minix/kernel/system.c

/* This task handles the interface between the kernel and user-level servers.
 * System services can be accessed by doing a system call. System calls are 
 * transformed into request messages, which are handled by this task. By 
 * convention, a sys_call() is transformed in a SYS_CALL request message that
 * is handled in a function named do_call(). 
 *
 * A private call vector is used to map all system calls to the functions that
 * handle them. The actual handler functions are contained in separate files
 * to keep this file clean. The call vector is used in the system task's main
 * loop to handle all incoming requests.  
 *
 * In addition to the main sys_task() entry point, which starts the main loop,
 * there are several other minor entry points:
 *   get_priv:		assign privilege structure to user or system process
 *   set_sendto_bit:	allow a process to send messages to a new target
 *   unset_sendto_bit:	disallow a process from sending messages to a target
 *   fill_sendto_mask:	fill the target mask of a given process
 *   send_sig:		send a signal directly to a system process
 *   cause_sig:		take action to cause a signal to occur via a signal mgr
 *   sig_delay_done:	tell PM that a process is not sending
 *   umap_bios:		map virtual address in BIOS_SEG to physical 
 *   get_randomness:	accumulate randomness in a buffer
 *   clear_endpoint:	remove a process' ability to send and receive messages
 *   sched_proc:	schedule a process
 *
 * Changes:
*    Nov 22, 2009   get_priv supports static priv ids (Cristiano Giuffrida)
 *   Aug 04, 2005   check if system call is allowed  (Jorrit N. Herder)
 *   Jul 20, 2005   send signal to services with message  (Jorrit N. Herder) 
 *   Jan 15, 2005   new, generalized virtual copy function  (Jorrit N. Herder)
 *   Oct 10, 2004   dispatch system calls from call vector  (Jorrit N. Herder)
 *   Sep 30, 2004   source code documentation updated  (Jorrit N. Herder)
 */

#include "debug.h"
#include "kernel.h"
#include "system.h"
#include "proc.h"
#include "vm.h"
#include "kernel/clock.h"
#include <stdlib.h>
#include <assert.h>
#include <signal.h>
#include <unistd.h>
#include <sys/sigcontext.h>
#include <minix/endpoint.h>
#include <minix/safecopies.h>

/* Declaration of the call vector that defines the mapping of system calls 
 * to handler functions. The vector is initialized in sys_init() with map(), 
 * which makes sure the system call numbers are ok. No space is allocated, 
 * because the dummy is declared extern. If an illegal call is given, the 
 * array size will be negative and this won't compile. 
 */
PRIVATE int (*call_vec[NR_SYS_CALLS])(struct proc * caller, message *m_ptr);

#define map(call_nr, handler) \
    {extern int dummy[NR_SYS_CALLS>(unsigned)(call_nr-KERNEL_CALL) ? 1:-1];} \
    call_vec[(call_nr-KERNEL_CALL)] = (handler)  

PRIVATE void kernel_call_finish(struct proc * caller, message *msg, int result)
{
  if(result == VMSUSPEND) {
	  /* Special case: message has to be saved for handling
	   * until VM tells us it's allowed. VM has been notified
	   * and we must wait for its reply to restart the call.
	   */
	  assert(RTS_ISSET(caller, RTS_VMREQUEST));
	  assert(caller->p_vmrequest.type == VMSTYPE_KERNELCALL);
	  caller->p_vmrequest.saved.reqmsg = *msg;
	  caller->p_misc_flags |= MF_KCALL_RESUME;
  } else {
	  /*
	   * call is finished, we could have been suspended because of VM,
	   * remove the request message
	   */
	  caller->p_vmrequest.saved.reqmsg.m_source = NONE;
	  if (result != EDONTREPLY) {
		  /* copy the result as a message to the original user buffer */
		  msg->m_source = SYSTEM;
		  msg->m_type = result;		/* report status of call */
#if DEBUG_DUMPIPC
	printmsgkresult(msg, caller);
#endif
		  if (copy_msg_to_user(caller, msg,
				  (message *)caller->p_delivermsg_vir)) {
			  printf("WARNING wrong user pointer 0x%08x from "
					  "process %s / %d\n",
					  caller->p_delivermsg_vir,
					  caller->p_name,
					  caller->p_endpoint);
		  }
	  }
  }
}

