An Introduction to CVS

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An Introduction to CVS
By Durai Raj
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Why CVS ?
Has one of your projects ever experienced this ?
Which is the latest version ?. God only knows
(sometimes myself too!!)
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A brief History of CVS

• CVS started out as a bunch of shell scripts
  written by Dick Grune, posted to the newsgroup
  comp.sources.unix' in December, 1986.
• In April, 1989, Brian Berliner designed and coded
  CVS. Jeff Polk later helped Brian with the
  design of the CVS module and vendor branch
  support.
• Since then CVS has been used to develop software
  by many programmers across the internet

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Requirements for VC

• Multiple Developers - concurrent Access
• History
• View diffs
• Rollback changes
• Release Management

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So what is CVS ?
Its like having your source files on a File
server and coordinate with your colleagues on the
version number youre working on.
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How Does CVS Work?

• CVS uses a Client / Server Architecture
• A Sys Admin Would Normally Install the Server
• The Server Maintains the Repository
• Developers Use the Client
• The Client Allows for Checking in/out, and
  Updating, etc..

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Client-server architecture

• separate server (UNIX or NT)
• no shared file systems
• a server process per connection

Ganapathy
Central Repository (sdgserver in our organization)
Nagaraj
Durai mansoor
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How Does CVS Version?

• CVS maintains a set of diffs that define the
  changes between each version
• Any version can be checked out from the
  repository by specifying the date
• cvs checkout -D yesterday ltprojgt or
• cvs checkout -D 12 days ago. ltprojgt or
• cvs checkout -D 23 August 2002 ltprojgt

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Idea of CVS

• The idea of the CVS is to create a file system,
  where each file has remembers all the
  modifications made to it. In other words it is
  all the versions of it at the same time.
• File system resides in a repository, that can be
  stored to local or remote host.
• All the files are edited outside of the
  repository in some working directory and in some
  phase synchronized with the repository.
• Files are moved to, from and updated from
  repository with special tool called cvs, which is
  available for most platforms

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Platform Support

• CVS ??for Linux
• CVS ??for Windows
• CVS ??for MAC
• CVS ??Port it to your desired platform?????

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CVS Features

• Concurrent access by multiple developers
• Multiple development lines in a single repository
• Grouping sources into modules
• Symbolic source tagging
• Diffs between versions
• Configurable logging support
• Binary files support
• Repository event triggers

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Concurrent Versions System

• Overview of CVS architecture.
• Repository structure.
• Basic development tasks in WinCvs.
• Branching and merging.
• Other CVS interfaces
• CVS internals

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Versioning Systems

• Versioning Systems allow
• multiple users to modify the same code
• To store one master copy of the source code
• To automate the update between versions
• Access to any previous state of the source code

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Handling Binary Files

• Line Feed Format Repository vs. Client
• Keyword Substitution
• Wrappers
• cvs admin -kb

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Web Access

• Look at CVS tree in the repository
• Browsing of a CVS repository
• ViewCVS
• http//viewcvs.sourceforge.net/
• CVSweb
• http//people.freebsd.org/fenner/cvsweb/

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CVS dos and don'ts

• Facilitates bug detection when software is
  modified
• Economy in disk space while saving versions
• Prevents code over-writing in a team project

• Not a build system
• Not a substitute for communication between
  developers or for management
• It will not create any magic for you.

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Limitations

• Best if you have an investment in nix
  environments
• Designed for programmers
• Concepts are hard to grasp
• Alien concept to designers

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Where it can be used ?

• Software Development
• Website Management
• Documentations
• Synchronization of distributed effort
• ... anywhere digital data evolves

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What Is CVS Used For?

• Open Source Projects
• Projects With a Large Number of Developers
• Storing Files That Benefit From Version Control
  ( /etc/ config files, or web pages )
• Taking Advantage of a Sandboxed Development
  Environment

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So What is it good for ?

