3 CVS Operations

It is assumed that you are already familiar with the basic operation of CVS.

The CVS repository is hosted on the repository machines. The CVS Repository Meisters <cvs@FreeBSD.org> are the ``owners'' of the CVS repository and are responsible for direct modification of it for the purposes of cleanup or fixing some grievous abuse of CVS by a committer. Should you cause some repository accident, say a bad cvs import or cvs tag operation, mail the CVS Repository Meisters <cvs@FreeBSD.org> (or call one of them) and report the problem to one of them. The only ones able to directly fiddle the repository bits on the repository hosts are the repomeisters. There are no login shells on ncvs.FreeBSD.org installed, except for the repomeisters.

CVS operations are done remotely by setting the CVSROOT environment variable to ncvs.FreeBSD.org:/home/ncvs and the CVS_RSH variable to ssh and then doing the appropriate check-out/check-in operations. If you wish to add something which is wholly new (like contrib-ified sources, etc), cvs import should be used. Refer to the cvs(1) manual page for usage.

If you need to use CVS add and delete operations in a manner that is effectively a mv(1) operation, then a repository copy is in order rather than using CVS add and delete. In a repository copy, a CVS Meister will copy the file(s) to their new name and/or location and let you know when it is done. The purpose of a repository copy is to preserve file change history, or logs. We in the FreeBSD Project greatly value the change history that CVS gives to the project.

CVS reference information, tutorials, and FAQs can also be found at: http://www.cvshome.org/docs/, and the information in Karl Fogel's chapters from ``Open Source Development with CVS'' are also very useful.

Dag-Erling C. Smørgrav <des@FreeBSD.org> also supplied the following ``mini primer'' for CVS.

1. Check out a module with the co or checkout command.

       % cvs checkout shazam
   

   This checks out a copy of the shazam module. If there is no shazam module in the modules file, it looks for a top-level directory named shazam instead.

   Table 1. Useful cvs checkout options

   -P	Do not create empty directories
   -l	Check out a single level, no subdirectories
   -rrev	Check out revision, branch or tag rev
   -Ddate	Check out the sources as they were on date date

   Practical FreeBSD examples:

   • Check out the miscfs module, which corresponds to src/sys/miscfs:

         % cvs co miscfs
     

     You now have a directory named miscfs with subdirectories CVS, deadfs, devfs, and so on. One of these (linprocfs) is empty.

   • Check out the same files, but with full path:

         % cvs co src/sys/miscfs
     

     You now have a directory named src, with subdirectories CVS and sys. src/sys has subdirectories CVS and miscfs, etc.

   • Check out the same files, but prunes empty directories:

         % cvs co -P miscfs
     

     You now have a directory named miscfs with subdirectories CVS, deadfs, devfs... but note that there is no linprocfs subdirectory, because there are no files in it.

   • Check out the directory miscfs, but none of the subdirectories:

         % cvs co -l miscfs
     

     You now have a directory named miscfs with just one subdirectory named CVS.

   • Check out the miscfs module as it is in the 4.X branch:

         % cvs co -rRELENG_4 miscfs
     

     You can modify the sources and commit along this branch.

   • Check out the miscfs module as it was in 3.4-RELEASE.

         % cvs co -rRELENG_3_4_0_RELEASE miscfs
     

     You will not be able to commit modifications, since RELENG_3_4_0_RELEASE is a point in time, not a branch.

   • Check out the miscfs module as it was on Jan 15 2000.

         % cvs co -D'01/15/2000' miscfs
     

     You will not be able to commit modifications.

   • Check out the miscfs module as it was one week ago.

         % cvs co -D'last week' miscfs
     

     You will not be able to commit modifications.

   Note that cvs stores metadata in subdirectories named CVS.

   Arguments to -D and -r are sticky, which means cvs will remember them later, e.g. when you do a cvs update.

2. Check the status of checked-out files with the status command.

       % cvs status shazam
   

   This displays the status of the shazam file or of every file in the shazam directory. For every file, the status is given as one of:

   Up-to-date	File is up-to-date and unmodified.
   Needs Patch	File is unmodified, but there is a newer revision in the repository.
   Locally Modified	File is up-to-date, but modified.
   Needs Merge	File is modified, and there is a newer revision in the repository.
   File had conflicts on merge	There were conflicts the last time this file was updated, and they have not been resolved yet.

