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minix/kernel/proc.c
Ben Gras 3dcb2886ff get/setpriority() and fsync() system calls
2005-07-01 18:01:33 +00:00

638 lines
24 KiB
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/* This file contains essentially all of the process and message handling.
* Together with "mpx.s" it forms the lowest layer of the MINIX kernel.
* There is one entry point from the outside:
*
* sys_call: a system call, i.e., the kernel is trapped with an INT
*
* As well as several entry points used from the interrupt and task level:
*
* lock_notify: notify a process of a system event
* lock_send: send a message to a process
* lock_ready: put a process on one of the ready queues
* lock_unready: remove a process from the ready queues
* lock_sched: a process has run too long; schedule another one
*
* Changes:
* , 2005 better protection in sys_call() (Jorrit N. Herder)
* May 26, 2005 optimized message passing functions (Jorrit N. Herder)
* May 24, 2005 new, queued NOTIFY system call (Jorrit N. Herder)
* Oct 28, 2004 new, non-blocking SEND and RECEIVE (Jorrit N. Herder)
* Oct 28, 2004 rewrite of sys_call() function (Jorrit N. Herder)
* Aug 19, 2004 generalized multilevel scheduling (Jorrit N. Herder)
*
* The code here is critical to make everything work and is important for the
* overall performance of the system. A large fraction of the code deals with
* list manipulation. To make this both easy to understand and fast to execute
* pointer pointers are used throughout the code. Pointer pointers prevent
* exceptions for the head or tail of a linked list.
*
* node_t *queue, *new_node; // assume these as global variables
* node_t **xpp = &queue; // get pointer pointer to head of queue
* while (*xpp != NULL) // find last pointer of the linked list
* xpp = &(*xpp)->next; // get pointer to next pointer
* *xpp = new_node; // now replace the end (the NULL pointer)
* new_node->next = NULL; // and mark the new end of the list
*
* For example, when adding a new node to the end of the list, one normally
* makes an exception for an empty list and looks up the end of the list for
* nonempty lists. As shown above, this is not required with pointer pointers.
*/
#include "kernel.h"
#include <minix/callnr.h>
#include <minix/com.h>
#include "proc.h"
#include "const.h"
#include "debug.h"
#include "ipc.h"
#include "sendmask.h"
/* Scheduling and message passing functions. The functions are available to
* other parts of the kernel through lock_...(). The lock temporarily disables
* interrupts to prevent race conditions.
*/
FORWARD _PROTOTYPE( int mini_send, (struct proc *caller_ptr, int dst,
message *m_ptr, unsigned flags) );
FORWARD _PROTOTYPE( int mini_receive, (struct proc *caller_ptr, int src,
message *m_ptr, unsigned flags) );
FORWARD _PROTOTYPE( int mini_notify, (struct proc *caller_ptr, int dst,
message *m_ptr ) );
FORWARD _PROTOTYPE( void ready, (struct proc *rp) );
FORWARD _PROTOTYPE( void unready, (struct proc *rp) );
FORWARD _PROTOTYPE( void sched, (struct proc *rp) );
FORWARD _PROTOTYPE( void pick_proc, (void) );
#define BuildMess(m,n) \
(m).NOTIFY_SOURCE = (n)->n_source, \
(m).NOTIFY_TYPE = (n)->n_type, \
(m).NOTIFY_FLAGS = (n)->n_flags, \
(m).NOTIFY_ARG = (n)->n_arg;
#if (CHIP == INTEL)
#define CopyMess(s,sp,sm,dp,dm) \
cp_mess(s, (sp)->p_memmap[D].mem_phys, (vir_bytes)sm, (dp)->p_memmap[D].mem_phys, (vir_bytes)dm)
#endif /* (CHIP == INTEL) */
#if (CHIP == M68000)
/* M68000 does not have cp_mess() in assembly like INTEL. Declare prototype
* for cp_mess() here and define the function below. Also define CopyMess.
*/
#endif /* (CHIP == M68000) */
/*===========================================================================*
* sys_call *
*===========================================================================*/
PUBLIC int sys_call(call_nr, src_dst, m_ptr)
int call_nr; /* system call number and flags */
int src_dst; /* src to receive from or dst to send to */
message *m_ptr; /* pointer to message in the caller's space */
{
/* System calls are done by trapping to the kernel with an INT instruction.
