mariadb/mysys/mf_iocache.c

/* Copyright (C) 2000 MySQL AB

   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; either version 2 of the License, or
   (at your option) any later version.

   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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

/*
  Cashing of files with only does (sequential) read or writes of fixed-
  length records. A read isn't allowed to go over file-length. A read is ok
  if it ends at file-length and next read can try to read after file-length
  (and get a EOF-error).
  Possibly use of asyncronic io.
  macros for read and writes for faster io.
  Used instead of FILE when reading or writing whole files.
  This code makes mf_rec_cache obsolete (currently only used by ISAM)
  One can change info->pos_in_file to a higher value to skip bytes in file if
  also info->read_pos is set to info->read_end.
  If called through open_cached_file(), then the temporary file will
  only be created if a write exeeds the file buffer or if one calls
  my_b_flush_io_cache().

  If one uses SEQ_READ_APPEND, then two buffers are allocated, one for
  reading and another for writing.  Reads are first done from disk and
  then done from the write buffer.  This is an efficient way to read
  from a log file when one is writing to it at the same time.
  For this to work, the file has to be opened in append mode!
  Note that when one uses SEQ_READ_APPEND, one MUST write using
  my_b_append !  This is needed because we need to lock the mutex
  every time we access the write buffer.

TODO:
  When one SEQ_READ_APPEND and we are reading and writing at the same time,
  each time the write buffer gets full and it's written to disk, we will
  always do a disk read to read a part of the buffer from disk to the
  read buffer.
  This should be fixed so that when we do a my_b_flush_io_cache() and
  we have been reading the write buffer, we should transfer the rest of the
  write buffer to the read buffer before we start to reuse it.
*/

#define MAP_TO_USE_RAID
#include "mysys_priv.h"
#include <m_string.h>
#ifdef HAVE_AIOWAIT
#include "mysys_err.h"
static void my_aiowait(my_aio_result *result);
#endif
#include <errno.h>

#ifdef THREAD
#define lock_append_buffer(info) \
 pthread_mutex_lock(&(info)->append_buffer_lock)
#define unlock_append_buffer(info) \
 pthread_mutex_unlock(&(info)->append_buffer_lock)
#else
#define lock_append_buffer(info)
#define unlock_append_buffer(info)
#endif

#define IO_ROUND_UP(X) (((X)+IO_SIZE-1) & ~(IO_SIZE-1))
#define IO_ROUND_DN(X) ( (X)            & ~(IO_SIZE-1))


/*
  Setup internal pointers inside IO_CACHE

  SYNOPSIS
    setup_io_cache()
    info		IO_CACHE handler

  NOTES
    This is called on automaticly on init or reinit of IO_CACHE
    It must be called externally if one moves or copies an IO_CACHE
    object.
*/

void setup_io_cache(IO_CACHE* info)
{
  /* Ensure that my_b_tell() and my_b_bytes_in_cache works */
  if (info->type == WRITE_CACHE)
  {
    info->current_pos= &info->write_pos;
    info->current_end= &info->write_end;
  }
  else
  {
    info->current_pos= &info->read_pos;
    info->current_end= &info->read_end;
  }
}


static void
init_functions(IO_CACHE* info)
{
  enum cache_type type= info->type;
  switch (type) {
  case READ_NET:
    /*
      Must be initialized by the caller. The problem is that
      _my_b_net_read has to be defined in sql directory because of
      the dependency on THD, and therefore cannot be visible to
      programs that link against mysys but know nothing about THD, such
      as myisamchk
    */
    break;
  case SEQ_READ_APPEND:
    info->read_function = _my_b_seq_read;
    info->write_function = 0;			/* Force a core if used */
    break;
  default:
    info->read_function =
#ifdef THREAD
                          info->share ? _my_b_read_r :
#endif
                                        _my_b_read;
    info->write_function = _my_b_write;
  }

  setup_io_cache(info);
}


/*
  Initialize an IO_CACHE object

  SYNOPSOS
    init_io_cache()
    info		cache handler to initialize
    file		File that should be associated to to the handler
			If == -1 then real_open_cached_file()
			will be called when it's time to open file.
    cachesize		Size of buffer to allocate for read/write
			If == 0 then use my_default_record_cache_size
    type		Type of cache
    seek_offset		Where cache should start reading/writing
    use_async_io	Set to 1 of we should use async_io (if avaiable)
    cache_myflags	Bitmap of differnt flags
			MY_WME | MY_FAE | MY_NABP | MY_FNABP |
			MY_DONT_CHECK_FILESIZE

  RETURN
    0  ok
    #  error
*/

int init_io_cache(IO_CACHE *info, File file, uint cachesize,
		  enum cache_type type, my_off_t seek_offset,
		  pbool use_async_io, myf cache_myflags)
{
  uint min_cache;
  my_off_t end_of_file= ~(my_off_t) 0;
  DBUG_ENTER("init_io_cache");
  DBUG_PRINT("enter",("cache: 0x%lx  type: %d  pos: %ld",
		      (ulong) info, (int) type, (ulong) seek_offset));

  info->file= file;
  info->type= TYPE_NOT_SET;	    /* Don't set it until mutex are created */
  info->pos_in_file= seek_offset;
  info->pre_close = info->pre_read = info->post_read = 0;
  info->arg = 0;
  info->alloced_buffer = 0;
  info->buffer=0;
  info->seek_not_done= test(file >= 0 && seek_offset != my_tell(file, MYF(0)));
  info->disk_writes= 0;
#ifdef THREAD
  info->share=0;
#endif