• Version control and connecting multiple developer
  together in one project, of course )
• Document management and archiving
• Nice way to do one project with multiple machines
  and still manage the versions
• Allows free experimenting on project
• Following the growth of the project
• Backupping - it forces one to take backups with
  neglible work very often

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Benefits of CVS

• Automatic, constant and forced backupping
• When programming, frees the development
• Gives freedom to choose afterwards, when the
  program is ready
• Saves all the versions for later use
• Clean way of saving only the necessary files and
  managing projects
• Gives freedom to develop on multiple machines
  simultaneously

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Fancy Features

• Multiple developer support (file locking, etc.)
• Bonsai - www-interface (for example see Gnome
  project)
• Keyword substitutions
• Development of several version at the same time
• Multiplatform-support (works even on obscure
  platforms like Windows)

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Concurrent checkout
Master Repository foo.c
Checkout does not lock the files in repository
checkout latest
checkout branch rel_1_fix
checkout V1.1
checkout V1.2
checkout latest
Sundar (Code walkthrough)
Ganesh
Mansoor
Subbu
Gopinath
checkin
checkin
checkin
X
X
V1.8 or 1.9
V1.2.2.2
checkin prohibited
V1.8 or 1.9
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CVS and the Development Cycle

• 1. Check out source files in working directory.
• 2. Edit source files.
• 3. Unit test your code.
• 4. Update working files to merge in changes from
  other developers (if necessary).
• 5. Test again if the sources were merged on step
  4.
• 6. Commit changes.
• 7. Repeat from step 2 until you have a new
  release.
• 8. Tag the release.
• 9. Submit the module name and release tag for
  integration build.

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Ideal development with CVS
Developer A
checkout
update
checkin
development
repository
Developer B
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Real development with CVS
Developer A
repository
Developer B
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How Do You Setup CVS?

• Most current nix distribution come with CVS
  installed from the get go
• Setting up the server basically just requires
  specifying where the repository will be housed
• In Linux Install gcvs for gui interface
• In Win Install Wincvs
• Tortoise CVS is also good

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Setting Up the Client

• CVS relies on two main environment variables
• CVS_ROOT specifies where the repository is
  located. This can be a network address, i.e..
  //sdgserver/sdgrepo

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Essential CVS Terminology - Repository

• CVS stores all files in a centralized directory
  called the repository. The directory is defined
  by the environment variable CVSROOT.

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Essential CVS Terminology - Module

• Modules are just the top level directories in the
  Repository.
• You can combine multiple modules in your own
  directory structure. See documentation for
  CVSROOT/modules
• incorporate generic libraries in your own source
  tree, but be able to maintain them individually.
• The files in the repository are organized in
  modules. Each module is made up of one or more
  files, and can include files from several
  directories. A typical usage is to define one
  module per project.

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Version Numbers

• Every file in a CVS repository can contain many
  versions, which are given version numbers in form
  x.y.x.y....
• The history of each file is tracked with an
  incrementing revision number
• For each revision there is a log entry
• Revision numbers have the format 1.25 if they're
  on the main trunk, branches have something like
  1.33.2.16

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Revision numbers
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Version Numbers

• Version numbering is automatic i.e. number y is
  automatically increased every time file is
  changed

1.1
1.2
1.3
1.4
1.5
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Tags

• A Tag is simply a symbolic name for a specific
  revision
• Tagging all files in one directory or module
  marks the current stage.
• Can be used as synonym for a revision in any
  CVS-command
• cvs tag lttagnamegt applies the tag to the current
  revision of each file
• Version numbers can be treated as a internal
  information in CVS and only symbolic names - tags
  for version used to mark releases.

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Branches

• Version number can contain more than two numbers
  to mark branches.
• Branch can start from any version and start
  developing independently from the rest of the
  software.
• In some point of the development of a branch, it
  can be merged to main trunk in necessary.

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Interaction with the repository

• Check out
• Syntax cvs checkout options module ...
• Add
• Syntax cvs add options file ...
• Remove
• Syntax cvs remove options file ...
• Examine status
• Syntax cvs status options file ...

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Interaction with the repository cont.

• Update
• Syntax cvs update options file ...
• Check in (commit)
• Syntax cvs commit options file ...
• Release module
• Syntax cvs release options module ...
• Import module
• Syntax cvs import options repository_dir
  vendor_tag release_tag
• Export module
• Syntax cvs export options module ...

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Branches

• Tag symbolic name for revision of file
• -v flag in status see tags and rev. nos.
• Tag all files at strategic points release
• -r flag in checkout checkout a rev. no.
• Need for branches good for bug-fixing
• Put modified code in branch and later merge with
  main trunk

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Modules

• modules are alias names to projects kept in the
  repository.
• More convenient to call a module name rather
  than a long pathname
• Example
• If repository is in
• \\Sdgserver\SDGREPO\FCS DRIVERS V1
• A module could declare this simply as DRIVERS

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Defining the module

• Get working copy of modules file
• Edit file to define new module
• Commit changes to modules file
• Release the working copy
• E.g. - cvs checkout CVSROOT/modules
• new line newdir newcode/newdir
• cvs commit m Added module modules
• cvs release d modules

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cvs Status

• Status gives the state of the file
• Up-to-date latest revision
• Locally modified not committed changes
• Locally added added but not committed
• Locally removed removed, not committed
• Needs checkout, Needs merge
• Unresolved Conflict update conflict
• Unknown

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What is WinCVS?

