Re: pathnames, etc. as required capabilities

On Fri, Apr 4, 2008 at 10:54 PM, Dave Peterson <[email protected]>
wrote:

> Hi,
>
> I have a little C++ program I wrote that uses RPM library
> calls to extract dependency info from RPM files, and then
> does some analysis on the extracted info.  As input, the
> program takes the entire set of RPMs in the CentOS 5
> distro.  Looking at the output, I notice that there are a
> number of capabilities required by packages in the distro
> but not shown as being provided by any package in the
> distro.  Almost all of these are full pathnames (for
> instance "/bin/sh" and "/bin/gzip").  The remaining few
> are strings that look like they specify things provided
> by the RPM library itself (such as
> "rpmlib(CompressedFileNames)" and
> "rpmlib(PartialHardlinkSets)").
>

OK.


>
> Based on these observations, I am guessing that the
> following conventions probably apply to strings extracted
> from RPM headers that represent required capabilities:
>
>    1.  Any capability string that looks like an absolute
>        pathname should be treated as one.  In addition
>        to packages that explicitly list such a
>        capability as being provided, any package whose
>        set of included files contains a matching
>        absolute pathname should be treated as providing
>        that capability.
>

Yes. Any capability that starts with a '/' is a file dependency.


>
>    2.  Any capability string that looks like
>        "rpmlib(...)" should be assumed to refer to
>        something provided by the RPM library itself.
>

Yes. Any capability enclosed by rpmlib(...) is provided by the rpm
implementation.


>
> Is this correct?  If so, I have a couple of questions:
>
>    - The RPM package that provides the RPM library
>      itself (rpm-4.4.2-37.el5.i386.rpm for CentOS 5)
>      doesn't list capabilities such as
>      "rpmlib(CompressedFileNames)".  Is there any way,
>      just by using RPM library calls to get info from
>      the RPM package, to determine whether it provides
>      things such as "rpmlib(CompressedFileNames)"?  If
>      not, how do I use RPM library calls to ask the RPM
>      library on an installed system which capabilities
>      of this type it provides?
>

Yes. Leme check ...

In rpm-4.4.2 the API to retrieve rpmlib(...) dependencies is:

/** \ingroup rpmtrans
 * Return copy of rpmlib internal provides.
 * @retval provNames    address of array of rpmlib internal provide names
 * @retval provFlags    address of array of rpmlib internal provide flags
 * @retval provVersions address of array of rpmlib internal provide versions
 * @return              no. of entries
 */
/*@unused@*/
int rpmGetRpmlibProvides(/*@null@*/ /*@out@*/ const char *** provNames,
                        /*@null@*/ /*@out@*/ int ** provFlags,
                        /*@null@*/ /*@out@*/ const char *** provVersions)
        /*@modifies *provNames, *provFlags, *provVersions @*/;

There's a different API in more recent rpm that returns a populated
dependency set instead of raw arrays.

But if you're writing an application that uses rpm libraries, you can also
just
ignore all rpmlib(...) dependencies. The dependencies are meant for rpmlib,
not for applications.

>
>    - Are there any kinds of strings other than absolute
>      pathnames and things like
>      "rpmlib(CompressedFileNames)" that an RPM header
>      may list as required but must be treated as special
>      cases?
>

The general
    Requires: foo(bar)
is an attempt at namespaces for dependencies. So the general answer is
that there are an infinite number of foo(bar) constructs, each of which
should be handled (in some ideal sense) by handing off to a namespace
handler.

In practice, "foo(bar)" is just a string that can be matched against other
strings,
noone really groks namespace for dependencies (although its kinda obvious
that
all dependencies that start with '/' are file dependencies, just another
name space).

Running
    rpm -qa --qf '[%{requirename|\n]' | grep '(' | sort -u
will give you a pretty clear idea of what namespace dependency strings are
currently in
use on your distro.

hth

73 de Jeff

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