Re: [dpdk-dev] [RFC PATCH] build: use libpcap only from pkg-config

[Bruce Richardson <bruce.richardson@intel.com>]

On Fri, Oct 09, 2020 at 10:09:11AM +0100, Luca Boccassi wrote:
> On Thu, 2020-10-08 at 18:08 +0100, Bruce Richardson wrote:
> > On Thu, Oct 08, 2020 at 06:05:36PM +0100, Bruce Richardson wrote:
> > > All recent linux distro's - including RHEL 8 and Ubuntu 18.04 - provide a
> > > pkg-config file for libpcap, and using other methods of finding the library
> > > can cause issues when cross-compiling, so we can limit build support for
> > > pcap versions without a .pc file.
> > > 
> > > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > > ---
> > >  config/meson.build | 8 +-------
> > >  1 file changed, 1 insertion(+), 7 deletions(-)
> > > 
> > > diff --git a/config/meson.build b/config/meson.build
> > > index 69f2aeb60..edc6c195a 100644
> > > --- a/config/meson.build
> > > +++ b/config/meson.build
> > > @@ -163,13 +163,7 @@ if libbsd.found()
> > >  endif
> > >  
> > >  # check for pcap
> > > -pcap_dep = dependency('pcap', required: false)
> > > -if pcap_dep.found()
> > > -	# pcap got a pkg-config file only in 1.9.0 and before that meson uses
> > > -	# an internal pcap-config finder, which is not compatible with
> > > -	# cross-compilation, so try to fallback to find_library
> > > -	pcap_dep = cc.find_library('pcap', required: false)
> > > -endif
> > > +pcap_dep = dependency('libpcap', required: false, method: 'pkg-config')
> > >  if pcap_dep.found() and cc.has_header('pcap.h', dependencies: pcap_dep)
> > >  	dpdk_conf.set('RTE_PORT_PCAP', 1)
> > >  	dpdk_extra_ldflags += '-lpcap'
> > 
> > Just sending this as an RFC for consideration, since I hit problems with
> > the pcap code when testing 32-bit (x32) builds, and remembered having hit
> > it previously too.
> > 
> > Does anyone see an issue with limiting our pcap detection to pkg-config
> > only in this case?
> > 
> > /Bruce
> 
> Sadly it's not yet available in Debian stable:
> 
> https://packages.debian.org/buster/amd64/libpcap0.8-dev/filelist
> 
> Also for Ubuntu 18.04, it's only available with the bionic-updates
> repository, and only for the past month - it shipped without it.
> 
> I'm absolutely keen on using only pkg-config (so much that I did the
> packaging changes myself to ship it in libpcap-dev [1][2]) but perhaps
> in the interest of compatibility it's better to wait next year, so that
> the new Debian stable supports it, and the Ubuntu 18.04 LTS fix had the
> chance to rollout everywhere?
> 

Thanks, that's exactly the sort of feedback I was looking for!

It seems to be the pcap-config support in meson which causes cross-building
issues, so I wonder would it still work ok if we changed this to only use
pkg-config for the initial search and then use find-library if that failed?

 # check for pcap
-pcap_dep = dependency('pcap', required: false)
-if pcap_dep.found()
-       # pcap got a pkg-config file only in 1.9.0 and before that meson uses
-       # an internal pcap-config finder, which is not compatible with
-       # cross-compilation, so try to fallback to find_library
+pcap_dep = dependency('libpcap', required: false, method: 'pkg-config')
+if not pcap_dep.found()
+       # pcap got a pkg-config file only in 1.9.0
        pcap_dep = cc.find_library('pcap', required: false)
 endif