Including sys/types.h must happen before SYS_pidfd_send_signal is checked,
because that header defines variable in normal conditions. When sys/types.h
does not have SYS_pidfd_send_signal then fallback is defined in config.h
that is included by default, and has therefore worked fine before and after
this change.
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
At times there is need in scripts to send multiple signals to a process.
Often these cases require some amount of waiting before follow-up signal
should be sent.
One common case is process termination, where first script tries to kill
process gracefully but if that does not work SIGKILL is sent. Functionality
like that is commonly done by periodically checking if signalled pid exist
or not, and if it does another signal is sent possibly to an unrelated
process that reused pid number. That means polling a pid is prone to a data
race. Also if the first signal immediately kills the process one polling
interval is lost in sleep.
Another example when multiple signal need to be sent is various daemon
process control situations, such as Upgrading Executable on the Fly (see
reference). This happens to be the case that inspired change author to make
sequential signaling a little bit easier.
Reference: http://nginx.org/en/docs/control.html#upgrade
Pull-request: https://github.com/karelzak/util-linux/pull/902
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
Karel Zak
Sami Kerola