* xm-sun3os4.h, xm-sun4os4.h, xconfig/decstation, xconfig/i386sco,

[binutils.git] / gdb / procfs.c

/* Machine independent support for SVR4 /proc (process file system) for GDB.
   Copyright (C) 1991 Free Software Foundation, Inc.
   Written by Fred Fish at Cygnus Support.

This file is part of GDB.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */


/*                      N  O  T  E  S

For information on the details of using /proc consult section proc(4)
in the UNIX System V Release 4 System Administrator's Reference Manual.

The general register and floating point register sets are manipulated by
separate ioctl's.  This file makes the assumption that if FP0_REGNUM is
defined, then support for the floating point register set is desired,
regardless of whether or not the actual target has floating point hardware.

 */



#include "param.h"

#ifdef USE_PROC_FS      /* Entire file goes away if not using /proc */

#include <stdio.h>
#include <sys/procfs.h>
#include <fcntl.h>
#include <errno.h>

#include "defs.h"
#include "ansidecl.h"
#include "inferior.h"
#include "target.h"

#ifndef PROC_NAME_FMT
#define PROC_NAME_FMT "/proc/%d"
#endif

extern void EXFUN(supply_gregset, (gregset_t *gregsetp));
extern void EXFUN(fill_gregset, (gregset_t *gresetp, int regno));

#if defined (FP0_REGNUM)
extern void EXFUN(supply_fpregset, (fpregset_t *fpregsetp));
extern void EXFUN(fill_fpregset, (fpregset_t *fpresetp, int regno));
#endif

#if 1   /* FIXME: Gross and ugly hack to resolve coredep.c global */
CORE_ADDR kernel_u_addr;
#endif

/*  All access to the inferior, either one started by gdb or one that has
    been attached to, is controlled by an instance of a procinfo structure,
    defined below.  Since gdb currently only handles one inferior at a time,
    the procinfo structure is statically allocated and only one exists at
    any given time. */

struct procinfo {
  int valid;                    /* Nonzero if pid, fd, & pathname are valid */
  int pid;                      /* Process ID of inferior */
  int fd;                       /* File descriptor for /proc entry */
  char *pathname;               /* Pathname to /proc entry */
  int was_stopped;              /* Nonzero if was stopped prior to attach */
  prrun_t prrun;                /* Control state when it is run */
  prstatus_t prstatus;          /* Current process status info */
  gregset_t gregset;            /* General register set */
  fpregset_t fpregset;          /* Floating point register set */
  fltset_t fltset;              /* Current traced hardware fault set */
  sigset_t trace;               /* Current traced signal set */
  sysset_t exitset;             /* Current traced system call exit set */
  sysset_t entryset;            /* Current traced system call entry set */
} pi;

/* Forward declarations of static functions so we don't have to worry
   about ordering within this file.  The EXFUN macro may be slightly
   misleading.  Should probably be called DCLFUN instead, or something
   more intuitive, since it can be used for both static and external
   definitions. */

static void EXFUN(proc_init_failed, (char *why));
static int EXFUN(open_proc_file, (int pid));
static void EXFUN(close_proc_file, (void));
static void EXFUN(unconditionally_kill_inferior, (void));

/*

GLOBAL FUNCTION

        ptrace -- override library version to force errors for /proc version

SYNOPSIS

        int ptrace (int request, int pid, int arg3, int arg4)

DESCRIPTION

        When gdb is configured to use /proc, it should not be calling
        or otherwise attempting to use ptrace.  In order to catch errors
        where use of /proc is configured, but some routine is still calling
        ptrace, we provide a local version of a function with that name
        that does nothing but issue an error message.
*/

int
DEFUN(ptrace, (request, pid, arg3, arg4),
      int request AND
      int pid AND
      int arg3 AND
      int arg4)
{
  error ("internal error - there is a call to ptrace() somewhere");
  /*NOTREACHED*/
}

/*

GLOBAL FUNCTION

        kill_inferior_fast -- kill inferior while gdb is exiting

SYNOPSIS

        void kill_inferior_fast (void)

DESCRIPTION

        This is used when GDB is exiting.  It gives less chance of error.

NOTES

        Don't attempt to kill attached inferiors since we may be called
        when gdb is in the process of aborting, and killing the attached
        inferior may be very anti-social.  This is particularly true if we
        were attached just so we could use the /proc facilities to get
        detailed information about it's status.

