Tales from the Gryphon

Recently, I have made fairly major changes to kernel-package, and there were some reports that I had managed to mess up cross compilation. And, not having a cross-compilation tool chain handy, I had to depend on the kindness of strangers to address that issue. And, given that I am much less personable than Ms Vivien Leigh, this is not something I particularly look forward to repeating.

At the onset, building a cross compiling tool chain seems a daunting task. This is not an activity one does frequently, and so one may be pardoned for being non-plussed by this. However, I have done this before, the most recent effort being creating one to compile rockbox binaries, so I had some idea where to start. Of course, since it is usually years between attempts to create cross-compiling tool chains, I generally forget how it is all done, and have to go hunting for details. Thank god for google.

Well, I am not the only one in the same pickle, apparently, for there are gobs of articles and HOWTOs out there, including some pretty comprehensive (and intimidating) general tool sets to designed to create cross compilers in the most generic fashion possible. Using them was not really an option, since I would forget how to drive them in a few months, and have a miniature version of the current problem again. Also, you know, I don’t feel comfortable using scripts that are too complex for me to understand – I mean, without understanding, how can there be trust?

Also, this time around, I could not decide whether to cross compile for arm-elf, as I did the last time, or for the newfangled armel target. A need for quickly changing the target for the cross compiler build mechanism would be nice. Manually building the tool chain makes a wrong decision here expensive, and I hate that. I am also getting fed up with having to root around on the internet every time I wanted to build a cross compiler. I came across a script by Uwe Hermann, which started me down the path of creating a script, with a help option, to store the instructions, without trying to be too general and thus getting overly complex. However, Uwe’s script hard coded too many things like version numbers and upstream source locations, and I know I would rapidly find updating the script irritating. Using Debian source packages would fix both of these issues.

I also wanted to use Debian sources as far as I could, to ensure that my cross compiler was as compatible as I could make it, though I did want to use newlib (I don’t know why, except that I can, and the docs sound cool). And of course the script should have a help option and do proper command line parsing, so that editing the script would be unnecessary.

Anyway, all this effort culminated in the following script: build cross toolchain, surprisingly compact. So I am now all set to try and cross compile a kernel the next time a kernel-package bug comes around. I thought that I would share this with the lazy web, while I was at it.

Enjoy.

The next thing, of course, is to get my script to create a qemu base image every week so I can move from user mode Linux to the much more nifty kvm, which is what all the cool kids use. And then I can even create an arm virtual machine to test my kernels with, something that user mode linux can’t easily do.

This is a continuation from before. I am digressing a little in this post. One of the things I want to get out of this exercise is to learn more about Ontologies and Ontology editors, and on the principle that you can never learn something unless you build something with it (aka bone knowledge), so this is gathering my thoughts to get started on creating an Ontology for package building. Perhaps this has been done before, and better, but I’ll probably learn more trying to create my own.

Also, I am playing around with code, an odd melange of my package building porcelain, and gitpkg, and other ideas bruited on IRC, and I don’t want to blog about something that would be embarrassing in the long run if some of the concepts I have milling around turn out to not meet the challenge of first contact with reality.

I want to create a ontology related to packaging software. It should be general enough to cater to the needs any packaging effort in a distribution agnostic and version control agnostic manner. It should enable us to talk about packaging schemes and mechanisms, compare different methods, and perhaps to work towards a common interchange mechanism good enough for people to share the efforts spent in packaging software.

The ontology should be able to describe common practices in packaging, concepts of upstream sources, versioning, commits, package versions, and other meta-data related to packages.

I am doing this ontology primarily for myself, but I hope this might be useful for other folks involved in packaging software.

