lib/stdio/fopen.c

   1 /*
   2  * fopen.c - open a stream
   3  */
   4 /* $Header$ */
   5
   6 #if     defined(_POSIX_SOURCE)
   7 #include        <sys/types.h>
   8 #endif
   9 #include        <stdio.h>
  10 #include        <stdlib.h>
  11 #include        "loc_incl.h"
  12 #include        <sys/stat.h>
  13
  14 #define PMODE           0666
  15
  16 /* The next 3 defines are true in all UNIX systems known to me.
  17  */
  18 #define O_RDONLY        0
  19 #define O_WRONLY        1
  20 #define O_RDWR          2
  21
  22 /* Since the O_CREAT flag is not available on all systems, we can't get it
  23  * from the standard library. Furthermore, even if we know that <fcntl.h>
  24  * contains such a flag, it's not sure whether it can be used, since we
  25  * might be cross-compiling for another system, which may use an entirely
  26  * different value for O_CREAT (or not support such a mode). The safest
  27  * thing is to just use the Version 7 semantics for open, and use creat()
  28  * whenever necessary.
  29  *
  30  * Another problem is O_APPEND, for which the same holds. When "a"
  31  * open-mode is used, an lseek() to the end is done before every write()
  32  * system-call.
  33  *
  34  * The O_CREAT, O_TRUNC and O_APPEND given here, are only for convenience.
  35  * They are not passed to open(), so the values don't have to match a value
  36  * from the real world. It is enough when they are unique.
  37  */
  38 #define O_CREAT         0x010
  39 #define O_TRUNC         0x020
  40 #define O_APPEND        0x040
  41
  42 int _open(const char *path, int flags);
  43 int _creat(const char *path, _mnx_Mode_t mode);
  44 int _close(int d);
  45
  46 FILE *
  47 fopen(const char *name, const char *mode)
  48 {
  49         register int i;
  50         int rwmode = 0, rwflags = 0;
  51         FILE *stream;
  52         struct stat st;
  53         int fd, flags = 0;
  54
  55         for (i = 0; __iotab[i] != 0 ; i++)
  56                 if ( i >= FOPEN_MAX-1 )
  57                         return (FILE *)NULL;
  58
  59         switch(*mode++) {
  60         case 'r':
  61                 flags |= _IOREAD | _IOREADING;
  62                 rwmode = O_RDONLY;
  63                 break;
  64         case 'w':
  65                 flags |= _IOWRITE | _IOWRITING;
  66                 rwmode = O_WRONLY;
  67                 rwflags = O_CREAT | O_TRUNC;
  68                 break;
  69         case 'a':
  70                 flags |= _IOWRITE | _IOWRITING | _IOAPPEND;
  71                 rwmode = O_WRONLY;
  72                 rwflags |= O_APPEND | O_CREAT;
  73                 break;
  74         default:
  75                 return (FILE *)NULL;
  76         }
  77
  78         while (*mode) {
  79                 switch(*mode++) {
  80                 case 'b':
  81                         continue;
  82                 case '+':
  83                         rwmode = O_RDWR;
  84                         flags |= _IOREAD | _IOWRITE;
  85                         continue;
  86                 /* The sequence may be followed by additional characters */
  87                 default:
  88                         break;
  89                 }
  90                 break;
  91         }
  92
  93         /* Perform a creat() when the file should be truncated or when
  94          * the file is opened for writing and the open() failed.
  95          */
  96         if ((rwflags & O_TRUNC)
  97             || (((fd = _open(name, rwmode)) < 0)
  98                     && (rwflags & O_CREAT))) {
  99                 if (((fd = _creat(name, PMODE)) > 0) && flags  | _IOREAD) {
 100                         (void) _close(fd);
 101                         fd = _open(name, rwmode);
 102                 }
 103
 104         }
 105
 106         if (fd < 0) return (FILE *)NULL;
 107
 108         if ( fstat( fd, &st ) < 0 ) {
 109                 _close(fd);
 110                 return (FILE *)NULL;
 111         }
 112
 113         if ( S_ISFIFO(st.st_mode) ) flags |= _IOFIFO;
 114
 115         if (( stream = (FILE *) malloc(sizeof(FILE))) == NULL ) {
 116                 _close(fd);
 117                 return (FILE *)NULL;
 118         }
 119
 120         if ((flags & (_IOREAD | _IOWRITE))  == (_IOREAD | _IOWRITE))
 121                 flags &= ~(_IOREADING | _IOWRITING);
 122
 123         stream->_count = 0;
 124         stream->_fd = fd;
 125         stream->_flags = flags;
 126         stream->_buf = NULL;
 127         __iotab[i] = stream;
 128         return stream;
 129 }