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[minix3.git] / minix / kernel / proc.c

/* 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
 *
 * Changes:
 *   Aug 19, 2005     rewrote scheduling code  (Jorrit N. Herder)
 *   Jul 25, 2005     rewrote system call handling  (Jorrit N. Herder)
 *   May 26, 2005     rewrote message passing functions  (Jorrit N. Herder)
 *   May 24, 2005     new notification system call  (Jorrit N. Herder)
 *   Oct 28, 2004     nonblocking send and receive calls  (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 <stddef.h>
#include <signal.h>
#include <assert.h>
#include <string.h>

#include "vm.h"
#include "clock.h"
#include "spinlock.h"
#include "arch_proto.h"

#include <minix/syslib.h>

/* Scheduling and message passing functions */
static void idle(void);
/**
 * Made public for use in clock.c (for user-space scheduling)
static int mini_send(struct proc *caller_ptr, endpoint_t dst_e, message
        *m_ptr, int flags);
*/
static int mini_receive(struct proc *caller_ptr, endpoint_t src,
        message *m_buff_usr, int flags);
static int mini_senda(struct proc *caller_ptr, asynmsg_t *table, size_t
        size);
static int deadlock(int function, register struct proc *caller,
        endpoint_t src_dst_e);
static int try_async(struct proc *caller_ptr);
static int try_one(endpoint_t receive_e, struct proc *src_ptr,
        struct proc *dst_ptr);
static struct proc * pick_proc(void);
static void enqueue_head(struct proc *rp);

/* all idles share the same idle_priv structure */
static struct priv idle_priv;

static void set_idle_name(char * name, int n)
{
        int i, c;
        int p_z = 0;

        if (n > 999) 
                n = 999; 

        name[0] = 'i'; 
        name[1] = 'd'; 
        name[2] = 'l'; 
        name[3] = 'e'; 

        for (i = 4, c = 100; c > 0; c /= 10) {
                int digit;

                digit = n / c;  
                n -= digit * c;  

                if (p_z || digit != 0 || c == 1) {
                        p_z = 1;
                        name[i++] = '0' + digit;
                }   
        }    

        name[i] = '\0';

}


#define PICK_ANY        1
#define PICK_HIGHERONLY 2

#define BuildNotifyMessage(m_ptr, src, dst_ptr) \
        memset((m_ptr), 0, sizeof(*(m_ptr)));                           \
        (m_ptr)->m_type = NOTIFY_MESSAGE;                               \
        (m_ptr)->m_notify.timestamp = get_monotonic();          \
        switch (src) {                                                  \
        case HARDWARE:                                                  \
                (m_ptr)->m_notify.interrupts =                  \
                        priv(dst_ptr)->s_int_pending;                   \
                priv(dst_ptr)->s_int_pending = 0;                       \
                break;                                                  \
        case SYSTEM:                                                    \
                memcpy(&(m_ptr)->m_notify.sigset,                       \
                        &priv(dst_ptr)->s_sig_pending,                  \
                        sizeof(sigset_t));                              \
                sigemptyset(&priv(dst_ptr)->s_sig_pending);             \
                break;                                                  \
        }

static message m_notify_buff = { 0, NOTIFY_MESSAGE };

void proc_init(void)
{
        struct proc * rp;
        struct priv *sp;
        int i;

        /* Clear the process table. Announce each slot as empty and set up
         * mappings for proc_addr() and proc_nr() macros. Do the same for the
         * table with privilege structures for the system processes. 
         */
        for (rp = BEG_PROC_ADDR, i = -NR_TASKS; rp < END_PROC_ADDR; ++rp, ++i) {
                rp->p_rts_flags = RTS_SLOT_FREE;/* initialize free slot */
                rp->p_magic = PMAGIC;
                rp->p_nr = i;                   /* proc number from ptr */
                rp->p_endpoint = _ENDPOINT(0, rp->p_nr); /* generation no. 0 */
                rp->p_scheduler = NULL;         /* no user space scheduler */
                rp->p_priority = 0;             /* no priority */
                rp->p_quantum_size_ms = 0;      /* no quantum size */

                /* arch-specific initialization */
                arch_proc_reset(rp);
        }
        for (sp = BEG_PRIV_ADDR, i = 0; sp < END_PRIV_ADDR; ++sp, ++i) {
                sp->s_proc_nr = NONE;           /* initialize as free */
                sp->s_id = (sys_id_t) i;        /* priv structure index */
                ppriv_addr[i] = sp;             /* priv ptr from number */
                sp->s_sig_mgr = NONE;           /* clear signal managers */
                sp->s_bak_sig_mgr = NONE;
        }

        idle_priv.s_flags = IDL_F;
        /* initialize IDLE structures for every CPU */
        for (i = 0; i < CONFIG_MAX_CPUS; i++) {
                struct proc * ip = get_cpu_var_ptr(i, idle_proc);
                ip->p_endpoint = IDLE;
                ip->p_priv = &idle_priv;
                /* must not let idle ever get scheduled */
                ip->p_rts_flags |= RTS_PROC_STOP;
                set_idle_name(ip->p_name, i);
        }
}

static void switch_address_space_idle(void)
{
#ifdef CONFIG_SMP
        /*
         * currently we bet that VM is always alive and its pages available so
         * when the CPU wakes up the kernel is mapped and no surprises happen.
         * This is only a problem if more than 1 cpus are available
         */
        switch_address_space(proc_addr(VM_PROC_NR));
#endif
}

/*===========================================================================*
 *                              idle                                         * 
 *===========================================================================*/
static void idle(void)
{
        struct proc * p;

        /* This function is called whenever there is no work to do.
         * Halt the CPU, and measure how many timestamp counter ticks are
         * spent not doing anything. This allows test setups to measure
         * the CPU utilization of certain workloads with high precision.
         */

        p = get_cpulocal_var(proc_ptr) = get_cpulocal_var_ptr(idle_proc);
        if (priv(p)->s_flags & BILLABLE)
                get_cpulocal_var(bill_ptr) = p;

        switch_address_space_idle();

#ifdef CONFIG_SMP
        get_cpulocal_var(cpu_is_idle) = 1;
        /* we don't need to keep time on APs as it is handled on the BSP */
        if (cpuid != bsp_cpu_id)
                stop_local_timer();
        else
#endif
        {
                /*
                 * If the timer has expired while in kernel we must
                 * rearm it before we go to sleep
                 */
                restart_local_timer();
        }

        /* start accounting for the idle time */
        context_stop(proc_addr(KERNEL));
#if !SPROFILE
        halt_cpu();
#else
        if (!sprofiling)
                halt_cpu();
        else {
                volatile int * v;

                v = get_cpulocal_var_ptr(idle_interrupted);
                interrupts_enable();
                while (!*v)
                        arch_pause();
                interrupts_disable();
                *v = 0;
        }
#endif
        /*
         * end of accounting for the idle task does not happen here, the kernel
         * is handling stuff for quite a while before it gets back here!
         */
}

/*===========================================================================*
 *                              vm_suspend                                *
 *===========================================================================*/
void vm_suspend(struct proc *caller, const struct proc *target,
        const vir_bytes linaddr, const vir_bytes len, const int type,
        const int writeflag)
{
        /* This range is not OK for this process. Set parameters
         * of the request and notify VM about the pending request.
         */
        assert(!RTS_ISSET(caller, RTS_VMREQUEST));
        assert(!RTS_ISSET(target, RTS_VMREQUEST));

        RTS_SET(caller, RTS_VMREQUEST);

        caller->p_vmrequest.req_type = VMPTYPE_CHECK;
        caller->p_vmrequest.target = target->p_endpoint;
        caller->p_vmrequest.params.check.start = linaddr;
        caller->p_vmrequest.params.check.length = len;
        caller->p_vmrequest.params.check.writeflag = writeflag;
        caller->p_vmrequest.type = type;

        /* Connect caller on vmrequest wait queue. */
        if(!(caller->p_vmrequest.nextrequestor = vmrequest))
                if(OK != send_sig(VM_PROC_NR, SIGKMEM))
                        panic("send_sig failed");
        vmrequest = caller;
}

