my_pread.c

/* Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

#include "mysys_priv.h"
#include "mysys_err.h"
#include "my_base.h"
#include <m_string.h>
#include <errno.h>
#if defined (HAVE_PREAD) && !defined(_WIN32)
#include <unistd.h>
#endif



/*
  Read a chunk of bytes from a file from a given position

  SYNOPSIOS
    my_pread()
    Filedes     File decsriptor
    Buffer      Buffer to read data into
    Count       Number of bytes to read
    offset      Position to read from
    MyFlags     Flags

  NOTES
    This differs from the normal pread() call in that we don't care
    to set the position in the file back to the original position
    if the system doesn't support pread().

  RETURN
    (size_t) -1   Error
    #             Number of bytes read
*/

size_t my_pread(File Filedes, uchar *Buffer, size_t Count, my_off_t offset,
                myf MyFlags)
{
  size_t readbytes;
  int error= 0;
#if !defined (HAVE_PREAD) && !defined (_WIN32)
  int save_errno;
#endif
  DBUG_ENTER("my_pread");
  DBUG_PRINT("my",("fd: %d  Seek: %llu  Buffer: %p  Count: %lu  MyFlags: %d",
             Filedes, (ulonglong)offset, Buffer, (ulong)Count, MyFlags));
  for (;;)
  {
    errno= 0;    /* Linux, Windows don't reset this on EOF/success */
#if !defined (HAVE_PREAD) && !defined (_WIN32)
    mysql_mutex_lock(&my_file_info[Filedes].mutex);
    readbytes= (uint) -1;
    error= (lseek(Filedes, offset, MY_SEEK_SET) == (my_off_t) -1 ||
           (readbytes= read(Filedes, Buffer, Count)) != Count);
    save_errno= errno;
    mysql_mutex_unlock(&my_file_info[Filedes].mutex);
    if (error)
      errno= save_errno;
#else
#if defined(_WIN32)
    readbytes= my_win_pread(Filedes, Buffer, Count, offset);
#else 
    readbytes= pread(Filedes, Buffer, Count, offset);
#endif
    error= (readbytes != Count);
#endif
    if(error)
    {
      my_errno= errno ? errno : -1;
      if (errno == 0 || (readbytes != (size_t) -1 &&
                      (MyFlags & (MY_NABP | MY_FNABP))))
         my_errno= HA_ERR_FILE_TOO_SHORT;

      DBUG_PRINT("warning",("Read only %d bytes off %u from %d, errno: %d",
                            (int) readbytes, (uint) Count,Filedes,my_errno));

      if ((readbytes == 0 || readbytes == (size_t) -1) && errno == EINTR)
      {
        DBUG_PRINT("debug", ("my_pread() was interrupted and returned %d",
                             (int) readbytes));
        continue;                              /* Interrupted */
      }

      if (MyFlags & (MY_WME | MY_FAE | MY_FNABP))
      {
        char errbuf[MYSYS_STRERROR_SIZE];
        if (readbytes == (size_t) -1)
          my_error(EE_READ, MYF(ME_BELL+ME_WAITTANG), my_filename(Filedes),
                   my_errno, my_strerror(errbuf, sizeof(errbuf), my_errno));
        else if (MyFlags & (MY_NABP | MY_FNABP))
          my_error(EE_EOFERR, MYF(ME_BELL+ME_WAITTANG), my_filename(Filedes),
                   my_errno, my_strerror(errbuf, sizeof(errbuf), my_errno));
      }
      if (readbytes == (size_t) -1 || (MyFlags & (MY_FNABP | MY_NABP)))
        DBUG_RETURN(MY_FILE_ERROR);         /* Return with error */
    }
    if (MyFlags & (MY_NABP | MY_FNABP))
      DBUG_RETURN(0);                      /* Read went ok; Return 0 */
    DBUG_RETURN(readbytes);                /* purecov: inspected */
  }
} /* my_pread */


/*
  Write a chunk of bytes to a file at a given position

  SYNOPSIOS
    my_pwrite()
    Filedes     File decsriptor
    Buffer      Buffer to write data from
    Count       Number of bytes to write
    offset      Position to write to
    MyFlags     Flags

  NOTES
    This differs from the normal pwrite() call in that we don't care
    to set the position in the file back to the original position
    if the system doesn't support pwrite()

  RETURN
    (size_t) -1   Error
    #             Number of bytes read
*/

size_t my_pwrite(File Filedes, const uchar *Buffer, size_t Count,
                 my_off_t offset, myf MyFlags)
{
  size_t writtenbytes, written;
  uint errors;

  DBUG_ENTER("my_pwrite");
  DBUG_PRINT("my",("fd: %d  Seek: %llu  Buffer: %p  Count: %lu  MyFlags: %d",
             Filedes, offset, Buffer, (ulong)Count, MyFlags));
  errors= 0;
  written= 0;

  for (;;)
  {
#if !defined (HAVE_PREAD) && !defined (_WIN32)
    int error;
    writtenbytes= (size_t) -1;
    mysql_mutex_lock(&my_file_info[Filedes].mutex);
    error= (lseek(Filedes, offset, MY_SEEK_SET) != (my_off_t) -1 &&
            (writtenbytes= write(Filedes, Buffer, Count)) == Count);
    mysql_mutex_unlock(&my_file_info[Filedes].mutex);
    if (error)
      break;
#elif defined (_WIN32)
    writtenbytes= my_win_pwrite(Filedes, Buffer, Count, offset);
#else
    writtenbytes= pwrite(Filedes, Buffer, Count, offset);
#endif
    if(writtenbytes == Count)
      break;
    my_errno= errno;
    if (writtenbytes != (size_t) -1)
    {
      written+= writtenbytes;
      Buffer+= writtenbytes;
      Count-= writtenbytes;
      offset+= writtenbytes;
    }
    DBUG_PRINT("error",("Write only %u bytes", (uint) writtenbytes));
#ifndef NO_BACKGROUND

    if (my_thread_var->abort)
      MyFlags&= ~ MY_WAIT_IF_FULL;              /* End if aborted by user */

    if ((my_errno == ENOSPC || my_errno == EDQUOT) &&
        (MyFlags & MY_WAIT_IF_FULL))
    {
      wait_for_free_space(my_filename(Filedes), errors);
      errors++;
      continue;
    }
    if ((writtenbytes && writtenbytes != (size_t) -1) || my_errno == EINTR)
      continue;                                 /* Retry */
#endif
    if (MyFlags & (MY_NABP | MY_FNABP))
    {
      if (MyFlags & (MY_WME | MY_FAE | MY_FNABP))
      {
        char errbuf[MYSYS_STRERROR_SIZE];
        my_error(EE_WRITE, MYF(ME_BELL | ME_WAITTANG), my_filename(Filedes),
                 my_errno, my_strerror(errbuf, sizeof(errbuf), my_errno));
      }
      DBUG_RETURN(MY_FILE_ERROR);               /* Error on read */
    }
    else
      break;                                    /* Return bytes written */
  }
  DBUG_EXECUTE_IF("check", my_seek(Filedes, -1, SEEK_SET, MYF(0)););
  if (MyFlags & (MY_NABP | MY_FNABP))
    DBUG_RETURN(0);                     /* Want only errors */
  DBUG_RETURN(writtenbytes+written); /* purecov: inspected */
} /* my_pwrite */