118 lines
2.7 KiB
C
118 lines
2.7 KiB
C
/*
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* fopen.c - open a stream
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*/
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/* $Id$ */
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#include <stdio.h>
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#include <stdlib.h>
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#include "loc_incl.h"
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#define PMODE 0666
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/* The next 3 defines are true in all UNIX systems known to me.
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*/
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#define O_RDONLY 0
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#define O_WRONLY 1
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#define O_RDWR 2
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/* Since the O_CREAT flag is not available on all systems, we can't get it
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* from the standard library. Furthermore, even if we know that <fcntl.h>
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* contains such a flag, it's not sure whether it can be used, since we
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* might be cross-compiling for another system, which may use an entirely
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* different value for O_CREAT (or not support such a mode). The safest
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* thing is to just use the Version 7 semantics for open, and use creat()
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* whenever necessary.
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*
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* Another problem is O_APPEND, for which the same holds. When "a"
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* open-mode is used, an lseek() to the end is done before every write()
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* system-call.
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*
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* The O_CREAT, O_TRUNC and O_APPEND given here, are only for convenience.
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* They are not passed to open(), so the values don't have to match a value
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* from the real world. It is enough when they are unique.
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*/
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#define O_CREAT 0x010
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#define O_TRUNC 0x020
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#define O_APPEND 0x040
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int _open(const char *path, int flags);
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int _creat(const char *path, int mode);
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int _close(int d);
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FILE *
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fopen(const char *name, const char *mode)
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{
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register int i;
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int rwmode = 0, rwflags = 0;
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FILE *stream;
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int fd, flags = 0;
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for (i = 0; __iotab[i] != 0 ; i++)
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if ( i >= FOPEN_MAX-1 )
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return (FILE *)NULL;
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switch(*mode++) {
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case 'r':
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flags |= _IOREAD | _IOREADING;
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rwmode = O_RDONLY;
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break;
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case 'w':
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flags |= _IOWRITE | _IOWRITING;
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rwmode = O_WRONLY;
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rwflags = O_CREAT | O_TRUNC;
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break;
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case 'a':
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flags |= _IOWRITE | _IOWRITING | _IOAPPEND;
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rwmode = O_WRONLY;
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rwflags |= O_APPEND | O_CREAT;
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break;
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default:
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return (FILE *)NULL;
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}
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while (*mode) {
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switch(*mode++) {
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case 'b':
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continue;
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case '+':
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rwmode = O_RDWR;
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flags |= _IOREAD | _IOWRITE;
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continue;
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/* The sequence may be followed by additional characters */
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default:
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break;
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}
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break;
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}
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/* Perform a creat() when the file should be truncated or when
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* the file is opened for writing and the open() failed.
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*/
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if ((rwflags & O_TRUNC)
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|| (((fd = _open(name, rwmode)) < 0)
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&& (rwflags & O_CREAT))) {
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if (((fd = _creat(name, PMODE)) > 0) && flags | _IOREAD) {
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(void) _close(fd);
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fd = _open(name, rwmode);
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}
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}
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if (fd < 0) return (FILE *)NULL;
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if (( stream = (FILE *) malloc(sizeof(FILE))) == NULL ) {
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_close(fd);
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return (FILE *)NULL;
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}
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if ((flags & (_IOREAD | _IOWRITE)) == (_IOREAD | _IOWRITE))
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flags &= ~(_IOREADING | _IOWRITING);
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stream->_count = 0;
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stream->_fd = fd;
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stream->_flags = flags;
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stream->_buf = NULL;
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__iotab[i] = stream;
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return stream;
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}
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