PRIVATE int kernel_call_dispatch(struct proc * caller, message *msg)
{
  int result = OK;
  int call_nr;
  
#if DEBUG_DUMPIPC
	printmsgkcall(msg, caller);
#endif
  call_nr = msg->m_type - KERNEL_CALL;

  /* See if the caller made a valid request and try to handle it. */
  if (call_nr < 0 || call_nr >= NR_SYS_CALLS) {	/* check call number */
	  printf("SYSTEM: illegal request %d from %d.\n",
			  call_nr,msg->m_source);
	  result = EBADREQUEST;			/* illegal message type */
  }
  else if (!GET_BIT(priv(caller)->s_k_call_mask, call_nr)) {
	  printf("SYSTEM: denied request %d from %d.\n",
			  call_nr,msg->m_source);
	  result = ECALLDENIED;			/* illegal message type */
  } else {
	  /* handle the system call */
	  if (call_vec[call_nr])
		  result = (*call_vec[call_nr])(caller, msg);
	  else {
		  printf("Unused kernel call %d from %d\n",
				  call_nr, caller->p_endpoint);
		  result = EBADREQUEST;
	  }
  }

  return result;
}

/*===========================================================================*
 *				kernel_call				     *
 *===========================================================================*/
/*
 * this function checks the basic syscall parameters and if accepted it
 * dispatches its handling to the right handler
 */
PUBLIC void kernel_call(message *m_user, struct proc * caller)
{
  int result = OK;
  message msg;

  caller->p_delivermsg_vir = (vir_bytes) m_user;
  /*
   * the ldt and cr3 of the caller process is loaded because it just've trapped
   * into the kernel or was already set in switch_to_user() before we resume
   * execution of an interrupted kernel call
   */
  if (copy_msg_from_user(caller, m_user, &msg) == 0) {
	  msg.m_source = caller->p_endpoint;
	  result = kernel_call_dispatch(caller, &msg);
  }
  else {
	  printf("WARNING wrong user pointer 0x%08x from process %s / %d\n",
			  m_user, caller->p_name, caller->p_endpoint);
	  result = EBADREQUEST;
  }

  kernel_call_finish(caller, &msg, result);
}

/*===========================================================================*
 *				initialize				     *
 *===========================================================================*/
PUBLIC void system_init(void)
{
  register struct priv *sp;
  int i;

  /* Initialize IRQ handler hooks. Mark all hooks available. */
  for (i=0; i<NR_IRQ_HOOKS; i++) {
      irq_hooks[i].proc_nr_e = NONE;
  }

  /* Initialize all alarm timers for all processes. */
  for (sp=BEG_PRIV_ADDR; sp < END_PRIV_ADDR; sp++) {
    tmr_inittimer(&(sp->s_alarm_timer));
  }

  /* Initialize the call vector to a safe default handler. Some system calls 
   * may be disabled or nonexistant. Then explicitely map known calls to their
   * handler functions. This is done with a macro that gives a compile error
   * if an illegal call number is used. The ordering is not important here.
   */
  for (i=0; i<NR_SYS_CALLS; i++) {
      call_vec[i] = NULL;
  }

  /* Process management. */
  map(SYS_FORK, do_fork); 		/* a process forked a new process */
  map(SYS_EXEC, do_exec);		/* update process after execute */
  map(SYS_CLEAR, do_clear);		/* clean up after process exit */
  map(SYS_EXIT, do_exit);		/* a system process wants to exit */
  map(SYS_PRIVCTL, do_privctl);		/* system privileges control */
  map(SYS_TRACE, do_trace);		/* request a trace operation */
  map(SYS_SETGRANT, do_setgrant);	/* get/set own parameters */
  map(SYS_RUNCTL, do_runctl);		/* set/clear stop flag of a process */
  map(SYS_UPDATE, do_update);		/* update a process into another */
  map(SYS_STATECTL, do_statectl);	/* let a process control its state */

