Re: [PATCH RFC 00/10] qapi: remove all TARGET_* conditionals from the schema

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 8/5/25 15:58, Daniel P. Berrangé wrote:
> Pierrick has proposed a series that introduces a concept of runtime
> conditionals to the QAPI schema, in order to adapt the TARGET_*
> conditionals currently used at build time:
> 
>    https://lists.nongnu.org/archive/html/qemu-devel/2025-05/msg01699.html
> 
> For the sake of comparison & evaluation, this series illustrates the
> alternative approach that we've discussed of entirely removing any
> concept of TARGET_* conditionals.
> 
> With this the QAPI schema varies solely based on CONFIG_* conditionals,
> and is thus invariant across different target emulators.
> 
> In this PoC I've taken the minimal effort approach to the problem.
> 
> The QAPI schema has removed the TARGET_* conditionals and in order to
> make all the emulators then compile, the stubs/ directory is populated
> with a bunch of files to provide dummy impls of the target specific QMP
> commands.
> 
> This is sufficient to make the current QEMU binaries build successfully.
> 
> To make the "single binary" concept work, however, would require
> additional followup work to eliminate the stubs.
> 
> Instead of having stubs we would need to de-couple the QMP command
> impl from the machine internals. This would likely require greater
> use of interfaces and/or virtual method dispatchers on the machine
> class. This would enable the 'qmp_XXXXX' command impls to exist
> once. Then they call out to virtual methods on the machine to provide
> the real impl, and/or generate an error if the virtual method is not
> implemented for the machine.

Note,  I don't see commands "per machine", but per device (including
CPU). When not specified, we iterate over device implementations / CPUs.

> 
> Daniel P. Berrangé (9):
>    qapi: expose rtc-reset-reinjection command unconditionally
>    qapi: expand docs for SEV commands
>    qapi: make SEV commands unconditionally available
>    qapi: expose query-gic-capability command unconditionally
>    qapi: make SGX commands unconditionally available
>    qapi: make Xen event commands unconditionally available
>    qapi: remove the misc-target.json file
>    qapi: make most CPU  commands unconditionally available
>    qapi: make s390x specific CPU commands unconditionally available
> 
> Philippe Mathieu-Daudé (1):
>    qapi: Make CpuModelExpansionInfo::deprecated-props optional and
>      generic
> 
>   hw/i386/kvm/xen-stubs.c               |  13 -
>   hw/i386/kvm/xen_evtchn.c              |   2 +-
>   hw/i386/monitor.c                     |   2 +-
>   hw/i386/sgx-stub.c                    |  13 -
>   hw/i386/sgx.c                         |   2 +-
>   hw/s390x/cpu-topology.c               |   4 +-
>   hw/s390x/s390-skeys.c                 |   1 -
>   include/hw/s390x/cpu-topology.h       |   2 +-
>   qapi/machine-s390x.json               | 120 ++++++
>   qapi/machine-target.json              | 523 --------------------------
>   qapi/machine.json                     | 363 ++++++++++++++++++
>   qapi/meson.build                      |   5 +-
>   qapi/misc-arm.json                    |  49 +++
>   qapi/misc-i386.json                   | 479 +++++++++++++++++++++++
>   qapi/misc-target.json                 | 504 -------------------------
>   qapi/qapi-schema.json                 |   5 +-
>   stubs/meson.build                     |   8 +
>   stubs/monitor-arm-gic.c               |  12 +
>   stubs/monitor-cpu-s390x-kvm.c         |  22 ++
>   stubs/monitor-cpu-s390x.c             |  23 ++
>   stubs/monitor-cpu.c                   |  21 ++
>   stubs/monitor-i386-rtc.c              |  10 +
>   stubs/monitor-i386-sev.c              |  36 ++
>   stubs/monitor-i386-sgx.c              |  17 +
>   stubs/monitor-i386-xen.c              |  16 +
>   target/arm/arm-qmp-cmds.c             |   4 +-
>   target/i386/cpu-system.c              |   2 +-
>   target/i386/cpu.c                     |   2 +-
>   target/i386/monitor.c                 |   1 -
>   target/i386/sev-system-stub.c         |  32 --
>   target/i386/sev.c                     |   2 +-
>   target/loongarch/loongarch-qmp-cmds.c |   2 +-
>   target/mips/system/mips-qmp-cmds.c    |  12 +-
>   target/ppc/ppc-qmp-cmds.c             |  12 +-
>   target/riscv/riscv-qmp-cmds.c         |   2 +-
>   target/s390x/cpu_models_system.c      |   2 +-
>   tests/qtest/qmp-cmd-test.c            |   1 +

Eh I did a very similar series last month which didn't pass local
review, I need to remember what was the issue...

$ git diff --stat eb3020b6ed2baca63..32235d621871df0ccc
  MAINTAINERS                                        |   3 ++
  qapi/machine-arm-target.json                       |  47 +++++++++++++++++
  qapi/machine-s390x-target.json                     | 301 
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  qapi/machine-target.json                           | 295 
--------------------------------------------------------------------------------------------------------
  qapi/{misc-target.json => machine-x86-target.json} |  94 
++++++++++++++++++----------------
  qapi/machine.json                                  |  44 ----------------
  qapi/qapi-schema.json                              |   4 +-
  include/hw/s390x/cpu-topology.h                    |   2 +-
  hw/i386/kvm/xen-stubs.c                            |   2 +-
  hw/i386/kvm/xen_evtchn.c                           |   2 +-
  hw/i386/monitor.c                                  |   2 +-
  hw/i386/sgx-stub.c                                 |   2 +-
  hw/i386/sgx.c                                      |   2 +-
  hw/s390x/s390-skeys.c                              |   1 -
  target/arm/arm-qmp-cmds.c                          |   3 +-
  target/i386/cpu-system.c                           |   1 +
  target/i386/cpu.c                                  |   3 ++
  target/i386/monitor.c                              |   2 +-
  target/i386/sev-system-stub.c                      |   2 +-
  target/i386/sev.c                                  |   2 +-
  target/s390x/cpu_models_system.c                   |   3 +-
  qapi/meson.build                                   |   4 +-
  22 files changed, 423 insertions(+), 398 deletions(-)

$ git log --oneline eb3020b6ed2baca63..32235d621871df0ccc | tac -r
c92b1454ef1 qapi: Restrict ARM specific schemas to ARM
9c708185fe4 qapi: Restrict CpuModelCompareResult to s390x target
c50cc3c438c qapi: Restrict s390x-specific schemas to s390x target
221ec7acf18 qapi: Restrict SGXEPCSection to x86 targets
a3606c5b23c qapi: Restrict x86-specific schemas to x86 targets
32235d62187 qapi: Guard x86 specific schemas with conditional