#define NEW_SCHED_Q 1 #define OLD_SEND 0 #define OLD_RECV 0 /* 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: send a notification to inform 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 so it can be run * lock_unready: remove a process from the ready queues * lock_sched: a process has run too long; schedule another one * lock_pick_proc: pick a process to run (used by system initialization) * * 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 #include #include "proc.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_rec, (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, (int queue) ); 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)) || iskernel(src_dst) && function != SENDREC) return(ECALLDENIED); /* Verify that requested source and/ or destination is a valid process. */ if (! isoksrc_dst(src_dst) && 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 flags */ #if DEAD_CODE { message m; if (caller_ptr->p_nr == MEMORY && src_dst == FS_PROC_NR) { CopyMess(caller_ptr->p_nr, caller_ptr, m_ptr, proc_addr(HARDWARE), &m); kprintf("MEMORY sendrec FS, m.m_type %d", m.m_type); kprintf("TTY_LINE %d", m.TTY_LINE); kprintf("TTY_REQ %d\n", m.TTY_REQUEST); } if (caller_ptr->p_nr == FS_PROC_NR && src_dst == MEMORY) { CopyMess(caller_ptr->p_nr, caller_ptr, m_ptr, proc_addr(HARDWARE), &m); kprintf("FS sendrec MEMORY, m.m_type %d\n", m.m_type); } } #endif /* fall through */ case SEND: if (! isalive(src_dst)) { result = EDEADDST; /* cannot send to the dead */ break; } mask_entry = isuser(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; } 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_rec(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 */ } /* 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; #if OLD_SEND register struct proc *next_ptr; register struct proc *xp; #else register struct proc **xpp; #endif dst_ptr = proc_addr(dst); /* pointer to destination's proc entry */ /* Check for deadlock by 'caller_ptr' and 'dst' sending to each other. */ if (dst_ptr->p_flags & SENDING) { next_ptr = proc_addr(dst_ptr->p_sendto); while (TRUE) { if (next_ptr == caller_ptr) return(ELOCKED); if (next_ptr->p_flags & SENDING) next_ptr = proc_addr(next_ptr->p_sendto); else break; } } /* 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_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_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_flags == 0) unready(caller_ptr); caller_ptr->p_flags |= SENDING; caller_ptr->p_sendto = dst; /* Process is now blocked. Put in on the destination's queue. */ #if OLD_SEND if ( (next_ptr = dst_ptr->p_caller_q) == NIL_PROC) dst_ptr->p_caller_q = caller_ptr; else { while (next_ptr->p_q_link != NIL_PROC) next_ptr = next_ptr->p_q_link; next_ptr->p_q_link = caller_ptr; } #else 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 */ #endif caller_ptr->p_q_link = NIL_PROC; /* mark new end of list */ } else { return(ENOTREADY); } return(OK); } /*===========================================================================* * mini_rec * *===========================================================================*/ PRIVATE int mini_rec(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. */ #if OLD_RECV register struct proc *sender_ptr; register struct proc *previous_ptr; #else register struct proc **xpp; #endif 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_flags & SENDING)) { /* Check caller queue. Use pointer pointers to keep code simple. */ #if OLD_RECV /* to hairy, unreadable */ for (sender_ptr = caller_ptr->p_caller_q; sender_ptr != NIL_PROC; previous_ptr = sender_ptr, sender_ptr = sender_ptr->p_q_link) { if (src == ANY || src == proc_nr(sender_ptr)) { /* An acceptable message has been found. */ CopyMess(sender_ptr->p_nr, sender_ptr, sender_ptr->p_messbuf, caller_ptr, m_ptr); if (sender_ptr == caller_ptr->p_caller_q) caller_ptr->p_caller_q = sender_ptr->p_q_link; else previous_ptr->p_q_link = sender_ptr->p_q_link; if ((sender_ptr->p_flags &= ~SENDING) == 0) ready(sender_ptr); /* deblock sender */ return(OK); } } #else 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_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 */ } #endif /* 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 - ¬ify_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_flags == 0) unready(caller_ptr); caller_ptr->p_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_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_flags &= ~RECEIVING; /* deblock destination */ if (dst_ptr->p_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 = ¬ify_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. This * function checks if it is called from an interrupt handler and ensures * that the correct message source is put on the notification. */ int result; struct proc *caller_ptr; lock(0, "notify"); caller_ptr = (k_reenter >= 0) ? proc_addr(HARDWARE) : proc_ptr; result = mini_notify(caller_ptr, dst, m_ptr); unlock(0); return(result); } /*===========================================================================* * pick_proc * *===========================================================================*/ PRIVATE void pick_proc() { /* Decide who to run now. A new process is selected by setting 'next_ptr'. * When a fresh user (or idle) process is selected, record it in 'bill_ptr', * so 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 (isuserp(rp) || isidlep(rp)) /* possible bill 'rp' */ bill_ptr = rp; return; } } } /*===========================================================================* * 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 */ register struct proc **xpp; /* iterate over queue */ #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 NEW_SCHED_Q if (isuserp(rp)) { /* add to front of queue */ rp->p_nextready = rdy_head[q]; /* chain current front */ rdy_head[q] = rp; /* rp becomes new front */ } else { /* add to end of queue */ xpp = &rdy_head[q]; /* find pointer to end */ while (*xpp != NIL_PROC) xpp = &(*xpp)->p_nextready; *xpp = rp; /* replace end with rp */ rp->p_nextready = NIL_PROC; /* mark end of queue */ } #else if (isuserp(rp)) { /* add to front of queue */ if (rdy_head[q] == NIL_PROC) rdy_tail[q] = rp; rp->p_nextready = rdy_head[q]; /* add to front of queue */ rdy_head[q] = rp; } else { if (rdy_head[q] != NIL_PROC) rdy_tail[q]->p_nextready = rp; /* add to end of queue */ else rdy_head[q] = rp; /* add to empty queue */ rdy_tail[q] = rp; rp->p_nextready = NIL_PROC; } #endif /* Run 'rp' next if it has a higher priority than 'proc_ptr' or 'next_ptr'. * This actually should be done via pick_proc(), but the message passing * functions rely on this side-effect. High priorities have a lower number. */ if (next_ptr && next_ptr->p_priority > rp->p_priority) next_ptr = rp; else if (proc_ptr->p_priority > rp->p_priority) next_ptr = rp; } /*===========================================================================* * 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 */ #if NEW_SCHED_Q register struct proc **xpp; /* iterate over queue */ #else register struct proc **qtail; /* queue's rdy_tail */ register struct proc *xp; #endif #if ENABLE_K_DEBUGGING if(!rp->p_ready) { kprintf("unready() already unready process\n", NO_NUM); } rp->p_ready = 0; #endif /* Side-effect for tasks: check if the task's stack still is ok? */ if (istaskp(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. */ #if NEW_SCHED_Q xpp = &rdy_head[q]; while (*xpp != NIL_PROC) { /* check entire queue */ if (*xpp == rp) { /* lookup unready process */ *xpp = (*xpp)->p_nextready; /* replace it with next */ if (rp == proc_ptr || rp == next_ptr) /* current process removed */ pick_proc(); /* pick new process to run */ break; } xpp = &(*xpp)->p_nextready; /* proceed to next */ } #else if ( (xp = rdy_head[q]) != NIL_PROC) { /* ready queue is empty */ if (xp == rp) { /* check head of queue */ rdy_head[q] = xp->p_nextready; /* new head of queue */ if (rp == proc_ptr || rp == next_ptr) /* current process removed */ pick_proc(); /* pick new process to run */ if(rp == rdy_tail[q]) rdy_tail[q] = NIL_PROC; } else { /* check body of queue */ while (xp->p_nextready != rp) /* stop if process is next */ if ( (xp = xp->p_nextready) == NIL_PROC) return; xp->p_nextready = xp->p_nextready->p_nextready; if (rdy_tail[q] == rp) /* possibly update tail */ rdy_tail[q] = xp; } } #endif } /*===========================================================================* * sched * *===========================================================================*/ PRIVATE void sched(queue) int queue; { /* The current process has run too long. If another low priority (user) * process is runnable, put the current process on the end of the user queue, * possibly promoting another user to head of the queue. */ register struct proc **xpp; register struct proc *xp; if (rdy_head[queue] == NIL_PROC) return; /* One or more user processes queued. */ #if NEW_SCHED_Q xp = rdy_head[queue]; /* save expired process */ rdy_head[queue] = xp->p_nextready; /* advance to next process */ xpp = &rdy_head[queue]; /* find end of queue */ while (*xpp != NIL_PROC) xpp = &(*xpp)->p_nextready; *xpp = xp; /* add expired to end */ xp->p_nextready = NIL_PROC; /* mark new end of queue */ #else rdy_tail[queue]->p_nextready = rdy_head[queue]; rdy_tail[queue] = rdy_head[queue]; rdy_head[queue] = rdy_head[queue]->p_nextready; rdy_tail[queue]->p_nextready = NIL_PROC; #endif pick_proc(); } /*==========================================================================* * lock_pick_proc * *==========================================================================*/ PUBLIC void lock_pick_proc() { /* Safe gateway to pick_proc() for tasks. */ lock(1, "pick_proc"); pick_proc(); unlock(1); } /*==========================================================================* * 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(queue) int queue; { /* Safe gateway to sched() for tasks. */ lock(5, "sched"); sched(queue); unlock(5); }