   You will also see the local revision and date, the revision number of the newest applicable version (``newest applicable'' because if you have a sticky date, tag or branch, it may not be the actual newest revision), and any sticky tags, dates or options.

3. Once you have checked something out, update it with the update command.

       % cvs update shazam
   

   This updates the shazam file or the contents of the shazam directory to the latest version along the branch you checked out. If you checked out a ``point in time'', does nothing unless the tags have moved in the repository or some other weird stuff is going on.

   Useful options, in addition to those listed above for checkout:

   -d	Check out any additional missing directories.
   -A	Update to head of main branch.
   -jrev	More magic (see below).

   If you checked out a module with -r or -D, running cvs update with a different -r or -D argument or with -A will select a new branch, revision or date. The -A option clears all sticky tags, dates or revisions whereas -r and -D set new ones.

   Theoretically, specifying HEAD as argument to -r will give you the same result as -A, but that is just theory.

   The -d option is useful if:

   • somebody has added subdirectories to the module you have checked out after you checked it out.

   • you checked out with -l, and later change your mind and want to check out the subdirectories as well.

   • you deleted some subdirectories and want to check them all back out.

   Watch the output of the cvs update with care. The letter in front of each filename indicates what was done with it:

   U	The file was updated without trouble.
   P	The file was updated without trouble (you will only see this when working against a remote repo).
   M	The file had been modified, and was merged without conflicts.
   C	The file had been modified, and was merged with conflicts.

   Merging is what happens if you check out a copy of some source code, modify it, then someone else commits a change, and you run cvs update. CVS notices that you have made local changes, and tries to merge your changes with the changes between the version you originally checked out and the one you updated to. If the changes are to separate portions of the file, it will almost always work fine (though the result might not be syntactically or semantically correct).

   CVS will print an M in front of every locally modified file even if there is no newer version in the repository, so cvs update is handy for getting a summary of what you have changed locally.

   If you get a C, then your changes conflicted with the changes in the repository (the changes were to the same lines, or neighboring lines, or you changed the local file so much that cvs can not figure out how to apply the repository's changes). You will have to go through the file manually and resolve the conflicts; they will be marked with rows of <, = and > signs. For every conflict, there will be a marker line with seven < signs and the name of the file, followed by a chunk of what your local file contained, followed by a separator line with seven = signs, followed by the corresponding chunk in the repository version, followed by a marker line with seven > signs and the revision number you updated to.

   The -j option is slightly voodoo. It updates the local file to the specified revision as if you used -r, but it does not change the recorded revision number or branch of the local file. It is not really useful except when used twice, in which case it will merge the changes between the two specified versions into the working copy.

   For instance, say you commit a change to shazam/shazam.c in FreeBSD-CURRENT and later want to MFC it. The change you want to MFC was revision 1.15:

   • Check out the FreeBSD-STABLE version of the shazam module:

         % cvs co -rRELENG_4 shazam
     

   • Apply the changes between rev 1.14 and 1.15:

         % cvs update -j1.14 -j1.15 shazam/shazam.c
     

   You will almost certainly get a conflict because of the $Id$ (or in FreeBSD's case, $FreeBSD$) lines, so you will have to edit the file to resolve the conflict (remove the marker lines and the second $Id$ line, leaving the original $Id$ line intact).

4. View differences between the local version and the repository version with the diff command.

       % cvs diff shazam
   

   shows you every modification you have made to the shazam file or module.

   Table 2. Useful cvs diff options

   -u	Uses the unified diff format.
   -c	Uses the context diff format.
   -N	Shows missing or added files.

   You always want to use -u, since unified diffs are much easier to read than almost any other diff format (in some circumstances, context diffs generated with the -c option may be better, but they are much bulkier). A unified diff consists of a series of hunks. Each hunk begins with a line that starts with two @ signs and specifies where in the file the differences are and how many lines they span. This is followed by a number of lines; some (preceded by a blank) are context; some (preceded by a - sign) are outtakes and some (preceded by a +) are additions.

   You can also diff against a different version than the one you checked out by specifying a version with -r or -D as in checkout or update, or even view the diffs between two arbitrary versions (without regard for what you have locally) by specifying two versions with -r or -D.

5. View log entries with the log command.

       % cvs log shazam
   

   If shazam is a file, this will print a header with information about this file, such as where in the repository this file is stored, which revision is the HEAD for this file, what branches this file is in, and any tags that are valid for this file. Then, for each revision of this file, a log message is printed. This includes the date and time of the commit, who did the commit, how many lines were added and/or deleted, and finally the log message that the committer who did the change wrote.

