dnf whatprovides and library files

[Radek Holy]

----- Original Message -----
> From: "Ed Greshko" <ed.greshko at greshko.com>
> To: users at lists.fedoraproject.org
> Sent: Wednesday, June 10, 2015 9:24:09 AM
> Subject: Re: dnf whatprovides and library files
> 
> On 06/10/15 14:55, Gordon Messmer wrote:
> > On 06/09/2015 04:53 PM, Ed Greshko wrote:
> >> I can't seem to get dnf to tell me what package supplies a library.
> > ...
> >> [root at f22k ~]# ll /lib64/libXv.so.1.0.0
> >> -rwxr-xr-x. 1 root root 19664 Aug 17  2014 /lib64/libXv.so.1.0.0
> >> [root at f22k ~]# dnf whatprovides /lib64/libXv.so.1.0.0
> >
> > That's the correct query for a file, but not a library.
> >
> > Two things:
> >
> > First, applications don't link against libXv.so.1.0.0, they link against
> > libXv.so.1.  It is up to the dynamic linker to locate that library within
> > the search path:
> >
> > $ ldd /usr/bin/xvinfo | grep libXv
> >     libXv.so.1 => /lib64/libXv.so.1 (0x00000032d3600000)
> >
> > You'll see the same string in the first column when a library is not found,
> > so that's the string that you look for.
> >
> > Second, rpm generates "provides" with pathless library names.  In the
> > example above, "xvinfo" is linked against "libXv.so.1".  rpm behaves the
> > same way.  Since the application is linked against "libXv.so.1" that is
> > the correct string to use when searching for a package that provides it.
> >
> > $ dnf whatprovides libXv.so.1
> > libXv-1.0.10-2.fc22.i686 : X.Org X11 libXv runtime library
> > Repo        : @System
> >
> 
> Thanks for the info....
> 
> But, just to be clear, the issue I'm addressing is what an average user may
> do in a given circumstance.  Upon seeing an error message such as this one,
> 
> error while loading shared libraries: /lib64/libexempi.so.3: file too short
> 
> assuming they know of dnf whatprovides I think it is more likely they will
> simply use copy/paste and issue the command "dnf whatprovides
> /lib64/libexempi.so.3"
> 
> Yes, the Subject I picked was not as accurate as it would be had I known then
> what I know now.  Maybe....  :-)
> 
> --
> Sorta what I want to say when folks habitually complain about Fedora -
> https://youtu.be/ZArl8fTfub4
> 
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> 

BTW, RPM can do that:

$ rpm --query --file /lib64/libXv.so.1.0.0

So, if RPM tracks these symlinks and if it provides an API to get this information, DNF could do the magic at least for the installed packages. But maybe it could become even more confusing for users since "whatprovides" would sometimes find the package and sometimes not depending on whether the package is installed or not. Maybe printing a warning would be sufficient...
-- 
Radek Holý
Associate Software Engineer
Software Management Team
Red Hat Czech