bootsvc is (typically) the first program loaded by usermode (contrast with userboot, which is loaded by the kernel).
bootsvc provides several system services:
After preparing these services, it launches one program from the bootfs. The program may be selected with a kernel command line argument
bootsvc.next (this default to
bin/devmgr currently). The launched program is provided with the bootfs mounted at
/boot and the loader service. The kernel command line arguments are provided to it via
envp. See the documentation in
system/core/bootsvc/main.cpp:LaunchNextProcess() for more details.