  if (!cachesize && !(cachesize= my_default_record_cache_size))
    DBUG_RETURN(1);				/* No cache requested */
  min_cache=use_async_io ? IO_SIZE*4 : IO_SIZE*2;
  if (type == READ_CACHE || type == SEQ_READ_APPEND)
  {						/* Assume file isn't growing */
    if (!(cache_myflags & MY_DONT_CHECK_FILESIZE))
    {
      /* Calculate end of file to avoid allocating oversized buffers */
      end_of_file=my_seek(file,0L,MY_SEEK_END,MYF(0));
      /* Need to reset seek_not_done now that we just did a seek. */
      info->seek_not_done= end_of_file == seek_offset ? 0 : 1;
      if (end_of_file < seek_offset)
	end_of_file=seek_offset;
      /* Trim cache size if the file is very small */
      if ((my_off_t) cachesize > end_of_file-seek_offset+IO_SIZE*2-1)
      {
	cachesize=(uint) (end_of_file-seek_offset)+IO_SIZE*2-1;
	use_async_io=0;				/* No need to use async */
      }
    }
  }
  cache_myflags &= ~MY_DONT_CHECK_FILESIZE;
  if (type != READ_NET && type != WRITE_NET)
  {
    /* Retry allocating memory in smaller blocks until we get one */
    for (;;)
    {
      uint buffer_block;
      cachesize=(uint) ((ulong) (cachesize + min_cache-1) &
			(ulong) ~(min_cache-1));
      if (cachesize < min_cache)
	cachesize = min_cache;
      buffer_block = cachesize;
      if (type == SEQ_READ_APPEND)
	buffer_block *= 2;
      if ((info->buffer=
	   (byte*) my_malloc(buffer_block,
			     MYF((cache_myflags & ~ MY_WME) |
				 (cachesize == min_cache ? MY_WME : 0)))) != 0)
      {
	info->write_buffer=info->buffer;
	if (type == SEQ_READ_APPEND)
	  info->write_buffer = info->buffer + cachesize;
	info->alloced_buffer=1;
	break;					/* Enough memory found */
      }
      if (cachesize == min_cache)
	DBUG_RETURN(2);				/* Can't alloc cache */
      cachesize= (uint) ((long) cachesize*3/4); /* Try with less memory */
    }
  }

  DBUG_PRINT("info",("init_io_cache: cachesize = %u",cachesize));
  info->read_length=info->buffer_length=cachesize;
  info->myflags=cache_myflags & ~(MY_NABP | MY_FNABP);
  info->request_pos= info->read_pos= info->write_pos = info->buffer;
  if (type == SEQ_READ_APPEND)
  {
    info->append_read_pos = info->write_pos = info->write_buffer;
    info->write_end = info->write_buffer + info->buffer_length;
#ifdef THREAD
    pthread_mutex_init(&info->append_buffer_lock,MY_MUTEX_INIT_FAST);
#endif
  }
#if defined(SAFE_MUTEX) && defined(THREAD)
  else
  {
    /* Clear mutex so that safe_mutex will notice that it's not initialized */
    bzero((char*) &info->append_buffer_lock, sizeof(info));
  }
#endif

  if (type == WRITE_CACHE)
    info->write_end=
      info->buffer+info->buffer_length- (seek_offset & (IO_SIZE-1));
  else
    info->read_end=info->buffer;		/* Nothing in cache */

  /* End_of_file may be changed by user later */
  info->end_of_file= end_of_file;
  info->error=0;
  info->type= type;
  init_functions(info);
#ifdef HAVE_AIOWAIT
  if (use_async_io && ! my_disable_async_io)
  {
    DBUG_PRINT("info",("Using async io"));
    info->read_length/=2;
    info->read_function=_my_b_async_read;
  }
  info->inited=info->aio_result.pending=0;
#endif
  DBUG_RETURN(0);
}						/* init_io_cache */

	/* Wait until current request is ready */

#ifdef HAVE_AIOWAIT
static void my_aiowait(my_aio_result *result)
{
  if (result->pending)
  {
    struct aio_result_t *tmp;
    for (;;)
    {
      if ((int) (tmp=aiowait((struct timeval *) 0)) == -1)
      {
	if (errno == EINTR)
	  continue;
	DBUG_PRINT("error",("No aio request, error: %d",errno));
	result->pending=0;			/* Assume everythings is ok */
	break;
      }
      ((my_aio_result*) tmp)->pending=0;
      if ((my_aio_result*) tmp == result)
	break;
    }
  }
  return;
}
#endif


/*
  Use this to reset cache to re-start reading or to change the type
  between READ_CACHE <-> WRITE_CACHE
  If we are doing a reinit of a cache where we have the start of the file
  in the cache, we are reusing this memory without flushing it to disk.
*/

my_bool reinit_io_cache(IO_CACHE *info, enum cache_type type,
			my_off_t seek_offset,
			pbool use_async_io __attribute__((unused)),
			pbool clear_cache)
{
  DBUG_ENTER("reinit_io_cache");
  DBUG_PRINT("enter",("cache: 0x%lx type: %d  seek_offset: %lu  clear_cache: %d",
		      (ulong) info, type, (ulong) seek_offset,
		      (int) clear_cache));

  /* One can't do reinit with the following types */
  DBUG_ASSERT(type != READ_NET && info->type != READ_NET &&
	      type != WRITE_NET && info->type != WRITE_NET &&
	      type != SEQ_READ_APPEND && info->type != SEQ_READ_APPEND);