  /* Signal handling. */
  map(SYS_KILL, do_kill); 		/* cause a process to be signaled */
  map(SYS_GETKSIG, do_getksig);		/* signal manager checks for signals */
  map(SYS_ENDKSIG, do_endksig);		/* signal manager finished signal */
  map(SYS_SIGSEND, do_sigsend);		/* start POSIX-style signal */
  map(SYS_SIGRETURN, do_sigreturn);	/* return from POSIX-style signal */

  /* Device I/O. */
  map(SYS_IRQCTL, do_irqctl);  		/* interrupt control operations */ 
  map(SYS_DEVIO, do_devio);   		/* inb, inw, inl, outb, outw, outl */ 
  map(SYS_VDEVIO, do_vdevio);  		/* vector with devio requests */ 

  /* Memory management. */
  map(SYS_NEWMAP, do_newmap);		/* set up a process memory map */
  map(SYS_SEGCTL, do_segctl);		/* add segment and get selector */
  map(SYS_MEMSET, do_memset);		/* write char to memory area */
  map(SYS_VMCTL, do_vmctl);		/* various VM process settings */

  /* Copying. */
  map(SYS_UMAP, do_umap);		/* map virtual to physical address */
  map(SYS_VIRCOPY, do_vircopy); 	/* use pure virtual addressing */
  map(SYS_PHYSCOPY, do_copy);	 	/* use physical addressing */
  map(SYS_SAFECOPYFROM, do_safecopy_from);/* copy with pre-granted permission */
  map(SYS_SAFECOPYTO, do_safecopy_to);	/* copy with pre-granted permission */
  map(SYS_VSAFECOPY, do_vsafecopy);	/* vectored safecopy */

  /* Mapping. */
  map(SYS_SAFEMAP, do_safemap);		/* map pages from other process */
  map(SYS_SAFEREVMAP, do_saferevmap);	/* grantor revokes the map grant */
  map(SYS_SAFEUNMAP, do_safeunmap);	/* requestor unmaps the mapped pages */

  /* Clock functionality. */
  map(SYS_TIMES, do_times);		/* get uptime and process times */
  map(SYS_SETALARM, do_setalarm);	/* schedule a synchronous alarm */
  map(SYS_STIME, do_stime);		/* set the boottime */
  map(SYS_VTIMER, do_vtimer);		/* set or retrieve a virtual timer */

  /* System control. */
  map(SYS_ABORT, do_abort);		/* abort MINIX */
  map(SYS_GETINFO, do_getinfo); 	/* request system information */ 
  map(SYS_SYSCTL, do_sysctl); 		/* misc system manipulation */ 

  /* Profiling. */
  map(SYS_SPROF, do_sprofile);         /* start/stop statistical profiling */
  map(SYS_CPROF, do_cprofile);         /* get/reset call profiling data */
  map(SYS_PROFBUF, do_profbuf);        /* announce locations to kernel */

  /* i386-specific. */
#if _MINIX_CHIP == _CHIP_INTEL
  map(SYS_INT86, do_int86);  		/* real-mode BIOS calls */ 
  map(SYS_READBIOS, do_readbios);	/* read from BIOS locations */
  map(SYS_IOPENABLE, do_iopenable); 	/* Enable I/O */
  map(SYS_SDEVIO, do_sdevio);		/* phys_insb, _insw, _outsb, _outsw */

  /* Machine state switching. */
  map(SYS_SETMCONTEXT, do_setmcontext); /* set machine context */
  map(SYS_GETMCONTEXT, do_getmcontext); /* get machine context */
#endif

  /* Scheduling */
  map(SYS_SCHEDULE, do_schedule);	/* reschedule a process */
  map(SYS_SCHEDCTL, do_schedctl);	/* change process scheduler */

