compiler/posixc/fseek.c

   1 /*
   2     Copyright © 1995-2013, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Change the position in a stream.
   6 */
   7
   8 #include <fcntl.h>
   9 #include <errno.h>
  10 #include <dos/dos.h>
  11 #include <proto/dos.h>
  12 #include "__stdio.h"
  13 #include "__fdesc.h"
  14
  15 /*****************************************************************************
  16
  17     NAME */
  18 #include <stdio.h>
  19
  20         int fseek (
  21
  22 /*  SYNOPSIS */
  23         FILE * stream,
  24         long   offset,
  25         int    whence)
  26
  27 /*  FUNCTION
  28         Change the current position in a stream.
  29
  30     INPUTS
  31         stream - Modify this stream
  32         offset, whence - How to modify the current position. whence
  33                 can be SEEK_SET, then offset is the absolute position
  34                 in the file (0 is the first byte), SEEK_CUR then the
  35                 position will change by offset (ie. -5 means to move
  36                 5 bytes to the beginning of the file) or SEEK_END.
  37                 SEEK_END means that the offset is relative to the
  38                 end of the file (-1 is the last byte and 0 is
  39                 the EOF).
  40
  41     RESULT
  42         0 on success and -1 on error. If an error occurred, the global
  43         variable errno is set.
  44
  45     NOTES
  46
  47     EXAMPLE
  48
  49     BUGS
  50     Not fully compatible with iso fseek, especially in 'ab' and 'a+b'
  51     modes
  52
  53     Since it's not possible to use Seek() for directories, this
  54     implementation fails with EISDIR for directory file descriptors.
  55
  56     SEE ALSO
  57         fopen(), fwrite()
  58
  59     INTERNALS
  60
  61 ******************************************************************************/
  62 {
  63     int cnt = 0;
  64     int finalseekposition = 0;
  65     int eofposition = 0;
  66     struct FileInfoBlock *fib = NULL;
  67     BPTR fh = BNULL;
  68     fdesc *fdesc = __getfdesc(stream->fd);
  69
  70     if (!fdesc)
  71     {
  72             errno = EBADF;
  73             return -1;
  74     }
  75
  76     if (fdesc->fcb->privflags & _FCB_ISDIR)
  77     {
  78         errno = EISDIR;
  79         return -1;
  80     }
  81
  82     fh = fdesc->fcb->handle;
  83
  84     /* This is buffered IO, flush the buffer before any Seek */
  85     Flush (fh);
  86
  87     /* Handling for fseek specific behaviour (not all cases handled) */
  88     /* Get current position */
  89     cnt = Seek (fh, 0, OFFSET_CURRENT);
  90     if (cnt == -1)
  91     {
  92         errno = __stdc_ioerr2errno (IoErr ());
  93         return -1;
  94     }
  95
  96     /* Get file size */
  97     fib = AllocDosObject(DOS_FIB, NULL);
  98     if (!fib)
  99     {
 100         errno = __stdc_ioerr2errno(IoErr());
 101         return -1;
 102     }
 103
 104     if (ExamineFH(fh, fib))
 105         eofposition = fib->fib_Size;
 106     else
 107     {
 108         /* Does not happen on sfs/affs */
 109         FreeDosObject(DOS_FIB, fib);
 110         fib = NULL;
 111         errno = EBADF;
 112         return -1;
 113     }
 114
 115     FreeDosObject(DOS_FIB, fib);
 116     fib = NULL;
 117
 118     switch(whence)
 119     {
 120         case SEEK_SET: finalseekposition = offset; break;
 121         case SEEK_CUR: finalseekposition = cnt + offset; break;
 122         case SEEK_END: finalseekposition = eofposition + offset; break;
 123         default:
 124             errno = EINVAL;
 125             return -1;
 126     }
 127
 128     /* Check conditions */
 129     /* Seek before beginning of file */
 130     if (finalseekposition < 0)
 131     {
 132         errno = EINVAL;
 133         return -1;
 134     }
 135
 136     /* Seek beyond end of file and in write mode */
 137     if (finalseekposition > eofposition)
 138     {
 139         if (fdesc->fcb->flags & O_WRITE)
 140         {
 141             /* Write '0' to fill up to requested size - compatible fseek does not write but allows write */
 142             int i = 0;
 143             int bytestowrite = finalseekposition - eofposition;
 144             int chunkcount = (bytestowrite)/128;
 145             char zeroarray[128] = {0};
 146
 147             Seek (fh, 0, OFFSET_END);
 148             for (i = 0; i < chunkcount; i++)
 149                 FWrite(fh, (STRPTR)zeroarray, 128, 1);
 150             FWrite(fh, (STRPTR)zeroarray, bytestowrite - (chunkcount * 128), 1);
 151             Flush (fh);
 152         }
 153     }
 154
 155     cnt = Seek (fh, finalseekposition, OFFSET_BEGINNING);
 156
 157     if (cnt == -1)
 158         errno = __stdc_ioerr2errno (IoErr ());
 159     else
 160     {
 161         /* It's specified that upon success fseek should clear EOF flag
 162            so here we go.
 163         */
 164         stream->flags &= ~(__POSIXC_STDIO_EOF);
 165         cnt = 0;
 166     }
 167
 168     return cnt;
 169 } /* fseek */