/*===========================================================================*
 *                              delivermsg                                *
 *===========================================================================*/
static void delivermsg(struct proc *rp)
{
        assert(!RTS_ISSET(rp, RTS_VMREQUEST));
        assert(rp->p_misc_flags & MF_DELIVERMSG);
        assert(rp->p_delivermsg.m_source != NONE);

        if (copy_msg_to_user(&rp->p_delivermsg,
                                (message *) rp->p_delivermsg_vir)) {
                if(rp->p_misc_flags & MF_MSGFAILED) {
                        /* 2nd consecutive failure means this won't succeed */
                        printf("WARNING wrong user pointer 0x%08lx from "
                                "process %s / %d\n",
                                rp->p_delivermsg_vir,
                                rp->p_name,
                                rp->p_endpoint);
                        cause_sig(rp->p_nr, SIGSEGV);
                } else {
                        /* 1st failure means we have to ask VM to handle it */
                        vm_suspend(rp, rp, rp->p_delivermsg_vir,
                                sizeof(message), VMSTYPE_DELIVERMSG, 1);
                        rp->p_misc_flags |= MF_MSGFAILED;
                }
        } else {
                /* Indicate message has been delivered; address is 'used'. */
                rp->p_delivermsg.m_source = NONE;
                rp->p_misc_flags &= ~(MF_DELIVERMSG|MF_MSGFAILED);

                if(!(rp->p_misc_flags & MF_CONTEXT_SET)) {
                        rp->p_reg.retreg = OK;
                }
        }
}

/*===========================================================================*
 *                              switch_to_user                               * 
 *===========================================================================*/
void switch_to_user(void)
{
        /* This function is called an instant before proc_ptr is
         * to be scheduled again.
         */
        struct proc * p;
#ifdef CONFIG_SMP
        int tlb_must_refresh = 0;
#endif

        p = get_cpulocal_var(proc_ptr);
        /*
         * if the current process is still runnable check the misc flags and let
         * it run unless it becomes not runnable in the meantime
         */
        if (proc_is_runnable(p))
                goto check_misc_flags;
        /*
         * if a process becomes not runnable while handling the misc flags, we
         * need to pick a new one here and start from scratch. Also if the
         * current process wasn't runnable, we pick a new one here
         */
not_runnable_pick_new:
        if (proc_is_preempted(p)) {
                p->p_rts_flags &= ~RTS_PREEMPTED;
                if (proc_is_runnable(p)) {
                        if (p->p_cpu_time_left)
                                enqueue_head(p);
                        else
                                enqueue(p);
                }
        }

        /*
         * if we have no process to run, set IDLE as the current process for
         * time accounting and put the cpu in an idle state. After the next
         * timer interrupt the execution resumes here and we can pick another
         * process. If there is still nothing runnable we "schedule" IDLE again
         */
        while (!(p = pick_proc())) {
                idle();
        }

        /* update the global variable */
        get_cpulocal_var(proc_ptr) = p;

#ifdef CONFIG_SMP
        if (p->p_misc_flags & MF_FLUSH_TLB && get_cpulocal_var(ptproc) == p)
                tlb_must_refresh = 1;
#endif
        switch_address_space(p);

check_misc_flags:

        assert(p);
        assert(proc_is_runnable(p));
        while (p->p_misc_flags &
                (MF_KCALL_RESUME | MF_DELIVERMSG |
                 MF_SC_DEFER | MF_SC_TRACE | MF_SC_ACTIVE)) {

                assert(proc_is_runnable(p));
                if (p->p_misc_flags & MF_KCALL_RESUME) {
                        kernel_call_resume(p);
                }
                else if (p->p_misc_flags & MF_DELIVERMSG) {
                        TRACE(VF_SCHEDULING, printf("delivering to %s / %d\n",
                                p->p_name, p->p_endpoint););
                        delivermsg(p);
                }
                else if (p->p_misc_flags & MF_SC_DEFER) {
                        /* Perform the system call that we deferred earlier. */

                        assert (!(p->p_misc_flags & MF_SC_ACTIVE));

                        arch_do_syscall(p);

                        /* If the process is stopped for signal delivery, and
                         * not blocked sending a message after the system call,
                         * inform PM.
                         */
                        if ((p->p_misc_flags & MF_SIG_DELAY) &&
                                        !RTS_ISSET(p, RTS_SENDING))
                                sig_delay_done(p);
                }
                else if (p->p_misc_flags & MF_SC_TRACE) {
                        /* Trigger a system call leave event if this was a
                         * system call. We must do this after processing the
                         * other flags above, both for tracing correctness and
                         * to be able to use 'break'.
                         */
                        if (!(p->p_misc_flags & MF_SC_ACTIVE))
                                break;

                        p->p_misc_flags &=
                                ~(MF_SC_TRACE | MF_SC_ACTIVE);

                        /* Signal the "leave system call" event.
                         * Block the process.
                         */
                        cause_sig(proc_nr(p), SIGTRAP);
                }
                else if (p->p_misc_flags & MF_SC_ACTIVE) {
                        /* If MF_SC_ACTIVE was set, remove it now:
                         * we're leaving the system call.
                         */
                        p->p_misc_flags &= ~MF_SC_ACTIVE;

                        break;
                }

                /*
                 * the selected process might not be runnable anymore. We have
                 * to checkit and schedule another one
                 */
                if (!proc_is_runnable(p))
                        goto not_runnable_pick_new;
        }
        /*
         * check the quantum left before it runs again. We must do it only here
         * as we are sure that a possible out-of-quantum message to the
         * scheduler will not collide with the regular ipc
         */
        if (!p->p_cpu_time_left)
                proc_no_time(p);
        /*
         * After handling the misc flags the selected process might not be
         * runnable anymore. We have to checkit and schedule another one
         */
        if (!proc_is_runnable(p))
                goto not_runnable_pick_new;

        TRACE(VF_SCHEDULING, printf("cpu %d starting %s / %d "
                                "pc 0x%08x\n",
                cpuid, p->p_name, p->p_endpoint, p->p_reg.pc););
#if DEBUG_TRACE
        p->p_schedules++;
#endif

        p = arch_finish_switch_to_user();
        assert(p->p_cpu_time_left);

        context_stop(proc_addr(KERNEL));

        /* If the process isn't the owner of FPU, enable the FPU exception */
        if (get_cpulocal_var(fpu_owner) != p)
                enable_fpu_exception();
        else
                disable_fpu_exception();

        /* If MF_CONTEXT_SET is set, don't clobber process state within
         * the kernel. The next kernel entry is OK again though.
         */
        p->p_misc_flags &= ~MF_CONTEXT_SET;

#if defined(__i386__)
        assert(p->p_seg.p_cr3 != 0);
#elif defined(__arm__)
        assert(p->p_seg.p_ttbr != 0);
#endif
#ifdef CONFIG_SMP
        if (p->p_misc_flags & MF_FLUSH_TLB) {
                if (tlb_must_refresh)
                        refresh_tlb();
                p->p_misc_flags &= ~MF_FLUSH_TLB;
        }
#endif
        
        restart_local_timer();
        
        /*
         * restore_user_context() carries out the actual mode switch from kernel
         * to userspace. This function does not return
         */
        restore_user_context(p);
        NOT_REACHABLE;
}

/*
 * handler for all synchronous IPC calls
 */
static int do_sync_ipc(struct proc * caller_ptr, /* who made the call */
                        int call_nr,    /* system call number and flags */
                        endpoint_t src_dst_e,   /* src or dst of the call */
                        message *m_ptr) /* users pointer to a message */
{
  int result;                                   /* the system call's result */
  int src_dst_p;                                /* Process slot number */
  char *callname;

  /* Check destination. RECEIVE is the only call that accepts ANY (in addition
   * to a real endpoint). The other calls (SEND, SENDREC, and NOTIFY) require an
   * endpoint to corresponds to a process. In addition, it is necessary to check
   * whether a process is allowed to send to a given destination.
   */
  assert(call_nr != SENDA);

  /* Only allow non-negative call_nr values less than 32 */
  if (call_nr < 0 || call_nr > IPCNO_HIGHEST || call_nr >= 32
      || !(callname = ipc_call_names[call_nr])) {
#if DEBUG_ENABLE_IPC_WARNINGS
      printf("sys_call: trap %d not allowed, caller %d, src_dst %d\n", 
          call_nr, proc_nr(caller_ptr), src_dst_e);
#endif
        return(ETRAPDENIED);            /* trap denied by mask or kernel */
  }

  if (src_dst_e == ANY)
  {
        if (call_nr != RECEIVE)
        {
#if 0
                printf("sys_call: %s by %d with bad endpoint %d\n", 
                        callname,
                        proc_nr(caller_ptr), src_dst_e);
#endif
                return EINVAL;
        }
        src_dst_p = (int) src_dst_e;
  }
  else
  {
        /* Require a valid source and/or destination process. */
        if(!isokendpt(src_dst_e, &src_dst_p)) {
#if 0
                printf("sys_call: %s by %d with bad endpoint %d\n", 
                        callname,
                        proc_nr(caller_ptr), src_dst_e);
#endif
                return EDEADSRCDST;
        }