  /* If the whole file is in memory, avoid flushing to disk */
  if (! clear_cache &&
      seek_offset >= info->pos_in_file &&
      seek_offset <= my_b_tell(info))
  {
    /* Reuse current buffer without flushing it to disk */
    byte *pos;
    if (info->type == WRITE_CACHE && type == READ_CACHE)
    {
      info->read_end=info->write_pos;
      info->end_of_file=my_b_tell(info);
      info->seek_not_done=1;
    }
    else if (type == WRITE_CACHE)
    {
      if (info->type == READ_CACHE)
      {
	info->write_end=info->write_buffer+info->buffer_length;
	info->seek_not_done=1;
      }
      info->end_of_file = ~(my_off_t) 0;
    }
    pos=info->request_pos+(seek_offset-info->pos_in_file);
    if (type == WRITE_CACHE)
      info->write_pos=pos;
    else
      info->read_pos= pos;
#ifdef HAVE_AIOWAIT
    my_aiowait(&info->aio_result);		/* Wait for outstanding req */
#endif
  }
  else
  {
    /*
      If we change from WRITE_CACHE to READ_CACHE, assume that everything
      after the current positions should be ignored
    */
    if (info->type == WRITE_CACHE && type == READ_CACHE)
      info->end_of_file=my_b_tell(info);
    /* flush cache if we want to reuse it */
    if (!clear_cache && my_b_flush_io_cache(info,1))
      DBUG_RETURN(1);
    info->pos_in_file=seek_offset;
    /* Better to do always do a seek */
    info->seek_not_done=1;
    info->request_pos=info->read_pos=info->write_pos=info->buffer;
    if (type == READ_CACHE)
    {
      info->read_end=info->buffer;		/* Nothing in cache */
    }
    else
    {
      info->write_end=(info->buffer + info->buffer_length -
		       (seek_offset & (IO_SIZE-1)));
      info->end_of_file= ~(my_off_t) 0;
    }
  }
  info->type=type;
  info->error=0;
  init_functions(info);

#ifdef HAVE_AIOWAIT
  if (use_async_io && ! my_disable_async_io &&
      ((ulong) info->buffer_length <
       (ulong) (info->end_of_file - seek_offset)))
  {
    info->read_length=info->buffer_length/2;
    info->read_function=_my_b_async_read;
  }
  info->inited=0;
#endif
  DBUG_RETURN(0);
} /* reinit_io_cache */



/*
  Read buffered.

  SYNOPSIS
    _my_b_read()
      info                      IO_CACHE pointer
      Buffer                    Buffer to retrieve count bytes from file
      Count                     Number of bytes to read into Buffer

  NOTE
    This function is only called from the my_b_read() macro when there
    isn't enough characters in the buffer to satisfy the request.

  WARNING

    When changing this function, be careful with handling file offsets
    (end-of_file, pos_in_file). Do not cast them to possibly smaller
    types than my_off_t unless you can be sure that their value fits.
    Same applies to differences of file offsets.

    When changing this function, check _my_b_read_r(). It might need the
    same change.

  RETURN
    0      we succeeded in reading all data
    1      Error: can't read requested characters
*/

int _my_b_read(register IO_CACHE *info, byte *Buffer, uint Count)
{
  uint length,diff_length,left_length;
  my_off_t max_length, pos_in_file;
  DBUG_ENTER("_my_b_read");

  if ((left_length=(uint) (info->read_end-info->read_pos)))
  {
    DBUG_ASSERT(Count >= left_length);	/* User is not using my_b_read() */
    memcpy(Buffer,info->read_pos, (size_t) (left_length));
    Buffer+=left_length;
    Count-=left_length;
  }

  /* pos_in_file always point on where info->buffer was read */
  pos_in_file=info->pos_in_file+(uint) (info->read_end - info->buffer);
  if (info->seek_not_done)
  {					/* File touched, do seek */
    VOID(my_seek(info->file,pos_in_file,MY_SEEK_SET,MYF(0)));
    info->seek_not_done=0;
  }
  diff_length=(uint) (pos_in_file & (IO_SIZE-1));
  if (Count >= (uint) (IO_SIZE+(IO_SIZE-diff_length)))
  {					/* Fill first intern buffer */
    uint read_length;
    if (info->end_of_file <= pos_in_file)
    {					/* End of file */
      info->error=(int) left_length;
      DBUG_RETURN(1);
    }
    length=(Count & (uint) ~(IO_SIZE-1))-diff_length;
    if ((read_length=my_read(info->file,Buffer,(uint) length,info->myflags))
	!= (uint) length)
    {
      info->error= (read_length == (uint) -1 ? -1 :
		    (int) (read_length+left_length));
      DBUG_RETURN(1);
    }
    Count-=length;
    Buffer+=length;
    pos_in_file+=length;
    left_length+=length;
    diff_length=0;
  }

  max_length=info->read_length-diff_length;
  if (info->type != READ_FIFO &&
      max_length > (info->end_of_file - pos_in_file))
    max_length = info->end_of_file - pos_in_file;
  if (!max_length)
  {
    if (Count)
    {
      info->error= left_length;		/* We only got this many char */
      DBUG_RETURN(1);
    }
    length=0;				/* Didn't read any chars */
  }
  else if ((length=my_read(info->file,info->buffer,(uint) max_length,
			   info->myflags)) < Count ||
	   length == (uint) -1)
  {
    if (length != (uint) -1)
      memcpy(Buffer,info->buffer,(size_t) length);
    info->pos_in_file= pos_in_file;
    info->error= length == (uint) -1 ? -1 : (int) (length+left_length);
    info->read_pos=info->read_end=info->buffer;
    DBUG_RETURN(1);
  }
  info->read_pos=info->buffer+Count;
  info->read_end=info->buffer+length;
  info->pos_in_file=pos_in_file;
  memcpy(Buffer,info->buffer,(size_t) Count);
  DBUG_RETURN(0);
}