*/

void
DEFUN_VOID(kill_inferior_fast)
{
  if (inferior_pid != 0 && !attach_flag)
    {
      unconditionally_kill_inferior ();
    }
}

/*

GLOBAL FUNCTION

        kill_inferior - kill any currently inferior

SYNOPSIS

        void kill_inferior (void)

DESCRIPTION

        Kill any current inferior.

NOTES

        Kills even attached inferiors.  Presumably the user has already
        been prompted that the inferior is an attached one rather than
        one started by gdb.  (FIXME?)

*/

void
DEFUN_VOID(kill_inferior)
{
  if (inferior_pid != 0)
    {
      unconditionally_kill_inferior ();
      target_mourn_inferior ();
    }
}

/*

LOCAL FUNCTION

        unconditionally_kill_inferior - terminate the inferior

SYNOPSIS

        static void unconditionally_kill_inferior (void)

DESCRIPTION

        Kill the current inferior.  Should not be called until it
        is at least tested that there is an inferior.

NOTE

        A possibly useful enhancement would be to first try sending
        the inferior a terminate signal, politely asking it to commit
        suicide, before we murder it.

*/

static void
DEFUN_VOID(unconditionally_kill_inferior)
{
  int signo;
  
  signo = SIGKILL;
  (void) ioctl (pi.fd, PIOCKILL, &signo);
  close_proc_file ();
  wait ((int *) 0);
}

/*

GLOBAL FUNCTION

        child_xfer_memory -- copy data to or from inferior memory space

SYNOPSIS

        int child_xfer_memory (CORE_ADDR memaddr, char *myaddr, int len,
                int dowrite, struct target_ops target)

DESCRIPTION

        Copy LEN bytes to/from inferior's memory starting at MEMADDR
        from/to debugger memory starting at MYADDR.  Copy from inferior
        if DOWRITE is zero or to inferior if DOWRITE is nonzero.
  
        Returns the length copied, which is either the LEN argument or
        zero.  This xfer function does not do partial moves, since child_ops
        doesn't allow memory operations to cross below us in the target stack
        anyway.

NOTES

        The /proc interface makes this an almost trivial task.
 */


int
DEFUN(child_xfer_memory, (memaddr, myaddr, len, dowrite, target),
      CORE_ADDR memaddr AND
      char *myaddr AND
      int len AND
      int dowrite AND
      struct target_ops target /* ignored */)
{
  int nbytes = 0;

  if (lseek (pi.fd, (off_t) memaddr, 0) == (off_t) memaddr)
    {
      if (dowrite)
        {
          nbytes = write (pi.fd, myaddr, len);
        }
      else
        {
          nbytes = read (pi.fd, myaddr, len);
        }
      if (nbytes < 0)
        {
          nbytes = 0;
        }
    }
  return (nbytes);
}

/*

GLOBAL FUNCTION

        store_inferior_registers -- copy register values back to inferior

SYNOPSIS

        void store_inferior_registers (int regno)

DESCRIPTION

        Store our current register values back into the inferior.  If
        REGNO is -1 then store all the register, otherwise store just
        the value specified by REGNO.

NOTES

        If we are storing only a single register, we first have to get all
        the current values from the process, overwrite the desired register
        in the gregset with the one we want from gdb's registers, and then
        send the whole set back to the process.  For writing all the
        registers, all we have to do is generate the gregset and send it to
        the process.

        Also note that the process has to be stopped on an event of interest
        for this to work, which basically means that it has to have been
        run under the control of one of the other /proc ioctl calls and not
        ptrace.  Since we don't use ptrace anyway, we don't worry about this
        fine point, but it is worth noting for future reference.

        Gdb is confused about what this function is supposed to return.
        Some versions return a value, others return nothing.  Some are
        declared to return a value and actually return nothing.  Gdb ignores
        anything returned.  (FIXME)

 */

void
DEFUN(store_inferior_registers, (regno),
      int regno)
{
  if (regno != -1)
    {
      (void) ioctl (pi.fd, PIOCGREG, &pi.gregset);
    }
  fill_gregset (&pi.gregset, regno);
  (void) ioctl (pi.fd, PIOCSREG, &pi.gregset);

#if defined (FP0_REGNUM)

  /* Now repeat everything using the floating point register set, if the
     target has floating point hardware. Since we ignore the returned value,
     we'll never know whether it worked or not anyway. */

  if (regno != -1)
    {
      (void) ioctl (pi.fd, PIOCGFPREG, &pi.fpregset);
    }
  fill_fpregset (&pi.fpregset, regno);
  (void) ioctl (pi.fd, PIOCSFPREG, &pi.fpregset);

#endif  /* FP0_REGNUM */

}

/*

GLOBAL FUNCTION

        inferior_proc_init - initialize access to a /proc entry

SYNOPSIS

        void inferior_proc_init (int pid)

DESCRIPTION

        When gdb starts an inferior, this function is called in the parent
        process immediately after the fork.  It waits for the child to stop
        on the return from the exec system call (the child itself takes care
        of ensuring that this is set up), then sets up the set of signals
        and faults that are to be traced.