        /* If the call is to send to a process, i.e., for SEND, SENDNB,
         * SENDREC or NOTIFY, verify that the caller is allowed to send to
         * the given destination. 
         */
        if (call_nr != RECEIVE)
        {
                if (!may_send_to(caller_ptr, src_dst_p)) {
#if DEBUG_ENABLE_IPC_WARNINGS
                        printf(
                        "sys_call: ipc mask denied %s from %d to %d\n",
                                callname,
                                caller_ptr->p_endpoint, src_dst_e);
#endif
                        return(ECALLDENIED);    /* call denied by ipc mask */
                }
        }
  }

  /* 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 (!(priv(caller_ptr)->s_trap_mask & (1 << call_nr))) {
#if DEBUG_ENABLE_IPC_WARNINGS
      printf("sys_call: %s not allowed, caller %d, src_dst %d\n", 
          callname, proc_nr(caller_ptr), src_dst_p);
#endif
        return(ETRAPDENIED);            /* trap denied by mask or kernel */
  }

  if (call_nr != SENDREC && call_nr != RECEIVE && iskerneln(src_dst_p)) {
#if DEBUG_ENABLE_IPC_WARNINGS
      printf("sys_call: trap %s not allowed, caller %d, src_dst %d\n",
           callname, proc_nr(caller_ptr), src_dst_e);
#endif
        return(ETRAPDENIED);            /* trap denied by mask or kernel */
  }

  switch(call_nr) {
  case SENDREC:
        /* A flag is set so that notifications cannot interrupt SENDREC. */
        caller_ptr->p_misc_flags |= MF_REPLY_PEND;
        /* fall through */
  case SEND:                    
        result = mini_send(caller_ptr, src_dst_e, m_ptr, 0);
        if (call_nr == SEND || result != OK)
                break;                          /* done, or SEND failed */
        /* fall through for SENDREC */
  case RECEIVE:                 
        if (call_nr == RECEIVE) {
                caller_ptr->p_misc_flags &= ~MF_REPLY_PEND;
                IPC_STATUS_CLEAR(caller_ptr);  /* clear IPC status code */
        }
        result = mini_receive(caller_ptr, src_dst_e, m_ptr, 0);
        break;
  case NOTIFY:
        result = mini_notify(caller_ptr, src_dst_e);
        break;
  case SENDNB:
        result = mini_send(caller_ptr, src_dst_e, m_ptr, NON_BLOCKING);
        break;
  default:
        result = EBADCALL;                      /* illegal system call */
  }

  /* Now, return the result of the system call to the caller. */
  return(result);
}

int do_ipc(reg_t r1, reg_t r2, reg_t r3)
{
  struct proc *const caller_ptr = get_cpulocal_var(proc_ptr);   /* get pointer to caller */
  int call_nr = (int) r1;

  assert(!RTS_ISSET(caller_ptr, RTS_SLOT_FREE));

  /* bill kernel time to this process. */
  kbill_ipc = caller_ptr;

  /* If this process is subject to system call tracing, handle that first. */
  if (caller_ptr->p_misc_flags & (MF_SC_TRACE | MF_SC_DEFER)) {
        /* Are we tracing this process, and is it the first sys_call entry? */
        if ((caller_ptr->p_misc_flags & (MF_SC_TRACE | MF_SC_DEFER)) ==
                                                        MF_SC_TRACE) {
                /* We must notify the tracer before processing the actual
                 * system call. If we don't, the tracer could not obtain the
                 * input message. Postpone the entire system call.
                 */
                caller_ptr->p_misc_flags &= ~MF_SC_TRACE;
                assert(!(caller_ptr->p_misc_flags & MF_SC_DEFER));
                caller_ptr->p_misc_flags |= MF_SC_DEFER;
                caller_ptr->p_defer.r1 = r1;
                caller_ptr->p_defer.r2 = r2;
                caller_ptr->p_defer.r3 = r3;

                /* Signal the "enter system call" event. Block the process. */
                cause_sig(proc_nr(caller_ptr), SIGTRAP);

                /* Preserve the return register's value. */
                return caller_ptr->p_reg.retreg;
        }

        /* If the MF_SC_DEFER flag is set, the syscall is now being resumed. */
        caller_ptr->p_misc_flags &= ~MF_SC_DEFER;

        assert (!(caller_ptr->p_misc_flags & MF_SC_ACTIVE));

        /* Set a flag to allow reliable tracing of leaving the system call. */
        caller_ptr->p_misc_flags |= MF_SC_ACTIVE;
  }

  if(caller_ptr->p_misc_flags & MF_DELIVERMSG) {
        panic("sys_call: MF_DELIVERMSG on for %s / %d\n",
                caller_ptr->p_name, caller_ptr->p_endpoint);
  }

  /* 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:  asynchronous call; deliver notification or mark pending
   *   - SENDA:   list of asynchronous send requests
   */
  switch(call_nr) {
        case SENDREC:
        case SEND:                      
        case RECEIVE:                   
        case NOTIFY:
        case SENDNB:
        {
            /* Process accounting for scheduling */
            caller_ptr->p_accounting.ipc_sync++;

            return do_sync_ipc(caller_ptr, call_nr, (endpoint_t) r2,
                            (message *) r3);
        }
        case SENDA:
        {
            /*
             * Get and check the size of the argument in bytes as it is a
             * table
             */
            size_t msg_size = (size_t) r2;
  
            /* Process accounting for scheduling */
            caller_ptr->p_accounting.ipc_async++;
 
            /* Limit size to something reasonable. An arbitrary choice is 16
             * times the number of process table entries.
             */
            if (msg_size > 16*(NR_TASKS + NR_PROCS))
                return EDOM;
            return mini_senda(caller_ptr, (asynmsg_t *) r3, msg_size);
        }
        case MINIX_KERNINFO:
        {
                /* It might not be initialized yet. */
                if(!minix_kerninfo_user) {
                        return EBADCALL;
                }

                arch_set_secondary_ipc_return(caller_ptr, minix_kerninfo_user);
                return OK;
        }
        default:
        return EBADCALL;                /* illegal system call */
  }
}

/*===========================================================================*
 *                              deadlock                                     * 
 *===========================================================================*/
static int deadlock(
  int function,                         /* trap number */
  register struct proc *cp,             /* pointer to caller */
  endpoint_t src_dst_e                  /* src or dst process */
)
{
/* Check for deadlock. This can happen if 'caller_ptr' and 'src_dst' have
 * a cyclic dependency of blocking send and receive calls. The only cyclic 
 * dependency that is not fatal is if the caller and target directly SEND(REC)
 * and RECEIVE to each other. If a deadlock is found, the group size is 
 * returned. Otherwise zero is returned. 
 */
  register struct proc *xp;                     /* process pointer */
  int group_size = 1;                           /* start with only caller */
#if DEBUG_ENABLE_IPC_WARNINGS
  static struct proc *processes[NR_PROCS + NR_TASKS];
  processes[0] = cp;
#endif

  while (src_dst_e != ANY) {                    /* check while process nr */
      int src_dst_slot;
      okendpt(src_dst_e, &src_dst_slot);
      xp = proc_addr(src_dst_slot);             /* follow chain of processes */
      assert(proc_ptr_ok(xp));
      assert(!RTS_ISSET(xp, RTS_SLOT_FREE));
#if DEBUG_ENABLE_IPC_WARNINGS
      processes[group_size] = xp;
#endif
      group_size ++;                            /* extra process in group */

      /* Check whether the last process in the chain has a dependency. If it 
       * has not, the cycle cannot be closed and we are done.
       */
      if((src_dst_e = P_BLOCKEDON(xp)) == NONE)
        return 0;

