Exercises

1. Using the time built-in command of the shell, try timing the operation of the program in Example 4-1 (copy.c) on your system.

   1. Experiment with different file and buffer sizes. You can set the buffer size using the -DBUF_SIZE=nbytes option when compiling the program.

   2. Modify the open() system call to include the O_SYNC flag. How much difference does this make to the speed for various buffer sizes?

   3. Try performing these timing tests on a range of file systems (e.g., ext3, XFS, Btrfs, and JFS). Are the results similar? Are the trends the same when going from small to large buffer sizes?

2. Time the operation of the filebuff/write_bytes.c program (provided in the source code distribution for this book) for various buffer sizes and file systems.

3. What is the effect of the following statements?

   fflush(fp);
   fsync(fileno(fp));

4. Explain why the output of the following code differs depending on whether standard output is redirected to a terminal or to a disk file.

   printf("If I had more time, \n");
   write(STDOUT_FILENO, "I would have written you a shorter letter.\n", 43);

5. The command tail [ -n num ] file prints the last num lines (ten by default) of the named file. Implement this command using I/O system calls (lseek(), read(), write(), and so on). Keep in mind the buffering issues described in this chapter, in order to make the implementation efficient.