re PR libfortran/39664 (Revision 145571 breaks stdio)

[thirdparty/gcc.git] / libgfortran / io / unix.c

/* Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008
   Free Software Foundation, Inc.
   Contributed by Andy Vaught
   F2003 I/O support contributed by Jerry DeLisle

This file is part of the GNU Fortran 95 runtime library (libgfortran).

Libgfortran 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, or (at your option)
any later version.

In addition to the permissions in the GNU General Public License, the
Free Software Foundation gives you unlimited permission to link the
compiled version of this file into combinations with other programs,
and to distribute those combinations without any restriction coming
from the use of this file.  (The General Public License restrictions
do apply in other respects; for example, they cover modification of
the file, and distribution when not linked into a combine
executable.)

Libgfortran 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 Libgfortran; see the file COPYING.  If not, write to
the Free Software Foundation, 51 Franklin Street, Fifth Floor,
Boston, MA 02110-1301, USA.  */

/* Unix stream I/O module */

#include "io.h"
#include <stdlib.h>
#include <limits.h>

#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <assert.h>

#include <string.h>
#include <errno.h>


/* For mingw, we don't identify files by their inode number, but by a
   64-bit identifier created from a BY_HANDLE_FILE_INFORMATION. */
#if defined(__MINGW32__) && !HAVE_WORKING_STAT

#define WIN32_LEAN_AND_MEAN
#include <windows.h>

static uint64_t
id_from_handle (HANDLE hFile)
{
  BY_HANDLE_FILE_INFORMATION FileInformation;

  if (hFile == INVALID_HANDLE_VALUE)
      return 0;

  memset (&FileInformation, 0, sizeof(FileInformation));
  if (!GetFileInformationByHandle (hFile, &FileInformation))
    return 0;

  return ((uint64_t) FileInformation.nFileIndexLow)
         | (((uint64_t) FileInformation.nFileIndexHigh) << 32);
}


static uint64_t
id_from_path (const char *path)
{
  HANDLE hFile;
  uint64_t res;

  if (!path || !*path || access (path, F_OK))
    return (uint64_t) -1;

  hFile = CreateFile (path, 0, 0, NULL, OPEN_EXISTING,
                      FILE_FLAG_BACKUP_SEMANTICS | FILE_ATTRIBUTE_READONLY,
                      NULL);
  res = id_from_handle (hFile);
  CloseHandle (hFile);
  return res;
}


static uint64_t
id_from_fd (const int fd)
{
  return id_from_handle ((HANDLE) _get_osfhandle (fd));
}

#endif

#ifndef PATH_MAX
#define PATH_MAX 1024
#endif

#ifndef PROT_READ
#define PROT_READ 1
#endif

#ifndef PROT_WRITE
#define PROT_WRITE 2
#endif

/* These flags aren't defined on all targets (mingw32), so provide them
   here.  */
#ifndef S_IRGRP
#define S_IRGRP 0
#endif

#ifndef S_IWGRP
#define S_IWGRP 0
#endif

#ifndef S_IROTH
#define S_IROTH 0
#endif

#ifndef S_IWOTH
#define S_IWOTH 0
#endif


/* Unix and internal stream I/O module */

static const int BUFFER_SIZE = 8192;

typedef struct
{
  stream st;

  gfc_offset buffer_offset;     /* File offset of the start of the buffer */
  gfc_offset physical_offset;   /* Current physical file offset */
  gfc_offset logical_offset;    /* Current logical file offset */
  gfc_offset file_length;       /* Length of the file, -1 if not seekable. */

  char *buffer;                 /* Pointer to the buffer.  */
  int fd;                       /* The POSIX file descriptor.  */

  int active;                   /* Length of valid bytes in the buffer */

  int prot;
  int ndirty;                   /* Dirty bytes starting at buffer_offset */

  int special_file;             /* =1 if the fd refers to a special file */
}
unix_stream;


/*move_pos_offset()--  Move the record pointer right or left
 *relative to current position */

int
move_pos_offset (stream* st, int pos_off)
{
  unix_stream * str = (unix_stream*)st;
  if (pos_off < 0)
    {
      str->logical_offset += pos_off;

      if (str->ndirty > str->logical_offset)
        {
          if (str->ndirty + pos_off > 0)
            str->ndirty += pos_off;
          else
            str->ndirty = 0;
        }

    return pos_off;
  }
  return 0;
}


/* fix_fd()-- Given a file descriptor, make sure it is not one of the
 * standard descriptors, returning a non-standard descriptor.  If the
 * user specifies that system errors should go to standard output,
 * then closes standard output, we don't want the system errors to a
 * file that has been given file descriptor 1 or 0.  We want to send
 * the error to the invalid descriptor. */

static int
fix_fd (int fd)
{
#ifdef HAVE_DUP
  int input, output, error;

  input = output = error = 0;

  /* Unix allocates the lowest descriptors first, so a loop is not
     required, but this order is. */
  if (fd == STDIN_FILENO)
    {
      fd = dup (fd);
      input = 1;
    }
  if (fd == STDOUT_FILENO)
    {
      fd = dup (fd);
      output = 1;
    }
  if (fd == STDERR_FILENO)
    {
      fd = dup (fd);
      error = 1;
    }

  if (input)
    close (STDIN_FILENO);
  if (output)
    close (STDOUT_FILENO);
  if (error)
    close (STDERR_FILENO);
#endif

  return fd;
}

int
is_preconnected (stream * s)
{
  int fd;

  fd = ((unix_stream *) s)->fd;
  if (fd == STDIN_FILENO || fd == STDOUT_FILENO || fd == STDERR_FILENO)
    return 1;
  else
    return 0;
}