      /* Now check if there is a cyclic dependency. For group sizes of two,  
       * a combination of SEND(REC) and RECEIVE is not fatal. Larger groups
       * or other combinations indicate a deadlock.  
       */
      if (src_dst_e == cp->p_endpoint) {        /* possible deadlock */
          if (group_size == 2) {                /* caller and src_dst */
              /* The function number is magically converted to flags. */
              if ((xp->p_rts_flags ^ (function << 2)) & RTS_SENDING) { 
                  return(0);                    /* not a deadlock */
              }
          }
#if DEBUG_ENABLE_IPC_WARNINGS
          {
                int i;
                printf("deadlock between these processes:\n");
                for(i = 0; i < group_size; i++) {
                        printf(" %10s ", processes[i]->p_name);
                }
                printf("\n\n");
                for(i = 0; i < group_size; i++) {
                        print_proc(processes[i]);
                        proc_stacktrace(processes[i]);
                }
          }
#endif
          return(group_size);                   /* deadlock found */
      }
  }
  return(0);                                    /* not a deadlock */
}

/*===========================================================================*
 *                              has_pending                                  * 
 *===========================================================================*/
static int has_pending(sys_map_t *map, int src_p, int asynm)
{
/* Check to see if there is a pending message from the desired source
 * available.
 */

  int src_id;
  sys_id_t id = NULL_PRIV_ID;
#ifdef CONFIG_SMP
  struct proc * p;
#endif

  /* Either check a specific bit in the mask map, or find the first bit set in
   * it (if any), depending on whether the receive was called on a specific
   * source endpoint.
   */
  if (src_p != ANY) {
        src_id = nr_to_id(src_p);
        if (get_sys_bit(*map, src_id)) {
#ifdef CONFIG_SMP
                p = proc_addr(id_to_nr(src_id));
                if (asynm && RTS_ISSET(p, RTS_VMINHIBIT))
                        p->p_misc_flags |= MF_SENDA_VM_MISS;
                else
#endif
                        id = src_id;
        }
  } else {
        /* Find a source with a pending message */
        for (src_id = 0; src_id < NR_SYS_PROCS; src_id += BITCHUNK_BITS) {
                if (get_sys_bits(*map, src_id) != 0) {
#ifdef CONFIG_SMP
                        while (src_id < NR_SYS_PROCS) {
                                while (!get_sys_bit(*map, src_id)) {
                                        if (src_id == NR_SYS_PROCS)
                                                goto quit_search;
                                        src_id++;
                                }
                                p = proc_addr(id_to_nr(src_id));
                                /*
                                 * We must not let kernel fiddle with pages of a
                                 * process which are currently being changed by
                                 * VM.  It is dangerous! So do not report such a
                                 * process as having pending async messages.
                                 * Skip it.
                                 */
                                if (asynm && RTS_ISSET(p, RTS_VMINHIBIT)) {
                                        p->p_misc_flags |= MF_SENDA_VM_MISS;
                                        src_id++;
                                } else
                                        goto quit_search;
                        }
#else
                        while (!get_sys_bit(*map, src_id)) src_id++;
                        goto quit_search;
#endif
                }
        }

quit_search:
        if (src_id < NR_SYS_PROCS)      /* Found one */
                id = src_id;
  }

  return(id);
}

/*===========================================================================*
 *                              has_pending_notify                           *
 *===========================================================================*/
int has_pending_notify(struct proc * caller, int src_p)
{
        sys_map_t * map = &priv(caller)->s_notify_pending;
        return has_pending(map, src_p, 0);
}

/*===========================================================================*
 *                              has_pending_asend                            *
 *===========================================================================*/
int has_pending_asend(struct proc * caller, int src_p)
{
        sys_map_t * map = &priv(caller)->s_asyn_pending;
        return has_pending(map, src_p, 1);
}

/*===========================================================================*
 *                              unset_notify_pending                         *
 *===========================================================================*/
void unset_notify_pending(struct proc * caller, int src_p)
{
        sys_map_t * map = &priv(caller)->s_notify_pending;
        unset_sys_bit(*map, src_p);
}

/*===========================================================================*
 *                              mini_send                                    * 
 *===========================================================================*/
int mini_send(
  register struct proc *caller_ptr,     /* who is trying to send a message? */
  endpoint_t dst_e,                     /* to whom is message being sent? */
  message *m_ptr,                       /* pointer to message buffer */
  const int 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;
  register struct proc **xpp;
  int dst_p;
  dst_p = _ENDPOINT_P(dst_e);
  dst_ptr = proc_addr(dst_p);

  if (RTS_ISSET(dst_ptr, RTS_NO_ENDPOINT))
  {
        return EDEADSRCDST;
  }

  /* Check if 'dst' is blocked waiting for this message. The destination's 
   * RTS_SENDING flag may be set when its SENDREC call blocked while sending.  
   */
  if (WILLRECEIVE(caller_ptr->p_endpoint, dst_ptr, (vir_bytes)m_ptr, NULL)) {
        int call;
        /* Destination is indeed waiting for this message. */
        assert(!(dst_ptr->p_misc_flags & MF_DELIVERMSG));       

        if (!(flags & FROM_KERNEL)) {
                if(copy_msg_from_user(m_ptr, &dst_ptr->p_delivermsg))
                        return EFAULT;
        } else {
                dst_ptr->p_delivermsg = *m_ptr;
                IPC_STATUS_ADD_FLAGS(dst_ptr, IPC_FLG_MSG_FROM_KERNEL);
        }

        dst_ptr->p_delivermsg.m_source = caller_ptr->p_endpoint;
        dst_ptr->p_misc_flags |= MF_DELIVERMSG;

        call = (caller_ptr->p_misc_flags & MF_REPLY_PEND ? SENDREC
                : (flags & NON_BLOCKING ? SENDNB : SEND));
        IPC_STATUS_ADD_CALL(dst_ptr, call);

        if (dst_ptr->p_misc_flags & MF_REPLY_PEND)
                dst_ptr->p_misc_flags &= ~MF_REPLY_PEND;

        RTS_UNSET(dst_ptr, RTS_RECEIVING);

#if DEBUG_IPC_HOOK
        hook_ipc_msgsend(&dst_ptr->p_delivermsg, caller_ptr, dst_ptr);
        hook_ipc_msgrecv(&dst_ptr->p_delivermsg, caller_ptr, dst_ptr);
#endif
  } else {
        if(flags & NON_BLOCKING) {
                return(ENOTREADY);
        }

        /* Check for a possible deadlock before actually blocking. */
        if (deadlock(SEND, caller_ptr, dst_e)) {
                return(ELOCKED);
        }

        /* Destination is not waiting.  Block and dequeue caller. */
        if (!(flags & FROM_KERNEL)) {
                if(copy_msg_from_user(m_ptr, &caller_ptr->p_sendmsg))
                        return EFAULT;
        } else {
                caller_ptr->p_sendmsg = *m_ptr;
                /*
                 * we need to remember that this message is from kernel so we
                 * can set the delivery status flags when the message is
                 * actually delivered
                 */
                caller_ptr->p_misc_flags |= MF_SENDING_FROM_KERNEL;
        }

        RTS_SET(caller_ptr, RTS_SENDING);
        caller_ptr->p_sendto_e = dst_e;

        /* Process is now blocked.  Put in on the destination's queue. */
        assert(caller_ptr->p_q_link == NULL);
        xpp = &dst_ptr->p_caller_q;             /* find end of list */
        while (*xpp) xpp = &(*xpp)->p_q_link;   
        *xpp = caller_ptr;                      /* add caller to end */

#if DEBUG_IPC_HOOK
        hook_ipc_msgsend(&caller_ptr->p_sendmsg, caller_ptr, dst_ptr);
#endif
  }
  return(OK);
}

/*===========================================================================*
 *                              mini_receive                                 * 
 *===========================================================================*/
static int mini_receive(struct proc * caller_ptr,
                        endpoint_t src_e, /* which message source is wanted */
                        message * m_buff_usr, /* pointer to message buffer */
                        const int 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.
 */
  register struct proc **xpp;
  int r, src_id, found, src_proc_nr, src_p;
  endpoint_t sender_e;

  assert(!(caller_ptr->p_misc_flags & MF_DELIVERMSG));

  /* This is where we want our message. */
  caller_ptr->p_delivermsg_vir = (vir_bytes) m_buff_usr;

  if(src_e == ANY) src_p = ANY;
  else
  {
        okendpt(src_e, &src_p);
        if (RTS_ISSET(proc_addr(src_p), RTS_NO_ENDPOINT))
        {
                return EDEADSRCDST;
        }
  }


  /* Check to see if a message from desired source is already available.  The
   * caller's RTS_SENDING flag may be set if SENDREC couldn't send. If it is
   * set, the process should be blocked.
   */
  if (!RTS_ISSET(caller_ptr, RTS_SENDING)) {

