There are some workloads that benefit from having a "true" init process
that reaps zombies. This change implements a minimal init as part of
vminitd and exposes an API to be able to use this init process in our
containers. signals will be forwarded, any child procs will be reaped
and the exit code of the actual workload will be propagated. The
LinuxContainer/LinuxPod API is a very simple bool to ask to use this as
our init process, and the init simply spawns whatever command you want
as a child underneath this.
```
➜ ./bin/cctl run --kernel bin/kernel.arm64 --init
/ # ps aux
PID USER TIME COMMAND
1 root 0:00 /.cz-init -- /bin/sh
2 root 0:00 /bin/sh
3 root 0:00 ps aux
```
Add support for parent death signal (pdeathSignal) to ensure child
processes receive a signal when the parent process dies. This addresses
the FIXME comment in Runc.execute().
## Changes
- Add pdeathSignal field to exec_command_attrs C struct
- Implement prctl(PR_SET_PDEATHSIG) in child process handler (Linux
only)
- Expose pdeathSignal through Command.Attrs Swift API
- Wire up pdeathSignal in Runc.execute() to remove FIXME
## Implementation Details
The implementation uses Linux-specific prctl() to set the parent death
signal, ensuring proper cleanup when parent processes terminate. The
feature is conditionally compiled for Linux only, maintaining
compatibility with other platforms.
Danny Canter