* The trap is caught and sys_call() is called to send or receive a message
* (or both). The caller is always given by 'proc_ptr'.
*/
register struct proc *caller_ptr = proc_ptr; /* get pointer to caller */
int function = call_nr & SYSCALL_FUNC; /* get system call function */
unsigned flags = call_nr & SYSCALL_FLAGS; /* get flags */
int mask_entry; /* bit to check in send mask */
int result; /* the system call's result */
vir_bytes vb; /* message buffer pointer as vir_bytes */
vir_clicks vlo, vhi; /* virtual clicks containing message to send */
/* Check if the process has privileges for the requested call. Calls to the
* kernel may only be SENDREC, because tasks always reply and may not block
* if the caller doesn't do receive().
*/
if (! (caller_ptr->p_call_mask & (1 << function)) ||
(iskerneln(src_dst) && function != SENDREC))
return(ECALLDENIED);
/* Require a valid source and/ or destination process, unless echoing. */
if (! (isokprocn(src_dst) || src_dst == ANY || function == ECHO))
return(EBADSRCDST);
/* Check validity of message pointer. */
vb = (vir_bytes) m_ptr;
vlo = vb >> CLICK_SHIFT; /* vir click for bottom of message */
vhi = (vb + MESS_SIZE - 1) >> CLICK_SHIFT; /* vir click for top of msg */
#if ALLOW_GAP_MESSAGES
/* This check allows a message to be anywhere in data or stack or gap.
* It will have to be made more elaborate later for machines which
* don't have the gap mapped.
*/
if (vlo < caller_ptr->p_memmap[D].mem_vir || vlo > vhi ||
vhi >= caller_ptr->p_memmap[S].mem_vir + caller_ptr->p_memmap[S].mem_len)
return(EFAULT);
#else
/* Check for messages wrapping around top of memory or outside data seg. */
if (vhi < vlo ||
vhi - caller_ptr->p_memmap[D].mem_vir >= caller_ptr->p_memmap[D].mem_len)
return(EFAULT);
#endif
/* Now check if the call is known and try to perform the request. The only
* system calls that exist in MINIX are sending and receiving messages.
* - SENDREC: combines SEND and RECEIVE in a single system call
* - SEND: sender blocks until its message has been delivered
* - RECEIVE: receiver blocks until an acceptable message has arrived
* - NOTIFY: sender continues; either directly deliver the message or
* queue the notification message until it can be delivered
* - ECHO: the message directly will be echoed to the sender
*/
switch(function) {
case SENDREC: /* has FRESH_ANSWER flag */
/* fall through */
case SEND:
if (isemptyn(src_dst)) {
result = EDEADDST; /* cannot send to the dead */
break;
}
#if DEAD_CODE /* to be replaced by better mechanism */
mask_entry = isuserp(proc_addr(src_dst)) ? USER_PROC_NR : src_dst;
if (! isallowed(caller_ptr->p_sendmask, mask_entry)) {
kprintf("WARNING: sys_call denied %d ", caller_ptr->p_nr);
kprintf("sending to %d\n", proc_addr(src_dst)->p_nr);
result = ECALLDENIED; /* call denied by send mask */
break;
}
#endif
result = mini_send(caller_ptr, src_dst, m_ptr, flags);
if (function == SEND || result != OK) {
break; /* done, or SEND failed */
} /* fall through for SENDREC */
case RECEIVE:
result = mini_receive(caller_ptr, src_dst, m_ptr, flags);
break;
case NOTIFY:
result = mini_notify(caller_ptr, src_dst, m_ptr);
break;
case ECHO:
kprintf("Echo message from process %s\n", proc_nr(caller_ptr));
CopyMess(caller_ptr->p_nr, caller_ptr, m_ptr, caller_ptr, m_ptr);
result = OK;
break;
default:
result = EBADCALL; /* illegal system call */
}
/* If the caller made a successfull, blocking system call it's priority may
* be raised. The priority have been lowered if a process consumed to many
* full quantums in a row to prevent damage from infinite loops
*/
if ((caller_ptr->p_priority > caller_ptr->p_max_priority) &&
! (flags & NON_BLOCKING) && (result == OK)) {
caller_ptr->p_priority = caller_ptr->p_max_priority;
caller_ptr->p_full_quantums = QUANTUMS(caller_ptr->p_priority);
}
/* Now, return the result of the system call to the caller. */
return(result);
}
/*===========================================================================*
* mini_send *
*===========================================================================*/
PRIVATE int mini_send(caller_ptr, dst, m_ptr, flags)
register struct proc *caller_ptr; /* who is trying to send a message? */
int dst; /* to whom is message being sent? */
message *m_ptr; /* pointer to message buffer */
unsigned flags; /* system call flags */
{
/* Send a message from 'caller_ptr' to 'dst'. If 'dst' is blocked waiting
* for this message, copy the message to it and unblock 'dst'. If 'dst' is
* not waiting at all, or is waiting for another source, queue 'caller_ptr'.