    /* Check if there are pending notifications, except for SENDREC. */
    if (! (caller_ptr->p_misc_flags & MF_REPLY_PEND)) {

        /* Check for pending notifications */
        src_id = has_pending_notify(caller_ptr, src_p);
        found = src_id != NULL_PRIV_ID;
        if(found) {
            src_proc_nr = id_to_nr(src_id);             /* get source proc */
            sender_e = proc_addr(src_proc_nr)->p_endpoint;
        }

        if (found && CANRECEIVE(src_e, sender_e, caller_ptr, 0,
          &m_notify_buff)) {

#if DEBUG_ENABLE_IPC_WARNINGS
            if(src_proc_nr == NONE) {
                printf("mini_receive: sending notify from NONE\n");
            }
#endif
            assert(src_proc_nr != NONE);
            unset_notify_pending(caller_ptr, src_id);   /* no longer pending */

            /* Found a suitable source, deliver the notification message. */
            assert(!(caller_ptr->p_misc_flags & MF_DELIVERMSG));        
            assert(src_e == ANY || sender_e == src_e);

            /* assemble message */
            BuildNotifyMessage(&caller_ptr->p_delivermsg, src_proc_nr, caller_ptr);
            caller_ptr->p_delivermsg.m_source = sender_e;
            caller_ptr->p_misc_flags |= MF_DELIVERMSG;

            IPC_STATUS_ADD_CALL(caller_ptr, NOTIFY);

            goto receive_done;
        }
    }

    /* Check for pending asynchronous messages */
    if (has_pending_asend(caller_ptr, src_p) != NULL_PRIV_ID) {
        if (src_p != ANY)
                r = try_one(src_e, proc_addr(src_p), caller_ptr);
        else
                r = try_async(caller_ptr);

        if (r == OK) {
            IPC_STATUS_ADD_CALL(caller_ptr, SENDA);
            goto receive_done;
        }
    }

    /* Check caller queue. Use pointer pointers to keep code simple. */
    xpp = &caller_ptr->p_caller_q;
    while (*xpp) {
        struct proc * sender = *xpp;
        endpoint_t sender_e = sender->p_endpoint;

        if (CANRECEIVE(src_e, sender_e, caller_ptr, 0, &sender->p_sendmsg)) {
            int call;
            assert(!RTS_ISSET(sender, RTS_SLOT_FREE));
            assert(!RTS_ISSET(sender, RTS_NO_ENDPOINT));

            /* Found acceptable message. Copy it and update status. */
            assert(!(caller_ptr->p_misc_flags & MF_DELIVERMSG));
            caller_ptr->p_delivermsg = sender->p_sendmsg;
            caller_ptr->p_delivermsg.m_source = sender->p_endpoint;
            caller_ptr->p_misc_flags |= MF_DELIVERMSG;
            RTS_UNSET(sender, RTS_SENDING);

            call = (sender->p_misc_flags & MF_REPLY_PEND ? SENDREC : SEND);
            IPC_STATUS_ADD_CALL(caller_ptr, call);

            /*
             * if the message is originally from the kernel on behalf of this
             * process, we must send the status flags accordingly
             */
            if (sender->p_misc_flags & MF_SENDING_FROM_KERNEL) {
                IPC_STATUS_ADD_FLAGS(caller_ptr, IPC_FLG_MSG_FROM_KERNEL);
                /* we can clean the flag now, not need anymore */
                sender->p_misc_flags &= ~MF_SENDING_FROM_KERNEL;
            }
            if (sender->p_misc_flags & MF_SIG_DELAY)
                sig_delay_done(sender);

#if DEBUG_IPC_HOOK
            hook_ipc_msgrecv(&caller_ptr->p_delivermsg, *xpp, caller_ptr);
#endif
                
            *xpp = sender->p_q_link;            /* remove from queue */
            sender->p_q_link = NULL;
            goto receive_done;
        }
        xpp = &sender->p_q_link;                /* 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)) {
      /* Check for a possible deadlock before actually blocking. */
      if (deadlock(RECEIVE, caller_ptr, src_e)) {
          return(ELOCKED);
      }

      caller_ptr->p_getfrom_e = src_e;          
      RTS_SET(caller_ptr, RTS_RECEIVING);
      return(OK);
  } else {
        return(ENOTREADY);
  }

receive_done:
  if (caller_ptr->p_misc_flags & MF_REPLY_PEND)
          caller_ptr->p_misc_flags &= ~MF_REPLY_PEND;
  return OK;
}

/*===========================================================================*
 *                              mini_notify                                  * 
 *===========================================================================*/
int mini_notify(
  const struct proc *caller_ptr,        /* sender of the notification */
  endpoint_t dst_e                      /* which process to notify */
)
{
  register struct proc *dst_ptr;
  int src_id;                           /* source id for late delivery */
  int dst_p;

  if (!isokendpt(dst_e, &dst_p)) {
        util_stacktrace();
        printf("mini_notify: bogus endpoint %d\n", dst_e);
        return EDEADSRCDST;
  }

  dst_ptr = proc_addr(dst_p);

  /* 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 (WILLRECEIVE(caller_ptr->p_endpoint, dst_ptr, 0, &m_notify_buff) &&
    !(dst_ptr->p_misc_flags & MF_REPLY_PEND)) {
      /* Destination is indeed waiting for a message. Assemble a notification 
       * message and deliver it. Copy from pseudo-source HARDWARE, since the
       * message is in the kernel's address space.
       */ 
      assert(!(dst_ptr->p_misc_flags & MF_DELIVERMSG));

      BuildNotifyMessage(&dst_ptr->p_delivermsg, proc_nr(caller_ptr), dst_ptr);
      dst_ptr->p_delivermsg.m_source = caller_ptr->p_endpoint;
      dst_ptr->p_misc_flags |= MF_DELIVERMSG;

      IPC_STATUS_ADD_CALL(dst_ptr, NOTIFY);
      RTS_UNSET(dst_ptr, RTS_RECEIVING);

      return(OK);
  } 

  /* Destination is not ready to receive the notification. Add it to the 
   * bit map with pending notifications. Note the indirectness: the privilege id
   * instead of the process number is used in the pending bit map.
   */ 
  src_id = priv(caller_ptr)->s_id;
  set_sys_bit(priv(dst_ptr)->s_notify_pending, src_id); 
  return(OK);
}

#define ASCOMPLAIN(caller, entry, field)        \
        printf("kernel:%s:%d: asyn failed for %s in %s "        \
        "(%d/%zu, tab 0x%lx)\n",__FILE__,__LINE__,      \
field, caller->p_name, entry, priv(caller)->s_asynsize, priv(caller)->s_asyntab)

#define A_RETR(entry) do {                      \
  if (data_copy(                                \
                caller_ptr->p_endpoint, table_v + (entry)*sizeof(asynmsg_t),\
                KERNEL, (vir_bytes) &tabent,    \
                sizeof(tabent)) != OK) {        \
                        ASCOMPLAIN(caller_ptr, entry, "message entry"); \
                        r = EFAULT;             \
                        goto asyn_error; \
  }                                             \
  else if(tabent.dst == SELF) { \
      tabent.dst = caller_ptr->p_endpoint; \
  } \
                         } while(0)

#define A_INSRT(entry) do {                     \
  if (data_copy(KERNEL, (vir_bytes) &tabent,    \
                caller_ptr->p_endpoint, table_v + (entry)*sizeof(asynmsg_t),\
                sizeof(tabent)) != OK) {        \
                        ASCOMPLAIN(caller_ptr, entry, "message entry"); \
                        /* Do NOT set r or goto asyn_error here! */ \
  }                                             \
                          } while(0)    

/*===========================================================================*
 *                              try_deliver_senda                            *
 *===========================================================================*/
int try_deliver_senda(struct proc *caller_ptr,
                                asynmsg_t *table,
                                size_t size)
{
  int r, dst_p, done, do_notify;
  unsigned int i;
  unsigned flags;
  endpoint_t dst;
  struct proc *dst_ptr;
  struct priv *privp;
  asynmsg_t tabent;
  const vir_bytes table_v = (vir_bytes) table;
  message *m_ptr = NULL;

  privp = priv(caller_ptr);

  /* Clear table */
  privp->s_asyntab = -1;
  privp->s_asynsize = 0;
  privp->s_asynendpoint = caller_ptr->p_endpoint;

  if (size == 0) return(OK);  /* Nothing to do, just return */

  /* Scan the table */
  do_notify = FALSE;
  done = TRUE;

