system.c

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/* 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
 *   send_sig:          send a signal directly to a system process
 *   cause_sig:         take action to cause a signal to occur via PM
 *   umap_local:        map virtual address in LOCAL_SEG to physical 
 *   umap_remote:       map virtual address in REMOTE_SEG to physical 
 *   umap_bios:         map virtual address in BIOS_SEG to physical 
 *   virtual_copy:      copy bytes from one virtual address to another 
 *   get_randomness:    accumulate randomness in a buffer
 *   clear_endpoint:    remove a process' ability to send and receive messages
 *
 * Changes:
 *   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 <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <sys/sigcontext.h>
#include <minix/endpoint.h>
#if (CHIP == INTEL)
#include <ibm/memory.h>
#include "protect.h"
#endif

/* 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. 
 */
PUBLIC int (*call_vec[NR_SYS_CALLS])(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)  

FORWARD _PROTOTYPE( void initialize, (void));

/*===========================================================================*
 *                              sys_task                                     *
 *===========================================================================*/
PUBLIC void sys_task()
{
/* Main entry point of sys_task.  Get the message and dispatch on type. */
  static message m;
  register int result;
  register struct proc *caller_ptr;
  unsigned int call_nr;
  int s;

  /* Initialize the system task. */
  initialize();

  while (TRUE) {
      /* Get work. Block and wait until a request message arrives. */
      receive(ANY, &m);                 
      call_nr = (unsigned) m.m_type - KERNEL_CALL;      
      who_e = m.m_source;
      okendpt(who_e, &who_p);
      caller_ptr = proc_addr(who_p);

      /* See if the caller made a valid request and try to handle it. */
      if (! (priv(caller_ptr)->s_call_mask & (1<<call_nr))) {
#if DEBUG_ENABLE_IPC_WARNINGS
          kprintf("SYSTEM: request %d from %d denied.\n", call_nr,m.m_source);
#endif
          result = ECALLDENIED;                 /* illegal message type */
      } else if (call_nr >= NR_SYS_CALLS) {             /* check call number */
#if DEBUG_ENABLE_IPC_WARNINGS
          kprintf("SYSTEM: illegal request %d from %d.\n", call_nr,m.m_source);
#endif
          result = EBADREQUEST;                 /* illegal message type */
      } 
      else {
          result = (*call_vec[call_nr])(&m);    /* handle the system call */
      }

      /* Send a reply, unless inhibited by a handler function. Use the kernel
       * function lock_send() to prevent a system call trap. The destination
       * is known to be blocked waiting for a message.
       */
      if (result != EDONTREPLY) {
          m.m_type = result;                    /* report status of call */
          if (OK != (s=lock_send(m.m_source, &m))) {
              kprintf("SYSTEM, reply to %d failed: %d\n", m.m_source, s);
          }
      }
  }
}

/*===========================================================================*
 *                              initialize                                   *
 *===========================================================================*/
PRIVATE void initialize(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] = do_unused;
  }

  /* Process management. */
  map(SYS_FORK, do_fork);               /* a process forked a new process */
  map(SYS_EXEC, do_exec);               /* update process after execute */
  map(SYS_EXIT, do_exit);               /* clean up after process exit */
  map(SYS_NICE, do_nice);               /* set scheduling priority */
  map(SYS_PRIVCTL, do_privctl);         /* system privileges control */
  map(SYS_TRACE, do_trace);             /* request a trace operation */

  /* Signal handling. */
  map(SYS_KILL, do_kill);               /* cause a process to be signaled */
  map(SYS_GETKSIG, do_getksig);         /* PM checks for pending signals */
  map(SYS_ENDKSIG, do_endksig);         /* PM finished processing 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_SDEVIO, do_sdevio);           /* phys_insb, _insw, _outsb, _outsw */
  map(SYS_VDEVIO, do_vdevio);           /* vector with devio requests */ 
  map(SYS_INT86, do_int86);             /* real-mode BIOS calls */ 

  /* 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_VM_SETBUF, do_vm_setbuf);     /* PM passes buffer for page tables */
  map(SYS_VM_MAP, do_vm_map);           /* Map/unmap physical (device) memory */

  /* Copying. */
  map(SYS_UMAP, do_umap);               /* map virtual to physical address */
  map(SYS_VIRCOPY, do_vircopy);         /* use pure virtual addressing */
  map(SYS_PHYSCOPY, do_physcopy);       /* use physical addressing */
  map(SYS_VIRVCOPY, do_virvcopy);       /* vector with copy requests */
  map(SYS_PHYSVCOPY, do_physvcopy);     /* vector with copy requests */