• WinCVS is a MS Windows GUI CVS client.
• WinCVS is an Open Source product, written in MS
  Visual C. Architecture supports different front
  ends.
• Latest version is 1.2.x is stable release
• Latest beta version is 1.3b8

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WinCVS on your desktop

• Configuration
• Main screen
• Checking out the sources
• Viewing source history
• Diff
• Commit
• Update
• Tag

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Guided Tour / Demo

• Importing an existing project to the repository
• Checking out a project to your work area
• Updating your work area
• Editing files, checking in/committing new
  versions to the repository
• Comparing changes between versions (diffing)
• Advanced features
• Customising CVS

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Guided Tour / Demo

• Importing an existing project to the repository
• Checking out a project to your work area
• Updating your work area
• Editing files, checking in/committing new
  versions to the repository
• Comparing changes between versions (diffing)
• Advanced features
• Customising CVS

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Guided Tour / Demo

• Importing an existing project to the repository
• Checking out a project to your work area
• Updating your work area
• Editing files, checking in/committing new
  versions to the repository
• Comparing changes between versions (diffing)
• Advanced features
• Customising CVS

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Guided Tour / Demo

• Importing an existing project to the repository
• Checking out a project to your work area
• Updating your work area
• Editing files, checking in/committing new
  versions to the repository
• Comparing changes between versions (diffing)
• Advanced features
• Customising CVS

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Guided Tour / Demo

• Importing an existing project to the repository
• Checking out a project to your work area
• Updating your work area
• Editing files, checking in/committing new
  versions to the repository
• Comparing changes between versions (diffing)
• Advanced features
• Customising CVS

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Guided Tour / Demo

• Importing an existing project to the repository
• Checking out a project to your work area
• Updating your work area
• Editing files, checking in/committing new
  versions to the repository
• Comparing changes between versions (diffing)
• Advanced features
• Customising CVS

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Guided Tour / Demo

• Importing an existing project to the repository
• Checking out a project to your work area
• Updating your work area
• Editing files, checking in/committing new
  versions to the repository
• Comparing changes between versions (diffing)
• Advanced features
• Customising CVS

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WinCVS Configuration
Your login
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WinCvs Main screen
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Checking out the sources
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Source history diff
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Commit, Update Tag
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When to commit

• Commit to mark a working state that you might
  want to return to later.
• Commit related files in a single operation. Use
  a common log message for all the files.
• Commit to backup your sources.
• Commit from an office desktop to be able to
  access the files from home much faster than
  through filesystem sharing.

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Working on branches
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Branch if you need ...

• to create sustaining (patch) releases
• to have multiple development lines from a single
  repository
• to do experimental development to merge later or
  forget about it
• to keep temporary state of development without
  affecting builds

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Common CVS commands

• cvs cvs-options command cmd-options files
• cvs checkout Check out source for editing.
• cvs add Add new file/directory to repository.
• cvs remove Remove an entry from the repository.
• cvs status Show status of checked out files.
• cvs log Show revision history for files.
• cvs diff Compare working files to version in
  repository or versions inside the repository.
• cvs update Bring working files into sync with
  repository.
• cvs commit check files into the repository
• cvs tag Label the sources.

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Advisory locks
Developer A

Developer B
Editors Developer A
Editors Developer A Developer B
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Links

• Official CVS site http//www.cyclic.com
• CVS Bubbles http//www.loria.fr/molli/cvs-index.
  html
• CVS for Web development http//durak.org81/cvswe
  bsites
• WinCvs http//www.wincvs.org
• jCVS http//www.jcvs.org/
• Netscapes Mozilla under CVS
• http//cvs-mirror.mozilla.org/webtools/tindertest
  /showbuilds.cgi?treeSeaMonkey
• FreeBSD CVS repository http//www.freebsd.org/sup
  port.htmlcvs

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QA

• QA
• Your Time

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About

• For suggestions durairaj_77_at_hotmail.com
• Thanks to Open Source Community
• Thanks to all my team members for their comments
  and suggestions.
• A special thanks to Vijay Ananth K for his
  motivation.