NOTES

        If proc_init_failed ever gets called, control returns to the command
        processing loop via the standard error handling code.
 */

void
DEFUN(inferior_proc_init, (int pid),
      int pid)
{
  if (!open_proc_file (pid))
    {
      proc_init_failed ("can't open process file");
    }
  else
    {
      (void) memset (&pi.prrun, 0, sizeof (pi.prrun));
      prfillset (&pi.prrun.pr_trace);
      prfillset (&pi.prrun.pr_fault);
      prdelset (&pi.prrun.pr_fault, FLTPAGE);
      if (ioctl (pi.fd, PIOCWSTOP, &pi.prstatus) < 0)
        {
          proc_init_failed ("PIOCWSTOP failed");
        }
      else if (ioctl (pi.fd, PIOCSTRACE, &pi.prrun.pr_trace) < 0)
        {
          proc_init_failed ("PIOCSTRACE failed");
        }
      else if (ioctl (pi.fd, PIOCSFAULT, &pi.prrun.pr_fault) < 0)
        {
          proc_init_failed ("PIOCSFAULT failed");
        }
    }
}

/*

GLOBAL FUNCTION

        proc_set_exec_trap -- arrange for exec'd child to halt at startup

SYNOPSIS

        void proc_set_exec_trap (void)

DESCRIPTION

        This function is called in the child process when starting up
        an inferior, prior to doing the exec of the actual inferior.
        It sets the child process's exitset to make exit from the exec
        system call an event of interest to stop on, and then simply
        returns.  The child does the exec, the system call returns, and
        the child stops at the first instruction, ready for the gdb
        parent process to take control of it.

NOTE

        We need to use all local variables since the child may be sharing
        it's data space with the parent, if vfork was used rather than
        fork.
 */

void
DEFUN_VOID(proc_set_exec_trap)
{
  sysset_t exitset;
  auto char procname[32];
  int fd;
  
  (void) sprintf (procname, PROC_NAME_FMT, getpid ());
  if ((fd = open (procname, O_RDWR)) < 0)
    {
      perror (procname);
      fflush (stderr);
      _exit (127);
    }
  premptyset (&exitset);
  praddset (&exitset, SYS_exec);
  praddset (&exitset, SYS_execve);
  if (ioctl (fd, PIOCSEXIT, &exitset) < 0)
    {
      perror (procname);
      fflush (stderr);
      _exit (127);
    }
}


#ifdef ATTACH_DETACH

/*

GLOBAL FUNCTION

        attach -- attach to an already existing process

SYNOPSIS

        int attach (int pid)

DESCRIPTION

        Attach to an already existing process with the specified process
        id.  If the process is not already stopped, query whether to
        stop it or not.

NOTES

        The option of stopping at attach time is specific to the /proc
        versions of gdb.  Versions using ptrace force the attachee
        to stop.

*/

int
DEFUN(attach, (pid),
      int pid)
{
  if (!open_proc_file (pid))
    {
      perror_with_name (pi.pathname);
      /* NOTREACHED */
    }
  
  /*  Get current status of process and if it is not already stopped,
      then stop it.  Remember whether or not it was stopped when we first
      examined it. */
  
  if (ioctl (pi.fd, PIOCSTATUS, &pi.prstatus) < 0)
    {
      print_sys_errmsg (pi.pathname, errno);
      close_proc_file ();
      error ("PIOCSTATUS failed");
    }
  if (pi.prstatus.pr_flags & (PR_STOPPED | PR_ISTOP))
    {
      pi.was_stopped = 1;
    }
  else
    {
      pi.was_stopped = 0;
      if (query ("Process is currently running, stop it? "))
        {
          if (ioctl (pi.fd, PIOCSTOP, &pi.prstatus) < 0)
            {
              print_sys_errmsg (pi.pathname, errno);
              close_proc_file ();
              error ("PIOCSTOP failed");
            }
        }
    }
  
