User:Toshio/AutoProvidesAndRequiresFilteringDraft

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Summary

Note.png
EPEL Differences
As of rpm-4.9 (Fedora 15), rpm has a standard method to enable filtering. This page documents that. EPEL5 and 6 do not have a recent enough version of rpm to follow these guidelines. See LINK_TO_OLD_GUIDELINES_IN_EPEL_NAMESPACE if your package is to be built there as well. (Toshio: Also merge or link the EPEL5 guidelines: EPEL:Packaging#Perl_Provides_and_Requires_Filtering on the EPEL6 page.)

The auto requires and provides system contained in RPM is quite useful; however, it sometimes picks up "private" package capabilities that shouldn't be advertised as global, things that are "just wrong", or things prohibited by policy (e.g. deps from inside %{_docdir}).

For example:

  • Various "plugin" packages (e.g. Pidgin, Perl, Apache, KDE) are marked as "providing" private shared libraries outside the system path.
  • Files in %{_docdir} are routinely scanned, and can trigger prov/req when this is explicitly forbidden by policy.


This Guideline describes how to filter provides and requires on Fedora.

  • MUST: Packages must not provide RPM dependency information when that information is not global in nature, or are otherwise handled (e.g. through a virtual provides system). e.g. a plugin package containing a binary shared library must not "provide" that library unless it is accessible through the system library paths.
  • MUST: When filtering automatically generated RPM dependency information, the filtering system implemented by Fedora must be used, except where there is a compelling reason to deviate from it.

Usage

Questionmark.png
Verify that the new method does not interfere with coloring
The old method had this warning: "They are not permitted in any other cases, because the macros interfere with the "coloring" of elf32/64 executables done internally by RPM to support multilib installs." I assume the new method doesn't have this limitation but should check with panu/rpm-team
Note.png
Escaping backslashes
Rpm interprets backslashes as part of its parsing of spec files. If you need to include a backslash in a regular expression, you have to double escape it (//).

Location of macro invocation

It's strongly recommended that these filtering macros be invoked before %description, but after any other definitions. This will keep them in a consistent place across packages, and help prevent them from being mixed up with other sections.

Preventing files/directories from being scanned for deps (pre-scan filtering)

The macros %__requires_exclude_from and %__provides_exclude_from can be defined in a spec file to keep the dependency generator from scanning specific files or directories for deps. These macros should be defined with a regular expression that matches all of the directories or files. For instance:

# Do not check any files in docdir for requires
%global __requires_exclude_from ^%{_docdir}/.*$

# Do not check .so files in the python_sitelib directory
# or any files in the application's directory for provides
%global __provides_exclude_from ^(%{python_sitelib}/*.\\.so|%{_datadir}/myapp/.*)$

Note that this macro replaces the %filter_provides_in macro from the old filtering guidelines but it does not do the same thing. In particular:

  • The old macro could be invoked multiple times. This one will only use the regex defined last.
  • The old macro advised against anchoring the beginning of the regex (Using "^"). This macro recommends anchoring as it doesn't suffer from the compatibility problems of the old one.
  • With the old macro it was common to specify a directory name to match everything in a directory recursively. With the new macro you may need to specify .* because you should be anchoring your regular expressions.

Filtering provides and requires after scanning

In addition to preventing rpm from scanning files and directories for automatic dependency generation you can also tell rpm to discard a discovered dependency before it records the dependency in the rpm metadata. Use __requires_exclude and __provides_exclude for this. These macros should be defined as regular expressions. If an entry that rpm's automatic dependency generator created matches the regular expression then it will be filtered out of the requires or provides. For example:

# This might be useful if plugins are being picked up by the dependency generator
%global __provides_exclude ^libfoo-plugin.so.*$

# Something like this could be used to prevent excess deps from an
# example python script in %doc
%global __requires_exclude ^/usr/bin/python$

These macros serves a similar purpose to the old %filter_from_provides macro but it has a different implementation. In particular, that macro took sed expressions whereas this one needs a regular expression.