}
/*===========================================================================*
 *				get_priv				     *
 *===========================================================================*/
PUBLIC int get_priv(rc, priv_id)
register struct proc *rc;		/* new (child) process pointer */
int priv_id;				/* privilege id */
{
/* Allocate a new privilege structure for a system process. Privilege ids
 * can be assigned either statically or dynamically.
 */
  register struct priv *sp;                 /* privilege structure */

  if(priv_id == NULL_PRIV_ID) {             /* allocate slot dynamically */
      for (sp = BEG_DYN_PRIV_ADDR; sp < END_DYN_PRIV_ADDR; ++sp) 
          if (sp->s_proc_nr == NONE) break;	
      if (sp >= END_DYN_PRIV_ADDR) return(ENOSPC);
  }
  else {                                    /* allocate slot from id */
      if(!is_static_priv_id(priv_id)) {
          return EINVAL;                    /* invalid static priv id */
      }
      if(priv[priv_id].s_proc_nr != NONE) {
          return EBUSY;                     /* slot already in use */
      }
      sp = &priv[priv_id];
  }
  rc->p_priv = sp;			    /* assign new slot */
  rc->p_priv->s_proc_nr = proc_nr(rc);	    /* set association */

  return(OK);
}

/*===========================================================================*
 *				set_sendto_bit				     *
 *===========================================================================*/
PUBLIC void set_sendto_bit(const struct proc *rp, int id)
{
/* Allow a process to send messages to the process(es) associated with the
 * system privilege structure with the given ID. 
 */

  /* Disallow the process from sending to a process privilege structure with no
   * associated process, and disallow the process from sending to itself.
   */
  if (id_to_nr(id) == NONE || priv_id(rp) == id) {
	unset_sys_bit(priv(rp)->s_ipc_to, id);
	return;
  }

  set_sys_bit(priv(rp)->s_ipc_to, id);

  /* The process that this process can now send to, must be able to reply (or
   * vice versa). Therefore, its send mask should be updated as well. Ignore
   * receivers that don't support traps other than RECEIVE, they can't reply
   * or send messages anyway.
   */
  if (priv_addr(id)->s_trap_mask & ~((1 << RECEIVE)))
      set_sys_bit(priv_addr(id)->s_ipc_to, priv_id(rp));
}

/*===========================================================================*
 *				unset_sendto_bit			     *
 *===========================================================================*/
PUBLIC void unset_sendto_bit(const struct proc *rp, int id)
{
/* Prevent a process from sending to another process. Retain the send mask
 * symmetry by also unsetting the bit for the other direction.
 */

  unset_sys_bit(priv(rp)->s_ipc_to, id);

  unset_sys_bit(priv_addr(id)->s_ipc_to, priv_id(rp));
}

/*===========================================================================*
 *			      fill_sendto_mask				     *
 *===========================================================================*/
PUBLIC void fill_sendto_mask(const struct proc *rp, sys_map_t *map)
{
  int i;

  for (i=0; i < NR_SYS_PROCS; i++) {
  	if (get_sys_bit(*map, i))
  		set_sendto_bit(rp, i);
  	else
  		unset_sendto_bit(rp, i);
  }
}

/*===========================================================================*
 *				send_sig				     *
 *===========================================================================*/
PUBLIC void send_sig(endpoint_t ep, int sig_nr)
{
/* Notify a system process about a signal. This is straightforward. Simply
 * set the signal that is to be delivered in the pending signals map and 
 * send a notification with source SYSTEM.
 */ 
  register struct proc *rp;
  int proc_nr;

  if(!isokendpt(ep, &proc_nr) || isemptyn(proc_nr))
	panic("send_sig to empty process: %d",  ep);

  rp = proc_addr(proc_nr);
  (void) sigaddset(&priv(rp)->s_sig_pending, sig_nr);
  mini_notify(proc_addr(SYSTEM), rp->p_endpoint);
}