  /*  Remember some things about the inferior that we will, or might, change
      so that we can restore them when we detach. */
  
  (void) ioctl (pi.fd, PIOCGTRACE, &pi.trace);
  (void) ioctl (pi.fd, PIOCGFAULT, &pi.fltset);
  (void) ioctl (pi.fd, PIOCGENTRY, &pi.entryset);
  (void) ioctl (pi.fd, PIOCGEXIT, &pi.exitset);
  
  /* Set up trace and fault sets, as gdb expects them. */
  
  (void) memset (&pi.prrun, 0, sizeof (pi.prrun));
  prfillset (&pi.prrun.pr_trace);
  prfillset (&pi.prrun.pr_fault);
  prdelset (&pi.prrun.pr_fault, FLTPAGE);
  if (ioctl (pi.fd, PIOCSFAULT, &pi.prrun.pr_fault))
    {
      print_sys_errmsg ("PIOCSFAULT failed");
    }
  if (ioctl (pi.fd, PIOCSTRACE, &pi.prrun.pr_trace))
    {
      print_sys_errmsg ("PIOCSTRACE failed");
    }
  attach_flag = 1;
  return (pid);
}

/*

GLOBAL FUNCTION

        detach -- detach from an attached-to process

SYNOPSIS

        void detach (int signal)

DESCRIPTION

        Detach from the current attachee.

        If signal is non-zero, the attachee is started running again and sent
        the specified signal.

        If signal is zero and the attachee was not already stopped when we
        attached to it, then we make it runnable again when we detach.

        Otherwise, we query whether or not to make the attachee runnable
        again, since we may simply want to leave it in the state it was in
        when we attached.

        We report any problems, but do not consider them errors, since we
        MUST detach even if some things don't seem to go right.  This may not
        be the ideal situation.  (FIXME).
 */

void
DEFUN(detach, (signal),
      int signal)
{
  if (signal)
    {
      struct siginfo siginfo;
      siginfo.si_signo = signal;
      siginfo.si_code = 0;
      siginfo.si_errno = 0;
      if (ioctl (pi.fd, PIOCSSIG, &siginfo) < 0)
        {
          print_sys_errmsg (pi.pathname, errno);
          printf ("PIOCSSIG failed.\n");
        }
    }
  if (ioctl (pi.fd, PIOCSEXIT, &pi.exitset) < 0)
    {
      print_sys_errmsg (pi.pathname, errno);
      printf ("PIOCSEXIT failed.\n");
    }
  if (ioctl (pi.fd, PIOCSENTRY, &pi.entryset) < 0)
    {
      print_sys_errmsg (pi.pathname, errno);
      printf ("PIOCSENTRY failed.\n");
    }
  if (ioctl (pi.fd, PIOCSTRACE, &pi.trace) < 0)
    {
      print_sys_errmsg (pi.pathname, errno);
      printf ("PIOCSTRACE failed.\n");
    }
  if (ioctl (pi.fd, PIOCSFAULT, &pi.fltset) < 0)
    {
      print_sys_errmsg (pi.pathname, errno);
      printf ("PIOCSFAULT failed.\n");
    }
  if (ioctl (pi.fd, PIOCSTATUS, &pi.prstatus) < 0)
    {
      print_sys_errmsg (pi.pathname, errno);
      printf ("PIOCSTATUS failed.\n");
    }
  else
    {
      if (signal || (pi.prstatus.pr_flags & (PR_STOPPED | PR_ISTOP)))
        {
          if (signal || !pi.was_stopped ||
              query ("Was stopped when attached, make it runnable again? "))
            {
              (void) memset (&pi.prrun, 0, sizeof (pi.prrun));
              pi.prrun.pr_flags = PRCFAULT;
              if (ioctl (pi.fd, PIOCRUN, &pi.prrun))
                {
                  print_sys_errmsg (pi.pathname, errno);
                  printf ("PIOCRUN failed.\n");
                }
            }
        }
    }
  close_proc_file ();
  attach_flag = 0;
}

/*

GLOBAL FUNCTION

        proc_wait -- emulate wait() as much as possible

SYNOPSIS

        int proc_wait (int *statloc)

DESCRIPTION

        Try to emulate wait() as much as possible.  Not sure why we can't
        just use wait(), but it seems to have problems when applied to a
        process being controlled with the /proc interface.

