This is another step towards multi-container support.
Previously, we delivered signals directly to the sandbox process (which then
forwarded the signal to PID 1 inside the sandbox). Similarly, we waited on a
container by waiting on the sandbox process itself. This approach will not work
when there are multiple containers inside the sandbox, and we need to
signal/wait on individual containers.
This CL adds two new messages, ContainerSignal and ContainerWait. These
messages include the id of the container to signal/wait. The controller inside
the sandbox receives these messages and signals/waits on the appropriate
process inside the sandbox.
The container id is plumbed into the sandbox, but it currently is not used. We
still end up signaling/waiting on PID 1 in all cases. Once we actually have
multiple containers inside the sandbox, we will need to keep some sort of map
of container id -> pid (or possibly pid namespace), and signal/kill the
appropriate process for the container.
PiperOrigin-RevId: 197028366
Change-Id: I07b4d5dc91ecd2affc1447e6b4bdd6b0b7360895
31386185fe