/*===========================================================================*
 *				cause_sig				     *
 *===========================================================================*/
PUBLIC void cause_sig(proc_nr, sig_nr)
proc_nr_t proc_nr;		/* process to be signalled */
int sig_nr;			/* signal to be sent */
{
/* A system process wants to send a signal to a process.  Examples are:
 *  - HARDWARE wanting to cause a SIGSEGV after a CPU exception
 *  - TTY wanting to cause SIGINT upon getting a DEL
 *  - FS wanting to cause SIGPIPE for a broken pipe 
 * Signals are handled by sending a message to the signal manager assigned to
 * the process. This function handles the signals and makes sure the signal
 * manager gets them by sending a notification. The process being signaled
 * is blocked while the signal manager has not finished all signals for it.
 * Race conditions between calls to this function and the system calls that
 * process pending kernel signals cannot exist. Signal related functions are
 * only called when a user process causes a CPU exception and from the kernel 
 * process level, which runs to completion.
 */
  register struct proc *rp, *sig_mgr_rp;
  endpoint_t sig_mgr;
  int sig_mgr_proc_nr;

  /* Lookup signal manager. */
  rp = proc_addr(proc_nr);
  sig_mgr = priv(rp)->s_sig_mgr;
  if(sig_mgr == SELF) sig_mgr = rp->p_endpoint;

  /* If the target is the signal manager of itself, send the signal directly. */
  if(rp->p_endpoint == sig_mgr) {
       if(SIGS_IS_LETHAL(sig_nr)) {
           /* If the signal is lethal, see if a backup signal manager exists. */
           sig_mgr = priv(rp)->s_bak_sig_mgr;
           if(sig_mgr != NONE && isokendpt(sig_mgr, &sig_mgr_proc_nr)) {
               priv(rp)->s_sig_mgr = sig_mgr;
               priv(rp)->s_bak_sig_mgr = NONE;
               sig_mgr_rp = proc_addr(sig_mgr_proc_nr);
               RTS_UNSET(sig_mgr_rp, RTS_NO_PRIV);
               cause_sig(proc_nr, sig_nr); /* try again with the new sig mgr. */
               return;
           }
           /* We are out of luck. Time to panic. */
           proc_stacktrace(rp);
           panic("cause_sig: sig manager %d gets lethal signal %d for itself",
	   	rp->p_endpoint, sig_nr);
       }
       (void) sigaddset(&priv(rp)->s_sig_pending, sig_nr);
       send_sig(rp->p_endpoint, SIGKSIGSM);
       return;
  }

  /* Check if the signal is already pending. Process it otherwise. */
  if (! sigismember(&rp->p_pending, sig_nr)) {
      (void) sigaddset(&rp->p_pending, sig_nr);
      if (! (RTS_ISSET(rp, RTS_SIGNALED))) {		/* other pending */
	  RTS_SET(rp, RTS_SIGNALED | RTS_SIG_PENDING);
          send_sig(sig_mgr, SIGKSIG);
      }
  }
}

/*===========================================================================*
 *				sig_delay_done				     *
 *===========================================================================*/
PUBLIC void sig_delay_done(struct proc *rp)
{
/* A process is now known not to send any direct messages.
 * Tell PM that the stop delay has ended, by sending a signal to the process.
 * Used for actual signal delivery.
 */

  rp->p_misc_flags &= ~MF_SIG_DELAY;

  cause_sig(proc_nr(rp), SIGSNDELAY);
}

#if _MINIX_CHIP == _CHIP_INTEL

/*===========================================================================*
 *				umap_bios				     *
 *===========================================================================*/
PUBLIC phys_bytes umap_bios(vir_addr, bytes)
vir_bytes vir_addr;		/* virtual address in BIOS segment */
vir_bytes bytes;		/* # of bytes to be copied */
{
/* Calculate the physical memory address at the BIOS. Note: currently, BIOS
 * address zero (the first BIOS interrupt vector) is not considered as an 
 * error here, but since the physical address will be zero as well, the 
 * calling function will think an error occurred. This is not a problem,
 * since no one uses the first BIOS interrupt vector.  
 */

