The Linux Programming Interface

Solutions to Selected Exercises 1435

Chapter 55

55-1. The following hold for flock() on Linux:

a) A series of shared locks can starve a process waiting to place an exclusive lock.

b) There are no rules regarding which process is granted the lock. Essentially,

the lock is granted to the process that is next scheduled. If that process

happens to be one that obtains a shared lock, then all other processes

requesting shared locks will also be able to have their requests granted

simultaneously.

55-2. The flock() system call doesn’t detect deadlock. This is true of most flock()

implementations, except those that implement flock() in terms of fcntl().

55-4. In all except early (1.2 and earlier) Linux kernels, the two types of locking operate

independently, and have no affect on one another.

Chapter 57

57-4. On Linux, the sendto() call fails with the error EPERM. On some other UNIX systems,

a different error results. Some other UNIX implementations don’t enforce this

constraint, letting a connected UNIX domain datagram socket receive datagrams

from a sender other than its peer.

Chapter 59

59-1. A solution is provided in the files read_line_buf.h and read_line_buf.c in the sockets

subdirectory in the source code distribution for this book.

59-2. A solution is provided in the files is_seqnum_v2_sv.c, is_seqnum_v2_cl.c, and

is_seqnum_v2.h in the sockets subdirectory in the source code distribution for this

book.

59-3. A solution is provided in the files unix_sockets.h, unix_sockets.c, us_xfr_v2.h,

us_xfr_v2_sv.c, and us_xfr_v2_cl.c in the sockets subdirectory in the source code

distribution for this book.

59-5. In the Internet domain, datagrams from a nonpeer socket are silently discarded.

Chapter 60

60-2. A solution is provided in the file sockets/is_echo_v2_sv.c in the source code

distribution for this book.

Chapter 61

61-1. Since the send and receive buffers for a TCP socket have a limited size, if the client

sent a large quantity of data, then it might fill these buffers, at which point a further

write() would (permanently) block the client before it read any of the server’s

response.

61-3. A solution is provided in the file sockets/sendfile.c in the source code distribution

for this book.