[libvirt] [PATCHv4 13/15] build: switch --with-qemu default from yes to check

[Daniel P. Berrangé]

On Fri, Jul 20, 2018 at 12:24:50PM +0200, Ján Tomko wrote:
> On Thu, Jul 19, 2018 at 07:38:15PM -0400, John Ferlan wrote:
> > 
> > 
> > On 07/18/2018 10:44 AM, Ján Tomko wrote:
> > > Unless explicitly requested, enable the QEMU driver
> > > only if the Jansson library is present.
> > > 
> > > Signed-off-by: Ján Tomko <jtomko at redhat.com>
> > > ---
> > >  m4/virt-driver-qemu.m4 | 6 +++++-
> > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > > 
> > 
> > Perhaps it's obvious for someone else, but I think there some sort of
> > dependency missing.
> > Starting with this patch I found that my with-qemu
> > "went away".
> > 
> > I have:
> > 
> > jansson.x86_64                           2.11-1.fc28
> > @fedora
> > 
> > 
> > But not:
> > 
> > jansson-devel         x86_64         2.11-1.fc28          fedora
> >  15 k
> > 
> > If I explicitly add --with-jansson onto the command line, then I get:
> > 
> > checking for JANSSON... no
> > configure: error: You must install the jansson >= 2.5 pkg-config module
> > to compile libvirt
> > error: configure failed
> > 
> > If I then install jansson-devel, the build succeeds.
> > 
> > Honestly I think we need to be much more in your face in this instance -
> > something isn't quite right and it eventually leads to some really
> > strange results because nothing in/for qemu is built, but you are left
> > with old build bits in your tree.  Eventually something fails.
> > 
> 
> There was not that much discussion about it:
> https://www.redhat.com/archives/libvir-list/2018-May/msg01321.html
> 
> I do not oppose reverting this bit and failing by default if we don't
> have a JSON library (as Andrea mentioned, more drivers might possibly
> require a working JSON implementation).

We use virjson.h throughout src/util and src/rpc so that code is
not even driver specific, however, there are not currently mingw
pacakges for jansson in Fedora at least. Maybe it will work, but
we would need someone todo the work to add that to Fedora before
we can consider making this mandatory.

Regards,
Daniel
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