*/
register struct proc *dst_ptr = proc_addr(dst);
register struct proc **xpp;
register struct proc *xp;
/* Check for deadlock by 'caller_ptr' and 'dst' sending to each other. */
xp = dst_ptr;
while (xp->p_rts_flags & SENDING) { /* check while sending */
xp = proc_addr(xp->p_sendto); /* get xp's destination */
if (xp == caller_ptr) return(ELOCKED); /* deadlock if cyclic */
}
/* Check if 'dst' is blocked waiting for this message. The destination's
* SENDING flag may be set when its SENDREC call blocked while sending.
*/
if ( (dst_ptr->p_rts_flags & (RECEIVING | SENDING)) == RECEIVING &&
(dst_ptr->p_getfrom == ANY || dst_ptr->p_getfrom == caller_ptr->p_nr)) {
/* Destination is indeed waiting for this message. */
CopyMess(caller_ptr->p_nr, caller_ptr, m_ptr, dst_ptr,
dst_ptr->p_messbuf);
if ((dst_ptr->p_rts_flags &= ~RECEIVING) == 0) ready(dst_ptr);
} else if ( ! (flags & NON_BLOCKING)) {
/* Destination is not waiting. Block and queue caller. */
caller_ptr->p_messbuf = m_ptr;
if (caller_ptr->p_rts_flags == 0) unready(caller_ptr);
caller_ptr->p_rts_flags |= SENDING;
caller_ptr->p_sendto = dst;
/* Process is now blocked. Put in on the destination's queue. */
xpp = &dst_ptr->p_caller_q; /* find end of list */
while (*xpp != NIL_PROC) xpp = &(*xpp)->p_q_link;
*xpp = caller_ptr; /* add caller to end */
caller_ptr->p_q_link = NIL_PROC; /* mark new end of list */
} else {
return(ENOTREADY);
}
return(OK);
}
/*===========================================================================*
* mini_receive *
*===========================================================================*/
PRIVATE int mini_receive(caller_ptr, src, m_ptr, flags)
register struct proc *caller_ptr; /* process trying to get message */
int src; /* which message source is wanted */
message *m_ptr; /* pointer to message buffer */
unsigned flags; /* system call flags */
{
/* A process or task wants to get a message. If a message is already queued,
* acquire it and deblock the sender. If no message from the desired source
* is available block the caller, unless the flags don't allow blocking.
*/
register struct proc **xpp;
register struct notification **ntf_q_pp;
message m;
int bit_nr;
/* Check to see if a message from desired source is already available.
* The caller's SENDING flag may be set if SENDREC couldn't send. If it is
* set, the process should be blocked.