NOTES

        We have a race problem here with no obvious solution.  We need to let
        the inferior run until it stops on an event of interest, which means
        that we need to use the PIOCWSTOP ioctl.  However, we cannot use this
        ioctl if the process is already stopped on something that is not an
        event of interest, or the call will hang indefinitely.  Thus we first
        use PIOCSTATUS to see if the process is not stopped.  If not, then we
        use PIOCWSTOP.  But during the window between the two, if the process
        stops for any reason that is not an event of interest (such as a job
        control signal) then gdb will hang.  One possible workaround is to set
        an alarm to wake up every minute of so and check to see if the process
        is still running, and if so, then reissue the PIOCWSTOP.  But this is
        a real kludge, so has not been implemented.  FIXME: investigate
        alternatives.

        FIXME:  Investigate why wait() seems to have problems with programs
        being control by /proc routines.

 */

int
DEFUN(proc_wait, (statloc),
      int *statloc)
{
  short what;
  short why;
  int statval = 0;
  int checkerr = 0;
  int rtnval = -1;
  
  if (ioctl (pi.fd, PIOCSTATUS, &pi.prstatus) < 0)
    {
      checkerr++;
    }
  else if (!(pi.prstatus.pr_flags & (PR_STOPPED | PR_ISTOP)))
    {
      if (ioctl (pi.fd, PIOCWSTOP, &pi.prstatus) < 0)
        {
          checkerr++;
        }
    }    
  if (checkerr)
    {
      if (errno == ENOENT)
        {
          rtnval = wait (&statval);
          if (rtnval != inferior_pid)
            {
              error ("PIOCWSTOP, wait failed, returned %d", rtnval);
              /* NOTREACHED */
            }
        }
      else
        {
          print_sys_errmsg (pi.pathname, errno);
          error ("PIOCSTATUS or PIOCWSTOP failed.");
          /* NOTREACHED */
        }
    }
  else if (pi.prstatus.pr_flags & (PR_STOPPED | PR_ISTOP))
    {
      rtnval = pi.prstatus.pr_pid;
      why = pi.prstatus.pr_why;
      what = pi.prstatus.pr_what;
      if (why == PR_SIGNALLED)
        {
          statval = (what << 8) | 0177;
        }
      else if ((why == PR_SYSEXIT) &&
               (what == SYS_exec || what == SYS_execve))
        {
          statval = (SIGTRAP << 8) | 0177;
        }
      else if (why == PR_REQUESTED)
        {
          statval = (SIGSTOP << 8) | 0177;
        }
      else if (why == PR_JOBCONTROL)
        {
          statval = (what << 8) | 0177;
        }
      else if (why == PR_FAULTED)
        {
          switch (what)
            {
            case FLTPRIV:
            case FLTILL:
              statval = (SIGILL << 8) | 0177;
              break;
            case FLTBPT:
            case FLTTRACE:
              statval = (SIGTRAP << 8) | 0177;
              break;
            case FLTSTACK:
            case FLTACCESS:
            case FLTBOUNDS:
              statval = (SIGSEGV << 8) | 0177;
              break;
            case FLTIOVF:
            case FLTIZDIV:
            case FLTFPE:
              statval = (SIGFPE << 8) | 0177;
              break;
            case FLTPAGE:               /* Recoverable page fault */
            default:
              rtnval = -1;
              error ("PIOCWSTOP, unknown why %d, what %d", why, what);
              /* NOTREACHED */
            }
        }
      else
        {
          rtnval = -1;
          error ("PIOCWSTOP, unknown why %d, what %d", why, what);
          /* NOTREACHED */
        }
    }
  else
    {
      error ("PIOCWSTOP, stopped for unknown/unhandled reason, flags %#x", 
             pi.prstatus.pr_flags);
          /* NOTREACHED */
    }
  if (statloc)
    {
      *statloc = statval;
    }
  return (rtnval);
}

/*

GLOBAL FUNCTION

        child_resume -- resume execution of the inferior process

SYNOPSIS

        void child_resume (int step, int signal)

DESCRIPTION

        Resume execution of the inferior process.  If STEP is nozero, then
        just single step it.  If SIGNAL is nonzero, restart it with that
        signal activated.