/* If the stream corresponds to a preconnected unit, we flush the
   corresponding C stream.  This is bugware for mixed C-Fortran codes
   where the C code doesn't flush I/O before returning.  */
void
flush_if_preconnected (stream * s)
{
  int fd;

  fd = ((unix_stream *) s)->fd;
  if (fd == STDIN_FILENO)
    fflush (stdin);
  else if (fd == STDOUT_FILENO)
    fflush (stdout);
  else if (fd == STDERR_FILENO)
    fflush (stderr);
}


/* get_oserror()-- Get the most recent operating system error.  For
 * unix, this is errno. */

const char *
get_oserror (void)
{
  return strerror (errno);
}


/********************************************************************
Raw I/O functions (read, write, seek, tell, truncate, close).

These functions wrap the basic POSIX I/O syscalls. Any deviation in
semantics is a bug, except the following: write restarts in case
of being interrupted by a signal, and as the first argument the
functions take the unix_stream struct rather than an integer file
descriptor. Also, for POSIX read() and write() a nbyte argument larger
than SSIZE_MAX is undefined; here the type of nbyte is ssize_t rather
than size_t as for POSIX read/write.
*********************************************************************/

static int
raw_flush (unix_stream * s  __attribute__ ((unused)))
{
  return 0;
}

static ssize_t
raw_read (unix_stream * s, void * buf, ssize_t nbyte)
{
  /* For read we can't do I/O in a loop like raw_write does, because
     that will break applications that wait for interactive I/O.  */
  return read (s->fd, buf, nbyte);
}

static ssize_t
raw_write (unix_stream * s, const void * buf, ssize_t nbyte)
{
  ssize_t trans, bytes_left;
  char *buf_st;

  bytes_left = nbyte;
  buf_st = (char *) buf;

  /* We must write in a loop since some systems don't restart system
     calls in case of a signal.  */
  while (bytes_left > 0)
    {
      trans = write (s->fd, buf_st, bytes_left);
      if (trans < 0)
        {
          if (errno == EINTR)
            continue;
          else
            return trans;
        }
      buf_st += trans;
      bytes_left -= trans;
    }

  return nbyte - bytes_left;
}

static off_t
raw_seek (unix_stream * s, off_t offset, int whence)
{
  return lseek (s->fd, offset, whence);
}

static off_t
raw_tell (unix_stream * s)
{
  return lseek (s->fd, 0, SEEK_CUR);
}

static int
raw_truncate (unix_stream * s, off_t length)
{
#ifdef HAVE_FTRUNCATE
  return ftruncate (s->fd, length);
#elif defined HAVE_CHSIZE
  return chsize (s->fd, length);
#else
  runtime_error ("required ftruncate or chsize support not present");
  return -1;
#endif
}

static int
raw_close (unix_stream * s)
{
  int retval;
  
  if (s->fd != STDOUT_FILENO
      && s->fd != STDERR_FILENO
      && s->fd != STDIN_FILENO)
    retval = close (s->fd);
  else
    retval = SUCCESS;
  free_mem (s);
  return retval;
}

static int
raw_init (unix_stream * s)
{
  s->st.read = (void *) raw_read;
  s->st.write = (void *) raw_write;
  s->st.seek = (void *) raw_seek;
  s->st.tell = (void *) raw_tell;
  s->st.trunc = (void *) raw_truncate;
  s->st.close = (void *) raw_close;
  s->st.flush = (void *) raw_flush;

  s->buffer = NULL;
  return 0;
}


/*********************************************************************
Buffered I/O functions. These functions have the same semantics as the
raw I/O functions above, except that they are buffered in order to
improve performance. The buffer must be flushed when switching from
reading to writing and vice versa.
*********************************************************************/

static int
buf_flush (unix_stream * s)
{
  int writelen;

  /* Flushing in read mode means discarding read bytes.  */
  s->active = 0;

  if (s->ndirty == 0)
    return 0;
  
  if (s->file_length != -1 && s->physical_offset != s->buffer_offset
      && lseek (s->fd, s->buffer_offset, SEEK_SET) < 0)
    return -1;

  writelen = raw_write (s, s->buffer, s->ndirty);

  s->physical_offset = s->buffer_offset + writelen;

  /* Don't increment file_length if the file is non-seekable.  */
  if (s->file_length != -1 && s->physical_offset > s->file_length)
      s->file_length = s->physical_offset;

  s->ndirty -= writelen;
  if (s->ndirty != 0)
    return -1;

  return 0;
}

static ssize_t
buf_read (unix_stream * s, void * buf, ssize_t nbyte)
{
  if (s->active == 0)
    s->buffer_offset = s->logical_offset;

