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

[Halil Pasic]

On Thu, 18 Feb 2021 15:44:47 +0100
Thomas Huth <thuth@redhat.com> wrote:

> 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 ?)
> 

Since everybody seems to agree, that that is the right way to move
forward, I can try moving things around like you and Connie suggested.

Regards,
Halil