So, here follow a set of concepts related to packaging software, people who like pretty pictures can click on the thumbnail on the right:

• software is a general term used to describe a collection of computer programs, procedures and documentation that perform some tasks on a computer system.
• software is what we are trying to package
• software has names
• software may exist as
  • source code
  • executable code
  • packaged code
• source code is any collection of statements or declarations written in some human-readable computer programming language.
• source code is usually held in one or more text files (blobs).
• A large collection of source code files may be organized into a directory tree, in which case it may also be known as a source tree.
• The source code may be converted into an executable format by a compiler, or executed on the fly from the human readable form with the aid of an interpreter.
• executable format is the form software must be in in order to be run. Running means to cause a computer “to perform indicated tasks according to encoded instructions.”
• software source code has one or more lines of development. Some Common specific lines of development for the software to be packaged are:
  • upstream line of development
  • feature branch is a line of development related to a new feature under development. Often the goal is to merge the feature branches into the upstream line of development
  • usually, all feature branches are merged into the integration branch, and the package is created from the integration branch.
  • integration branch is the line of development of software that is to be packaged
• some software lines of development have releases
• releases have release dates
• some releases have release versions
• source code may be stored in a version control repository, and maintain history.
• Trees are a collection of blobs and other trees (directories and sub-directories). A tree object describes the state of a directory hierarchy at a particular given time.
• Blobs are simply chunks of binary data - they are the contents of files.
• a tree can be converted into an archive and back
• In git, directories are represented by tree object. They refer to blobs that have the contents of files (file name, access mode, etc is all stored in the tree), and to other trees for sub-directories.
• Commits (or “changesets”) mark points in the history of a line of development, and references to parent commits.
• A commit refers to a tree that represents the state of the files at the time of the commit.
• HEAD is the most recent commit in a line of development or branch.
• A working directory is a directory that corresponds, but might not be identical, to a commit in the version control repository
• Commits from the version control system can be checked out into the working directory
• uncommitted changes are changes in the working directory that make it different from the corresponding commit. Some call the working directory to be in a “dirty” state.
• uncommited changes be checked in into the version control system, creating a new commit
• The working directory may contain a ignore file
• ignore file contains the names of files in the working directory that should be “ignored” by the version control system.
• In git, a commit may also contains references to parent commits.
  • If there is more than one parent commit, then the commit is a merge
  • If there are no parent commits, it is an initial commit
• references, or heads, or branches, are movable references to a commit. On a fresh commit, the head or branch reference is moved to the new commit.
• lines of development are usually stored as a branch in the version control repository.
• A new branch may be created by branching from an existing branch
• a patch is a file that contains difference listings between two trees.
• A patch file can be used to transform (patch) one tree into another (tree).
• A quilt series is a method of representing an integration branch as a collection of a series of patches. These patches can be applied in sequence to the upstream branch to produce the integration branch.
• A tag is a named reference to a specific commit, and is not normally moved to point to a different commit.
• A package is an archive format of software created to be installed by a package management system or a self-sufficient installer, derived by transforming a tree associated with an integration branch.
• packages have package names
• package names are related to upstream software names
• packages have package versions
• package versions may have
  • an upstream version component
  • a distribution or packaging specific component
• package versions are related to upstream software versions
• helper packages provide libraries and other support facilities to help compile an integration branch ultimately yielding a package

This is a continuation from before.

Before I go plunging into writing code for a generic vcs-pkg implementation, I wanted to take a close look at my current, working, non-generic implementation: making sure that the generic implementation can support at least this one concrete work-flow will keep me grounded.

One of the features of my home grown porcelain for building package has been that I use a fixed layout for all the packages I maintain. There is a top level directory for all working trees. Each package gets a sub-directory under this working area. And in each package sub-directory, are the upstream versions, the checked out VCS working directory, and anything else package related. With this layout, knowing the package name is enough to locate the working directory. This enable me to, for example, hack away at a package in Emacs, and when done, go to any open terminal window, and say stage_release kernel-package or tag_releases ucf without needing to know what the current directory is (usually, the packages working directory is several levels deep — /usr/local/git/debian/make-dfsg/make-dfsg-3.91, for instance.

However, this is less palatable for a generic tool – imposing a directory structure layout is pretty heavy. And I guess I can always create a function called cdwd, or something, to take away the tedium of typing out long cd commands.

Anyway, looking at my code, there is the information that the scripts seem to need in order to do their work.