  /* Is the data we want in the buffer?  */
  if (s->logical_offset + nbyte <= s->buffer_offset + s->active
      && s->buffer_offset <= s->logical_offset)
    memcpy (buf, s->buffer + (s->logical_offset - s->buffer_offset), nbyte);
  else
    {
      /* First copy the active bytes if applicable, then read the rest
         either directly or filling the buffer.  */
      char *p;
      int nread = 0;
      ssize_t to_read, did_read;
      gfc_offset new_logical;
      
      p = (char *) buf;
      if (s->logical_offset >= s->buffer_offset 
          && s->buffer_offset + s->active >= s->logical_offset)
        {
          nread = s->active - (s->logical_offset - s->buffer_offset);
          memcpy (buf, s->buffer + (s->logical_offset - s->buffer_offset), 
                  nread);
          p += nread;
        }
      /* At this point we consider all bytes in the buffer discarded.  */
      to_read = nbyte - nread;
      new_logical = s->logical_offset + nread;
      if (s->file_length != -1 && s->physical_offset != new_logical
          && lseek (s->fd, new_logical, SEEK_SET) < 0)
        return -1;
      s->buffer_offset = s->physical_offset = new_logical;
      if (to_read <= BUFFER_SIZE/2)
        {
          did_read = raw_read (s, s->buffer, BUFFER_SIZE);
          s->physical_offset += did_read;
          s->active = did_read;
          did_read = (did_read > to_read) ? to_read : did_read;
          memcpy (p, s->buffer, did_read);
        }
      else
        {
          did_read = raw_read (s, p, to_read);
          s->physical_offset += did_read;
          s->active = 0;
        }
      nbyte = did_read + nread;
    }
  s->logical_offset += nbyte;
  return nbyte;
}

static ssize_t
buf_write (unix_stream * s, const void * buf, ssize_t nbyte)
{
  if (s->ndirty == 0)
    s->buffer_offset = s->logical_offset;

  /* Does the data fit into the buffer?  As a special case, if the
     buffer is empty and the request is bigger than BUFFER_SIZE/2,
     write directly. This avoids the case where the buffer would have
     to be flushed at every write.  */
  if (!(s->ndirty == 0 && nbyte > BUFFER_SIZE/2)
      && s->logical_offset + nbyte <= s->buffer_offset + BUFFER_SIZE
      && s->buffer_offset <= s->logical_offset
      && s->buffer_offset + s->ndirty >= s->logical_offset)
    {
      memcpy (s->buffer + (s->logical_offset - s->buffer_offset), buf, nbyte);
      int nd = (s->logical_offset - s->buffer_offset) + nbyte;
      if (nd > s->ndirty)
        s->ndirty = nd;
    }
  else
    {
      /* Flush, and either fill the buffer with the new data, or if
         the request is bigger than the buffer size, write directly
         bypassing the buffer.  */
      buf_flush (s);
      if (nbyte <= BUFFER_SIZE/2)
        {
          memcpy (s->buffer, buf, nbyte);
          s->buffer_offset = s->logical_offset;
          s->ndirty += nbyte;
        }
      else
        {
          if (s->file_length != -1 && s->physical_offset != s->logical_offset
              && lseek (s->fd, s->logical_offset, SEEK_SET) < 0)
            return -1;
          nbyte = raw_write (s, buf, nbyte);
          s->physical_offset += nbyte;
        }
    }
  s->logical_offset += nbyte;
  /* Don't increment file_length if the file is non-seekable.  */
  if (s->file_length != -1 && s->logical_offset > s->file_length)
    s->file_length = s->logical_offset;
  return nbyte;
}

static off_t
buf_seek (unix_stream * s, off_t offset, int whence)
{
  switch (whence)
    {
    case SEEK_SET:
      break;
    case SEEK_CUR:
      offset += s->logical_offset;
      break;
    case SEEK_END:
      offset += s->file_length;
      break;
    default:
      return -1;
    }
  if (offset < 0)
    {
      errno = EINVAL;
      return -1;
    }
  s->logical_offset = offset;
  return offset;
}

static off_t
buf_tell (unix_stream * s)
{
  return s->logical_offset;
}

static int
buf_truncate (unix_stream * s, off_t length)
{
  int r;

  if (buf_flush (s) != 0)
    return -1;
  r = raw_truncate (s, length);
  if (r == 0)
    s->file_length = length;
  return r;
}

static int
buf_close (unix_stream * s)
{
  if (buf_flush (s) != 0)
    return -1;
  free_mem (s->buffer);
  return raw_close (s);
}

static int
buf_init (unix_stream * s)
{
  s->st.read = (void *) buf_read;
  s->st.write = (void *) buf_write;
  s->st.seek = (void *) buf_seek;
  s->st.tell = (void *) buf_tell;
  s->st.trunc = (void *) buf_truncate;
  s->st.close = (void *) buf_close;
  s->st.flush = (void *) buf_flush;

  s->buffer = get_mem (BUFFER_SIZE);
  return 0;
}


/*********************************************************************
  memory stream functions - These are used for internal files

  The idea here is that a single stream structure is created and all
  requests must be satisfied from it.  The location and size of the
  buffer is the character variable supplied to the READ or WRITE
  statement.

