Re: [PATCH for-8.0 00/30] Meson changes for QEMU 8.0

[Paolo Bonzini]

On 12/16/22 16:35, Daniel P. Berrangé wrote:
> So after applying this series, at least on Fedora, I barely needed
> configure at all, in so muc as the following successfully built AFAICT:
>
> $ mkdir build
> $ cat > build/config-host.mak <<EOF
> all:
> GIT=git
> GIT_SUBMODULES=ui/keycodemapdb tests/fp/berkeley-testfloat-3 
> tests/fp/berkeley-softfloat-3 dtc
> GIT_SUBMODULES_ACTION=update
> CONFIG_POSIX=y
> CONFIG_LINUX=y
> SRC_PATH=/home/berrange/src/virt/qemu
> TARGET_DIRS=x86_64-softmmu
> CONFIG_PLUGIN=y
> HAVE_GDB_BIN=/usr/bin/gdb
> ENGINE=podman
> ROMS=pc-bios/optionrom
> MAKE=make
> PYTHON=/usr/bin/python3 -B
> GENISOIMAGE=/usr/bin/genisoimage
> MESON=/usr/bin/meson
> NINJA=/usr/bin/ninja
> PKG_CONFIG=
> CC=cc
> EXESUF=
> TCG_TESTS_TARGETS= x86_64-softmmu
> EOF
> $ meson build
> $ ninja -C build

Yep.  It wouldn't build the firmwares though, or be able to run TCG or 
Avocado tests.  This kind of build system orchestration is the remaining 
task of configure (see new docs in patch 28).  It's not really possible 
for it to go away, it's beyond Meson's capabilities and intentions.

I would also like to move Python virtual environment configuration to 
configure.  This would give a lot more flexibility in whether to use 
network or not, for example, and is in line with submodule handling that 
is already in configure.

> Out of the things in config-host.mak there, a few meson already knows,
> like CC, SRC_PATH, 50% would be just a meson find_program() command,
> a couple would need meson args (eg TARGET_DIRS), and some just look
> redundant, eg CONFIG_LINUX largely duplicates __linux__, and
> CONFIG_POSIX is effectively  !_WIN32.

There are a couple like ENGINE or HAVE_GDB_BIN that are only needed by 
non-QEMU parts of the build system, and I don't think it makes much 
sense to move those detections out of configure.

But yeah, the OS symbols are pretty low-hanging fruit.  In fact 
meson.build recomputes them:

  config_host_data.set('CONFIG_POSIX', targetos != 'windows')

... and with Windriver's patches to get much closer to POSIX/Windows 
feature parity, the Makefiles don't use them as much as they did.

Paolo