  /* Limit size to something reasonable. An arbitrary choice is 16
   * times the number of process table entries.
   *
   * (this check has been duplicated in sys_call but is left here
   * as a sanity check)
   */
  if (size > 16*(NR_TASKS + NR_PROCS)) {
    r = EDOM;
    return r;
  }

  for (i = 0; i < size; i++) {
        /* Process each entry in the table and store the result in the table.
         * If we're done handling a message, copy the result to the sender. */

        dst = NONE;
        /* Copy message to kernel */
        A_RETR(i);
        flags = tabent.flags;
        dst = tabent.dst;

        if (flags == 0) continue; /* Skip empty entries */

        /* 'flags' field must contain only valid bits */
        if(flags & ~(AMF_VALID|AMF_DONE|AMF_NOTIFY|AMF_NOREPLY|AMF_NOTIFY_ERR)) {
                r = EINVAL;
                goto asyn_error;
        }
        if (!(flags & AMF_VALID)) { /* Must contain message */
                r = EINVAL;
                goto asyn_error;
        }
        if (flags & AMF_DONE) continue; /* Already done processing */

        r = OK;
        if (!isokendpt(tabent.dst, &dst_p)) 
                r = EDEADSRCDST; /* Bad destination, report the error */
        else if (iskerneln(dst_p)) 
                r = ECALLDENIED; /* Asyn sends to the kernel are not allowed */
        else if (!may_asynsend_to(caller_ptr, dst_p))
                r = ECALLDENIED; /* Send denied by IPC mask */
        else    /* r == OK */
                dst_ptr = proc_addr(dst_p);

        /* XXX: RTS_NO_ENDPOINT should be removed */
        if (r == OK && RTS_ISSET(dst_ptr, RTS_NO_ENDPOINT)) {
                r = EDEADSRCDST;
        }

        /* Check if 'dst' is blocked waiting for this message.
         * If AMF_NOREPLY is set, do not satisfy the receiving part of
         * a SENDREC.
         */
        if (r == OK && WILLRECEIVE(caller_ptr->p_endpoint, dst_ptr,
            (vir_bytes)&table[i].msg, NULL) &&
            (!(flags&AMF_NOREPLY) || !(dst_ptr->p_misc_flags&MF_REPLY_PEND))) {
                /* Destination is indeed waiting for this message. */
                dst_ptr->p_delivermsg = tabent.msg;
                dst_ptr->p_delivermsg.m_source = caller_ptr->p_endpoint;
                dst_ptr->p_misc_flags |= MF_DELIVERMSG;
                IPC_STATUS_ADD_CALL(dst_ptr, SENDA);
                RTS_UNSET(dst_ptr, RTS_RECEIVING);
#if DEBUG_IPC_HOOK
                hook_ipc_msgrecv(&dst_ptr->p_delivermsg, caller_ptr, dst_ptr);
#endif
        } else if (r == OK) {
                /* Inform receiver that something is pending */
                set_sys_bit(priv(dst_ptr)->s_asyn_pending, 
                            priv(caller_ptr)->s_id); 
                done = FALSE;
                continue;
        } 

        /* Store results */
        tabent.result = r;
        tabent.flags = flags | AMF_DONE;
        if (flags & AMF_NOTIFY)
                do_notify = TRUE;
        else if (r != OK && (flags & AMF_NOTIFY_ERR))
                do_notify = TRUE;
        A_INSRT(i);     /* Copy results to caller; ignore errors */
        continue;

asyn_error:
        if (dst != NONE)
                printf("KERNEL senda error %d to %d\n", r, dst);
        else
                printf("KERNEL senda error %d\n", r);
  }

  if (do_notify) 
        mini_notify(proc_addr(ASYNCM), caller_ptr->p_endpoint);

  if (!done) {
        privp->s_asyntab = (vir_bytes) table;
        privp->s_asynsize = size;
  }

  return(OK);
}

/*===========================================================================*
 *                              mini_senda                                   *
 *===========================================================================*/
static int mini_senda(struct proc *caller_ptr, asynmsg_t *table, size_t size)
{
  struct priv *privp;

  privp = priv(caller_ptr);
  if (!(privp->s_flags & SYS_PROC)) {
        printf( "mini_senda: warning caller has no privilege structure\n");
        return(EPERM);
  }

  return try_deliver_senda(caller_ptr, table, size);
}


/*===========================================================================*
 *                              try_async                                    * 
 *===========================================================================*/
static int try_async(struct proc * caller_ptr)
{
  int r;
  struct priv *privp;
  struct proc *src_ptr;
  sys_map_t *map;

  map = &priv(caller_ptr)->s_asyn_pending;

  /* Try all privilege structures */
  for (privp = BEG_PRIV_ADDR; privp < END_PRIV_ADDR; ++privp)  {
        if (privp->s_proc_nr == NONE)
                continue;

        if (!get_sys_bit(*map, privp->s_id)) 
                continue;

        src_ptr = proc_addr(privp->s_proc_nr);

#ifdef CONFIG_SMP
        /*
         * Do not copy from a process which does not have a stable address space
         * due to VM fiddling with it
         */
        if (RTS_ISSET(src_ptr, RTS_VMINHIBIT)) {
                src_ptr->p_misc_flags |= MF_SENDA_VM_MISS;
                continue;
        }
#endif

        assert(!(caller_ptr->p_misc_flags & MF_DELIVERMSG));
        if ((r = try_one(ANY, src_ptr, caller_ptr)) == OK)
                return(r);
  }

  return(ESRCH);
}


/*===========================================================================*
 *                              try_one                                      *
 *===========================================================================*/
static int try_one(endpoint_t receive_e, struct proc *src_ptr,
    struct proc *dst_ptr)
{
/* Try to receive an asynchronous message from 'src_ptr' */
  int r = EAGAIN, done, do_notify;
  unsigned int flags, i;
  size_t size;
  endpoint_t dst, src_e;
  struct proc *caller_ptr;
  struct priv *privp;
  asynmsg_t tabent;
  vir_bytes table_v;

  privp = priv(src_ptr);
  if (!(privp->s_flags & SYS_PROC)) return(EPERM);
  size = privp->s_asynsize;
  table_v = privp->s_asyntab;

  /* Clear table pending message flag. We're done unless we're not. */
  unset_sys_bit(priv(dst_ptr)->s_asyn_pending, privp->s_id);

  if (size == 0) return(EAGAIN);
  if (privp->s_asynendpoint != src_ptr->p_endpoint) return EAGAIN;
  if (!may_asynsend_to(src_ptr, proc_nr(dst_ptr))) return (ECALLDENIED);

  caller_ptr = src_ptr; /* Needed for A_ macros later on */
  src_e = src_ptr->p_endpoint;

  /* Scan the table */
  do_notify = FALSE;
  done = TRUE;

  for (i = 0; i < size; i++) {
        /* Process each entry in the table and store the result in the table.
         * If we're done handling a message, copy the result to the sender.
         * Some checks done in mini_senda are duplicated here, as the sender
         * could've altered the contents of the table in the meantime.
         */

        /* Copy message to kernel */
        A_RETR(i);
        flags = tabent.flags;
        dst = tabent.dst;

        if (flags == 0) continue;       /* Skip empty entries */

        /* 'flags' field must contain only valid bits */
        if(flags & ~(AMF_VALID|AMF_DONE|AMF_NOTIFY|AMF_NOREPLY|AMF_NOTIFY_ERR))
                r = EINVAL;
        else if (!(flags & AMF_VALID)) /* Must contain message */
                r = EINVAL; 
        else if (flags & AMF_DONE) continue; /* Already done processing */

        /* Clear done flag. The sender is done sending when all messages in the
         * table are marked done or empty. However, we will know that only
         * the next time we enter this function or when the sender decides to
         * send additional asynchronous messages and manages to deliver them
         * all.
         */
        done = FALSE;

        if (r == EINVAL)
                goto store_result;

        /* Message must be directed at receiving end */
        if (dst != dst_ptr->p_endpoint) continue;

        if (!CANRECEIVE(receive_e, src_e, dst_ptr,
                table_v + i*sizeof(asynmsg_t) + offsetof(struct asynmsg,msg),
                NULL)) {
                continue;
        }

        /* If AMF_NOREPLY is set, then this message is not a reply to a
         * SENDREC and thus should not satisfy the receiving part of the
         * SENDREC. This message is to be delivered later.
         */
        if ((flags & AMF_NOREPLY) && (dst_ptr->p_misc_flags & MF_REPLY_PEND)) 
                continue;