• Staging area. This is where software to be built is exported (and this area is visible from my build virtual machine).
  • User specified (configuration)
• Working Area. This is the location where all my packaging work happens. Each package I work on has a sub-directory in here, and the working directories for each package live in the package sub-directory. Note: Should not be needed.
  • User specified.
• Working directory. This is the checked out tree from the VCS, and this is the place where we get the source tree from which the package can be built.
  • Since we know the location of the working are, if the package name is known, we can just look in the package’s sub-directory in the working area.
    • For rpm based sources, look for the spec file
    • For Debian sources, locate debian/rules
  • If package name is not known, look for spec or debian/rules in the current directory, and parse either the spec file or debian/changelog.
  • If in a VCS directory, look for the base of the tree
    • tla tree-root
    • bzr info
    • git rev-parse --show cdup
    • hg root
    • You have to climb the tree for subversion
  • If you are in a debian directory, and changelog and rules files exist

  Then, look for the spec file or debian/rules in the base directory

• package name
  • User specified, on the command line
  • If in the working directory of the package, can be parsed from the spec or changelog files.
• upstream tar archive
  • Usually located in the parent directory of the working directory (the package specific sub-directory of the working area)
  • If pristine-tar is in use, given two trees (branches, commits. etc), namely:
    • a tree for upstream (default: the branch ~upstream~)
    • a tree for the delta (default: the branch ~pristine-tar~)

    The tree can be generated

  • Given an upstream tree (default: the branch ~upstream~), a tar archive can be generated, but is likely to be not bit-for-bit identical to the original tar archive.

So, if I do away with the whole working area layout convention, this can be reduced to just requiring the user to:

• Specify Staging area
• Call the script in the working directory (dpkg-buildpackage imposes this too).
• Either use pristine-tar or have the upstream tar archive in the parent directory of the working directory

Hmm. One user specified directory, where the results are dumped. I can live with that. However, gitpkg has a different concept: it works purely on the git objects, you feed it upto three tree objects, the first being the tree with sources to build, and the second and third trees being looked at only if the upstream tar archive can not be located, and passes the trees to pristine tar to re-construct the upstram tar. The package name and version are constructed after the source-tar archive is extracted to the staging area. I like the minimality of this.

This is continued here.

I have been involved in vcs-pkg.org since around the time it started, a couple of years ago. The discussion has been interesting, and I learned a lot about the benefits and disadvantages of serializing patches (and collecting integration deltas in the feature branches and the specific ordering of the feature branches) and maintaining integration branches (where the integration deltas are collected purely in the integration branch, but might tend to get lost in the history, and a fresh integration branch having to re-invent the integration deltas afresh).

However, one of the things we have been lax about is getting down to brass tacks and getting around to being able to create generic packaging tools (though for the folks on the serializing patches side of the debate we have the excellent quilt and the topgit packages).

I have recently mostly automated my git based work-flow, and have built fancy porcelain around my git repository setup. During IRC discussion, the gitpkg script came up. This seems almost usable, apart from not having any built-in pristine-tar support, and also not supporting git submodules, which make is less useful an alternative than my current porcelain.

But it seems to me that we are pretty close to being able to create a distribution, layout, and patch handler agnostic script that builds distribution packages directly from version control, as long as we take care not to bind people into distributions or tool specific straitjackets. To these ends, I wanted to see what are the tasks that we want a package building script to perform. Here is what I came up with.

1. Provide a copy of one or more upstream source tar-balls in the staging area where the package will be built. This staging area may or may not be the working directory checked out from the underlying VCS; my experience has been that most tools of the ilk have a temporary staging directory of some kind.
2. Provide a directory tree of the sources from which the package is to be built in the staging area
3. Run one or more commands or shell scripts in the staging area to create the package. These series of commands might be very complex, creating and running virtual machines, chroot jails, satisfying build dependencies, using copy-on-write mechanisms, running unit tests and lintian/puiparts checks on the results. But the building a package script may just punt on these scripts to a user specified hook.

The first and third steps above are pretty straight forward, and fairly uncontroversial.

The upstream sources may be handled by one of these three alternatives:

1. compressed tar archives of the upstream sources are available, and may be copied.
2. There is a pristine-tar VCS branch, which in conjunction with the upstream branch, may be used to reproduce the upstream tr archive
3. Export and create an archive from the upstream branch, which may not have the same checksum as the original branch

The command to run may be supplied by the user in a configuration file or option, and may default based on the native distribution, to dpkg-buildpackage or rpm. There are a number of already mature mechanisms to take a source directory and upstream tar archive and produce packages from that point, and the wheel need not be re-invented.