#ifdef THREAD
/* Prepare IO_CACHE for shared use */
void init_io_cache_share(IO_CACHE *info, IO_CACHE_SHARE *s, uint num_threads)
{
  DBUG_ASSERT(info->type == READ_CACHE);
  pthread_mutex_init(&s->mutex, MY_MUTEX_INIT_FAST);
  pthread_cond_init (&s->cond, 0);
  s->total=s->count=num_threads-1;
  s->active=0;
  info->share=s;
  info->read_function=_my_b_read_r;
  info->current_pos= info->current_end= 0;
}

/*
  Remove a thread from shared access to IO_CACHE
  Every thread should do that on exit for not
  to deadlock other threads
*/
void remove_io_thread(IO_CACHE *info)
{
  IO_CACHE_SHARE *s=info->share;

  pthread_mutex_lock(&s->mutex);
  s->total--;
  if (! s->count--)
    pthread_cond_signal(&s->cond);
  pthread_mutex_unlock(&s->mutex);
}

static int lock_io_cache(IO_CACHE *info, my_off_t pos)
{
  int total;
  IO_CACHE_SHARE *s=info->share;

  pthread_mutex_lock(&s->mutex);
  if (!s->count)
  {
    s->count=s->total;
    return 1;
  }

  total=s->total;
  s->count--;
  while (!s->active || s->active->pos_in_file < pos)
    pthread_cond_wait(&s->cond, &s->mutex);

  if (s->total < total &&
      (!s->active || s->active->pos_in_file < pos))
    return 1;

  pthread_mutex_unlock(&s->mutex);
  return 0;
}

static void unlock_io_cache(IO_CACHE *info)
{
  pthread_cond_broadcast(&info->share->cond);
  pthread_mutex_unlock(&info->share->mutex);
}


/*
  Read from IO_CACHE when it is shared between several threads.

  SYNOPSIS
    _my_b_read_r()
      info                      IO_CACHE pointer
      Buffer                    Buffer to retrieve count bytes from file
      Count                     Number of bytes to read into Buffer

  NOTE
    This function is only called from the my_b_read() macro when there
    isn't enough characters in the buffer to satisfy the request.

  IMPLEMENTATION

    It works as follows: when a thread tries to read from a file (that
    is, after using all the data from the (shared) buffer), it just
    hangs on lock_io_cache(), wating for other threads. When the very
    last thread attempts a read, lock_io_cache() returns 1, the thread
    does actual IO and unlock_io_cache(), which signals all the waiting
    threads that data is in the buffer.

  WARNING

    When changing this function, be careful with handling file offsets
    (end-of_file, pos_in_file). Do not cast them to possibly smaller
    types than my_off_t unless you can be sure that their value fits.
    Same applies to differences of file offsets. (Bug #11527)

    When changing this function, check _my_b_read(). It might need the
    same change.

  RETURN
    0      we succeeded in reading all data
    1      Error: can't read requested characters
*/

int _my_b_read_r(register IO_CACHE *info, byte *Buffer, uint Count)
{
  my_off_t pos_in_file;
  uint length, diff_length, left_length;
  DBUG_ENTER("_my_b_read_r");

  if ((left_length= (uint) (info->read_end - info->read_pos)))
  {
    DBUG_ASSERT(Count >= left_length);	/* User is not using my_b_read() */
    memcpy(Buffer, info->read_pos, (size_t) (left_length));
    Buffer+= left_length;
    Count-= left_length;
  }
  while (Count)
  {
    int cnt, len;

    pos_in_file= info->pos_in_file + (info->read_end - info->buffer);
    diff_length= (uint) (pos_in_file & (IO_SIZE-1));
    length=IO_ROUND_UP(Count+diff_length)-diff_length;
    length=(length <= info->read_length) ?
                   length + IO_ROUND_DN(info->read_length - length) :
                   length - IO_ROUND_UP(length - info->read_length) ;
    if (info->type != READ_FIFO &&
	(length > (info->end_of_file - pos_in_file)))
      length= (uint) (info->end_of_file - pos_in_file);
    if (length == 0)
    {
      info->error= (int) left_length;
      DBUG_RETURN(1);
    }
    if (lock_io_cache(info, pos_in_file))
    {
      info->share->active=info;
      if (info->seek_not_done)             /* File touched, do seek */
        VOID(my_seek(info->file,pos_in_file,MY_SEEK_SET,MYF(0)));
      len=(int)my_read(info->file,info->buffer, length, info->myflags);
      info->read_end=info->buffer + (len == -1 ? 0 : len);
      info->error=(len == (int)length ? 0 : len);
      info->pos_in_file=pos_in_file;
      unlock_io_cache(info);
    }
    else
    {
      info->error=          info->share->active->error;
      info->read_end=       info->share->active->read_end;
      info->pos_in_file=    info->share->active->pos_in_file;
      len= (int) (info->error == -1 ? -1 : info->read_end-info->buffer);
    }
    info->read_pos=info->buffer;
    info->seek_not_done=0;
    if (len <= 0)
    {
      info->error= (int) left_length;
      DBUG_RETURN(1);
    }
    cnt= ((uint) len > Count) ? (int) Count : len;
    memcpy(Buffer, info->read_pos, (size_t) cnt);
    Count -= cnt;
    Buffer+= cnt;
    left_length+= cnt;
    info->read_pos+= cnt;
  }
  DBUG_RETURN(0);
}
#endif


