
* note to a 32-bit VM coredump.
* @vmsd: State description for migration.
* @legacy_vmsd: Legacy state description for migration.
* Do not use in new targets, use #DeviceClass::vmsd instead.
* @gdb_num_core_regs: Number of core registers accessible to GDB.
* @gdb_core_xml_file: File name for core registers GDB XML description.
* @gdb_stop_before_watchpoint: Indicates whether GDB expects the CPU to stop
@ -177,7 +178,7 @@ struct CPUClass {
int (*write_elf32_qemunote)(WriteCoreDumpFunction f, CPUState *cpu,
void *opaque);
const VMStateDescription *vmsd;
const VMStateDescription *legacy_vmsd;
const char *gdb_core_xml_file;
gchar * (*gdb_arch_name)(CPUState *cpu);
const char * (*gdb_get_dynamic_xml)(CPUState *cpu, const char *xmlname);