        /* Destination is ready to receive the message; deliver it */
        r = OK;
        dst_ptr->p_delivermsg = tabent.msg;
        dst_ptr->p_delivermsg.m_source = src_ptr->p_endpoint;
        dst_ptr->p_misc_flags |= MF_DELIVERMSG;
#if DEBUG_IPC_HOOK
        hook_ipc_msgrecv(&dst_ptr->p_delivermsg, src_ptr, dst_ptr);
#endif

store_result:
        /* Store results for sender. We may just have started delivering a
         * message, so we must not return an error to the caller in the case
         * that storing the results triggers an error!
         */
        tabent.result = r;
        tabent.flags = flags | AMF_DONE;
        if (flags & AMF_NOTIFY) do_notify = TRUE;
        else if (r != OK && (flags & AMF_NOTIFY_ERR)) do_notify = TRUE;
        A_INSRT(i);     /* Copy results to sender; ignore errors */

        break;
  }

  if (do_notify) 
        mini_notify(proc_addr(ASYNCM), src_ptr->p_endpoint);

  if (done) {
        privp->s_asyntab = -1;
        privp->s_asynsize = 0;
  } else {
        set_sys_bit(priv(dst_ptr)->s_asyn_pending, privp->s_id);
  }

asyn_error:
  return(r);
}

/*===========================================================================*
 *                              cancel_async                                 *
 *===========================================================================*/
int cancel_async(struct proc *src_ptr, struct proc *dst_ptr)
{
/* Cancel asynchronous messages from src to dst, because dst is not interested
 * in them (e.g., dst has been restarted) */
  int done, do_notify;
  unsigned int flags, i;
  size_t size;
  endpoint_t dst;
  struct proc *caller_ptr;
  struct priv *privp;
  asynmsg_t tabent;
  vir_bytes table_v;

  privp = priv(src_ptr);
  if (!(privp->s_flags & SYS_PROC)) return(EPERM);
  size = privp->s_asynsize;
  table_v = privp->s_asyntab;

  /* Clear table pending message flag. We're done unless we're not. */
  privp->s_asyntab = -1;
  privp->s_asynsize = 0;
  unset_sys_bit(priv(dst_ptr)->s_asyn_pending, privp->s_id);

  if (size == 0) return(EAGAIN);
  if (!may_send_to(src_ptr, proc_nr(dst_ptr))) return(ECALLDENIED);

  caller_ptr = src_ptr; /* Needed for A_ macros later on */

  /* Scan the table */
  do_notify = FALSE;
  done = TRUE;


  for (i = 0; i < size; i++) {
        /* Process each entry in the table and store the result in the table.
         * If we're done handling a message, copy the result to the sender.
         * Some checks done in mini_senda are duplicated here, as the sender
         * could've altered the contents of the table in the mean time.
         */

        int r = EDEADSRCDST;    /* Cancel delivery due to dead dst */

        /* Copy message to kernel */
        A_RETR(i);
        flags = tabent.flags;
        dst = tabent.dst;

        if (flags == 0) continue;       /* Skip empty entries */

        /* 'flags' field must contain only valid bits */
        if(flags & ~(AMF_VALID|AMF_DONE|AMF_NOTIFY|AMF_NOREPLY|AMF_NOTIFY_ERR))
                r = EINVAL;
        else if (!(flags & AMF_VALID)) /* Must contain message */
                r = EINVAL; 
        else if (flags & AMF_DONE) continue; /* Already done processing */

        /* Message must be directed at receiving end */
        if (dst != dst_ptr->p_endpoint) {
                done = FALSE;
                continue;
        }

        /* Store results for sender */
        tabent.result = r;
        tabent.flags = flags | AMF_DONE;
        if (flags & AMF_NOTIFY) do_notify = TRUE;
        else if (r != OK && (flags & AMF_NOTIFY_ERR)) do_notify = TRUE;
        A_INSRT(i);     /* Copy results to sender; ignore errors */
  }

  if (do_notify) 
        mini_notify(proc_addr(ASYNCM), src_ptr->p_endpoint);

  if (!done) {
        privp->s_asyntab = table_v;
        privp->s_asynsize = size;
  }

asyn_error:
  return(OK);
}

/*===========================================================================*
 *                              enqueue                                      * 
 *===========================================================================*/
void enqueue(
  register struct proc *rp      /* this process is now runnable */
)
{
/* Add 'rp' to one of the queues of runnable processes.  This function is 
 * responsible for inserting a process into one of the scheduling queues. 
 * The mechanism is implemented here.   The actual scheduling policy is
 * defined in sched() and pick_proc().
 *
 * This function can be used x-cpu as it always uses the queues of the cpu the
 * process is assigned to.
 */
  int q = rp->p_priority;                       /* scheduling queue to use */
  struct proc **rdy_head, **rdy_tail;
  
  assert(proc_is_runnable(rp));

  assert(q >= 0);

  rdy_head = get_cpu_var(rp->p_cpu, run_q_head);
  rdy_tail = get_cpu_var(rp->p_cpu, run_q_tail);

  /* Now add the process to the queue. */
  if (!rdy_head[q]) {           /* add to empty queue */
      rdy_head[q] = rdy_tail[q] = rp;           /* create a new queue */
      rp->p_nextready = NULL;           /* mark new end */
  } 
  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 = NULL;           /* mark new end */
  }

  if (cpuid == rp->p_cpu) {
          /*
           * enqueueing a process with a higher priority than the current one,
           * it gets preempted. The current process must be preemptible. Testing
           * the priority also makes sure that a process does not preempt itself
           */
          struct proc * p;
          p = get_cpulocal_var(proc_ptr);
          assert(p);
          if((p->p_priority > rp->p_priority) &&
                          (priv(p)->s_flags & PREEMPTIBLE))
                  RTS_SET(p, RTS_PREEMPTED); /* calls dequeue() */
  }
#ifdef CONFIG_SMP
  /*
   * if the process was enqueued on a different cpu and the cpu is idle, i.e.
   * the time is off, we need to wake up that cpu and let it schedule this new
   * process
   */
  else if (get_cpu_var(rp->p_cpu, cpu_is_idle)) {
          smp_schedule(rp->p_cpu);
  }
#endif

  /* Make note of when this process was added to queue */
  read_tsc_64(&(get_cpulocal_var(proc_ptr)->p_accounting.enter_queue));


#if DEBUG_SANITYCHECKS
  assert(runqueues_ok_local());
#endif
}

/*===========================================================================*
 *                              enqueue_head                                 *
 *===========================================================================*/
/*
 * put a process at the front of its run queue. It comes handy when a process is
 * preempted and removed from run queue to not to have a currently not-runnable
 * process on a run queue. We have to put this process back at the fron to be
 * fair
 */
static void enqueue_head(struct proc *rp)
{
  const int q = rp->p_priority;                 /* scheduling queue to use */

  struct proc **rdy_head, **rdy_tail;

  assert(proc_ptr_ok(rp));
  assert(proc_is_runnable(rp));

  /*
   * the process was runnable without its quantum expired when dequeued. A
   * process with no time left should have been handled else and differently
   */
  assert(rp->p_cpu_time_left);

  assert(q >= 0);


  rdy_head = get_cpu_var(rp->p_cpu, run_q_head);
  rdy_tail = get_cpu_var(rp->p_cpu, run_q_tail);

  /* Now add the process to the queue. */
  if (!rdy_head[q]) {           /* add to empty queue */
        rdy_head[q] = rdy_tail[q] = rp;         /* create a new queue */
        rp->p_nextready = NULL;                 /* mark new end */
  } else {                                      /* add to head of queue */
        rp->p_nextready = rdy_head[q];          /* chain head of queue */
        rdy_head[q] = rp;                       /* set new queue head */
  }

  /* Make note of when this process was added to queue */
  read_tsc_64(&(get_cpulocal_var(proc_ptr->p_accounting.enter_queue)));


  /* Process accounting for scheduling */
  rp->p_accounting.dequeues--;
  rp->p_accounting.preempted++;