/*
  Do sequential read from the SEQ_READ_APPEND cache
  we do this in three stages:
   - first read from info->buffer
   - then if there are still data to read, try the file descriptor
   - afterwards, if there are still data to read, try append buffer
*/

int _my_b_seq_read(register IO_CACHE *info, byte *Buffer, uint Count)
{
  uint length,diff_length,left_length,save_count;
  my_off_t max_length, pos_in_file;
  save_count=Count;

  /* first, read the regular buffer */
  if ((left_length=(uint) (info->read_end-info->read_pos)))
  {
    DBUG_ASSERT(Count > left_length);	/* User is not using my_b_read() */
    memcpy(Buffer,info->read_pos, (size_t) (left_length));
    Buffer+=left_length;
    Count-=left_length;
  }
  lock_append_buffer(info);

  /* pos_in_file always point on where info->buffer was read */
  if ((pos_in_file=info->pos_in_file+(uint) (info->read_end - info->buffer)) >=
      info->end_of_file)
    goto read_append_buffer;

  /*
    With read-append cache we must always do a seek before we read,
    because the write could have moved the file pointer astray
  */
  VOID(my_seek(info->file,pos_in_file,MY_SEEK_SET,MYF(0)));
  info->seek_not_done=0;

  diff_length=(uint) (pos_in_file & (IO_SIZE-1));

  /* now the second stage begins - read from file descriptor */
  if (Count >= (uint) (IO_SIZE+(IO_SIZE-diff_length)))
  {					/* Fill first intern buffer */
    uint read_length;

    length=(Count & (uint) ~(IO_SIZE-1))-diff_length;
    if ((read_length=my_read(info->file,Buffer,(uint) length,info->myflags)) ==
	(uint)-1)
    {
      info->error= -1;
      unlock_append_buffer(info);
      return 1;
    }
    Count-=read_length;
    Buffer+=read_length;
    pos_in_file+=read_length;

    if (read_length != (uint) length)
    {
      /*
	We only got part of data;  Read the rest of the data from the
	write buffer
      */
      goto read_append_buffer;
    }
    left_length+=length;
    diff_length=0;
  }

  max_length=info->read_length-diff_length;
  if (max_length > (info->end_of_file - pos_in_file))
    max_length = info->end_of_file - pos_in_file;
  if (!max_length)
  {
    if (Count)
      goto read_append_buffer;
    length=0;				/* Didn't read any more chars */
  }
  else
  {
    length=my_read(info->file,info->buffer,(uint) max_length,
		   info->myflags);
    if (length == (uint) -1)
    {
      info->error= -1;
      unlock_append_buffer(info);
      return 1;
    }
    if (length < Count)
    {
      memcpy(Buffer,info->buffer,(size_t) length);
      Count -= length;
      Buffer += length;

      /*
	 added the line below to make
	 DBUG_ASSERT(pos_in_file==info->end_of_file) pass.
	 otherwise this does not appear to be needed
      */
      pos_in_file += length;
      goto read_append_buffer;
    }
  }
  unlock_append_buffer(info);
  info->read_pos=info->buffer+Count;
  info->read_end=info->buffer+length;
  info->pos_in_file=pos_in_file;
  memcpy(Buffer,info->buffer,(size_t) Count);
  return 0;

read_append_buffer:

  /*
     Read data from the current write buffer.
     Count should never be == 0 here (The code will work even if count is 0)
  */

  {
    /* First copy the data to Count */
    uint len_in_buff = (uint) (info->write_pos - info->append_read_pos);
    uint copy_len;
    uint transfer_len;

    DBUG_ASSERT(info->append_read_pos <= info->write_pos);
    /*
      TODO: figure out if the assert below is needed or correct.
    */
    DBUG_ASSERT(pos_in_file == info->end_of_file);
    copy_len=min(Count, len_in_buff);
    memcpy(Buffer, info->append_read_pos, copy_len);
    info->append_read_pos += copy_len;
    Count -= copy_len;
    if (Count)
      info->error = save_count - Count;

    /* Fill read buffer with data from write buffer */
    memcpy(info->buffer, info->append_read_pos,
	   (size_t) (transfer_len=len_in_buff - copy_len));
    info->read_pos= info->buffer;
    info->read_end= info->buffer+transfer_len;
    info->append_read_pos=info->write_pos;
    info->pos_in_file=pos_in_file+copy_len;
    info->end_of_file+=len_in_buff;
  }
  unlock_append_buffer(info);
  return Count ? 1 : 0;
}


#ifdef HAVE_AIOWAIT

int _my_b_async_read(register IO_CACHE *info, byte *Buffer, uint Count)
{
  uint length,read_length,diff_length,left_length,use_length,org_Count;
  my_off_t max_length;
  my_off_t next_pos_in_file;
  byte *read_buffer;

  memcpy(Buffer,info->read_pos,
	 (size_t) (left_length=(uint) (info->read_end-info->read_pos)));
  Buffer+=left_length;
  org_Count=Count;
  Count-=left_length;

  if (info->inited)
  {						/* wait for read block */
    info->inited=0;				/* No more block to read */
    my_aiowait(&info->aio_result);		/* Wait for outstanding req */
    if (info->aio_result.result.aio_errno)
    {
      if (info->myflags & MY_WME)
	my_error(EE_READ, MYF(ME_BELL+ME_WAITTANG),
		 my_filename(info->file),
		 info->aio_result.result.aio_errno);
      my_errno=info->aio_result.result.aio_errno;
      info->error= -1;
      return(1);
    }
    if (! (read_length = (uint) info->aio_result.result.aio_return) ||
	read_length == (uint) -1)
    {
      my_errno=0;				/* For testing */
      info->error= (read_length == (uint) -1 ? -1 :
		    (int) (read_length+left_length));
      return(1);
    }
    info->pos_in_file+=(uint) (info->read_end - info->request_pos);

    if (info->request_pos != info->buffer)
      info->request_pos=info->buffer;
    else
      info->request_pos=info->buffer+info->read_length;
    info->read_pos=info->request_pos;
    next_pos_in_file=info->aio_read_pos+read_length;

