Xinu Ch1-5 Notes

Ch1
the term kernel
to refer to the code that remains resident in memory and provides key services such as
support for concurrent processes.
Throughout the text, we will assume the term operating system refers to the kernel, and does not include all additional facilities. (loaders, linkers ...)

Ch2
process creation functions: create , resume return to the caller immediately
after starting a new process
#include <kernel.h> should be the first include
used polled I/O (kprintf) in debugging

Ch3
referencing and unassigned  address causes the hardware to raise an exception
(bus exception)
#3.9 is important
#top of stack is higher address
#exception == Trap , related to the instruction ( instruction can be restarted)
# interrupted has nothing to do with the current instruction

Ch4
initialization of the data structure is final step in design
( since initialization is the transient state)
so first desin the data structures when the system is runnign,
and then figure out how to initialize the data structures, so as
not to sacrifice good design for easy initialization

key for head node is MAXKEY, and key for tail is MINKEY
(3ashan priority el head tb2a akbar 7aga momkena,
we priority el tail tb2a el minimum) ( if the list is used a
priority queue)

Ch5
proctab implementation : when a process terminates, its process id will be reused
however the implementation tries to maximize the time between the reuse of an ID.

# mostly, process priorities remain static

# in xinu, the current process is not in the ready list,
to provide fast access its ID is present in currpid

#before calling resched, the current process's state must be changed to
the desired next state

ctxsw : context switch

#(5.12) at least one process must be ready at all times or else resched function will fail
becuz code is designed to assume at least one process will be eligible to execute
at any time. ( that's why there is a NULL PROCESS, will be switched to when
all other processes are blocked or waiting for IO)


Ch6 :
lessa ma2aretsh