  /* Clock functionality. */
  map(SYS_TIMES, do_times);             /* get uptime and process times */
  map(SYS_SETALARM, do_setalarm);       /* schedule a synchronous alarm */

  /* System control. */
  map(SYS_ABORT, do_abort);             /* abort MINIX */
  map(SYS_GETINFO, do_getinfo);         /* request system information */ 
  map(SYS_IOPENABLE, do_iopenable);     /* Enable I/O */
}

/*===========================================================================*
 *                              get_priv                                     *
 *===========================================================================*/
PUBLIC int get_priv(rc, proc_type)
register struct proc *rc;               /* new (child) process pointer */
int proc_type;                          /* system or user process flag */
{
/* Get a privilege structure. All user processes share the same privilege 
 * structure. System processes get their own privilege structure. 
 */
  register struct priv *sp;                     /* privilege structure */

  if (proc_type == SYS_PROC) {                  /* find a new slot */
      for (sp = BEG_PRIV_ADDR; sp < END_PRIV_ADDR; ++sp) 
          if (sp->s_proc_nr == NONE && sp->s_id != USER_PRIV_ID) break; 
      if (sp->s_proc_nr != NONE) return(ENOSPC);
      rc->p_priv = sp;                          /* assign new slot */
      rc->p_priv->s_proc_nr = proc_nr(rc);      /* set association */
      rc->p_priv->s_flags = SYS_PROC;           /* mark as privileged */
  } else {
      rc->p_priv = &priv[USER_PRIV_ID];         /* use shared slot */
      rc->p_priv->s_proc_nr = INIT_PROC_NR;     /* set association */
      rc->p_priv->s_flags = 0;                  /* no initial flags */
  }
  return(OK);
}

/*===========================================================================*
 *                              get_randomness                               *
 *===========================================================================*/
PUBLIC void get_randomness(source)
int source;
{
/* On machines with the RDTSC (cycle counter read instruction - pentium
 * and up), use that for high-resolution raw entropy gathering. Otherwise,
 * use the realtime clock (tick resolution).
 *
 * Unfortunately this test is run-time - we don't want to bother with
 * compiling different kernels for different machines.
 *
 * On machines without RDTSC, we use read_clock().
 */
  int r_next;
  unsigned long tsc_high, tsc_low;

  source %= RANDOM_SOURCES;
  r_next= krandom.bin[source].r_next;
  if (machine.processor > 486) {
      read_tsc(&tsc_high, &tsc_low);
      krandom.bin[source].r_buf[r_next] = tsc_low;
  } else {
      krandom.bin[source].r_buf[r_next] = read_clock();
  }
  if (krandom.bin[source].r_size < RANDOM_ELEMENTS) {
        krandom.bin[source].r_size ++;
  }
  krandom.bin[source].r_next = (r_next + 1 ) % RANDOM_ELEMENTS;
}

/*===========================================================================*
 *                              send_sig                                     *
 *===========================================================================*/
PUBLIC void send_sig(int proc_nr, 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.
 *
 * Process number is verified to avoid writing in random places, but we
 * don't kprintf() or panic() because that causes send_sig() invocations.
 */ 
  register struct proc *rp;
  static int n;

  if(!isokprocn(proc_nr) || isemptyn(proc_nr))
        return;

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

/*===========================================================================*
 *                              cause_sig                                    *
 *===========================================================================*/
PUBLIC void cause_sig(proc_nr, sig_nr)
int proc_nr;                    /* process to be signalled */
int sig_nr;                     /* signal to be sent, 1 to _NSIG */
{
/* 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 PM.  This function handles the 
 * signals and makes sure the PM gets them by sending a notification. The 
 * process being signaled is blocked while PM 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;

  /* Check if the signal is already pending. Process it otherwise. */
  rp = proc_addr(proc_nr);
  if (! sigismember(&rp->p_pending, sig_nr)) {
      sigaddset(&rp->p_pending, sig_nr);
      if (! (rp->p_rts_flags & SIGNALED)) {             /* other pending */
          if (rp->p_rts_flags == 0) lock_dequeue(rp);   /* make not ready */
          rp->p_rts_flags |= SIGNALED | SIG_PENDING;    /* update flags */
          send_sig(PM_PROC_NR, SIGKSIG);
      }
  }
}

/*===========================================================================*
 *                              umap_bios                                    *
 *===========================================================================*/
PUBLIC phys_bytes umap_bios(rp, vir_addr, bytes)
register struct proc *rp;       /* pointer to proc table entry for process */
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;

