bhyvectl: support querying VM pidHEADmain

Extend bhyvectl(8) to support querying VM pid using the
`--get-vm-pid` flag.

This is useful in monitor mode when the VM pid differs
from the main bhyve(8) process run by the user. Knowing the VM pid
is necessary, for example, to query process resource usage or
trigger ACPI shutdown with SIGTERM.

Of course, it could be obtained by matching the monitor process
children by the process title, but it's a little more complex
and fragile than it could be.

Implement that by adding the "get_vm_pid" IPC command,
and using it to implement `bhyvectl --get-vm-pid`, which
prints the VM PID.

When the VM PID is not known, ESRCH is returned.

Reviewed by:	bnovkov (previous iteration without man changes)
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D59108

0 files changed, 0 insertions, 0 deletions