So the hardest part of the task is to present, in the staging area, for further processing, a directory tree of the source package, ready for the distribution specific build commands. This part of the solution is likely to be VCS specific.

This post is getting long, so I’ll defer presenting my evolving implementation of a generic vcs-pkg tool, git flavour, to the next blog post.

This is continued here.

There are a lot of little git scripts and tools being written by a lot of people. Including a lot of tools written by people I have a lot of respect for. And yet, they are mostly useless for me. Take git-pkg. Can’t use it. Does not work with git submodules. Then there is our nice, new, shiny, incredibly bodacious “3.0 (git)” source format. Again, useless: does not cater to submodules.

I like submodules. They are nice. They allow for projects to take upstream sources, add Debian packaging instructions, and put them into git. They allow you to stitch together disparate projects, with different authors, and different release schedules and goals, into a coherent, integrated, software project.

Yes, I use git submodules for my Debian packaging. I think it is conceptually and practically the correct solution. Why submodules? Well, one of the first things I discovered was that most of the packaging for my packages was very similar – but not identical. Unfortunately, the previous incarnation of my packages with a monolithic rules file in each ./debian/ directory, it was easy for the rules files in packages to get out of sync – and there was no easy way to merge changes in the common portions an any sane automated fashion. The ./debian/ directories for all my packages package that they are instrumental in packaging. So, since I make the ./debian/ directories branches of the same project, it is far easier to package a new package, or to roll out a new feature when policy changes – the same commit can be applied across all the branches, and thus all my source packages, easily. With a separate debian-dir project, I can separate the management of the packaging rules from the package code itself.

Also, I have abstracted out the really common bits across all my packages into a ./debian.common directory, which is yet another project, and included in as a submodule in all the packages – so there is a central place to change the common bits, without having to duplicate my efforts 30-odd times.

Now people are complaining since they have no idea how to clone my package repositories, since apparently no one actually pays attention to a file called .gitmodules, and even when they do, they, and the tools they use, have no clue what to do with it. I am tired of sending emails with one off-cluebats, and I am building my own porcelain around something I hope to present as a generic vcs-pkg implementation soon. The firs step is a wrapper around git-clone, that understands git submodules.

So, here is the browsable code (there is a link in there to the downloadable sources too). Complete with a built in man page. Takes the same arguments as git-clone, but with fewer options. Have fun.

With tonight’s upload of kernel-package, the recent flurry of activity on this package (8 uploads in 6 days) is drawing to a close. I think most of the functionality I started to put into place is now in place, and all reported regressions and bugs in the new 12.XX version have been fixed. The only known deficiency is in the support of Xen dom0 images, and for that I am waiting for kernel version 2.6.30, where Linus has reportedly incorporated Xen patches. In the meanwhile, kernel-package seems to be working well, and I am turning my attention to other things.

But, before I go, here is another example kernel postinst hook script (which, BTW, looks way better with syntax highlighting CSS on my blog than it does in a rss feed or an aggregator site).

    1  #! /bin/sh
    2  
    3  set -e
    4  
    5  if [ -n "$INITRD" ] && [ "$INITRD" = 'No' ]; then
    6      exit 0
    7  fi
    8  version="$1"
    9  vmlinuz_location="$2"
   10  
   11  
   12  if [ -n "$DEB_MAINT_PARAMS" ]; then
   13      eval set -- "$DEB_MAINT_PARAMS"
   14      if [ -z "$1" ] || [ "$1" != "configure" ]; then
   15          exit 0;
   16      fi
   17  fi
   18  
   19  # passing the kernel version is required
   20  [ -z "$version" ] && exit 1
   21  
   22  if [  -n "$vmlinuz_location" ]; then
   23      # Where is the image located? We'll place the initrd there.
   24      boot=$(dirname "$vmlinuz_location")
   25      bootarg="-b $boot"
   26  fi
   27  
   28  # Update the initramfs
   29  update-initramfs -c -t -k "$version" $bootarg
   30  
   31  exit 0

With the new kernel-package hitting Sid today, and the fact that it no longer does symlink handling by default, I thought it was time that we had an example script that shows how to do that. This is a fairly full featured script, feel free to cull down to use just what you want.

