wlroots uses wl_event_loop_add_signal to handle SIGUSR1 from Xwayland.
wl_event_loop_add_signal works by masking the signal and receiving it from a
signalfd. The signal mask is preserved across fork and exec, so subprocesses
spawned by Sway start with SIGUSR1 masked. Most subprocesses do not expect this
and never unmask the signal, resulting in missing functionality or unexpected
behavior for processes that use SIGUSR1 (such as i3status).
Fix this by unmasking all signals between fork and exec.
- child would leak in the workspace_record_pid path
- removing malloc lets us get rid of That Comment nobody seems
to remember what it was about
- we would leak pipe fds on first fork failling
- we didn't return an error if second fork failed
- the final executed process still had both pipe fds
(would show up in /proc/23560/fd in launched programs)
- we would write twice to the pipe if execl failed for some reason
(e.g. if /bin/sh doesn't exist?!)
When you spawn a process with the exec command, sway now notes the
workspace you had focused and the pid of the child process, then assigns
that workspace to the child when its window appears.
Some of this is carried over from sway 0.15, but with some major
refactoring and centralization of state.