  /* Check all acceptable ranges. */
  if (vir_addr >= BIOS_MEM_BEGIN && vir_addr + bytes <= BIOS_MEM_END)
  	return (phys_bytes) vir_addr;
  else if (vir_addr >= BASE_MEM_TOP && vir_addr + bytes <= UPPER_MEM_END)
  	return (phys_bytes) vir_addr;

  printf("Warning, error in umap_bios, virtual address 0x%x\n", vir_addr);
  return 0;
}
#endif

/*===========================================================================*
 *                              umap_grant                                   *
 *===========================================================================*/
PUBLIC phys_bytes umap_grant(rp, grant, bytes)
struct proc *rp;                /* pointer to proc table entry for process */
cp_grant_id_t grant;            /* grant no. */
vir_bytes bytes;                /* size */
{
        int proc_nr;
        vir_bytes offset, ret;
        endpoint_t granter;

        /* See if the grant in that process is sensible, and 
         * find out the virtual address and (optionally) new
         * process for that address.
         *
         * Then convert that process to a slot number.
         */
        if(verify_grant(rp->p_endpoint, ANY, grant, bytes, 0, 0,
                &offset, &granter) != OK) {
		printf("SYSTEM: umap_grant: verify_grant failed\n");
                return 0;
        }

        if(!isokendpt(granter, &proc_nr)) {
		printf("SYSTEM: umap_grant: isokendpt failed\n");
                return 0;
        }
 
        /* Do the mapping from virtual to physical. */
        ret = umap_virtual(proc_addr(proc_nr), D, offset, bytes);
	if(!ret) {
		printf("SYSTEM:umap_grant:umap_virtual failed; grant %s:%d -> %s: vir 0x%lx\n",
			rp->p_name, grant, 
			proc_addr(proc_nr)->p_name, offset);
	}
	return ret;
}

/*===========================================================================*
 *			         clear_ipc				     *
 *===========================================================================*/
PRIVATE void clear_ipc(
  register struct proc *rc	/* slot of process to clean up */
)
{
/* Clear IPC data for a given process slot. */
  struct proc **xpp;			/* iterate over caller queue */

  if (RTS_ISSET(rc, RTS_SENDING)) {
      int target_proc;

      okendpt(rc->p_sendto_e, &target_proc);
      xpp = &proc_addr(target_proc)->p_caller_q; /* destination's queue */
      while (*xpp) {		/* check entire queue */
          if (*xpp == rc) {			/* process is on the queue */
              *xpp = (*xpp)->p_q_link;		/* replace by next process */
#if DEBUG_ENABLE_IPC_WARNINGS
	      printf("endpoint %d / %s removed from queue at %d\n",
	          rc->p_endpoint, rc->p_name, rc->p_sendto_e);
#endif
              break;				/* can only be queued once */
          }
          xpp = &(*xpp)->p_q_link;		/* proceed to next queued */
      }
      RTS_UNSET(rc, RTS_SENDING);
  }
  RTS_UNSET(rc, RTS_RECEIVING);
}

/*===========================================================================*
 *			         clear_endpoint				     *
 *===========================================================================*/
PUBLIC void clear_endpoint(rc)
register struct proc *rc;		/* slot of process to clean up */
{
  if(isemptyp(rc)) panic("clear_proc: empty process: %d",  rc->p_endpoint);

  /* Make sure that the exiting process is no longer scheduled. */
  RTS_SET(rc, RTS_NO_ENDPOINT);
  if (priv(rc)->s_flags & SYS_PROC)
  {
	priv(rc)->s_asynsize= 0;
  }

  /* If the process happens to be queued trying to send a
   * message, then it must be removed from the message queues.
   */
  clear_ipc(rc);

  /* Likewise, if another process was sending or receive a message to or from 
   * the exiting process, it must be alerted that process no longer is alive.
   * Check all processes. 
   */
  clear_ipc_refs(rc, EDEADSRCDST);

}

/*===========================================================================*
 *			       clear_ipc_refs				     *
 *===========================================================================*/
PUBLIC void clear_ipc_refs(rc, caller_ret)
register struct proc *rc;		/* slot of process to clean up */
int caller_ret;				/* code to return on callers */
{
/* Clear IPC references for a given process slot. */
  struct proc *rp;			/* iterate over process table */

  for (rp = BEG_PROC_ADDR; rp < END_PROC_ADDR; rp++) {
      if(isemptyp(rp))
	continue;