NOTE

        It may not be absolutely necessary to specify the PC value for
        restarting, but to be safe we use the value that gdb considers
        to be current.  One case where this might be necessary is if the
        user explicitly changes the PC value that gdb considers to be
        current.  FIXME:  Investigate if this is necessary or not.
 */

void
DEFUN(child_resume, (step, signal),
      int step AND
      int signal)
{
  errno = 0;
  pi.prrun.pr_flags = PRSVADDR | PRSTRACE | PRSFAULT | PRCFAULT;
  pi.prrun.pr_vaddr = (caddr_t) *(int *) &registers[REGISTER_BYTE (PC_REGNUM)];
  if (signal)
    {
      if (signal != pi.prstatus.pr_cursig)
        {
          struct siginfo siginfo;
          siginfo.si_signo = signal;
          siginfo.si_code = 0;
          siginfo.si_errno = 0;
          (void) ioctl (pi.fd, PIOCSSIG, &siginfo);
        }
    }
  else
    {
      pi.prrun.pr_flags |= PRCSIG;
    }
  if (step)
    {
      pi.prrun.pr_flags |= PRSTEP;
    }
  if (ioctl (pi.fd, PIOCRUN, &pi.prrun) != 0)
    {
      perror_with_name (pi.pathname);
      /* NOTREACHED */
    }
}

/*

GLOBAL FUNCTION

        fetch_inferior_registers -- fetch current registers from inferior

SYNOPSIS

        void fetch_inferior_registers (void)

DESCRIPTION

        Read the current values of the inferior's registers, both the
        general register set and floating point registers (if supported)
        and update gdb's idea of their current values.

*/

void
DEFUN_VOID(fetch_inferior_registers)
{
  if (ioctl (pi.fd, PIOCGREG, &pi.gregset) != -1)
    {
      supply_gregset (&pi.gregset);
    }
#if defined (FP0_REGNUM)
  if (ioctl (pi.fd, PIOCGFPREG, &pi.fpregset) != -1)
    {
      supply_fpregset (&pi.fpregset);
    }
#endif
}

#endif  /* ATTACH_DETACH */

/*

LOCAL FUNCTION

        proc_init_failed - called whenever /proc access initialization fails

SYNOPSIS

        static void proc_init_failed (char *why)

DESCRIPTION

        This function is called whenever initialization of access to a /proc
        entry fails.  It prints a suitable error message, does some cleanup,
        and then invokes the standard error processing routine which dumps
        us back into the command loop.
 */

static void
DEFUN(proc_init_failed, (why),
      char *why)
{
  print_sys_errmsg (pi.pathname, errno);
  (void) kill (pi.pid, SIGKILL);
  close_proc_file ();
  error (why);
  /* NOTREACHED */
}

/*

LOCAL FUNCTION

        close_proc_file - close any currently open /proc entry

SYNOPSIS

        static void close_proc_file (void)

DESCRIPTION

        Close any currently open /proc entry and mark the process information
        entry as invalid.  In order to ensure that we don't try to reuse any
        stale information, the pid, fd, and pathnames are explicitly
        invalidated, which may be overkill.

 */

static void
DEFUN_VOID(close_proc_file)
{
  pi.pid = 0;
  if (pi.valid)
    {
      (void) close (pi.fd);
    }
  pi.fd = -1;
  if (pi.pathname)
    {
      free (pi.pathname);
      pi.pathname = NULL;
    }
  pi.valid = 0;
}

/*

LOCAL FUNCTION

        open_proc_file - open a /proc entry for a given process id

SYNOPSIS

        static int open_proc_file (pid)

DESCRIPTION

        Given a process id, close the existing open /proc entry (if any)
        and open one for the new process id.  Once it is open, then
        mark the local process information structure as valid, which
        guarantees that the pid, fd, and pathname fields match an open
        /proc entry.  Returns zero if the open fails, nonzero otherwise.

        Note that the pathname is left intact, even when the open fails,
        so that callers can use it to construct meaningful error messages
        rather than just "file open failed".
 */

static int
DEFUN(open_proc_file, (pid),
      int pid)
{
  pi.valid = 0;
  if (pi.valid)
    {
      (void) close (pi.fd);
    }
  if (pi.pathname == NULL)
    {
      pi.pathname = xmalloc (32);
    }
  sprintf (pi.pathname, PROC_NAME_FMT, pid);
  if ((pi.fd = open (pi.pathname, O_RDWR)) >= 0)
    {
      pi.valid = 1;
      pi.pid = pid;
    }
  return (pi.valid);
}

#endif  /* USE_PROC_FS */