I’ll post a couple of ther scripts, if there is interest in this. BTW, this script does far more than the old kernel-package postisnt script ever did.

Have fun.

    1  #!/bin/sh -
    2  #                               -*- Mode: Sh -*- 
    3  # 
    4  # This is an example of a script that can be run as a postinst hook,
    5  # and manages the symbolic links in a manner similar to the kernel
    6  # image default behaviour, except that the latest two versions (as
    7  # determined by ls -lct) are kept. You can modify this script 
    8  # 
    9  # Copyright 2003, 2004, 2005, 2006, 2007, 2008, 2009 Manoj Srivastava
   10  # Copyright 2009 Darren Salt
   11  
   12  set -e
   13  
   14  # The dir where symlinks are managed
   15  SYMLINKDIR=/
   16  
   17  if [ $# -ne 2 ]; then
   18      echo Usage: $0 version location
   19      exit 2
   20  fi
   21  
   22  version="$1"
   23  vmlinuz_location="$2"
   24  vmlinuz_dir="$(dirname "$2")"
   25  
   26  cd $SYMLINKDIR || exit 1
   27  
   28  if [ -n "$DEB_MAINT_PARAMS" ]; then
   29      eval set -- "$DEB_MAINT_PARAMS"
   30  fi
   31  
   32  if [ -z "$1" ] || [ "$1" != "configure" ]; then
   33      exit 0;
   34  fi
   35  
   36  rm -f vmlinuz vmlinuz.old vmlinuz-rd vmlinuz-rd.old initrd.img initrd.img.old 
   37  
   38  # Create a temporary file safely
   39  if [ -x /bin/tempfile ]; then
   40      outfile=$(tempfile -p outp -m 0600);
   41  else
   42      set -e
   43      mkdir /tmp/kernel-image-$version-$$
   44      outfile=/tmp/kernel-image-$version-$$/output
   45  fi
   46  
   47  (cd "$vmlinuz_dir" && ls -ct vmlinuz-*) > $outfile
   48  
   49  STD="$(head -n 1 $outfile |             sed 's/vmlinuz-//')" 
   50  OLD="$(head -n 2 $outfile | tail -n 1 | sed 's/vmlinuz-//')" 
   51  
   52  if [ "X$STD" = "X" ]; then
   53      exit 0;
   54  fi
   55  
   56  # If you want version-specific links, here's how to start
   57  STD24="$(grep vmlinuz-2.4 $outfile | head -n 1 | sed 's/vmlinuz-//')" || true
   58  OLD24="$(grep vmlinuz-2.4 $outfile | head -n 1 | tail -n 1 | sed 's/vmlinuz-//')" || true
   59  
   60  STD25="$(grep vmlinuz-2.5 $outfile | head -n 1 | sed 's/vmlinuz-//')" || true
   61  OLD25="$(grep vmlinuz-2.5 $outfile | head -n 1 | tail -n 1 | sed 's/vmlinuz-//')" || true
   62  
   63  echo Booting $STD, old is $OLD
   64  
   65  if [ -f "$vmlinuz_dir/"initrd.img-$STD ] ; then 
   66     ln -s "$vmlinuz_dir/"initrd.img-$STD initrd.img
   67     ln -s "$vmlinuz_dir/"vmlinuz-$STD vmlinuz-rd
   68  else
   69     ln -s "$vmlinuz_dir/"vmlinuz-$STD vmlinuz
   70  fi
   71  
   72  if [ "X$OLD" != "X" ]; then
   73      if [ -f "$vmlinuz_dir/"initrd.img-$OLD ] ; then
   74      ln -s "$vmlinuz_dir/"initrd.img-$OLD initrd.img.old
   75      ln -s "$vmlinuz_dir/"vmlinuz-$OLD vmlinuz-rd.old
   76      else
   77      ln -s "$vmlinuz_dir/"vmlinuz-$OLD vmlinuz.old
   78      fi
   79  fi
   80  
   81  # if [ "X$STD24" != "X" ]; then
   82  #     if [ -f "$vmlinuz_dir/"initrd.img-$STD24 ] ; then 
   83  #     ln -s "$vmlinuz_dir/"initrd.img-$STD24 initrd24.img
   84  #     ln -s "$vmlinuz_dir/"vmlinuz-$STD24 vmlinuz24-rd
   85  #     else
   86  #     ln -s "$vmlinuz_dir/"vmlinuz-$STD24 vmlinuz24
   87  #     fi
   88  # fi
   89  # if [ "X$OLD24" != "X" ]; then
   90  #     if [ -f "$vmlinuz_dir/"initrd.img-$OLD24 ] ; then
   91  #     ln -s "$vmlinuz_dir/"initrd.img-$OLD24 initrd24.img.old
   92  #     ln -s "$vmlinuz_dir/"vmlinuz-$OLD vmlinuz24-rd.old
   93  #     else
   94  #     ln -s "$vmlinuz_dir/"vmlinuz-$OLD vmlinuz24.old
   95  #     fi
   96  # fi
   97  
   98  # Run boot loaders here.
   99  #lilo
  100  
  101  rm -f $outfile 
  102  if [ -d /tmp/kernel-image-$version-$$ ]; then
  103      rmdir /tmp/kernel-image-$version-$$
  104  fi
  105  
  106  exit 0

