System Call Modules
System call modules are simply KLDs that install a system call. In operating systems, a system call, also known as a system service request, is the mechanism an application uses to request service from the operating system's kernel.
There are three items that are unique to each system call module: the system call function, the
sysent structure, and the offset value.
The System Call Function
The system call function implements the system call. Its function prototype is defined in the
<sys/sysent.h> header as:
typedef int sy_call_t(struct thread *, void *); ...