*********************************************************************/


char *
mem_alloc_r (stream * strm, int * len)
{
  unix_stream * s = (unix_stream *) strm;
  gfc_offset n;
  gfc_offset where = s->logical_offset;

  if (where < s->buffer_offset || where > s->buffer_offset + s->active)
    return NULL;

  n = s->buffer_offset + s->active - where;
  if (*len > n)
    *len = n;

  s->logical_offset = where + *len;

  return s->buffer + (where - s->buffer_offset);
}


char *
mem_alloc_w (stream * strm, int * len)
{
  unix_stream * s = (unix_stream *) strm;
  gfc_offset m;
  gfc_offset where = s->logical_offset;

  m = where + *len;

  if (where < s->buffer_offset)
    return NULL;

  if (m > s->file_length)
    return NULL;

  s->logical_offset = m;

  return s->buffer + (where - s->buffer_offset);
}


/* Stream read function for internal units.  */

static ssize_t
mem_read (stream * s, void * buf, ssize_t nbytes)
{
  void *p;
  int nb = nbytes;

  p = mem_alloc_r (s, &nb);
  if (p)
    {
      memcpy (buf, p, nb);
      return (ssize_t) nb;
    }
  else
    return 0;
}


/* Stream write function for internal units. This is not actually used
   at the moment, as all internal IO is formatted and the formatted IO
   routines use mem_alloc_w_at.  */

static ssize_t
mem_write (stream * s, const void * buf, ssize_t nbytes)
{
  void *p;
  int nb = nbytes;

  p = mem_alloc_w (s, &nb);
  if (p)
    {
      memcpy (p, buf, nb);
      return (ssize_t) nb;
    }
  else
    return 0;
}


static off_t
mem_seek (stream * strm, off_t offset, int whence)
{
  unix_stream * s = (unix_stream *) strm;
  switch (whence)
    {
    case SEEK_SET:
      break;
    case SEEK_CUR:
      offset += s->logical_offset;
      break;
    case SEEK_END:
      offset += s->file_length;
      break;
    default:
      return -1;
    }

  /* Note that for internal array I/O it's actually possible to have a
     negative offset, so don't check for that.  */
  if (offset > s->file_length)
    {
      errno = EINVAL;
      return -1;
    }

  s->logical_offset = offset;

  /* Returning < 0 is the error indicator for sseek(), so return 0 if
     offset is negative.  Thus if the return value is 0, the caller
     has to use stell() to get the real value of logical_offset.  */
  if (offset >= 0)
    return offset;
  return 0;
}


static off_t
mem_tell (stream * s)
{
  return ((unix_stream *)s)->logical_offset;
}


static int
mem_truncate (unix_stream * s __attribute__ ((unused)), 
              off_t length __attribute__ ((unused)))
{
  return 0;
}


static int
mem_flush (unix_stream * s __attribute__ ((unused)))
{
  return 0;
}


static int
mem_close (unix_stream * s)
{
  if (s != NULL)
    free_mem (s);

  return 0;
}


/*********************************************************************
  Public functions -- A reimplementation of this module needs to
  define functional equivalents of the following.
*********************************************************************/

/* empty_internal_buffer()-- Zero the buffer of Internal file */

void
empty_internal_buffer(stream *strm)
{
  unix_stream * s = (unix_stream *) strm;
  memset(s->buffer, ' ', s->file_length);
}

/* open_internal()-- Returns a stream structure from an internal file */

stream *
open_internal (char *base, int length, gfc_offset offset)
{
  unix_stream *s;

  s = get_mem (sizeof (unix_stream));
  memset (s, '\0', sizeof (unix_stream));

  s->buffer = base;
  s->buffer_offset = offset;

  s->logical_offset = 0;
  s->active = s->file_length = length;

  s->st.close = (void *) mem_close;
  s->st.seek = (void *) mem_seek;
  s->st.tell = (void *) mem_tell;
  s->st.trunc = (void *) mem_truncate;
  s->st.read = (void *) mem_read;
  s->st.write = (void *) mem_write;
  s->st.flush = (void *) mem_flush;

  return (stream *) s;
}


/* fd_to_stream()-- Given an open file descriptor, build a stream
 * around it. */

static stream *
fd_to_stream (int fd, int prot)
{
  struct stat statbuf;
  unix_stream *s;

  s = get_mem (sizeof (unix_stream));
  memset (s, '\0', sizeof (unix_stream));

  s->fd = fd;
  s->buffer_offset = 0;
  s->physical_offset = 0;
  s->logical_offset = 0;
  s->prot = prot;

  /* Get the current length of the file. */

  fstat (fd, &statbuf);

  if (lseek (fd, 0, SEEK_CUR) == (off_t) -1)
    s->file_length = -1;
  else
    s->file_length = S_ISREG (statbuf.st_mode) ? statbuf.st_size : -1;

  s->special_file = !S_ISREG (statbuf.st_mode);

  if (isatty (s->fd) || options.all_unbuffered
      ||(options.unbuffered_preconnected && 
         (s->fd == STDIN_FILENO 
          || s->fd == STDOUT_FILENO 
          || s->fd == STDERR_FILENO)))
    raw_init (s);
  else
    buf_init (s);

  return (stream *) s;
}


/* Given the Fortran unit number, convert it to a C file descriptor.  */

int
unit_to_fd (int unit)
{
  gfc_unit *us;
  int fd;

  us = find_unit (unit);
  if (us == NULL)
    return -1;

  fd = ((unix_stream *) us->s)->fd;
  unlock_unit (us);
  return fd;
}


/* unpack_filename()-- Given a fortran string and a pointer to a
 * buffer that is PATH_MAX characters, convert the fortran string to a
 * C string in the buffer.  Returns nonzero if this is not possible.  */

