Re: [PATCH 1/1] hw/s390x: modularize virtio-gpu-ccw

[Thomas Huth <thuth@redhat.com>]

On 18/02/2021 11.34, Halil Pasic wrote:
> On Thu, 18 Feb 2021 10:23:16 +0100
> Thomas Huth <thuth@redhat.com> wrote:
> 
>>> Since the virtio-gpu-ccw device depends on the hw-display-virtio-gpu
>>> module, which provides the type virtio-gpu-device, packaging the
>>> hw-display-virtio-gpu module as a separate package that may or may not
>>> be installed along with the qemu package leads to problems. Namely if
>>> the hw-display-virtio-gpu is absent, qemu continues to advertise
>>> virtio-gpu-ccw, but it aborts not only when one attempts using
>>> virtio-gpu-ccw, but also when libvirtd's capability probing tries
>>> to instantiate the type to introspect it.
>>>
>>> Let us thus introduce a module named hw-s390x-virtio-gpu-ccw that
>>> is going to provide the virtio-gpu-ccw device. The hw-s390x prefix
>>> was chosen because it is not a portable device.
>>>
>>> With virtio-gpu-ccw built as a module, the correct way to package a
>>> modularized qemu is to require that hw-display-virtio-gpu must be
>>> installed whenever the module hw-s390x-virtio-gpu-ccw.
>>>
>>> Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
>>> ---
>>>    hw/s390x/meson.build | 17 ++++++++++++++++-
>>>    util/module.c        |  1 +
>>>    2 files changed, 17 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/hw/s390x/meson.build b/hw/s390x/meson.build
>>> index 2a7818d94b..153b1309fb 100644
>>> --- a/hw/s390x/meson.build
>>> +++ b/hw/s390x/meson.build
>>> @@ -34,7 +34,6 @@ virtio_ss.add(files('virtio-ccw.c'))
>>>    virtio_ss.add(when: 'CONFIG_VIRTIO_BALLOON', if_true: files('virtio-ccw-balloon.c'))
>>>    virtio_ss.add(when: 'CONFIG_VIRTIO_BLK', if_true: files('virtio-ccw-blk.c'))
>>>    virtio_ss.add(when: 'CONFIG_VIRTIO_CRYPTO', if_true: files('virtio-ccw-crypto.c'))
>>> -virtio_ss.add(when: 'CONFIG_VIRTIO_GPU', if_true: files('virtio-ccw-gpu.c'))
>>>    virtio_ss.add(when: 'CONFIG_VIRTIO_INPUT', if_true: files('virtio-ccw-input.c'))
>>>    virtio_ss.add(when: 'CONFIG_VIRTIO_NET', if_true: files('virtio-ccw-net.c'))
>>>    virtio_ss.add(when: 'CONFIG_VIRTIO_RNG', if_true: files('virtio-ccw-rng.c'))
>>> @@ -46,3 +45,19 @@ virtio_ss.add(when: 'CONFIG_VHOST_USER_FS', if_true: files('vhost-user-fs-ccw.c'
>>>    s390x_ss.add_all(when: 'CONFIG_VIRTIO_CCW', if_true: virtio_ss)
>>>    
>>>    hw_arch += {'s390x': s390x_ss}
>>> +
>>> +if target.startswith('s390x')
>>> +  hw_s390x_modules = {}
>>> +
>>> +  hw_s390x_modules_c_args = ['-DNEED_CPU_H',
>>> +	      '-DCONFIG_TARGET="@0@-config-target.h"'.format(target)]
>>> +  hw_s390x_modules_inc = [include_directories('../../target' / config_target['TARGET_BASE_ARCH'])]
>>> +  hw_s390x_modules_dependencies = declare_dependency(
>>> +	       include_directories: hw_s390x_modules_inc, compile_args: hw_s390x_modules_c_args)
>>
>> Basically the patch looks fine to me, but I wonder why all that above lines
>> (related to hw_s390x_modules_dependencies) are requred at all? The other
>> display modules in hw/display/meson.build also do not need to re-define
>> c_args for example?
> 
> The explanation is simple. Unlike most devices, the ccw devices aren't
> portable. In particular both css.c and css.h includes "cpu.h", and
> virtio-ccw-gpu.c includes "qemu/osdep.h". Furthermore osdep.h contains:
> #ifdef NEED_CPU_H
> #include CONFIG_TARGET
> #else
> #include "exec/poison.h"
> #endif
> so if we don't have NEED_CPU_H, among others CONFIG_KVM is poisoned, and
> CONFIG_KVM is used in "css.h". Frankly, I can't tell under what circumstances
> does css need "cpu.h".
As far as I can see, the only real reason right now is the CONFIG_KVM 
section in css.h. I think you could simply move that into another header 
file instead (cpu.h ?)

  Thomas