#if DEAD_CODE   /* brutal fix, if the above is too restrictive */
  if (vir_addr >= BIOS_MEM_BEGIN && vir_addr + bytes <= UPPER_MEM_END)
        return (phys_bytes) vir_addr;
#endif

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

/*===========================================================================*
 *                              umap_local                                   *
 *===========================================================================*/
PUBLIC phys_bytes umap_local(rp, seg, vir_addr, bytes)
register struct proc *rp;       /* pointer to proc table entry for process */
int seg;                        /* T, D, or S segment */
vir_bytes vir_addr;             /* virtual address in bytes within the seg */
vir_bytes bytes;                /* # of bytes to be copied */
{
/* Calculate the physical memory address for a given virtual address. */
  vir_clicks vc;                /* the virtual address in clicks */
  phys_bytes pa;                /* intermediate variables as phys_bytes */
#if (CHIP == INTEL)
  phys_bytes seg_base;
#endif

  /* If 'seg' is D it could really be S and vice versa.  T really means T.
   * If the virtual address falls in the gap,  it causes a problem. On the
   * 8088 it is probably a legal stack reference, since "stackfaults" are
   * not detected by the hardware.  On 8088s, the gap is called S and
   * accepted, but on other machines it is called D and rejected.
   * The Atari ST behaves like the 8088 in this respect.
   */

  if (bytes <= 0) return( (phys_bytes) 0);
  if (vir_addr + bytes <= vir_addr) return 0;   /* overflow */
  vc = (vir_addr + bytes - 1) >> CLICK_SHIFT;   /* last click of data */

#if (CHIP == INTEL) || (CHIP == M68000)
  if (seg != T)
        seg = (vc < rp->p_memmap[D].mem_vir + rp->p_memmap[D].mem_len ? D : S);
#else
  if (seg != T)
        seg = (vc < rp->p_memmap[S].mem_vir ? D : S);
#endif

  if ((vir_addr>>CLICK_SHIFT) >= rp->p_memmap[seg].mem_vir + 
        rp->p_memmap[seg].mem_len) return( (phys_bytes) 0 );

  if (vc >= rp->p_memmap[seg].mem_vir + 
        rp->p_memmap[seg].mem_len) return( (phys_bytes) 0 );

#if (CHIP == INTEL)
  seg_base = (phys_bytes) rp->p_memmap[seg].mem_phys;
  seg_base = seg_base << CLICK_SHIFT;   /* segment origin in bytes */
#endif
  pa = (phys_bytes) vir_addr;
#if (CHIP != M68000)
  pa -= rp->p_memmap[seg].mem_vir << CLICK_SHIFT;
  return(seg_base + pa);
#endif
#if (CHIP == M68000)
  pa -= (phys_bytes)rp->p_memmap[seg].mem_vir << CLICK_SHIFT;
  pa += (phys_bytes)rp->p_memmap[seg].mem_phys << CLICK_SHIFT;
  return(pa);
#endif
}

/*===========================================================================*
 *                              umap_remote                                  *
 *===========================================================================*/
PUBLIC phys_bytes umap_remote(rp, seg, vir_addr, bytes)
register struct proc *rp;       /* pointer to proc table entry for process */
int seg;                        /* index of remote segment */
vir_bytes vir_addr;             /* virtual address in bytes within the seg */
vir_bytes bytes;                /* # of bytes to be copied */
{
/* Calculate the physical memory address for a given virtual address. */
  struct far_mem *fm;

  if (bytes <= 0) return( (phys_bytes) 0);
  if (seg < 0 || seg >= NR_REMOTE_SEGS) return( (phys_bytes) 0);

  fm = &rp->p_priv->s_farmem[seg];
  if (! fm->in_use) return( (phys_bytes) 0);
  if (vir_addr + bytes > fm->mem_len) return( (phys_bytes) 0);

  return(fm->mem_phys + (phys_bytes) vir_addr); 
}

/*===========================================================================*
 *                              virtual_copy                                 *
 *===========================================================================*/
PUBLIC int virtual_copy(src_addr, dst_addr, bytes)
struct vir_addr *src_addr;      /* source virtual address */
struct vir_addr *dst_addr;      /* destination virtual address */
vir_bytes bytes;                /* # of bytes to copy  */
{
/* Copy bytes from virtual address src_addr to virtual address dst_addr. 
 * Virtual addresses can be in ABS, LOCAL_SEG, REMOTE_SEG, or BIOS_SEG.
 */
  struct vir_addr *vir_addr[2]; /* virtual source and destination address */
  phys_bytes phys_addr[2];      /* absolute source and destination */ 
  int seg_index;
  int i;

