compiler/posixc/lseek.c

   1 /*
   2     Copyright © 1995-2012, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Reposition read/write file offset.
   6 */
   7 #include <errno.h>
   8 #include <dos/dos.h>
   9 #include <proto/dos.h>
  10 #include <exec/exec.h>
  11 #include <proto/exec.h>
  12 #include <clib/macros.h>
  13 #include "__fdesc.h"
  14
  15 /*****************************************************************************
  16
  17     NAME */
  18 #include <unistd.h>
  19
  20         off_t lseek (
  21
  22 /*  SYNOPSIS */
  23         int    filedes,
  24         off_t  offset,
  25         int    whence)
  26
  27 /*  FUNCTION
  28         Reposition read/write file offset
  29
  30     INPUTS
  31         filedef - the filedescriptor being modified
  32         offset, whence -
  33                   How to modify the current position. whence
  34                   can be SEEK_SET, then offset is the absolute position
  35                   in the file (0 is the first byte), SEEK_CUR then the
  36                   position will change by offset (ie. -5 means to move
  37                   5 bytes to the beginning of the file) or SEEK_END.
  38                   SEEK_END means that the offset is relative to the
  39                   end of the file (-1 is the last byte and 0 is
  40                   the EOF).
  41
  42     RESULT
  43         The new position on success and -1 on error. If an error occurred, the global
  44         variable errno is set.
  45
  46     NOTES
  47
  48     EXAMPLE
  49
  50     BUGS
  51         File is extended with zeros if desired position is beyond the end of
  52         file.
  53
  54         Since it's not possible to use Seek() for directories, this
  55         implementation fails with EISDIR for directory file descriptors.
  56
  57     SEE ALSO
  58         fopen(), fwrite()
  59
  60     INTERNALS
  61
  62 ******************************************************************************/
  63 {
  64     int  cnt;
  65     fdesc *fdesc = __getfdesc(filedes);
  66
  67     if (!fdesc)
  68     {
  69         errno = EBADF;
  70         return -1;
  71     }
  72
  73     if(fdesc->fcb->privflags & _FCB_ISDIR)
  74     {
  75         errno = EISDIR;
  76         return -1;
  77     }
  78
  79     FLUSHONREADCHECK
  80
  81     switch (whence)
  82     {
  83         case SEEK_SET: whence = OFFSET_BEGINNING; break;
  84         case SEEK_CUR: whence = OFFSET_CURRENT; break;
  85         case SEEK_END: whence = OFFSET_END; break;
  86
  87         default:
  88             errno = EINVAL;
  89             return -1;
  90     }
  91
  92     cnt = Seek (fdesc->fcb->handle, offset, whence);
  93
  94     if (cnt == -1)
  95     {
  96         if(IoErr() == ERROR_SEEK_ERROR)
  97         {
  98             LONG saved_error = IoErr();
  99             /* Most likely we tried to seek behind EOF. POSIX lseek allows
 100                that, and if anything is written at the end on the gap,
 101                reads from the gap should return 0 unless some real data
 102                is written there. Since implementing it would be rather
 103                difficult, we simply extend the file by writing zeros
 104                and hope for the best. */
 105             LONG abs_cur_pos = Seek(fdesc->fcb->handle, 0, OFFSET_CURRENT);
 106             if(abs_cur_pos == -1)
 107                 goto error;
 108             LONG file_size = Seek(fdesc->fcb->handle, 0, OFFSET_END);
 109             if(file_size == -1)
 110                 goto error;
 111             /* Now compute how much we have to extend the file */
 112             LONG abs_new_pos = 0;
 113             switch(whence)
 114             {
 115                 case OFFSET_BEGINNING: abs_new_pos = offset; break;
 116                 case OFFSET_CURRENT: abs_new_pos = abs_cur_pos + offset; break;
 117                 case OFFSET_END: abs_new_pos = file_size + offset; break;
 118             }
 119             if(abs_new_pos > abs_cur_pos)
 120             {
 121                 ULONG bufsize = 4096;
 122                 APTR zeros = AllocMem(bufsize, MEMF_ANY | MEMF_CLEAR);
 123                 if(!zeros)
 124                 {
 125                     /* Restore previous position */
 126                     Seek(fdesc->fcb->handle, abs_cur_pos, OFFSET_BEGINNING);
 127                     errno = ENOMEM;
 128                     return -1;
 129                 }
 130
 131                 LONG towrite = abs_new_pos - abs_cur_pos;
 132                 do
 133                 {
 134                     Write(fdesc->fcb->handle, zeros, MIN(towrite, bufsize));
 135                     towrite -= bufsize;
 136                 }
 137                 while(towrite > 0);
 138
 139                 FreeMem(zeros, bufsize);
 140             }
 141             else
 142             {
 143                 /* Hmm, that's strange. Looks like ERROR_SEEK_ERROR has
 144                    been caused by something else */
 145                 SetIoErr(saved_error);
 146                 goto error;
 147             }
 148         }
 149         else
 150             goto error;
 151     }
 152
 153     return Seek(fdesc->fcb->handle, 0, OFFSET_CURRENT);
 154 error:
 155     errno = __stdc_ioerr2errno (IoErr ());
 156     return (off_t) -1;
 157 } /* lseek */