int
unpack_filename (char *cstring, const char *fstring, int len)
{
  len = fstrlen (fstring, len);
  if (len >= PATH_MAX)
    return 1;

  memmove (cstring, fstring, len);
  cstring[len] = '\0';

  return 0;
}


/* tempfile()-- Generate a temporary filename for a scratch file and
 * open it.  mkstemp() opens the file for reading and writing, but the
 * library mode prevents anything that is not allowed.  The descriptor
 * is returned, which is -1 on error.  The template is pointed to by 
 * opp->file, which is copied into the unit structure
 * and freed later. */

static int
tempfile (st_parameter_open *opp)
{
  const char *tempdir;
  char *template;
  int fd;

  tempdir = getenv ("GFORTRAN_TMPDIR");
  if (tempdir == NULL)
    tempdir = getenv ("TMP");
  if (tempdir == NULL)
    tempdir = getenv ("TEMP");
  if (tempdir == NULL)
    tempdir = DEFAULT_TEMPDIR;

  template = get_mem (strlen (tempdir) + 20);

  sprintf (template, "%s/gfortrantmpXXXXXX", tempdir);

#ifdef HAVE_MKSTEMP

  fd = mkstemp (template);

#else /* HAVE_MKSTEMP */

  if (mktemp (template))
    do
#if defined(HAVE_CRLF) && defined(O_BINARY)
      fd = open (template, O_RDWR | O_CREAT | O_EXCL | O_BINARY,
                 S_IREAD | S_IWRITE);
#else
      fd = open (template, O_RDWR | O_CREAT | O_EXCL, S_IREAD | S_IWRITE);
#endif
    while (!(fd == -1 && errno == EEXIST) && mktemp (template));
  else
    fd = -1;

#endif /* HAVE_MKSTEMP */

  if (fd < 0)
    free_mem (template);
  else
    {
      opp->file = template;
      opp->file_len = strlen (template);        /* Don't include trailing nul */
    }

  return fd;
}


/* regular_file()-- Open a regular file.
 * Change flags->action if it is ACTION_UNSPECIFIED on entry,
 * unless an error occurs.
 * Returns the descriptor, which is less than zero on error. */

static int
regular_file (st_parameter_open *opp, unit_flags *flags)
{
  char path[PATH_MAX + 1];
  int mode;
  int rwflag;
  int crflag;
  int fd;

  if (unpack_filename (path, opp->file, opp->file_len))
    {
      errno = ENOENT;           /* Fake an OS error */
      return -1;
    }

  rwflag = 0;

  switch (flags->action)
    {
    case ACTION_READ:
      rwflag = O_RDONLY;
      break;

    case ACTION_WRITE:
      rwflag = O_WRONLY;
      break;

    case ACTION_READWRITE:
    case ACTION_UNSPECIFIED:
      rwflag = O_RDWR;
      break;

    default:
      internal_error (&opp->common, "regular_file(): Bad action");
    }

  switch (flags->status)
    {
    case STATUS_NEW:
      crflag = O_CREAT | O_EXCL;
      break;

    case STATUS_OLD:            /* open will fail if the file does not exist*/
      crflag = 0;
      break;

    case STATUS_UNKNOWN:
    case STATUS_SCRATCH:
      crflag = O_CREAT;
      break;

    case STATUS_REPLACE:
      crflag = O_CREAT | O_TRUNC;
      break;

    default:
      internal_error (&opp->common, "regular_file(): Bad status");
    }

  /* rwflag |= O_LARGEFILE; */

#if defined(HAVE_CRLF) && defined(O_BINARY)
  crflag |= O_BINARY;
#endif

  mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH;
  fd = open (path, rwflag | crflag, mode);
  if (flags->action != ACTION_UNSPECIFIED)
    return fd;

  if (fd >= 0)
    {
      flags->action = ACTION_READWRITE;
      return fd;
    }
  if (errno != EACCES && errno != EROFS)
     return fd;

  /* retry for read-only access */
  rwflag = O_RDONLY;
  fd = open (path, rwflag | crflag, mode);
  if (fd >=0)
    {
      flags->action = ACTION_READ;
      return fd;                /* success */
    }
  
  if (errno != EACCES)
    return fd;                  /* failure */

  /* retry for write-only access */
  rwflag = O_WRONLY;
  fd = open (path, rwflag | crflag, mode);
  if (fd >=0)
    {
      flags->action = ACTION_WRITE;
      return fd;                /* success */
    }
  return fd;                    /* failure */
}


/* open_external()-- Open an external file, unix specific version.
 * Change flags->action if it is ACTION_UNSPECIFIED on entry.
 * Returns NULL on operating system error. */

stream *
open_external (st_parameter_open *opp, unit_flags *flags)
{
  int fd, prot;

  if (flags->status == STATUS_SCRATCH)
    {
      fd = tempfile (opp);
      if (flags->action == ACTION_UNSPECIFIED)
        flags->action = ACTION_READWRITE;