	/* Check if pos_in_file is changed
	   (_ni_read_cache may have skipped some bytes) */

    if (info->aio_read_pos < info->pos_in_file)
    {						/* Fix if skipped bytes */
      if (info->aio_read_pos + read_length < info->pos_in_file)
      {
	read_length=0;				/* Skip block */
	next_pos_in_file=info->pos_in_file;
      }
      else
      {
	my_off_t offset= (info->pos_in_file - info->aio_read_pos);
	info->pos_in_file=info->aio_read_pos; /* Whe are here */
	info->read_pos=info->request_pos+offset;
	read_length-=offset;			/* Bytes left from read_pos */
      }
    }
#ifndef DBUG_OFF
    if (info->aio_read_pos > info->pos_in_file)
    {
      my_errno=EINVAL;
      return(info->read_length= -1);
    }
#endif
	/* Copy found bytes to buffer */
    length=min(Count,read_length);
    memcpy(Buffer,info->read_pos,(size_t) length);
    Buffer+=length;
    Count-=length;
    left_length+=length;
    info->read_end=info->rc_pos+read_length;
    info->read_pos+=length;
  }
  else
    next_pos_in_file=(info->pos_in_file+ (uint)
		      (info->read_end - info->request_pos));

	/* If reading large blocks, or first read or read with skip */
  if (Count)
  {
    if (next_pos_in_file == info->end_of_file)
    {
      info->error=(int) (read_length+left_length);
      return 1;
    }
    VOID(my_seek(info->file,next_pos_in_file,MY_SEEK_SET,MYF(0)));
    read_length=IO_SIZE*2- (uint) (next_pos_in_file & (IO_SIZE-1));
    if (Count < read_length)
    {					/* Small block, read to cache */
      if ((read_length=my_read(info->file,info->request_pos,
			       read_length, info->myflags)) == (uint) -1)
	return info->error= -1;
      use_length=min(Count,read_length);
      memcpy(Buffer,info->request_pos,(size_t) use_length);
      info->read_pos=info->request_pos+Count;
      info->read_end=info->request_pos+read_length;
      info->pos_in_file=next_pos_in_file;	/* Start of block in cache */
      next_pos_in_file+=read_length;

      if (Count != use_length)
      {					/* Didn't find hole block */
	if (info->myflags & (MY_WME | MY_FAE | MY_FNABP) && Count != org_Count)
	  my_error(EE_EOFERR, MYF(ME_BELL+ME_WAITTANG),
		   my_filename(info->file),my_errno);
	info->error=(int) (read_length+left_length);
	return 1;
      }
    }
    else
    {						/* Big block, don't cache it */
      if ((read_length=my_read(info->file,Buffer,(uint) Count,info->myflags))
	  != Count)
      {
	info->error= read_length == (uint)  -1 ? -1 : read_length+left_length;
	return 1;
      }
      info->read_pos=info->read_end=info->request_pos;
      info->pos_in_file=(next_pos_in_file+=Count);
    }
  }

	/* Read next block with asyncronic io */
  max_length=info->end_of_file - next_pos_in_file;
  diff_length=(next_pos_in_file & (IO_SIZE-1));

  if (max_length > (my_off_t) info->read_length - diff_length)
    max_length= (my_off_t) info->read_length - diff_length;
  if (info->request_pos != info->buffer)
    read_buffer=info->buffer;
  else
    read_buffer=info->buffer+info->read_length;
  info->aio_read_pos=next_pos_in_file;
  if (max_length)
  {
    info->aio_result.result.aio_errno=AIO_INPROGRESS;	/* Marker for test */
    DBUG_PRINT("aioread",("filepos: %ld  length: %ld",
			  (ulong) next_pos_in_file,(ulong) max_length));
    if (aioread(info->file,read_buffer,(int) max_length,
		(my_off_t) next_pos_in_file,MY_SEEK_SET,
		&info->aio_result.result))
    {						/* Skip async io */
      my_errno=errno;
      DBUG_PRINT("error",("got error: %d, aio_result: %d from aioread, async skipped",
			  errno, info->aio_result.result.aio_errno));
      if (info->request_pos != info->buffer)
      {
	bmove(info->buffer,info->request_pos,
	      (uint) (info->read_end - info->read_pos));
	info->request_pos=info->buffer;
	info->read_pos-=info->read_length;
	info->read_end-=info->read_length;
      }
      info->read_length=info->buffer_length;	/* Use hole buffer */
      info->read_function=_my_b_read;		/* Use normal IO_READ next */
    }
    else
      info->inited=info->aio_result.pending=1;
  }
  return 0;					/* Block read, async in use */
} /* _my_b_async_read */
#endif


