release/src/router/mysql/mysys/my_seek.c

   1 /*
   2    Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; version 2 of the License.
   7
   8    This program is distributed in the hope that it will be useful,
   9    but WITHOUT ANY WARRANTY; without even the implied warranty of
  10    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11    GNU General Public License for more details.
  12
  13    You should have received a copy of the GNU General Public License
  14    along with this program; if not, write to the Free Software
  15    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA
  16 */
  17
  18 #include "mysys_priv.h"
  19 #include "mysys_err.h"
  20
  21 /*
  22   Seek to a position in a file.
  23
  24   ARGUMENTS
  25   File fd          The file descriptor
  26   my_off_t pos     The expected position (absolute or relative)
  27   int whence       A direction parameter and one of
  28                    {SEEK_SET, SEEK_CUR, SEEK_END}
  29   myf MyFlags      MY_THREADSAFE must be set in case my_seek may be mixed
  30                    with my_pread/my_pwrite calls and fd is shared among
  31                    threads.
  32
  33   DESCRIPTION
  34     The my_seek  function  is a wrapper around the system call lseek and
  35     repositions  the  offset of the file descriptor fd to the argument
  36     offset according to the directive whence as follows:
  37       SEEK_SET    The offset is set to offset bytes.
  38       SEEK_CUR    The offset is set to its current location plus offset bytes
  39       SEEK_END    The offset is set to the size of the file plus offset bytes
  40
  41   RETURN VALUE
  42     my_off_t newpos    The new position in the file.
  43     MY_FILEPOS_ERROR   An error was encountered while performing
  44                        the seek. my_errno is set to indicate the
  45                        actual error.
  46 */
  47
  48 my_off_t my_seek(File fd, my_off_t pos, int whence, myf MyFlags)
  49 {
  50   reg1 os_off_t newpos= -1;
  51   DBUG_ENTER("my_seek");
  52   DBUG_PRINT("my",("Fd: %d  Hpos: %lu  Pos: %lu  Whence: %d  MyFlags: %d",
  53                    fd, (ulong) (((ulonglong) pos) >> 32), (ulong) pos,
  54                    whence, MyFlags));
  55   DBUG_ASSERT(pos != MY_FILEPOS_ERROR);         /* safety check */
  56
  57   /*
  58       Make sure we are using a valid file descriptor!
  59   */
  60   DBUG_ASSERT(fd != -1);
  61 #if defined(THREAD) && !defined(HAVE_PREAD)
  62   if (MyFlags & MY_THREADSAFE)
  63   {
  64     pthread_mutex_lock(&my_file_info[fd].mutex);
  65     newpos= lseek(fd, pos, whence);
  66     pthread_mutex_unlock(&my_file_info[fd].mutex);
  67   }
  68   else
  69 #endif
  70     newpos= lseek(fd, pos, whence);
  71   if (newpos == (os_off_t) -1)
  72   {
  73     my_errno=errno;
  74     if (MyFlags & MY_WME)
  75       my_error(EE_CANT_SEEK, MYF(0), my_filename(fd), my_errno);
  76     DBUG_PRINT("error",("lseek: %lu  errno: %d", (ulong) newpos,errno));
  77     DBUG_RETURN(MY_FILEPOS_ERROR);
  78   }
  79   if ((my_off_t) newpos != pos)
  80   {
  81     DBUG_PRINT("exit",("pos: %lu", (ulong) newpos));
  82   }
  83   DBUG_RETURN((my_off_t) newpos);
  84 } /* my_seek */
  85
  86
  87         /* Tell current position of file */
  88         /* ARGSUSED */
  89
  90 my_off_t my_tell(File fd, myf MyFlags)
  91 {
  92   os_off_t pos;
  93   DBUG_ENTER("my_tell");
  94   DBUG_PRINT("my",("Fd: %d  MyFlags: %d",fd, MyFlags));
  95   DBUG_ASSERT(fd >= 0);
  96 #ifdef HAVE_TELL
  97   pos=tell(fd);
  98 #else
  99   pos=lseek(fd, 0L, MY_SEEK_CUR);
 100 #endif
 101   if (pos == (os_off_t) -1)
 102   {
 103     my_errno=errno;
 104     if (MyFlags & MY_WME)
 105       my_error(EE_CANT_SEEK, MYF(0), my_filename(fd), my_errno);
 106     DBUG_PRINT("error", ("tell: %lu  errno: %d", (ulong) pos, my_errno));
 107   }
 108   DBUG_PRINT("exit",("pos: %lu", (ulong) pos));
 109   DBUG_RETURN((my_off_t) pos);
 110 } /* my_tell */