The Linux Programming Interface

FSOLUTIONS TO SELECTED EXERCISES

Chapter 5

5-3.     A solution is provided in the file fileio/atomic_append.c in the source code distribution for this book. Here is an example of the results that we see when we run this program as suggested:

$ ls -l f1 f2-rw-------    1 mtk      users      2000000 Jan  9 11:14 f1-rw-------    1 mtk      users      1999962 Jan  9 11:14 f2

Because the combination of lseek() plus write() is not atomic, one instance of the program sometimes overwrote bytes written by the other instance. As a result, the file f2 contains less than 2 million bytes.

5-4.     A call to dup() can be rewritten as:

fd = fcntl(oldfd, F_DUPFD, 0);

A call to dup2() can be rewritten as:

if (oldfd == newfd) {                /* oldfd == newfd ...