#if HAVE_UNLINK_OPEN_FILE
      /* We can unlink scratch files now and it will go away when closed. */
      if (fd >= 0)
        unlink (opp->file);
#endif
    }
  else
    {
      /* regular_file resets flags->action if it is ACTION_UNSPECIFIED and
       * if it succeeds */
      fd = regular_file (opp, flags);
    }

  if (fd < 0)
    return NULL;
  fd = fix_fd (fd);

  switch (flags->action)
    {
    case ACTION_READ:
      prot = PROT_READ;
      break;

    case ACTION_WRITE:
      prot = PROT_WRITE;
      break;

    case ACTION_READWRITE:
      prot = PROT_READ | PROT_WRITE;
      break;

    default:
      internal_error (&opp->common, "open_external(): Bad action");
    }

  return fd_to_stream (fd, prot);
}


/* input_stream()-- Return a stream pointer to the default input stream.
 * Called on initialization. */

stream *
input_stream (void)
{
  return fd_to_stream (STDIN_FILENO, PROT_READ);
}


/* output_stream()-- Return a stream pointer to the default output stream.
 * Called on initialization. */

stream *
output_stream (void)
{
  stream * s;

#if defined(HAVE_CRLF) && defined(HAVE_SETMODE)
  setmode (STDOUT_FILENO, O_BINARY);
#endif

  s = fd_to_stream (STDOUT_FILENO, PROT_WRITE);
  return s;
}


/* error_stream()-- Return a stream pointer to the default error stream.
 * Called on initialization. */

stream *
error_stream (void)
{
  stream * s;

#if defined(HAVE_CRLF) && defined(HAVE_SETMODE)
  setmode (STDERR_FILENO, O_BINARY);
#endif

  s = fd_to_stream (STDERR_FILENO, PROT_WRITE);
  return s;
}


/* st_vprintf()-- vprintf function for error output.  To avoid buffer
   overruns, we limit the length of the buffer to ST_VPRINTF_SIZE.  2k
   is big enough to completely fill a 80x25 terminal, so it shuld be
   OK.  We use a direct write() because it is simpler and least likely
   to be clobbered by memory corruption.  Writing an error message
   longer than that is an error.  */

#define ST_VPRINTF_SIZE 2048

int
st_vprintf (const char *format, va_list ap)
{
  static char buffer[ST_VPRINTF_SIZE];
  int written;
  int fd;

  fd = options.use_stderr ? STDERR_FILENO : STDOUT_FILENO;
#ifdef HAVE_VSNPRINTF
  written = vsnprintf(buffer, ST_VPRINTF_SIZE, format, ap);
#else
  written = vsprintf(buffer, format, ap);

  if (written >= ST_VPRINTF_SIZE-1)
    {
      /* The error message was longer than our buffer.  Ouch.  Because
         we may have messed up things badly, report the error and
         quit.  */
#define ERROR_MESSAGE "Internal error: buffer overrun in st_vprintf()\n"
      write (fd, buffer, ST_VPRINTF_SIZE-1);
      write (fd, ERROR_MESSAGE, strlen(ERROR_MESSAGE));
      sys_exit(2);
#undef ERROR_MESSAGE

    }
#endif

  written = write (fd, buffer, written);
  return written;
}

/* st_printf()-- printf() function for error output.  This just calls
   st_vprintf() to do the actual work.  */

int
st_printf (const char *format, ...)
{
  int written;
  va_list ap;
  va_start (ap, format);
  written = st_vprintf(format, ap);
  va_end (ap);
  return written;
}


/* compare_file_filename()-- Given an open stream and a fortran string
 * that is a filename, figure out if the file is the same as the
 * filename. */

int
compare_file_filename (gfc_unit *u, const char *name, int len)
{
  char path[PATH_MAX + 1];
  struct stat st1;
#ifdef HAVE_WORKING_STAT
  struct stat st2;
#else
# ifdef __MINGW32__
  uint64_t id1, id2;
# endif
#endif

  if (unpack_filename (path, name, len))
    return 0;                   /* Can't be the same */

  /* If the filename doesn't exist, then there is no match with the
   * existing file. */

  if (stat (path, &st1) < 0)
    return 0;

#ifdef HAVE_WORKING_STAT
  fstat (((unix_stream *) (u->s))->fd, &st2);
  return (st1.st_dev == st2.st_dev) && (st1.st_ino == st2.st_ino);
#else

# ifdef __MINGW32__
  /* We try to match files by a unique ID.  On some filesystems (network
     fs and FAT), we can't generate this unique ID, and will simply compare
     filenames.  */
  id1 = id_from_path (path);
  id2 = id_from_fd (((unix_stream *) (u->s))->fd);
  if (id1 || id2)
    return (id1 == id2);
# endif

  if (len != u->file_len)
    return 0;
  return (memcmp(path, u->file, len) == 0);
#endif
}


#ifdef HAVE_WORKING_STAT
# define FIND_FILE0_DECL struct stat *st
# define FIND_FILE0_ARGS st
#else
# define FIND_FILE0_DECL uint64_t id, const char *file, gfc_charlen_type file_len
# define FIND_FILE0_ARGS id, file, file_len
#endif

/* find_file0()-- Recursive work function for find_file() */

static gfc_unit *
find_file0 (gfc_unit *u, FIND_FILE0_DECL)
{
  gfc_unit *v;
#if defined(__MINGW32__) && !HAVE_WORKING_STAT
  uint64_t id1;
#endif

  if (u == NULL)
    return NULL;

