pdeath-readme

This patch provides a mechanism for a child process to be sent a
signal when its parent process dies. In some ways it is similar to the
way a child process send a signal to its parent when the child changes
state (dies, exits or is suspended), except that the child process is
not notified when the parent is suspended. The child is sent a signal
*only* when the parent dies or exits.
To control what signal is sent to the child, a new syscall has been
defined: prctl(). As yet there is no support in any of the standard C
libraries for this syscall.

This patch is designed to be of use for threading libraries. The
current version of LinuxThreads (0.6 at time of writing) has a
"manager" thread which wakes up periodically to see of the parent
process (the main thread) has died, and if so it can then kill the
child processes (other threads). This periodic waking is a bit ugly
and consumes some system resources. With this patch a threads library
could request a signal be delivered to the manager thread when the
parent (main thread) dies.

The default action when a process dies is that it will not send any
signal to its children. Each child process can change this by calling
prctl(2) thus:

#include <linux/prctl.h>
	prctl (PR_SET_PDEATHSIG, sig);

where <sig> is the signal that should be sent when the parent dies. If
this is 0 then no signal is sent.

The patch is against virgin 2.1.56. It is also compatible with my
select and fastpoll patches. It patches against 2.1.52+ except for
failures patching the CREDITS file. It has been included in 2.1.57.