   If shazam is a directory, then the log information described above is printed for each file in the directory in turn. Unless you give the -l to log, the log for all subdirectories of shazam is printed too, in a recursive manner.

   Use the log command to view the history of one or more files, as it is stored in the CVS repository. You can even use it to view the log message of a specific revision, if you add the -rrev to the log command:

       % cvs log -r1.2 shazam
   

   This will print only the log message for revision 1.2 of file shazam if it is a file, or the log message for revision 1.2 of each file under shazam if it is a directory.

6. See who did what with the annotate command. This command shows you each line of the specified file or files, along with which user most recently changed that line.

       % cvs annotate shazam
   

7. Add new files with the add command.

   Create the file, cvs add it, then cvs commit it.

   Similarly, you can add new directories by creating them and then cvs adding them. Note that you do not need to commit directories.

8. Remove obsolete files with the remove command.

   Remove the file, then cvs rm it, then cvs commit it.

9. Commit with the commit or checkin command.

   Table 3. Useful cvs commit options

   -f	Force a commit of an unmodified file.
   -mmsg	Specify a commit message on the command line rather than invoking an editor.

   Use the -f option if you realize that you left out important information from the commit message.

   Good commit messages are important. They tell others why you did the changes you did, not just right here and now, but months or years from now when someone wonders why some seemingly illogical or inefficient piece of code snuck into your source file. It is also an invaluable aid to deciding which changes to MFC and which not to MFC.

   Commit messages should be clear, concise and provide a reasonable summary to give an indication of what was changed and why.

   Commit messages should provide enough information to enable a third party to decide if the change is relevant to them and if they need to read the change itself.

   Avoid committing several unrelated changes in one go. It makes merging difficult, and also makes it harder to determine which change is the culprit if a bug crops up.

   Avoid committing style or whitespace fixes and functionality fixes in one go. It makes merging difficult, and also makes it harder to understand just what functional changes were made. In the case of documentation files, it can make the job of the translation teams more complicated, as it becomes difficult for them to determine exactly what content changes need to be translated.

   Avoid committing changes to multiple files in one go with a generic, vague message. Instead, commit each file (or small, related groups of files) with tailored commit messages.

   Before committing, always:

   • verify which branch you are committing to, using cvs status.

   • review your diffs, using cvs diff

   Also, ALWAYS specify which files to commit explicitly on the command line, so you do not accidentally commit other files than the ones you intended - cvs commit without any arguments will commit every modification in your current working directory and every subdirectory.

Additional tips and tricks:

1. You can place commonly used options in your ~/.cvsrc, like this:

       cvs -z3
       diff -Nu
       update -Pd
       checkout -P
   

   This example says:

   • always use compression level 3 when talking to a remote server. This is a life-saver when working over a slow connection.

   • always use the -N (show added or removed files) and -u (unified diff format) options to diff(1).

   • always use the -P (prune empty directories) and -d (check out new directories) options when updating.

   • always use the -P (prune empty directories) option when checking out.

2. Use Eivind Eklund's cdiff script to view unidiffs. It is a wrapper for less(1) that adds ANSI color codes to make hunk headers, outtakes and additions stand out; context and garbage are unmodified. It also expands tabs properly (tabs often look wrong in diffs because of the extra character in front of each line).

   http://people.FreeBSD.org/~eivind/cdiff

   Simply use it instead of more(1) or less(1):

       % cvs diff -Nu shazam | cdiff
   

   Alternatively some editors like vim(1) ( editors/vim5) have color support and when used as a pager with color syntax highlighting switched on will highlight many types of file, including diffs, patches, and cvs/rcs logs.

       % echo "syn on" >> ~/.vimrc 
       % cvs diff -Nu shazam | vim -
       % cvs log shazam | vim -
   

3. CVS is old, arcane, crufty and buggy, and sometimes exhibits non-deterministic behavior which some claim as proof that it is actually merely the Newtonian manifestation of a sentient transdimensional entity. It is not humanly possible to know its every quirk inside out, so do not be afraid to ask the resident AI (CVS Repository Meisters <cvs@FreeBSD.org>) for help.

4. Do not leave the cvs commit command in commit message editing mode for too long (more than 2-3 minutes). It locks the directory you are working with and will prevent other developers from committing into the same directory. If you have to type a long commit message, type it before executing cvs commit, and insert it into the commit message.