#ifdef HAVE_WORKING_STAT
  if (u->s != NULL
      && fstat (((unix_stream *) u->s)->fd, &st[1]) >= 0 &&
      st[0].st_dev == st[1].st_dev && st[0].st_ino == st[1].st_ino)
    return u;
#else
# ifdef __MINGW32__ 
  if (u->s && ((id1 = id_from_fd (((unix_stream *) u->s)->fd)) || id1))
    {
      if (id == id1)
        return u;
    }
  else
# endif
    if (compare_string (u->file_len, u->file, file_len, file) == 0)
      return u;
#endif

  v = find_file0 (u->left, FIND_FILE0_ARGS);
  if (v != NULL)
    return v;

  v = find_file0 (u->right, FIND_FILE0_ARGS);
  if (v != NULL)
    return v;

  return NULL;
}


/* find_file()-- Take the current filename and see if there is a unit
 * that has the file already open.  Returns a pointer to the unit if so. */

gfc_unit *
find_file (const char *file, gfc_charlen_type file_len)
{
  char path[PATH_MAX + 1];
  struct stat st[2];
  gfc_unit *u;
  uint64_t id;

  if (unpack_filename (path, file, file_len))
    return NULL;

  if (stat (path, &st[0]) < 0)
    return NULL;

#if defined(__MINGW32__) && !HAVE_WORKING_STAT
  id = id_from_path (path);
#else
  id = 0;
#endif

  __gthread_mutex_lock (&unit_lock);
retry:
  u = find_file0 (unit_root, FIND_FILE0_ARGS);
  if (u != NULL)
    {
      /* Fast path.  */
      if (! __gthread_mutex_trylock (&u->lock))
        {
          /* assert (u->closed == 0); */
          __gthread_mutex_unlock (&unit_lock);
          return u;
        }

      inc_waiting_locked (u);
    }
  __gthread_mutex_unlock (&unit_lock);
  if (u != NULL)
    {
      __gthread_mutex_lock (&u->lock);
      if (u->closed)
        {
          __gthread_mutex_lock (&unit_lock);
          __gthread_mutex_unlock (&u->lock);
          if (predec_waiting_locked (u) == 0)
            free_mem (u);
          goto retry;
        }

      dec_waiting_unlocked (u);
    }
  return u;
}

static gfc_unit *
flush_all_units_1 (gfc_unit *u, int min_unit)
{
  while (u != NULL)
    {
      if (u->unit_number > min_unit)
        {
          gfc_unit *r = flush_all_units_1 (u->left, min_unit);
          if (r != NULL)
            return r;
        }
      if (u->unit_number >= min_unit)
        {
          if (__gthread_mutex_trylock (&u->lock))
            return u;
          if (u->s)
            sflush (u->s);
          __gthread_mutex_unlock (&u->lock);
        }
      u = u->right;
    }
  return NULL;
}

void
flush_all_units (void)
{
  gfc_unit *u;
  int min_unit = 0;

  __gthread_mutex_lock (&unit_lock);
  do
    {
      u = flush_all_units_1 (unit_root, min_unit);
      if (u != NULL)
        inc_waiting_locked (u);
      __gthread_mutex_unlock (&unit_lock);
      if (u == NULL)
        return;

      __gthread_mutex_lock (&u->lock);

      min_unit = u->unit_number + 1;

      if (u->closed == 0)
        {
          sflush (u->s);
          __gthread_mutex_lock (&unit_lock);
          __gthread_mutex_unlock (&u->lock);
          (void) predec_waiting_locked (u);
        }
      else
        {
          __gthread_mutex_lock (&unit_lock);
          __gthread_mutex_unlock (&u->lock);
          if (predec_waiting_locked (u) == 0)
            free_mem (u);
        }
    }
  while (1);
}


/* delete_file()-- Given a unit structure, delete the file associated
 * with the unit.  Returns nonzero if something went wrong. */

int
delete_file (gfc_unit * u)
{
  char path[PATH_MAX + 1];

  if (unpack_filename (path, u->file, u->file_len))
    {                           /* Shouldn't be possible */
      errno = ENOENT;
      return 1;
    }

  return unlink (path);
}


/* file_exists()-- Returns nonzero if the current filename exists on
 * the system */

int
file_exists (const char *file, gfc_charlen_type file_len)
{
  char path[PATH_MAX + 1];
  struct stat statbuf;

  if (unpack_filename (path, file, file_len))
    return 0;

  if (stat (path, &statbuf) < 0)
    return 0;

  return 1;
}



static const char yes[] = "YES", no[] = "NO", unknown[] = "UNKNOWN";