*/
if (!(caller_ptr->p_rts_flags & SENDING)) {
/* Check caller queue. Use pointer pointers to keep code simple. */
xpp = &caller_ptr->p_caller_q;
while (*xpp != NIL_PROC) {
if (src == ANY || src == proc_nr(*xpp)) {
/* Found acceptable message. Copy it and update status. */
CopyMess((*xpp)->p_nr, *xpp, (*xpp)->p_messbuf, caller_ptr, m_ptr);
if (((*xpp)->p_rts_flags &= ~SENDING) == 0) ready(*xpp);
*xpp = (*xpp)->p_q_link; /* remove from queue */
return(OK); /* report success */
}
xpp = &(*xpp)->p_q_link; /* proceed to next */
}
/* Check if there are pending notifications, except for SENDREC. */
if (! (flags & FRESH_ANSWER)) {
ntf_q_pp = &caller_ptr->p_ntf_q; /* get pointer pointer */
while (*ntf_q_pp != NULL) {
if (src == ANY || src == (*ntf_q_pp)->n_source) {
/* Found notification. Assemble and copy message. */
BuildMess(m, *ntf_q_pp);
CopyMess((*ntf_q_pp)->n_source, proc_addr(HARDWARE), &m,
caller_ptr, m_ptr);
/* Remove notification from queue and bit map. */
bit_nr = (int) (*ntf_q_pp - &notify_buffer[0]);
*ntf_q_pp = (*ntf_q_pp)->n_next;/* remove from queue */
free_bit(bit_nr, notify_bitmap, NR_NOTIFY_BUFS);
return(OK); /* report success */
}
ntf_q_pp = &(*ntf_q_pp)->n_next; /* proceed to next */
}
}
}
/* No suitable message is available or the caller couldn't send in SENDREC.
* Block the process trying to receive, unless the flags tell otherwise.
*/
if ( ! (flags & NON_BLOCKING)) {
caller_ptr->p_getfrom = src;
caller_ptr->p_messbuf = m_ptr;
if (caller_ptr->p_rts_flags == 0) unready(caller_ptr);
caller_ptr->p_rts_flags |= RECEIVING;
return(OK);
} else {
return(ENOTREADY);
}
}
/*===========================================================================*
* mini_notify *
*===========================================================================*/
PRIVATE int mini_notify(caller_ptr, dst, m_ptr)
register struct proc *caller_ptr; /* process trying to notify */
int dst; /* which process to notify */
message *m_ptr; /* pointer to message buffer */
{
register struct proc *dst_ptr = proc_addr(dst);
register struct notification *ntf_p ;
register struct notification **ntf_q_pp;
int ntf_index;
message ntf_mess;
/* Check to see if target is blocked waiting for this message. A process
* can be both sending and receiving during a SENDREC system call.
*/
if ( (dst_ptr->p_rts_flags & (RECEIVING|SENDING)) == RECEIVING &&
(dst_ptr->p_getfrom == ANY || dst_ptr->p_getfrom == caller_ptr->p_nr)) {
/* Destination is indeed waiting for this message. */
CopyMess(proc_nr(caller_ptr), caller_ptr, m_ptr,
dst_ptr, dst_ptr->p_messbuf);
dst_ptr->p_rts_flags &= ~RECEIVING; /* deblock destination */
if (dst_ptr->p_rts_flags == 0) ready(dst_ptr);
return(OK);
}
/* Destination is not ready. Add the notification to the pending queue.
* Get pointer to notification message. Don't copy if already in kernel.
*/
if (! iskernelp(caller_ptr)) {
CopyMess(proc_nr(caller_ptr), caller_ptr, m_ptr,
proc_addr(HARDWARE), &ntf_mess);
m_ptr = &ntf_mess;
}
/* Enqueue the message. Existing notifications with the same source
* and type are overwritten with newer ones. New notifications that
* are not yet on the list are added to the end.
*/
ntf_q_pp = &dst_ptr->p_ntf_q;
while (*ntf_q_pp != NULL) {
/* Replace notifications with same source and type. */
if ((*ntf_q_pp)->n_type == m_ptr->NOTIFY_TYPE &&
(*ntf_q_pp)->n_source == proc_nr(caller_ptr)) {
(*ntf_q_pp)->n_flags = m_ptr->NOTIFY_FLAGS;
(*ntf_q_pp)->n_arg = m_ptr->NOTIFY_ARG;
return(OK);
}
ntf_q_pp = &(*ntf_q_pp)->n_next;
}
/* Add to end of queue (found above). Get a free notification buffer. */
if ((ntf_index = alloc_bit(notify_bitmap, NR_NOTIFY_BUFS)) < 0)
return(ENOSPC);
ntf_p = &notify_buffer[ntf_index]; /* get pointer to buffer */
ntf_p->n_source = proc_nr(caller_ptr);/* store notification data */
ntf_p->n_type = m_ptr->NOTIFY_TYPE;
ntf_p->n_flags = m_ptr->NOTIFY_FLAGS;
ntf_p->n_arg = m_ptr->NOTIFY_ARG;
*ntf_q_pp = ntf_p; /* add to end of queue */
ntf_p->n_next = NULL; /* mark new end of queue */
return(OK);
}
/*==========================================================================*
* lock_notify *
*==========================================================================*/
PUBLIC int lock_notify(dst, m_ptr)
int dst; /* to whom is message being sent? */
message *m_ptr; /* pointer to message buffer */
{
/* Safe gateway to mini_notify() for tasks and interrupt handlers. MINIX
* kernel is not reentrant, which means to interrupts are disabled after
* the first kernel entry (hardware interrupt, trap, or exception). Locking
* work is done by temporarily disabling interrupts.
