What are the implications of supporting BSD functionality in user mode servers within the Mach operating system?
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Answer:Mach operating system supports the BSD functionality in user mode servers.When the user process makes a BSD call,it traps into kernel mode and the kernel copies the arguments to the user level server.A context switch is then made and the user level performs the
requested operation and computes the results which are then copied back to the kernel space.Another context switch takes place to the original process which is in kernel mode and the process eventually transitions from kernel mode to user mode along with the results of
the BSD call.Therefore,in order to perform the BSD call,there are two kernel crossings and two process switches thereby resulting in a large overhead.This is significantly higher than the cost if the BSD functionality is supported within the kernel.