Assignment 8: Kernel Programming: File system annotation

The standard Unix file system provides very basic meta data, such as the owner and the file creation time. For searching files, it would be highly desirable to be able to add additional comments, label the content and to provide display hints. (Services such as MacOSX Spotlight provide such a feature, albeit outside the kernel.)

In this assignment, you will augment the existing Linux file system to add a set of search terms, a color and a media type string.

You could store the additional information either as part of the inode entry or in a separate datastructure. Since extending the inode structure would require creating a new file system, you may find it easier to store this information separately, indexed by the inode number. You can assume that comments and content type are limited to 255 bytes. The content type is a string such as "text/plain" or "application/pdf". You should also record when the information was last changed.

When a file is removed, the additional information should also be deleted.

System Calls

You will implement two system calls, one to annotate a file, the other to retrieve the annotation. Your system call annotate() should allow somebody who has write permission to the file to annotate the file:

  int annotate(char *filename, int color, char *comments, char *contenttype);

To retrieve the annotation, use

  int statx(char *filename, int *color, int comment_length, char *comments,
    int content_length, char *contenttype);

Here, *_length contains the length of the buffer that the caller allocates for this parameter. If there is no additional file information, the function should return -1 and set errno.

Your program must check the file permissions and set errno accordingly.

The color value is an RGB value, with 8 bits each.

Test Program

For testing, create a simple user mode program that annotates a file:

   annotate filename color comments content-type

The color should be specified as a six-digit hex RGB value, such as 0305ab.

A new program, statx, should display this additional information, such as

   statx test.txt
   Change:   Sun Feb  4 16:50:51 2007
   Color:    #0305ab
   Comments: helpful hints for OS homework
   Content:  text/plain

If you have time and interest (sorry, no extra credit), you may also want to modify the Linux ls command to use the stored color information instead of the current highlighting algorithm.

What to Submit

You must submit a single file named .tar.gz or .tgz. Any other filename and we will dock points! The tar file should contain the the kernel patch, the README file, sample output and testing programs.

Your README file should describe what changes you made to the kernel, how to run your test programs and what the expected output should be.

For each programming part, if your program(s) do not work, you must submit file named nonworking.txt. Inside this file, you need to describe what problems you ran into, where your program fails and what you think are the reasons.