/* Read one byte when buffer is empty */

int _my_b_get(IO_CACHE *info)
{
  byte buff;
  IO_CACHE_CALLBACK pre_read,post_read;
  if ((pre_read = info->pre_read))
    (*pre_read)(info);
  if ((*(info)->read_function)(info,&buff,1))
    return my_b_EOF;
  if ((post_read = info->post_read))
    (*post_read)(info);
  return (int) (uchar) buff;
}

	/* Returns != 0 if error on write */

int _my_b_write(register IO_CACHE *info, const byte *Buffer, uint Count)
{
  uint rest_length,length;

  if (info->pos_in_file+info->buffer_length > info->end_of_file)
  {
    my_errno=errno=EFBIG;
    return info->error = -1;
  }

  rest_length=(uint) (info->write_end - info->write_pos);
  memcpy(info->write_pos,Buffer,(size_t) rest_length);
  Buffer+=rest_length;
  Count-=rest_length;
  info->write_pos+=rest_length;
  if (my_b_flush_io_cache(info,1))
    return 1;
  if (Count >= IO_SIZE)
  {					/* Fill first intern buffer */
    length=Count & (uint) ~(IO_SIZE-1);
    if (info->seek_not_done)
    {					/* File touched, do seek */
      VOID(my_seek(info->file,info->pos_in_file,MY_SEEK_SET,MYF(0)));
      info->seek_not_done=0;
    }
    if (my_write(info->file,Buffer,(uint) length,info->myflags | MY_NABP))
      return info->error= -1;
    Count-=length;
    Buffer+=length;
    info->pos_in_file+=length;
  }
  memcpy(info->write_pos,Buffer,(size_t) Count);
  info->write_pos+=Count;
  return 0;
}


/*
  Append a block to the write buffer.
  This is done with the buffer locked to ensure that we don't read from
  the write buffer before we are ready with it.
*/

int my_b_append(register IO_CACHE *info, const byte *Buffer, uint Count)
{
  uint rest_length,length;

  lock_append_buffer(info);
  rest_length=(uint) (info->write_end - info->write_pos);
  if (Count <= rest_length)
    goto end;
  memcpy(info->write_pos,Buffer,(size_t) rest_length);
  Buffer+=rest_length;
  Count-=rest_length;
  info->write_pos+=rest_length;
  if (my_b_flush_io_cache(info,0))
  {
    unlock_append_buffer(info);
    return 1;
  }
  if (Count >= IO_SIZE)
  {					/* Fill first intern buffer */
    length=Count & (uint) ~(IO_SIZE-1);
    if (my_write(info->file,Buffer,(uint) length,info->myflags | MY_NABP))
    {
      unlock_append_buffer(info);
      return info->error= -1;
    }
    Count-=length;
    Buffer+=length;
    info->end_of_file+=length;
  }

end:
  memcpy(info->write_pos,Buffer,(size_t) Count);
  info->write_pos+=Count;
  unlock_append_buffer(info);
  return 0;
}


int my_b_safe_write(IO_CACHE *info, const byte *Buffer, uint Count)
{
  /*
    Sasha: We are not writing this with the ? operator to avoid hitting
    a possible compiler bug. At least gcc 2.95 cannot deal with 
    several layers of ternary operators that evaluated comma(,) operator
    expressions inside - I do have a test case if somebody wants it
  */
  if (info->type == SEQ_READ_APPEND)
    return my_b_append(info, Buffer, Count);
  return my_b_write(info, Buffer, Count);
}


/*
  Write a block to disk where part of the data may be inside the record
  buffer.  As all write calls to the data goes through the cache,
  we will never get a seek over the end of the buffer
*/

int my_block_write(register IO_CACHE *info, const byte *Buffer, uint Count,
		   my_off_t pos)
{
  uint length;
  int error=0;

  if (pos < info->pos_in_file)
  {
    /* Of no overlap, write everything without buffering */
    if (pos + Count <= info->pos_in_file)
      return my_pwrite(info->file, Buffer, Count, pos,
		       info->myflags | MY_NABP);
    /* Write the part of the block that is before buffer */
    length= (uint) (info->pos_in_file - pos);
    if (my_pwrite(info->file, Buffer, length, pos, info->myflags | MY_NABP))
      info->error=error=-1;
    Buffer+=length;
    pos+=  length;
    Count-= length;
#ifndef HAVE_PREAD
    info->seek_not_done=1;
#endif
  }

  /* Check if we want to write inside the used part of the buffer.*/
  length= (uint) (info->write_end - info->buffer);
  if (pos < info->pos_in_file + length)
  {
    uint offset= (uint) (pos - info->pos_in_file);
    length-=offset;
    if (length > Count)
      length=Count;
    memcpy(info->buffer+offset, Buffer, length);
    Buffer+=length;
    Count-= length;
    /* Fix length of buffer if the new data was larger */
    if (info->buffer+length > info->write_pos)
      info->write_pos=info->buffer+length;
    if (!Count)
      return (error);
  }
  /* Write at the end of the current buffer; This is the normal case */
  if (_my_b_write(info, Buffer, Count))
    error= -1;
  return error;
}


