MacCVS Pro

Technical Differences Between the GNU CVS Client and MacCVS Pro

Please note: This document will be changed significantly when MacCVS Pro 2.5 is released.

Note: This document assumes that you are very familiar with the operation of GNU CVS and it's internal algorithms and data structures for maintaining version control. For information on CVS, please refer to http://www.cyclic.com.

Introduction

MacCVS Pro was not designed simply to be CVS on the Macintosh, it was designed to be extremely easy to use and much more Mac-savvy. Additionally, we wanted to leverage our existing development tools Metrowerks CodeWarrior, Projector, MPW) with our new CVS client.

Trying to develop for all these factors was not easy and we have had to resort to changing the way our client works compared to the GNU CVS client.

These issues should not affect the normal user of MacCVS Pro, but for people wanting to migrate from other Macintosh CVS tools, this can present a problem.

Issues in Storing CVS Entries Information

The entries information contains the file's name in the repository, current version on the user's disk, the date it was checked out, and tag and conflict information. The GNU CVS client stores it's entries information in an "Entries" file, "Entries.Static" file, and "Entries.Log" file inside the "CVS" directory of each source directory.

An example of a CVS "Entries" file: 

    /friends.html/1.1.1.1/Tue Mar 24 22:03:46 1998//
    /index.html/1.1.1.1/Tue Mar 24 22:03:46 1998//
    /links.html/1.1.1.1/Tue Mar 24 22:03:46 1998//
    /morepix.html/1.1.1.1/Tue Mar 24 22:03:46 1998//
    /pgpkey.txt/1.1.1.1/Tue Mar 24 22:03:46 1998//
    /pictures.html/1.1.1.1/Tue Mar 24 22:03:46 1998//
    /projects.html/1.1.1.1/Tue Mar 24 22:03:46 1998//
    /resume.html/1.1.1.1/Tue Mar 24 22:03:46 1998//

MacCVS Pro utilizes the Macintosh resource fork of each respective file to store this information. We did this so we could utilize the MPW Projector 'ckid' resource- a cornerstone of Macintosh source code control. Also, we felt that this would be a much faster way to store this information and it makes it easier for the front-end graphical interface to detect if a file has been moved or renamed.

MacCVS Pro stores entries information in two places in the resource fork: the MPW Projector 'ckid' resource and our own 'mcvs' resource. We mainly use the 'ckid' resource to signal that the file is under source control so that features, like modified read only status, in most source code editors work correctly. Since documentation on the MPW Projector 'ckid' resource was sparse, we avoided trying to utilize some of the advanced features of this resource.

The actual CVS entries information is stored in the 'mcvs' resource (ID 128) along with a couple extra items.

The format of the 'ckid' and 'mcvs' resources can be found at the bottom of this document.

Differences Inside the CVS Directory

As alluded to above, the GNU CVS client stores all it's entries information and other stuff in "CVS" directories in each source directory. MacCVS Pro does a similar thing, creating invisible "CVS" folders in each source directory. However there are some differences as to what files we store in there and what data we store in those files. Here is the run down:

File Name: Repository

Purpose: Stores the remote path of where the particular source directory is stored in the repository.

Differences in MacCVS Pro: MacCVS Pro uses this but it only stores the path name relative to the CVSROOT, not the full path name. There are also some differences in what path name it stores, especially if you are checking out a module with the (-d dir) aliasing feature. Since we have no documentation explaining how to correctly write this file, we've had to "guess" in some cases as to how it is supposed to work.


File Name: Root

Purpose: Stores the CVSROOT path of the repository that user checked out the particular source directory from.

Differences in MacCVS Pro: MacCVS Pro creates this file in all "CVS" directories but does not use it currently.

File Name: Tag

Purpose: Stores the tag of the particular source directory.

Differences in MacCVS Pro: None. We use this exactly the same way.

MacCVS Resource Data Formats

'ckid' Resource Format

Below is the format for a 'ckid' resource. This is also documented in the MPW documentation. 

        UInt32      fChecksum;
        UInt32      fLocation;
        UInt16      fCurrentVersion;
        UInt16      fCheckedOutBySomeone;
        UInt8       fBranch;
        UInt8       fModifyReadOnly;
        UInt32      fUnused;
        UInt32      fCheckoutTime;
        UInt32      fFilesModificationDate;
        UInt32      fProjectID1;
        UInt32      fProjectID2;
        UInt16      fUserID;
        UInt16      fFileID;
        UInt16      fRevisionID;

Following this header are 5 Pascal style strings. Each string is separated by a NULL (0x00) byte. The strings are NOT stored with 255 bytes by default- only the byte amount of the text (plus the length byte) is stored in the resource. 

        PString     fRemotePathPStr;
        (EOS)
        PString     fUserNamePStr;
        (EOS)
        PString     fRevisionPStr;
        (EOS)
        PString     fFileNamePStr;
        (EOS)
        PString     fTaskPStr;
        (EOS)

After the Pascal strings is a 16 bit wide integer that describes the length of the checkin comment data. The check in comment text follows immediately after words. 

        UInt16      fCommentLen;
        char[]      fCommentData;
'mcvs' Resource Format

Below is the format for a 'mcvs' resource. This is a special resource used by MacCVS Pro to store CVS entry information. 

        UInt32      fVersion;
        UInt32      fFlags;
        UInt32      fRefCon;

Following this header are 9 Pascal style strings. Each string is separated by a NULL (0x00) byte. The strings are NOT stored with 255 bytes by default- only the byte amount of the text (plus the length byte) is stored in the resource. 

        PString     fFileNamePStr;
        (EOS)
        PString     fRevisionPStr;
        (EOS)
        PString     fConflictsPStr;
        (EOS)
        PString     fOptionsPStr;
        (EOS)
        PString     fTagPStr;
        (EOS)
        PString     fUnused1PStr;
        (EOS)
        PString     fUnused2PStr;
        (EOS)
        PString     fUnused3PStr;
        (EOS)
        PString     fUnused4PStr;
        (EOS)

After the Pascal strings is a 16 bit wide integer that describes the length of the remote path string. The remote path text follows immediately after words. 

        UInt16      fRemotePathLen;
        char[]      fRemotePath;

'mcvs' field information:

  • fVersion This is always 0xFABB0003.
  • fFlags There currently is only one flag: if bit 1 is set, then that means this file is an AppleSingle file in the repository.

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