A new version of kernel-package in Incoming at the time of writing adds support for creating a package which contains the Linux kernel debug image. This means the debugging information for the modules in the kernel image package, and the uncompressed vmlinux image. This builds on suggestions and code from Troy Heber, Theodore Y. Ts’o, and Dann Frazier.

As support for kexec/kdump support becomes more real, it will be very useful to be able to build kernels that have debugging information available, but not necessarily to install the debugging information on every single client system.

The .ko object files are stripped of the debugging information before they are placed in the standard linux-image installation package. However, before that, a copy of the vmlinux and unstripped .ko files are saved in a “debuginfo” package, and everything except for the debugging information is removed from them using objcopy --keep-only-debug. This means that if someone ends up with a crash dump, they can send it to a support engineer and only the support engineer needs to install the debuginfo package and use the “crash” utility to debug the crash dump. It’s also useful for developers, since the debuginfo information can be stored somewhere outside of /lib for storing its debug information, for example. This is useful for keeping the size of the root partition small, for those who keep / separate from /usr.

The locations used are compatible also with SystemTap, which provides free software infrastructure to simplify the gathering of information about the running Linux system. This assists diagnosis of a performance or functional problem. SystemTap eliminates the need for the developer to go through the tedious and disruptive instrument, recompile, install, and reboot sequence that may be otherwise required to collect data.

Also, I had to clear out some FUD about kernel-package from the ircbot dpkg on the OFTC Debian IRC channel, since someone had implied that kernel-package was some how obsolete. As can be seen, it is being actively developed, and features are being added apace.

A few hours ago, a new version of kernel-package was uploaded to experimental. This is a major change,and I would appreciate it if folks took it out for a spin, kicked the tires, and provide feedback about where this version is lacking.

This is only part of the way along in this development cycle. I would like to add a debug-info separation, either in a different directory than / in the image packages, or a separate package by itself. I would also like to create an overlay directory for /usr/share/kernel-package/, so people can inject code or override the defaults for kernel-package easily. I am also willing to make any changes to standardize the handling of hook scripts for kernel packages in Debian.

I have been thinking some more about how to improve ucf. One of the things that struck me was that based on my earlier analysis there are only five actions that ucf can take, and the decision about the actions depends on the state it finds the configuration file in on the target machine, and there are only eight of those. Now, thinking back to my days as a VLSI designer back in the halcyon days of electrical engineering, This is a pretty simple state machine. It is not as neat as it could be (where just three variables would be needed to keep track of things, but still, it bears investigation. This would be a way for converting the current procedural ucf into a functional programming model.

Hop over here for a look at how that went — it was fun, and afforded me an opportunity to demonstrate how well org handles snippets.