On Tue, 2020-10-27 at 11:07 +0100, Michal Privoznik wrote:

On 10/26/20 10:53 PM, Neal Gompa wrote:

...

As it turns out, the rather complicated structure that is currently used for enabling or disabling features in the libvirt build does not cleanly map well to RPM's bcond feature.

Consequently, we need these back in order to support trivially activating these features through extra macros as build inputs.

This reverts commit 31d687a3218c9072d7050dd608e013e063ca180f.

Signed-off-by: Neal Gompa <ngompa13@gmail.com> --- libvirt.spec.in | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-)

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

and pushed.

I'm not convinced reverting this was the right call. The way RPM conditional macros work is that, if you have %{!?macro:value} that will expand to 'value' if 'macro' is *not* defined, and to nothing otherwise. So if you have for example %define with_fuse 0%{!?_without_fuse:0} that means that, if you pass --define '_without_fuse 1' to rpmbuild the line will expand to %define with_fuse 0 and if you don't pass the extra option to rpmbuild it will instead expand to %define with_fuse 00 The two are clearly equivalent, so there is no point in keeping the conditional macro - it merely obfuscates the logic. Of course things would be different if you had %define with_fuse 0%{!?_without_fuse:1} instead: in this case, the line would expand to %define with_fuse 0 and %define with_fuse 01 respectively, which means the feature would be enabled by default but could optionally be disabled by passing the correct argument to rpmbuild, as expected. We have plenty similar macros in libvirt.spec, and since they work just as intended 31d687a3218c didn't touch them. Note that in this case I've removed # fuse is used to provide virtualized /proc for LXC %if %{with_lxc} %define with_fuse 0%{!?_without_fuse:1} %endif from the spec to make sure that the value for the 'fuse' option passed to Meson depended solely on the value of the _without_fuse macro, and then checked the rpmbuild output to compare. -- Andrea Bolognani / Red Hat / Virtualization

On Tue, Oct 27, 2020 at 9:30 AM Andrea Bolognani <abologna@redhat.com> wrote:

On Tue, 2020-10-27 at 14:05 +0100, Andrea Bolognani wrote:

...

I'm not convinced reverting this was the right call.

The way RPM conditional macros work is that, if you have

%{!?macro:value}

that will expand to 'value' if 'macro' is *not* defined, and to nothing otherwise. So if you have for example

%define with_fuse 0%{!?_without_fuse:0}

that means that, if you pass

--define '_without_fuse 1'

to rpmbuild the line will expand to

%define with_fuse 0

and if you don't pass the extra option to rpmbuild it will instead expand to

%define with_fuse 00

The two are clearly equivalent, so there is no point in keeping the conditional macro - it merely obfuscates the logic.

Of course things would be different if you had

%define with_fuse 0%{!?_without_fuse:1}

instead: in this case, the line would expand to

%define with_fuse 0

and

%define with_fuse 01

respectively, which means the feature would be enabled by default but could optionally be disabled by passing the correct argument to rpmbuild, as expected. We have plenty similar macros in libvirt.spec, and since they work just as intended 31d687a3218c didn't touch them.

Note that in this case I've removed

# fuse is used to provide virtualized /proc for LXC %if %{with_lxc} %define with_fuse 0%{!?_without_fuse:1} %endif

from the spec to make sure that the value for the 'fuse' option passed to Meson depended solely on the value of the _without_fuse macro, and then checked the rpmbuild output to compare.

Ugh, you're right, and those values need to be changed to 1.

Also note that I'm aware you want to eventually push for adoption of the standard bcond macros, and I fully stand behind that desire! If this patch had been the first in a series that introduced bcond support and was clearing the path for that, I would have zero problems with it. As it is, however, you're simply reintroducing some of the obfuscation we had recently managed to get rid of, without getting anything in return.

Fixing this so that I can switch to bconds is going to be a massive rewrite of how feature enablement works. That is not something I can push for a 6.9.0 freeze break patch. My in-progress rewrite is going to be a massive break in how this is managed... -- 真実はいつも一つ！/ Always, there's only one truth!