/* inquire_sequential()-- Given a fortran string, determine if the
 * file is suitable for sequential access.  Returns a C-style
 * string. */

const char *
inquire_sequential (const char *string, int len)
{
  char path[PATH_MAX + 1];
  struct stat statbuf;

  if (string == NULL ||
      unpack_filename (path, string, len) || stat (path, &statbuf) < 0)
    return unknown;

  if (S_ISREG (statbuf.st_mode) ||
      S_ISCHR (statbuf.st_mode) || S_ISFIFO (statbuf.st_mode))
    return unknown;

  if (S_ISDIR (statbuf.st_mode) || S_ISBLK (statbuf.st_mode))
    return no;

  return unknown;
}


/* inquire_direct()-- Given a fortran string, determine if the file is
 * suitable for direct access.  Returns a C-style string. */

const char *
inquire_direct (const char *string, int len)
{
  char path[PATH_MAX + 1];
  struct stat statbuf;

  if (string == NULL ||
      unpack_filename (path, string, len) || stat (path, &statbuf) < 0)
    return unknown;

  if (S_ISREG (statbuf.st_mode) || S_ISBLK (statbuf.st_mode))
    return unknown;

  if (S_ISDIR (statbuf.st_mode) ||
      S_ISCHR (statbuf.st_mode) || S_ISFIFO (statbuf.st_mode))
    return no;

  return unknown;
}


/* inquire_formatted()-- Given a fortran string, determine if the file
 * is suitable for formatted form.  Returns a C-style string. */

const char *
inquire_formatted (const char *string, int len)
{
  char path[PATH_MAX + 1];
  struct stat statbuf;

  if (string == NULL ||
      unpack_filename (path, string, len) || stat (path, &statbuf) < 0)
    return unknown;

  if (S_ISREG (statbuf.st_mode) ||
      S_ISBLK (statbuf.st_mode) ||
      S_ISCHR (statbuf.st_mode) || S_ISFIFO (statbuf.st_mode))
    return unknown;

  if (S_ISDIR (statbuf.st_mode))
    return no;

  return unknown;
}


/* inquire_unformatted()-- Given a fortran string, determine if the file
 * is suitable for unformatted form.  Returns a C-style string. */

const char *
inquire_unformatted (const char *string, int len)
{
  return inquire_formatted (string, len);
}


#ifndef HAVE_ACCESS

#ifndef W_OK
#define W_OK 2
#endif

#ifndef R_OK
#define R_OK 4
#endif

/* Fallback implementation of access() on systems that don't have it.
   Only modes R_OK and W_OK are used in this file.  */

static int
fallback_access (const char *path, int mode)
{
  if ((mode & R_OK) && open (path, O_RDONLY) < 0)
    return -1;

  if ((mode & W_OK) && open (path, O_WRONLY) < 0)
    return -1;

  return 0;
}

#undef access
#define access fallback_access
#endif


/* inquire_access()-- Given a fortran string, determine if the file is
 * suitable for access. */

static const char *
inquire_access (const char *string, int len, int mode)
{
  char path[PATH_MAX + 1];

  if (string == NULL || unpack_filename (path, string, len) ||
      access (path, mode) < 0)
    return no;

  return yes;
}


/* inquire_read()-- Given a fortran string, determine if the file is
 * suitable for READ access. */

const char *
inquire_read (const char *string, int len)
{
  return inquire_access (string, len, R_OK);
}


/* inquire_write()-- Given a fortran string, determine if the file is
 * suitable for READ access. */

const char *
inquire_write (const char *string, int len)
{
  return inquire_access (string, len, W_OK);
}


/* inquire_readwrite()-- Given a fortran string, determine if the file is
 * suitable for read and write access. */

const char *
inquire_readwrite (const char *string, int len)
{
  return inquire_access (string, len, R_OK | W_OK);
}


/* file_length()-- Return the file length in bytes, -1 if unknown */

gfc_offset
file_length (stream * s)
{
  off_t curr, end;
  if (!is_seekable (s))
    return -1;
  curr = stell (s);
  if (curr == -1)
    return curr;
  end = sseek (s, 0, SEEK_END);
  sseek (s, curr, SEEK_SET);
  return end;
}


/* is_seekable()-- Return nonzero if the stream is seekable, zero if
 * it is not */

int
is_seekable (stream *s)
{
  /* By convention, if file_length == -1, the file is not
     seekable.  */
  return ((unix_stream *) s)->file_length!=-1;
}


/* is_special()-- Return nonzero if the stream is not a regular file.  */

int
is_special (stream *s)
{
  return ((unix_stream *) s)->special_file;
}


int
stream_isatty (stream *s)
{
  return isatty (((unix_stream *) s)->fd);
}

char *
stream_ttyname (stream *s __attribute__ ((unused)))
{
#ifdef HAVE_TTYNAME
  return ttyname (((unix_stream *) s)->fd);
#else
  return NULL;
#endif
}


/* How files are stored:  This is an operating-system specific issue,
   and therefore belongs here.  There are three cases to consider.

   Direct Access:
      Records are written as block of bytes corresponding to the record
      length of the file.  This goes for both formatted and unformatted
      records.  Positioning is done explicitly for each data transfer,
      so positioning is not much of an issue.

   Sequential Formatted:
      Records are separated by newline characters.  The newline character
      is prohibited from appearing in a string.  If it does, this will be
      messed up on the next read.  End of file is also the end of a record.

   Sequential Unformatted:
      In this case, we are merely copying bytes to and from main storage,
      yet we need to keep track of varying record lengths.  We adopt
      the solution used by f2c.  Each record contains a pair of length
      markers:

        Length of record n in bytes
        Data of record n
        Length of record n in bytes

        Length of record n+1 in bytes
        Data of record n+1
        Length of record n+1 in bytes

     The length is stored at the end of a record to allow backspacing to the
     previous record.  Between data transfer statements, the file pointer
     is left pointing to the first length of the current record.

     ENDFILE records are never explicitly stored.

*/