Linux Kernel Architecture

Chapter 5: Locking and Interprocess Communication

information on the implementation structure, I willnot discuss specific cases but restrict myself to a

description of the key mechanisms.

Table 5-3: Some System Calls Relating to Signals

System call Function

kill Sends a signal to all processes of a process group.

tkill Sends a signal to a single process.

sigpending Checks whether there are pending signals.

sigprocmask Manipulates a bitmask of blocked signals.

sigsuspend Sleeps until a specific signal is received.

Sending Signals

Despite their names,killandtkillsend any signal to a process group or to a single process, respec-

tively. As both functions are basically identical,^14 I discuss onlysys_tkill, whose code flow diagram is

shown in Figure 5-9.

sys_tkill

Cancel processing

do_tkill

find_task_by_vpid

check_kill_permission

specific_send_sig_info

sig_ignored?

send_signal

signal_wake_up

Figure 5-9: Code flow diagram forsys_tkill.

(^14) sys_killsends the signal to several processes that are interpreted according to the form of the PID passed.
❑ pid> 0 sends the signal to the process with the specified PID.
❑ pid= 0 sends the signal to all members of the process group of the task that sent the signal.
❑ pid=− 1 sends the signal to all processes withpid> 1.
❑ pid=−pgrp<− 1 sends the signal to all members of thepgrpprocess group.