Re: [PATCH v4 1/8] qdev: Implement qdev_create_fake_machine() for user emulation

[Philippe Mathieu-Daudé]

On 3/1/25 15:24, Richard Henderson wrote:
> On 1/2/25 13:17, Philippe Mathieu-Daudé wrote:
> > When a QDev instance is realized, qdev_get_machine() ends up called.
> > In the next commit, qdev_get_machine() will require a "machine"
> > container to be always present. To satisfy this QOM containers design,
> > Implement qdev_create_fake_machine() which creates a fake "machine"
> > container for user emulation.
> >
> > On system emulation, qemu_create_machine() is called from qemu_init().
> > For user emulation, since the TCG accelerator always calls
> > tcg_init_machine(), we use it to hook our fake machine creation.
> >
> > Suggested-by: Peter Xu <peterx@redhat.com>
> > Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> > ---
> >   include/hw/qdev-core.h | 10 ++++++++++
> >   accel/tcg/tcg-all.c    |  8 +++++++-
> >   hw/core/qdev-user.c    | 21 +++++++++++++++++++++
> >   hw/core/meson.build    |  1 +
> >   4 files changed, 39 insertions(+), 1 deletion(-)
> >   create mode 100644 hw/core/qdev-user.c
> >
> > diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
> > index e6ef80b7fd0..b83b1439968 100644
> > --- a/include/hw/qdev-core.h
> > +++ b/include/hw/qdev-core.h
> > @@ -1027,6 +1027,16 @@ const char *qdev_fw_name(DeviceState *dev);
> >   void qdev_assert_realized_properly(void);
> >   Object *qdev_get_machine(void);
> > +/**
> > + * qdev_create_fake_machine(): Create a fake machine container.
> > + *
> > + * .. note::
> > + *    This function is a kludge for user emulation (USER_ONLY)
> > + *    because when thread (TYPE_CPU) are realized, qdev_realize()
> > + *    access a machine container.
> > + */
> > +Object *qdev_create_fake_machine(void);
> > +
> >   /**
> >    * qdev_get_human_name() - Return a human-readable name for a device
> >    * @dev: The device. Must be a valid and non-NULL pointer.
> > diff --git a/accel/tcg/tcg-all.c b/accel/tcg/tcg-all.c
> > index c2565758876..95adaacee82 100644
> > --- a/accel/tcg/tcg-all.c
> > +++ b/accel/tcg/tcg-all.c
> > @@ -35,7 +35,9 @@
> >   #include "qemu/atomic.h"
> >   #include "qapi/qapi-builtin-visit.h"
> >   #include "qemu/units.h"
> > -#if !defined(CONFIG_USER_ONLY)
> > +#if defined(CONFIG_USER_ONLY)
> > +#include "hw/qdev-core.h"
> > +#else
> >   #include "hw/boards.h"
> >   #endif
> >   #include "internal-common.h"
> > @@ -124,6 +126,10 @@ static int tcg_init_machine(MachineState *ms)
> >       tcg_prologue_init();
> >   #endif
> > +#ifdef CONFIG_USER_ONLY
> > +    qdev_create_fake_machine();
> > +#endif
>
> No need to return the fake machine, it seems.

My first reasoning was about avoiding ASan leak warnings, planning
to release that container on exit(), but I'm clearly over-engineering
what is meant to be a kludge.

>   With that,
>
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

I'll remove and merge directly, thanks!