| 3.1 | When reading or writing a disk file, are the functions described in this chapter really unbuffered? Explain. |
| Section 3.12, without calling the fcntl function. Be sure to handle errors correctly. |
| 3.3 | Assume that a process executes the following three function calls:fd1 = open(pathname, oflags);
fd2 = dup(fd1);
fd3 = open(pathname, oflags);
Draw the resulting picture, similar to Figure 3.8. Which descriptors are affected by an fcntl on fd1 with a command of F_SETFD? Which descriptors are affected by an fcntl on fd1 with a command of F_SETFL? |
| 3.4 | The following sequence of code has been observed in various programs:dup2(fd, 0);
dup2(fd, 1);
dup2(fd, 2);
if (fd > 2)
close(fd);
To see why the if test is needed, assume that fd is 1 and draw a picture of what happens to the three descriptor entries and the corresponding file table entry with each call to dup2. Then assume that fd is 3 and draw the same picture. |
| 3.5 | The Bourne shell, Bourne-again shell, and Korn shell notationdigit1 >&digit2
says to redirect descriptor digit1 to the same file as descriptor digit2 . What is the difference between the two commands./a.out > outfile 2>&1
./a.out 2>&1 > outfile
(Hint: the shells process their command lines from left to right.) |
| 3.6 | If you open a file for readwrite with the append flag, can you still read from anywhere in the file using lseek? Can you use lseek to replace existing data in the file? Write a program to verify this. |
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