#if DEBUG_SANITYCHECKS
  assert(runqueues_ok_local());
#endif
}

/*===========================================================================*
 *                              dequeue                                      * 
 *===========================================================================*/
void dequeue(struct proc *rp)
/* this process is no longer runnable */
{
/* A process must be removed from the scheduling queues, for example, because
 * it has blocked.  If the currently active process is removed, a new process
 * is picked to run by calling pick_proc().
 *
 * This function can operate x-cpu as it always removes the process from the
 * queue of the cpu the process is currently assigned to.
 */
  int q = rp->p_priority;               /* queue to use */
  struct proc **xpp;                    /* iterate over queue */
  struct proc *prev_xp;
  u64_t tsc, tsc_delta;

  struct proc **rdy_tail;

  assert(proc_ptr_ok(rp));
  assert(!proc_is_runnable(rp));

  /* Side-effect for kernel: check if the task's stack still is ok? */
  assert (!iskernelp(rp) || *priv(rp)->s_stack_guard == STACK_GUARD);

  rdy_tail = get_cpu_var(rp->p_cpu, run_q_tail);

  /* 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 = NULL;                               
  for (xpp = get_cpu_var_ptr(rp->p_cpu, run_q_head[q]); *xpp;
                  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 */
          }

          break;
      }
      prev_xp = *xpp;                           /* save previous in chain */
  }

        
  /* Process accounting for scheduling */
  rp->p_accounting.dequeues++;

  /* this is not all that accurate on virtual machines, especially with
     IO bound processes that only spend a short amount of time in the queue
     at a time. */
  if (rp->p_accounting.enter_queue) {
        read_tsc_64(&tsc);
        tsc_delta = tsc - rp->p_accounting.enter_queue;
        rp->p_accounting.time_in_queue = rp->p_accounting.time_in_queue +
                tsc_delta;
        rp->p_accounting.enter_queue = 0;
  }

  /* For ps(1), remember when the process was last dequeued. */
  rp->p_dequeued = get_monotonic();

#if DEBUG_SANITYCHECKS
  assert(runqueues_ok_local());
#endif
}

/*===========================================================================*
 *                              pick_proc                                    * 
 *===========================================================================*/
static struct proc * pick_proc(void)
{
/* Decide who to run now.  A new process is selected and returned.
 * When a billable process is selected, record it in 'bill_ptr', so that the 
 * clock task can tell who to bill for system time.
 *
 * This function always uses the run queues of the local cpu!
 */
  register struct proc *rp;                     /* process to run */
  struct proc **rdy_head;
  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.
   * If there are no processes ready to run, return NULL.
   */
  rdy_head = get_cpulocal_var(run_q_head);
  for (q=0; q < NR_SCHED_QUEUES; q++) { 
        if(!(rp = rdy_head[q])) {
                TRACE(VF_PICKPROC, printf("cpu %d queue %d empty\n", cpuid, q););
                continue;
        }
        assert(proc_is_runnable(rp));
        if (priv(rp)->s_flags & BILLABLE)               
                get_cpulocal_var(bill_ptr) = rp; /* bill for system time */
        return rp;
  }
  return NULL;
}

/*===========================================================================*
 *                              endpoint_lookup                              *
 *===========================================================================*/
struct proc *endpoint_lookup(endpoint_t e)
{
        int n;

        if(!isokendpt(e, &n)) return NULL;

        return proc_addr(n);
}

/*===========================================================================*
 *                              isokendpt_f                                  *
 *===========================================================================*/
#if DEBUG_ENABLE_IPC_WARNINGS
int isokendpt_f(const char * file, int line, endpoint_t e, int * p,
        const int fatalflag)
#else
int isokendpt_f(endpoint_t e, int * p, const int fatalflag)
#endif
{
        int ok = 0;
        /* Convert an endpoint number into a process number.
         * Return nonzero if the process is alive with the corresponding
         * generation number, zero otherwise.
         *
         * This function is called with file and line number by the
         * isokendpt_d macro if DEBUG_ENABLE_IPC_WARNINGS is defined,
         * otherwise without. This allows us to print the where the
         * conversion was attempted, making the errors verbose without
         * adding code for that at every call.
         * 
         * If fatalflag is nonzero, we must panic if the conversion doesn't
         * succeed.
         */
        *p = _ENDPOINT_P(e);
        ok = 0;
        if(isokprocn(*p) && !isemptyn(*p) && proc_addr(*p)->p_endpoint == e)
                ok = 1;
        if(!ok && fatalflag)
                panic("invalid endpoint: %d",  e);
        return ok;
}

static void notify_scheduler(struct proc *p)
{
        message m_no_quantum;
        int err;

        assert(!proc_kernel_scheduler(p));

        /* dequeue the process */
        RTS_SET(p, RTS_NO_QUANTUM);
        /*
         * Notify the process's scheduler that it has run out of
         * quantum. This is done by sending a message to the scheduler
         * on the process's behalf
         */
        m_no_quantum.m_source = p->p_endpoint;
        m_no_quantum.m_type   = SCHEDULING_NO_QUANTUM;
        m_no_quantum.m_krn_lsys_schedule.acnt_queue = cpu_time_2_ms(p->p_accounting.time_in_queue);
        m_no_quantum.m_krn_lsys_schedule.acnt_deqs      = p->p_accounting.dequeues;
        m_no_quantum.m_krn_lsys_schedule.acnt_ipc_sync  = p->p_accounting.ipc_sync;
        m_no_quantum.m_krn_lsys_schedule.acnt_ipc_async = p->p_accounting.ipc_async;
        m_no_quantum.m_krn_lsys_schedule.acnt_preempt   = p->p_accounting.preempted;
        m_no_quantum.m_krn_lsys_schedule.acnt_cpu       = cpuid;
        m_no_quantum.m_krn_lsys_schedule.acnt_cpu_load  = cpu_load();

        /* Reset accounting */
        reset_proc_accounting(p);

        if ((err = mini_send(p, p->p_scheduler->p_endpoint,
                                        &m_no_quantum, FROM_KERNEL))) {
                panic("WARNING: Scheduling: mini_send returned %d\n", err);
        }
}

void proc_no_time(struct proc * p)
{
        if (!proc_kernel_scheduler(p) && priv(p)->s_flags & PREEMPTIBLE) {
                /* this dequeues the process */
                notify_scheduler(p);
        }
        else {
                /*
                 * non-preemptible processes only need their quantum to
                 * be renewed. In fact, they by pass scheduling
                 */
                p->p_cpu_time_left = ms_2_cpu_time(p->p_quantum_size_ms);
#if DEBUG_RACE
                RTS_SET(p, RTS_PREEMPTED);
                RTS_UNSET(p, RTS_PREEMPTED);
#endif
        }
}

void reset_proc_accounting(struct proc *p)
{
  p->p_accounting.preempted = 0;
  p->p_accounting.ipc_sync  = 0;
  p->p_accounting.ipc_async = 0;
  p->p_accounting.dequeues  = 0;
  p->p_accounting.time_in_queue = 0;
  p->p_accounting.enter_queue = 0;
}
        
void copr_not_available_handler(void)
{
        struct proc * p;
        struct proc ** local_fpu_owner;
        /*
         * Disable the FPU exception (both for the kernel and for the process
         * once it's scheduled), and initialize or restore the FPU state.
         */

        disable_fpu_exception();

        p = get_cpulocal_var(proc_ptr);

        /* if FPU is not owned by anyone, do not store anything */
        local_fpu_owner = get_cpulocal_var_ptr(fpu_owner);
        if (*local_fpu_owner != NULL) {
                assert(*local_fpu_owner != p);
                save_local_fpu(*local_fpu_owner, FALSE /*retain*/);
        }

        /*
         * restore the current process' state and let it run again, do not
         * schedule!
         */
        if (restore_fpu(p) != OK) {
                /* Restoring FPU state failed. This is always the process's own
                 * fault. Send a signal, and schedule another process instead.
                 */
                *local_fpu_owner = NULL;                /* release FPU */
                cause_sig(proc_nr(p), SIGFPE);
                return;
        }

        *local_fpu_owner = p;
        context_stop(proc_addr(KERNEL));
        restore_user_context(p);
        NOT_REACHABLE;
}

void release_fpu(struct proc * p) {
        struct proc ** fpu_owner_ptr;

        fpu_owner_ptr = get_cpu_var_ptr(p->p_cpu, fpu_owner);

        if (*fpu_owner_ptr == p)
                *fpu_owner_ptr = NULL;
}

void ser_dump_proc(void)
{
        struct proc *pp;

        for (pp= BEG_PROC_ADDR; pp < END_PROC_ADDR; pp++)
        {
                if (isemptyp(pp))
                        continue;
                print_proc_recursive(pp);
        }
}