Introductory Concurrent Version System (CVS)

1
Introductory Concurrent Version System (CVS)

• UCR Technical Seminar
• 10/23/03
• Dan Berger dberger_at_cs.ucr.edu

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Adgenda

• Introduction
• What is configuration management?
• Key concepts.
• CVS Workflow
• Copy-Modify-Merge
• Getting Started with CVS
• Creating a repository
• Importing assets
• Checking in Checking Out
• Using CVS
• Managing Change

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Introduction What is CM?

• Record Keeping
• What assets (source, binary) went into producing
  some product?
• What did this asset look like at some point in
  the past?
• Collaboration
• Who's working on which assets?
• Who worked on this asset last?
• Who made a specific change to this asset (and
  when?)

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Introduction Key Concepts

• Repository The master copy of the assets.
• Contains all revision history for all assets.
• Working Directory (aka sandbox) a developers
  private copy of the assets.
• Contains a copy of a particular version of assets.

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CVS Workflow

• CVS allows multiple people to be working on the
  same set of assets at the same time.
• Copy-Modify-Merge means you take a copy of the
  assets, modify your local copy, and merge your
  changes back in to the master repository.

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CVS Workflow (cont.)

• cvs checkout ltprojectgt
• edit to your hearts content
• cvs update
• resolve conflicts
• cvs commit

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Getting Started w/ CVS

• Creating a Repository (one time only)
• Importing Assets
• Checking out a working copy
• Viewing changes
• Committing changes
• Working with previous versions

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Creating a Repository

• export CVSROOT/CVSRoot
• cvs init
• ls l CVSROOT
• drwx------ CVSROOT/
• There are some magic files in CVSROOT/CVSROOT
  ignore them for now.

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Importing Assets

• importing places a copy of an existing directory
  tree (rooted at pwd) into the repository
• cvs import mod-path vendor release
• mod-path is the directory under CVSROOT to
  import the files into
• vendor and release are more complicated but (for
  our purposes) less important.
• I suggest vendorwhoami, releaseinitial.

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Importing Assets Example

• cvs import cvs-seminar/hello-world\ whoami
  initial \
• m initial import
• N cvs-seminar/hello-world/hello.C
• N cvs-seminar/hello-world/Makefile
• No conflicts created by this import

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Importing Assets (Cont.)

• Importing assets doesnt touch the files in the
  current directory.
• That also means changes to the files in the
  working directory arent tracked.
• We need to get a copy from the repository first

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Getting a Working Copy

• cvs checkout \
• cvs-seminar/hello-world
• cvs checkout Updating cvs-seminar/hello-world
• U cvs-seminar/hello-world/Makefile
• U cvs-seminar/hello-world/hello.C
• ls l cvs-seminar/
• CVS/
• ls l cvs-seminar/hello-world
• CVS/
• hello.C
• Makefile

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Viewing Changes

• Imagine we changed the files fixing the typo in
  hello.C and adding a default target to the
  Makefile.
• Before we commit these changes, wed like to see
  what we actually changed
• cvs can show us which files have changed, and/or
  the specific changes to the files.

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cvs -n update

• cvs n update
• cvs update Updating .
• M Makefile
• M hello.C
• ? hello
• the leading M indicates the file has been
  Modified. The ? means the file isnt being
  managed by CVS.

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cvs diff

• cvs diff hello.C
• Index hello.C
• RCS file
• retrieving version 1.1.1.1
• diff r 1.1.1.1 hello.C
• 11c11
• lt cout ltlt Helllo, world! ltlt endl
• ---
• gt cout ltlt Hello, world! ltlt endl

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cvs status

• cvs status will tell you the status of a file in
  your working copy.
• cvs status hello.C
• File hello.C Status Up-to-date
• Working revision x.x
• Repository revision x.x

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Adding Files

• CVS will essentially ignore new files, until
  you tell it theyre important and should be
  managed.
• cvs add README
• cvs add scheduling file README for addition
• cvs add use cvs commit to add this file
  permanently

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Deleting Files

• first, remove the file from your working copy
  (with rm), then
• cvs delete file
• cvs remove scheduling FILE for removal
• cvs remove use cvs commit to remove \
• this file permanently
• cvs commit
• Removing FILE
• /FILE,v lt-- FILE
• new revision delete previous revision 1.1
• done

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Removing Files (cont.)

• CVS doesnt actually remove the file, it places
  it into the Attic.
• You can still retrieve any version of the
  deleted file
• cvs up r X.Y FILE
• U FILE

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Renaming

• One place where CVS makes life difficult.
  Renaming files is non-trivial.
• Two methods
• one that preserves change history, but requires
  file system access to the repository,
• and one that breaks change history but can be
  done completely through the client.