*/
int result;
/* Exception or interrupt occurred, thus already locked. */
if (k_reenter >= 0) {
result = mini_notify(proc_addr(HARDWARE), dst, m_ptr);
}
/* Call from task level, locking is required. */
else {
lock(0, "notify");
result = mini_notify(proc_ptr, dst, m_ptr);
unlock(0);
}
return(result);
}
/*===========================================================================*
* ready *
*===========================================================================*/
PRIVATE void ready(rp)
register struct proc *rp; /* this process is now runnable */
{
/* Add 'rp' to one of the queues of runnable processes. */
register int q = rp->p_priority; /* scheduling queue to use */
#if ENABLE_K_DEBUGGING
if(rp->p_ready) {
kprintf("ready() already ready process\n", NO_NUM);
}
rp->p_ready = 1;
#endif
/* Processes, in principle, are added to the end of the queue. However,
* user processes are added in front of the queue, because this is a bit
* fairer to I/O bound processes.
*/
if (rdy_head[q] == NIL_PROC) { /* add to empty queue */
rdy_head[q] = rdy_tail[q] = rp; /* create a new queue */
rp->p_nextready = NIL_PROC; /* mark new end */
}
else if (rp->p_flags & SCHED_Q_HEAD) { /* add to head of queue */
rp->p_nextready = rdy_head[q]; /* chain head of queue */
rdy_head[q] = rp; /* set new queue head */
}
else { /* add to tail of queue */
rdy_tail[q]->p_nextready = rp; /* chain tail of queue */
rdy_tail[q] = rp; /* set new queue tail */
rp->p_nextready = NIL_PROC; /* mark new end */
}
pick_proc(); /* select next to run */
}
/*===========================================================================*
* unready *
*===========================================================================*/
PRIVATE void unready(rp)
register struct proc *rp; /* this process is no longer runnable */
{
/* A process has blocked. See ready for a description of the queues. */
register int q = rp->p_priority; /* queue to use */
register struct proc **xpp; /* iterate over queue */
register struct proc *prev_xp;
#if ENABLE_K_DEBUGGING
if(!rp->p_ready) {
kprintf("unready() already unready process\n", NO_NUM);
}
rp->p_ready = 0;
#endif
/* Side-effect for kernel: check if the task's stack still is ok? */
if (iskernelp(rp)) {
if (*rp->p_stguard != STACK_GUARD)
panic("stack overrun by task", proc_nr(rp));
}
/* Now make sure that the process is not in its ready queue. Remove the
* process if it is found. A process can be made unready even if it is not
* running by being sent a signal that kills it.
*/
prev_xp = NIL_PROC;
for (xpp = &rdy_head[q]; *xpp != NIL_PROC; xpp = &(*xpp)->p_nextready) {
if (*xpp == rp) { /* found process to remove */
*xpp = (*xpp)->p_nextready; /* replace with next chain */
if (rp == rdy_tail[q]) /* queue tail removed */
rdy_tail[q] = prev_xp; /* set new tail */
if (rp == proc_ptr || rp == next_ptr) /* active process removed */
pick_proc(); /* pick new process to run */
break;
}
prev_xp = *xpp; /* save previous in chain */
}
}
/*===========================================================================*
* sched *
*===========================================================================*/
PRIVATE void sched(sched_ptr)
struct proc *sched_ptr; /* quantum eating process */
{
int q;
/* Check if this process is preemptible, otherwise leave it as is. */
if (! (sched_ptr->p_flags & PREEMPTIBLE)) {
kprintf("Warning, sched for nonpreemptible proc %d\n", sched_ptr->p_nr);
return;
}
if (sched_ptr->p_nr == IS_PROC_NR) {
kprintf("Scheduling IS: pri: %d, ", sched_ptr->p_priority);
kprintf("qua %d", sched_ptr->p_full_quantums);
}
/* Process exceeded the maximum number of full quantums it is allowed
* to use in a row. Lower the process' priority, but make sure we don't
* end up in the IDLE queue. This helps to limit the damage caused by
* for example infinite loops in high-priority processes.