      /* Unset pending notification bits. */
      unset_sys_bit(priv(rp)->s_notify_pending, priv(rc)->s_id);

      /* XXX FIXME: Cleanup should be done for senda() as well. For this to be
       * done in a realistic way, we need a better implementation of senda
       * with a bitmap similar to s_notify_pending for notify() rather than
       * a single global MF_ASYNMSG flag. The current arrangement exposes
       * several performance issues.
       */

      /* Check if process depends on given process. */
      if (P_BLOCKEDON(rp) == rc->p_endpoint) {
          rp->p_reg.retreg = caller_ret;	/* return requested code */
	  clear_ipc(rp);
      }
  }
}

/*===========================================================================*
 *                              kernel_call_resume                           *
 *===========================================================================*/
PUBLIC void kernel_call_resume(struct proc *caller)
{
	int result;

	assert(!RTS_ISSET(caller, RTS_SLOT_FREE));
	assert(!RTS_ISSET(caller, RTS_VMREQUEST));

	assert(caller->p_vmrequest.saved.reqmsg.m_source == caller->p_endpoint);

	/*
	printf("KERNEL_CALL restart from %s / %d rts 0x%08x misc 0x%08x\n",
			caller->p_name, caller->p_endpoint,
			caller->p_rts_flags, caller->p_misc_flags);
	 */

	/* re-execute the kernel call, with MF_KCALL_RESUME still set so
	 * the call knows this is a retry.
	 */
	result = kernel_call_dispatch(caller, &caller->p_vmrequest.saved.reqmsg);
	/*
	 * we are resuming the kernel call so we have to remove this flag so it
	 * can be set again
	 */
	caller->p_misc_flags &= ~MF_KCALL_RESUME;
	kernel_call_finish(caller, &caller->p_vmrequest.saved.reqmsg, result);
}

/*===========================================================================*
 *                               sched_proc                                  *
 *===========================================================================*/
PUBLIC int sched_proc(struct proc *p,
			int priority,
			int quantum,
			int cpu)
{
	/* Make sure the values given are within the allowed range.*/
	if ((priority < TASK_Q && priority != -1) || priority > NR_SCHED_QUEUES)
		return(EINVAL);

	if (quantum < 1 && quantum != -1)
		return(EINVAL);

#ifdef CONFIG_SMP
	if ((cpu < 0 && cpu != -1) || (cpu > 0 && (unsigned) cpu >= ncpus))
		return(EINVAL);
	if (cpu != -1 && !(cpu_is_ready(cpu)))
		return EBADCPU;
#endif

	/* In some cases, we might be rescheduling a runnable process. In such
	 * a case (i.e. if we are updating the priority) we set the NO_QUANTUM
	 * flag before the generic unset to dequeue/enqueue the process
	 */

	/* FIXME this preempts the process, do we really want to do that ?*/

	/* FIXME this is a problem for SMP if the processes currently runs on a
	 * different CPU */
	if (proc_is_runnable(p)) {
#ifdef CONFIG_SMP
		if (p->p_cpu != cpuid && cpu != -1 && cpu != p->p_cpu) {
			smp_schedule_migrate_proc(p, cpu);
		}
#endif

		RTS_SET(p, RTS_NO_QUANTUM);
	}

	if (proc_is_runnable(p))
		RTS_SET(p, RTS_NO_QUANTUM);

	if (priority != -1)
		p->p_priority = priority;
	if (quantum != -1) {
		p->p_quantum_size_ms = quantum;
		p->p_cpu_time_left = ms_2_cpu_time(quantum);
	}
#ifdef CONFIG_SMP
	if (cpu != -1)
		p->p_cpu = cpu;
#endif

	/* Clear the scheduling bit and enqueue the process */
	RTS_UNSET(p, RTS_NO_QUANTUM);

	return OK;
}