  /* Check copy count. */
  if (bytes <= 0) return(EDOM);

  /* Do some more checks and map virtual addresses to physical addresses. */
  vir_addr[_SRC_] = src_addr;
  vir_addr[_DST_] = dst_addr;
  for (i=_SRC_; i<=_DST_; i++) {
        int proc_nr, type;
        struct proc *p;

        type = vir_addr[i]->segment & SEGMENT_TYPE;
        if(type != PHYS_SEG && isokendpt(vir_addr[i]->proc_nr_e, &proc_nr))
           p = proc_addr(proc_nr);
        else
           p = NULL;

      /* Get physical address. */
      switch(type) {
      case LOCAL_SEG:
          if(!p) return EDEADSRCDST;
          seg_index = vir_addr[i]->segment & SEGMENT_INDEX;
          phys_addr[i] = umap_local(p, seg_index, vir_addr[i]->offset, bytes);
          break;
      case REMOTE_SEG:
          if(!p) return EDEADSRCDST;
          seg_index = vir_addr[i]->segment & SEGMENT_INDEX;
          phys_addr[i] = umap_remote(p, seg_index, vir_addr[i]->offset, bytes);
          break;
      case BIOS_SEG:
          if(!p) return EDEADSRCDST;
          phys_addr[i] = umap_bios(p, vir_addr[i]->offset, bytes );
          break;
      case PHYS_SEG:
          phys_addr[i] = vir_addr[i]->offset;
          break;
      default:
          return(EINVAL);
      }

      /* Check if mapping succeeded. */
      if (phys_addr[i] <= 0 && vir_addr[i]->segment != PHYS_SEG) 
          return(EFAULT);
  }

  /* Now copy bytes between physical addresseses. */
  phys_copy(phys_addr[_SRC_], phys_addr[_DST_], (phys_bytes) bytes);
  return(OK);
}


/*===========================================================================*
 *                               clear_endpoint                              *
 *===========================================================================*/
PUBLIC void clear_endpoint(rc)
register struct proc *rc;               /* slot of process to clean up */
{
  register struct proc *rp;             /* iterate over process table */
  register struct proc **xpp;           /* iterate over caller queue */
  int i;
  int sys_id;

  if(isemptyp(rc)) panic("clear_proc: empty process", proc_nr(rc));

  /* Make sure that the exiting process is no longer scheduled. */
  if (rc->p_rts_flags == 0) lock_dequeue(rc);
  rc->p_rts_flags |= NO_ENDPOINT;

  /* If the process happens to be queued trying to send a
   * message, then it must be removed from the message queues.
   */
  if (rc->p_rts_flags & SENDING) {
      int target_proc;

      okendpt(rc->p_sendto_e, &target_proc);
      xpp = &proc_addr(target_proc)->p_caller_q; /* destination's queue */
      while (*xpp != NIL_PROC) {                /* 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
              kprintf("Proc %d removed from queue at %d\n",
                  proc_nr(rc), rc->p_sendto_e);
#endif
              break;                            /* can only be queued once */
          }
          xpp = &(*xpp)->p_q_link;              /* proceed to next queued */
      }
      rc->p_rts_flags &= ~SENDING;
  }
  rc->p_rts_flags &= ~RECEIVING;

  /* 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. 
   */
  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);

      /* Check if process is receiving from exiting process. */
      if ((rp->p_rts_flags & RECEIVING) && rp->p_getfrom_e == rc->p_endpoint) {
          rp->p_reg.retreg = ESRCDIED;          /* report source died */
          rp->p_rts_flags &= ~RECEIVING;        /* no longer receiving */
#if DEBUG_ENABLE_IPC_WARNINGS
          kprintf("Proc %d receive dead src %d\n", proc_nr(rp), proc_nr(rc));
#endif
          if (rp->p_rts_flags == 0) lock_enqueue(rp);/* let process run again */
      } 
      if ((rp->p_rts_flags & SENDING) && rp->p_sendto_e == rc->p_endpoint) {
          rp->p_reg.retreg = EDSTDIED;          /* report destination died */
          rp->p_rts_flags &= ~SENDING;          /* no longer sending */
#if DEBUG_ENABLE_IPC_WARNINGS
          kprintf("Proc %d send dead dst %d\n", proc_nr(rp), proc_nr(rc));
#endif
          if (rp->p_rts_flags == 0) lock_enqueue(rp);/* let process run again */
      } 
  }
}

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