Hold off the calling process until the process that's associated with the file descriptor reaches a point of interest.
You must have opened the file descriptor for writing. Use the DCMD_PROC_RUN command to set up the point of interest. If you don't want to block the calling process, use DCMD_PROC_EVENT instead of DCMD_PROC_WAITSTOP.
The argument is a pointer to a procfs_status structure (see debug_thread_t in <sys/debug.h>) that's filled with status information on return. For example:
procfs_status my_status; devctl( fd, DCMD_PROC_WAITSTOP, &my_status, sizeof my_status, 0);
For more information about the contents of this structure, see "Thread information," earlier in this chapter.