* This is a rare situation, so the overhead is acceptable.
*/
if (-- sched_ptr->p_full_quantums <= 0) { /* exceeded threshold */
if (sched_ptr->p_priority + 1 < IDLE_Q ) {
unready(sched_ptr); /* remove from queues */
sched_ptr->p_priority ++; /* lower priority */
ready(sched_ptr); /* add to new queue */
kprintf("Warning, proc %d got lower priority: ", sched_ptr->p_nr);
kprintf("%d\n", sched_ptr->p_priority);
}
sched_ptr->p_full_quantums = QUANTUMS(sched_ptr->p_priority);
}
/* The current process has run too long. If another low priority (user)
* process is runnable, put the current process on the tail of its queue,
* possibly promoting another user to head of the queue. Don't do anything
* if the queue is empty, or the process to be scheduled is not the head.
*/
q = sched_ptr->p_priority; /* convenient shorthand */
if (rdy_head[q] == sched_ptr) {
rdy_tail[q]->p_nextready = rdy_head[q]; /* add expired to end */
rdy_tail[q] = rdy_head[q]; /* set new queue tail */
rdy_head[q] = rdy_head[q]->p_nextready; /* set new queue head */
rdy_tail[q]->p_nextready = NIL_PROC; /* mark new queue end */
}
/* Give the expired process a new quantum and see who is next to run. */
sched_ptr->p_sched_ticks = sched_ptr->p_quantum_size;
pick_proc();
if (sched_ptr->p_nr == IS_PROC_NR) {
kprintf("Next proc: %d, ", next_ptr->p_nr);
kprintf("pri: %d, ", next_ptr->p_priority);
kprintf("qua: %d\n", next_ptr->p_full_quantums);
}
}
/*===========================================================================*
* pick_proc *
*===========================================================================*/
PRIVATE void pick_proc()
{
/* Decide who to run now. A new process is selected by setting 'next_ptr'.
* When a billable process is selected, record it in 'bill_ptr', so that the
* clock task can tell who to bill for system time.
*/
register struct proc *rp; /* process to run */
int q; /* iterate over queues */
/* Check each of the scheduling queues for ready processes. The number of
* queues is defined in proc.h, and priorities are set in the task table.
* The lowest queue contains IDLE, which is always ready.
*/
for (q=0; q < NR_SCHED_QUEUES; q++) {
if ( (rp = rdy_head[q]) != NIL_PROC) {
next_ptr = rp; /* run process 'rp' next */
if (rp->p_flags & BILLABLE)
bill_ptr = rp; /* bill for system time */
return;
}
}
}
/*==========================================================================*
* lock_send *
*==========================================================================*/
PUBLIC int lock_send(dst, m_ptr)
int dst; /* to whom is message being sent? */
message *m_ptr; /* pointer to message buffer */
{
/* Safe gateway to mini_send() for tasks. */
int result;
lock(2, "send");
result = mini_send(proc_ptr, dst, m_ptr, NON_BLOCKING);
unlock(2);
return(result);
}
/*==========================================================================*
* lock_ready *
*==========================================================================*/
PUBLIC void lock_ready(rp)
struct proc *rp; /* this process is now runnable */
{
/* Safe gateway to ready() for tasks. */
lock(3, "ready");
ready(rp);
unlock(3);
}
/*==========================================================================*
* lock_unready *
*==========================================================================*/
PUBLIC void lock_unready(rp)
struct proc *rp; /* this process is no longer runnable */
{
/* Safe gateway to unready() for tasks. */
lock(4, "unready");
unready(rp);
unlock(4);
}
/*==========================================================================*
* lock_sched *
*==========================================================================*/
PUBLIC void lock_sched(sched_ptr)
struct proc *sched_ptr;
{
/* Safe gateway to sched() for tasks. */
lock(5, "sched");
sched(sched_ptr);
unlock(5);
}
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