Working with upstream - installing Perl modules from CPAN

On FOSDEM there is going to be a Linux distribution mini-conference where I am going to give a talk about Packaging perl and CPAN modules

I gave an improvised talk about the subject yesterday in front of the Rehovot Perl Mongers. Now I am going to try to summarize that talk and further collect my thoughts on the subject. Your comments are most welcome!

The problem

When a user needs to install a Perl module from CPAN she has several choices based on the operating system and the perl distribution she is using. A usual case is that her company is using Fedora 9 or some other several years old Linux distribution. She now needs to install various modules. Checking the rpms available in the official Fedora distribution she sees that most of the modules she needs are not available. (BTW I am using Fedora here as an example, this would be basically the same with any other Linux distribution.)

Her choices are now

  1. Find an rpm of the CPAN package(s) somewhere else
  2. Install using the CPAN client (or manually) into the system
  3. Install using the CPAN client (or manually) into a private directory (with or without the help of local::lib)
  4. Build her own rpm from the CPAN package
  5. Open a ticket on the Fedora bug tracker that she needs this module

As far as I know the standard recommendation of Fedora and Debian developers is to always use the packages that come with the distribution. But that can't be done in this case.

How many CPAN packages are available in the distribution?

I don't have up-to-date data but two years ago I created a report on the distribution of CPAN modules via various downstream distributors. Back in May 2007 there were 12,422 packages on CPAN. Debian stable had 971 and the latest Ubuntu had 1,007. Even FreeBSD had only 2,594 packages.(The numbers for Fedora were probably incorrect on that report but as far as I know they were always lower than those of Debian.)

That is, less than 10% packaged for Debian and Ubuntu. A lot less for other distributions.

Today there are 19,500 distributions on CPAN and I don't know the number of packaged modules in the various distros but I doubt they had increased the percentage they cover.

While we know there are many packages on CPAN that are broken or useless or both I think we can assume that a much larger percentage is actually useful. Maybe not for the general public of programmers but in niche areas.

This means that in most cases people will have to find alternative ways to install Perl modules from CPAN.

I am not sure what the Fedora developers would suggest in such situation but I think they would suggest 5 and not recommend any of the 1-4 options above. While I am not a speaker of the Perl community I think people from that group would probably suggest one of those four and tell you to forget about 5.

Frankly I think most of the people - especially from the industry would never open a request to add a package to Fedora. For one thing they are trained that they should not talk to the supplier as that will charge money or that they have to go through their own boss to do this. They are also educated - by the commercial vendors - that it does not help much to ask for any bug fix or additional feature. Most likely the vendor won't do it. Neither of these are true for Debian or Fedora or for the other community based distributions but most of the people in the industry are probably not aware of that.

Why so few?

When I ask the distributors why are there so - relatively - few packages in their distributions they usually give two reasons.

  1. Lack of volunteers to add the packages and then maintain them
  2. No one asks for the packages

The first one could be improved by either reducing the time needed to (re)package a CPAN distribution or by increasing the number of volunteers.

Reducing the time needed could be done by further automation of the packaging process and better integration between the CPAN toolchain an the packaging systems. For this the CPAN Authors community and the more general Perl community needs to understand what are the time consuming parts of the packaging process and see if we can solve those issues already before they reach the downstream distributors.

One such issue we discussed earlier was the clear licensing of each file distributed in the package. We need to further discuss the issues and give that as a feedback to the CPAN authors.

Regarding the lack of volunteers. I am not sure I have any idea how help that but maybe giving a talk on how and why to become a Debian/Fedora/Mandriva/SuSE/etc packager on some of the Perl Events such as the Perl Monger meetings, Perl Workshops and YAPCs will yield some result.

As to the lack of request to include packages. I already described two - probably invalid but nevertheless existing reasons why people won't request the additional packages.

There is also a valid reason though: It won't help them. Even if they open a ticket and even if the Fedora Perl packaging team adds that package to Rawhide immediately that will go into Fedora 13 or whatever the next version will be. It won't help on the Fedora 9 she has in production NOW.

So I don't expect many of them to open requests.

What about Windows?

While this is a preparation for FOSDEM I would like to look at Perl and CPAN on other operating systems.

On Windows people have 2 major choices to use Perl native:

Active Perl and Strawberry Perl for Windows.

ActiveState provides a set of binary repackaged versions of the CPAN modules. In a way it is very similar to what the Linux distributions do except that their build and repackaging system is totally automatic. In that report from 2007 we can see that ActiveState provided 6,370 CPAN packages for Windows. Roughly 50% of the total packages. In addition there are third party packagers who build ppm packages for Windows. Kobesearch helps finding those.

Strawberry Perl on the other hand is using the CPAN client with a default configuration making it very easy if time consuming to install any CPAN module from source. At least those that don't have external dependencies.

The frustration to use the CPAN client

While many members of the Perl community are satisfied with the way the CPAN client(s) work when you talk to people who are just users you are suddenly flooded with complaints.

For one, the CPAN client is not configured on the Linux distributions. When I run it for the first time it asks me all kinds of questions. Most of them could be answered automatically but I think actually all of them could be preconfigured. Once that is done later on once in a while further configuration is needed. (e.g. I think after installing Module::Build).

Some of the packages have dependencies outside of CPAN. In some cases this is solved by an Alien package on CPAN which - I guess - makes it further difficult to package the modules downstream as they might already have that dependency included in another package. [dist://Alien::wxWidgtes] solves this issue by being able to work with the already installed wxWidgets library and install its own version only if necessary. I still wonder if this causes extra headaches to the packager or not?

Then there is the question of recursive installation. I agree with the distributors that the preferred way to install a CPAN package would be via their installation tool using their repositories but I also need to install packages not available from their repository. So what if I am installing package A that is not in the Fedora repository that depends on package B that is? I won't check this manually but I'd prefer to get B from Fedora and install only A via the CPAN client. Once I am done, I'd like to have a report telling me which packages were installed from Fedora and which directly from CPAN so I can easily send a request to the Fedora developers.

I read there are some improvements in the CPAN client in this area. I hope we will see full integration with the downstream packagers including the above multi-sourcing.

What can be done?

There are several ways to reduce the frustration of our end-users and make our life simple as well.

I'd like to restart the effort to get information from the downstream packagers and create reports that can be easily used by the CPAN authors and the users. That would include the names of all the CPAN packages distributed by Fedora along with version number, number of patches, number of open bugs and other information if available.

The very same data could be used to build an add-on to to be able to install either from CPAN or from the rpm/deb repositories in a recursive way.

I'd like to hear what are the most time consuming problems the downstream packagers face and what would be their suggestion to solve those issues?


There is no conclusion. I am looking for feedback from both CPAN authors, packagers and "just plain users". How could we improve the whole process of getting this code work on your system?