Re: [Qemu-devel] [PATCHv6 3/5] fw_cfg: move assert() and linking of fw_cfg device to the machine into instance_init()

[Eduardo Habkost]

On Mon, Jun 19, 2017 at 01:59:07PM +0100, Mark Cave-Ayland wrote:
> In preparation for calling fw_cfg_init1() during realize rather than during
> init, move the assert() checking for existing fw_cfg devices and the linking
> of the device to the machine with object_property_add_child() to a new
> fw_cfg instance_init() function.
> 
> This guarantees that we will still assert() correctly if more than one fw_cfg
> device is instantiated by accident.
> 
> Signed-off-by: Mark Cave-Ayland <address@hidden>
> Reviewed-by: Laszlo Ersek <address@hidden>
> Tested-by: Laszlo Ersek <address@hidden>
> ---
>  hw/nvram/fw_cfg.c |   14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
> index 99bdbc2..af45012 100644
> --- a/hw/nvram/fw_cfg.c
> +++ b/hw/nvram/fw_cfg.c
> @@ -915,10 +915,6 @@ static void fw_cfg_init1(DeviceState *dev)
>      MachineState *machine = MACHINE(qdev_get_machine());
>      uint32_t version = FW_CFG_VERSION;
>  
> -    assert(!object_resolve_path(FW_CFG_PATH, NULL));
> -
> -    object_property_add_child(OBJECT(machine), FW_CFG_NAME, OBJECT(s), NULL);
> -
>      qdev_init_nofail(dev);
>  
>      fw_cfg_add_bytes(s, FW_CFG_SIGNATURE, (char *)"QEMU", 4);
> @@ -1020,6 +1016,15 @@ FWCfgState *fw_cfg_find(void)
>      return FW_CFG(object_resolve_path(FW_CFG_PATH, NULL));
>  }
>  
> +static void fw_cfg_init(Object *obj)
> +{
> +    MachineState *machine = MACHINE(qdev_get_machine());
> +
> +    assert(!object_resolve_path(FW_CFG_PATH, NULL));
> +
> +    object_property_add_child(OBJECT(machine), FW_CFG_NAME, obj, NULL);

I don't think this belongs to instance_init.  We must always be
able to instantiate objects without crashing QEMU or affecting
QEMU global state.  This patch makes device-list-properties
crash:

  $ qemu-system-x86_64 -display none -qmp unix:/tmp/qmp,server,nowait &
  [1] 2848
  $ echo 'device-list-properties typename=fw_cfg_mem' | ./scripts/qmp/qmp-shell 
/tmp/qmp
  Welcome to the QMP low-level shell!
  Connected to QEMU 2.9.50
  
  qemu-system-x86_64: qemu/hw/nvram/fw_cfg.c:974: fw_cfg_init: Assertion 
`!object_resolve_path(FW_CFG_PATH, NULL)' failed.
  (QEMU) Disconnected
  [1]+  Aborted                 (core dumped) qemu-system-x86_64 -display none 
-qmp unix:/tmp/qmp,server,nowait
  $ 


I suggest moving this check to realize, like the rest of
fw_cfg_init1(), but change it to do proper error reporting
instead of asserting.

> +}
> +
>  static void fw_cfg_class_init(ObjectClass *klass, void *data)
>  {
>      DeviceClass *dc = DEVICE_CLASS(klass);
> @@ -1033,6 +1038,7 @@ static const TypeInfo fw_cfg_info = {
>      .parent        = TYPE_SYS_BUS_DEVICE,
>      .abstract      = true,
>      .instance_size = sizeof(FWCfgState),
> +    .instance_init = fw_cfg_init,
>      .class_init    = fw_cfg_class_init,
>  };
>  
> -- 
> 1.7.10.4
> 

-- 
Eduardo