Simplified macros for common cases

In some cases, the filtering of extraneous Provides: is fairly generic to all packages which provide similar things. There are simple macros that setup filters correctly for those cases so that you can do the filtering with one line. If you need to filter a bit more than the simple macro provides, you still have the option to use the macros listed above.

Perl

Perl extension modules can be filtered using this macro:

%{?perl_default_filter}

This is equivalent to:

%global __provides_exclude_from %{perl_vendorarch}/auto/.*\\.so$|%{perl_archlib}/.*\\.so$|%{_docdir}
%global __requires_exclude_from %{_docdir}
%global __provides_exclude perl\\(VMS|perl\\(Win32|perl\\(DB\\)|perl\\(UNIVERSAL\\)
%global __requires_exclude perl\\(VMS|perl\\(Win32
Warning (medium size).png
Be careful if you customize
If you want to use both %{?perl_default_filter} and customized __provides_* or __requires_* macros be sure that your customizations also capture the original regex. For instance, %global __requires_exclude_from %{_docdir}|%{_datadir}/my-package/examples.

Examples

Pidgin plugin package

On a x86_64 machine, the pidgin-libnotify provides pidgin-libnotify.so()(64bit) which it shouldn't as this library is not inside the paths searched by the system for libraries. It's a private, not global, "provides" and as such must not be exposed globally by RPM.

To filter this out, we could use:

%global __provides_filter_from ^%{_libdir}/purple-2/.*\.so$

Private Libraries

At this time, filtering of private libraries is non-trivial. This is because the symbols you want to filter from the private libraries are usually required by the public applications that the package ships. In order to filter, you need to find out what symbols rpm is extracting for the private library and then remove those in both %__provides_exclude and %__requires_exclude.

As an example, pretend you are packaging an application foo that creates %{_libdir}/foo/libprivate.so that you want to filter and %{_bindir}/foobar that requires that private library. You could:

  1. First build the rpm: $ rpmbuild -ba foo.spec
  2. then determine what provides rpm decided for the private library:
    $ rpm -qp foo-1.0-1.x86_64.rpm</code>
    <pre>libprivate.so()(64bit)  
    foo = 1.0-1.fc19
    foo(x86-64) = 1.0-1.fc19
    
  3. See that "libprivate.so()(64bit)" appears to be the only symbol that rpm extracted for this package. Note that on 32 bit, the provides will be libprivate.so so your regex needs to capture both.
  4. Add the excludes to the spec file for both requires and provides:
    [...]
    %global _privatelibs libprivate.so.*
    %global __provides_exclude ^(%{_privatelibs})$
    %global __requires_exclude ^(%{_privatelibs})$
    [...]
    
  5. You can take a look at a more complex example on the mailing list. This can be a pain to maintain if the upstream changes the names of its private libraries but it is the only way to deal with this at present.

    Arch-specific extensions to scripting languages

    e.g. to ensure an arch-specific perl-* package won't provide or require things that it shouldn't, we could use an invocation as such:

    # we don't want to provide private Perl extension libs
    %{?perl_default_filter}
    

    A recipe for python:

    # we don't want to provide private python extension libs in either the python2 or python3 dirs
    %global __provides_exclude_from ^(%{python_sitearch}|%{python3_sitearch})/.*\\.so$
    

     %_docdir filtering

    By policy, nothing under %_docdir is allowed to either "provide" or "require" anything. We can prevent this from happening by preventing anything under %_docdir from being scanned:

    # we don't want to either provide or require anything from _docdir, per policy
    %global __provides_exclude_from ^%{_docdir}/.*$
    %global __requires_exclude_from ^%{_docdir}/.*$
    

    Additional Information

    Additional information about rpm-4.9's dependency generator can be found here: http://rpm.org/wiki/PackagerDocs/DependencyGenerator