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Renaming The Easy Way

• cp old-name new-name
• rm old-name
• cvs delete old-name
• cvs add new-name
• cvs commit
• You can explain the rename in the log message,
  and point viewers to the old-name for complete
  revision history.

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Committing Changes

• Once were happy with our changes, we need to
  commit them to the repository.
• We can commit all our changes, or changes to an
  individual file (often dangerous).

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Checking In Example

• cvs commit
• cvs commit Examining .
• Checking in Makefile
• /Makefile,v lt-- Makefile
• new revision 1.2 previous revision 1.1
• RCS file /README,v
• done
• Checking in README
• /README,v lt-- README
• initial revision 1.1
• done
• Checking in hello.C
• /hello.C,v lt-- hello.C
• new revision 1.2 previous revision 1.1
• done

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Working with Versions

• the r tag can be provided to CVS commands, and
  it will cause them to affect a specific version
  of the named asset.
• For example
• cvs diff r 1.1 Makefile
• You can also check out previous versions of files
  (cvs co r x.x filename), and even commit to
  (branch from) previous versions of files.

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Diff and Patch

• Not strictly CVS related, but terribly valuable
  tools.
• diff generates the differences between two (sets
  of) files.
• patch can apply that set of differences to
  another file

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Diff Example

• Say I have two copies of my project
• unmodified-copy and modified-copy
• diff Naurw unmodified-copy \ modified-copy
• CVS will do this also, without having two
  versions checked out
• cvs diff auw r other-version

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Patch Example

• Once I have a unified diff (the u to diff), I
  can apply the changes specified in the diff to
  another file
• patch lt diff-file
• This also works with trees of files.
• Read the man page to patch for more options.

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CVS Version Numbers

• Imported files have an initial version of 1.1.1.1
  theres a reason, but for now just ignore it.
• Normal version numbers are w.x cvs
  automatically increments x each time you commit
  changes to the file. It never automatically
  increments w.
• If you branch a file, its version number becomes
  w.x.y.z. Were not going to talk about branches
  in this talk. (Advanced CVS, anyone?)

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CVS Magic Strings

• Some strings have special meaning to CVS, and if
  they appear in your files, CVS will evaluate
  them during checkout.
• Id is the most common/useful, it gets
  evaluated to a string of the form
• Id Makefile,v 1.2.1.3 2003/10/20 \ 230820
  dberger Exp

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CVS and Binary Files

• CVS assumes that files are text unless told
  otherwise. This can cause issues if a binary
  file (like a jpg, PDF, etc.) contains one of the
  magic strings mentioned above.
• This can be handled two ways file-by-file, or by
  file extension
• cvsadmin kb file
• or adding the extension to cvswrappers (more
  later)

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CVSROOT/CVSROOT

• CVSROOT/ contains control files many of which
  are only interesting if youre using CVS in a
  group.
• CVSROOT is just another module so you can check
  it out/diff it/commit to it.
• DONT TOUCH THESE FILES DIRECTLY!
• Remember cvswrappers? It lives here it
  allows hooks to run when files go in or out of
  CVS. Theres a sample linked from the tech
  seminar page.

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Accessing CVS Remotely

• Three methods, pserver, rsh, ext.
• pserver is a cvs-specific network protocol, its
  not encrypted and has to be setup by the remote
  admin so were going to ignore it.
• rsh is just too horrible for words, which leaves
  ext
• export CVS_RSHssh
• export CVSROOT \ extuser_at_host/path/to/cvs
  root
• note that cvsroot is the directory containing
  CVSROOT/

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Remote CVS (cont.)

• Note that if your CVS repository is NFS exported
  and always available directly (I.e. its in your
  home directory), you dont need to use the ext
  method to reach it.
• export CVSROOT/home//CVSRoot

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What We Didnt Cover

• cvs watchers and editors
• anonymous cvs
• CVS and IDEs (emacs/eclipse, etc)
• Permissions
• Tagging
• Branching
• Merging
• Detecting and Resolving Conflicts

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Subversion

• ltskepticgt a better CVS lt/skepticgt
• You cant set it up for yourself (its repository
  cant live on an NFS share, like your home
  directory).
• The command line interface is very similar
  (intentionally).

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Where to Find More

• CVS Home Page http//www.cvshome.org
• CVS Online Book http//cvsbook.red-bean.com
• CVS GUIs http//www.wincvs.org
• TortoiseCVS (Windows Explorer Extension)
  http//www.tortoisecvs.org
• Subversion Home Page http//subversion.tigris.org
  
• Subversion Online Book (draft)
  http//svnbook.red-bean.com