Re: [PATCH 1 of 5 V2] remus: add libnl3 dependency to autoconf scripts

[Shriram Rajagopalan <rshriram@cs.ubc.ca>]

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On Wed, Oct 9, 2013 at 1:06 AM, Ian Campbell <Ian.Campbell@citrix.com>wrote:

> On Tue, 2013-10-08 at 19:14 -0700, Shriram Rajagopalan wrote:
>
> >
> >         > +# Check for libnl3 >=3.2.8. If present enable remus network
> >         buffering.
> >         > +PKG_CHECK_EXISTS([libnl-3.0 >= 3.2.8 libnl-route-3.0 >=
> >         3.2.8 libnl-cli-3.0 >= 3.2.8],
> >         > +             [libnl3_lib="y"], [libnl3_lib="n"])
> >         > +AC_CHECK_HEADER([netlink/route/qdisc/plug.h],
> >         [libnl3_dev="y"], [libnl3_dev="n"])
> >
> >
> >         Aren't these a bit redundant? i.e. doesn't PKG_CHECK_EXISTS
> >         cover the development headers?
>
> > Unfortunately, libnl3 does not have a pkgconfig .pc file for its dev
> > headers. So there is no standard way to check for these headers.
> > Debian has libnl-3-dev. OpenSUSE has libnl3-devel, etc.
>
> I think you are confused about what pkg-config and .pc files are.
>
> They are part of the "dev headers" and describe how to compile and link
> against the library. You are entitled to assume that if pkg-config
> returns that the pkg exists you can use it and link against it etc.
>
> IOW the .pc file is exactly the standard way to check for these things.
>
>
I am a little confused. I do know that if pkg exists, then
linking/compiling isn't an issue.

The issue with libnl3 is "compiling" - i.e., dev headers, that libxl uses
to invoke libnl API.
There is no pkg-config module for libnl3 development headers (Just like the
ones for
libraries: libnl-3.0, libnl-route-3.0, etc) [see
http://git.infradead.org/users/tgr/libnl.git/tree ]

It has package config files for libnl-3.0.pc (-lnl-3), libnl-route-3.0.pc
(-lnl-route-3)
but none for dev headers.

Do they get installed along with the libraries ? Don't think so (atleast on
debian & ubuntu).

root@localhost:~# apt-cache search libnl
libnl-3-200 - library for dealing with netlink sockets
libnl-3-dev - development library and headers for libnl-3
libnl-cli-3-200 - library for dealing with netlink sockets - cli helpers
libnl-cli-3-dev - development library and headers for libnl-cli-3
libnl-route-3-200 - library for dealing with netlink sockets - route
interface
libnl-route-3-dev - development library and headers for libnl-route-3


So what do you suggest ?

 >         > +         AC_SUBST(remus_netbuf, [n])
> >         > +         ],[
> >         > +         LIBNL3_LIBS="-lnl-3 -lnl-route-3"
> >
> >
> >         Since libnl3 uses pkg-cofnig, these should come from there I
> >         think.
> >         There's probably a macro in pkg-config.m4 to help?
>
> > None that I could find.
>
> Looks like PKG_CHECK_MODULES sets <PKG>_CFLAGS and _LDFLAGS.
>
> See
>
> https://www.flameeyes.eu/autotools-mythbuster/pkgconfig/pkg_check_modules.htmland
> https://developer.gnome.org/anjuta-build-tutorial/stable/library-autotools.html.enfor info (first two hits on google for "pkg-config autoconf")
>
> Ian.
>
>
>

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