	/* Flush write cache */

#ifdef THREAD
#define LOCK_APPEND_BUFFER if (need_append_buffer_lock) \
  lock_append_buffer(info);
#define UNLOCK_APPEND_BUFFER if (need_append_buffer_lock) \
  unlock_append_buffer(info);
#else
#define LOCK_APPEND_BUFFER
#define UNLOCK_APPEND_BUFFER
#endif


int my_b_flush_io_cache(IO_CACHE *info, int need_append_buffer_lock)
{
  uint length;
  my_bool append_cache;
  my_off_t pos_in_file;
  DBUG_ENTER("my_b_flush_io_cache");

  if (!(append_cache = (info->type == SEQ_READ_APPEND)))
    need_append_buffer_lock=0;

  if (info->type == WRITE_CACHE || append_cache)
  {
    if (info->file == -1)
    {
      if (real_open_cached_file(info))
	DBUG_RETURN((info->error= -1));
    }
    LOCK_APPEND_BUFFER;

    if ((length=(uint) (info->write_pos - info->write_buffer)))
    {
      pos_in_file=info->pos_in_file;
      /*
	If we have append cache, we always open the file with
	O_APPEND which moves the pos to EOF automatically on every write
      */
      if (!append_cache && info->seek_not_done)
      {					/* File touched, do seek */
	if (my_seek(info->file,pos_in_file,MY_SEEK_SET,MYF(0)) ==
	    MY_FILEPOS_ERROR)
	{
	  UNLOCK_APPEND_BUFFER;
	  DBUG_RETURN((info->error= -1));
	}
	if (!append_cache)
	  info->seek_not_done=0;
      }
      if (!append_cache)
	info->pos_in_file+=length;
      info->write_end= (info->write_buffer+info->buffer_length-
			((pos_in_file+length) & (IO_SIZE-1)));

      if (my_write(info->file,info->write_buffer,length,
		   info->myflags | MY_NABP))
	info->error= -1;
      else
	info->error= 0;
      if (!append_cache)
      {
        set_if_bigger(info->end_of_file,(pos_in_file+length));
      }
      else
      {
	info->end_of_file+=(info->write_pos-info->append_read_pos);
	DBUG_ASSERT(info->end_of_file == my_tell(info->file,MYF(0)));
      }

      info->append_read_pos=info->write_pos=info->write_buffer;
      ++info->disk_writes;
      UNLOCK_APPEND_BUFFER;
      DBUG_RETURN(info->error);
    }
  }
#ifdef HAVE_AIOWAIT
  else if (info->type != READ_NET)
  {
    my_aiowait(&info->aio_result);		/* Wait for outstanding req */
    info->inited=0;
  }
#endif
  UNLOCK_APPEND_BUFFER;
  DBUG_RETURN(0);
}

/*
  Free an IO_CACHE object

  SYNOPSOS
    end_io_cache()
    info		IO_CACHE Handle to free

  NOTES
    It's currently safe to call this if one has called init_io_cache()
    on the 'info' object, even if init_io_cache() failed.
    This function is also safe to call twice with the same handle.

  RETURN
   0  ok
   #  Error
*/

int end_io_cache(IO_CACHE *info)
{
  int error=0;
  IO_CACHE_CALLBACK pre_close;
  DBUG_ENTER("end_io_cache");
  DBUG_PRINT("enter",("cache: 0x%lx", (ulong) info));

#ifdef THREAD
  /*
    if IO_CACHE is shared between several threads, only one
    thread needs to call end_io_cache() - just as init_io_cache()
    should be called only once and then memcopy'ed
  */
  if (info->share)
  {
    pthread_cond_destroy(&info->share->cond);
    pthread_mutex_destroy(&info->share->mutex);
    info->share=0;
  }
#endif

  if ((pre_close=info->pre_close))
  {
    (*pre_close)(info);
    info->pre_close= 0;
  }
  if (info->alloced_buffer)
  {
    info->alloced_buffer=0;
    if (info->file != -1)			/* File doesn't exist */
      error= my_b_flush_io_cache(info,1);
    my_free((gptr) info->buffer,MYF(MY_WME));
    info->buffer=info->read_pos=(byte*) 0;
  }
  if (info->type == SEQ_READ_APPEND)
  {
    /* Destroy allocated mutex */
    info->type= TYPE_NOT_SET;
#ifdef THREAD
    pthread_mutex_destroy(&info->append_buffer_lock);
#endif
  }
  DBUG_RETURN(error);
} /* end_io_cache */


/**********************************************************************
 Testing of MF_IOCACHE
**********************************************************************/

#ifdef MAIN

#include <my_dir.h>

void die(const char* fmt, ...)
{
  va_list va_args;
  va_start(va_args,fmt);
  fprintf(stderr,"Error:");
  vfprintf(stderr, fmt,va_args);
  fprintf(stderr,", errno=%d\n", errno);
  exit(1);
}

int open_file(const char* fname, IO_CACHE* info, int cache_size)
{
  int fd;
  if ((fd=my_open(fname,O_CREAT | O_RDWR,MYF(MY_WME))) < 0)
    die("Could not open %s", fname);
  if (init_io_cache(info, fd, cache_size, SEQ_READ_APPEND, 0,0,MYF(MY_WME)))
    die("failed in init_io_cache()");
  return fd;
}

void close_file(IO_CACHE* info)
{
  end_io_cache(info);
  my_close(info->file, MYF(MY_WME));
}

int main(int argc, char** argv)
{
  IO_CACHE sra_cache; /* SEQ_READ_APPEND */
  MY_STAT status;
  const char* fname="/tmp/iocache.test";
  int cache_size=16384;
  char llstr_buf[22];
  int max_block,total_bytes=0;
  int i,num_loops=100,error=0;
  char *p;
  char* block, *block_end;
  MY_INIT(argv[0]);
  max_block = cache_size*3;
  if (!(block=(char*)my_malloc(max_block,MYF(MY_WME))))
    die("Not enough memory to allocate test block");
  block_end = block + max_block;
  for (p = block,i=0; p < block_end;i++)
  {
    *p++ = (char)i;
  }
  if (my_stat(fname,&status, MYF(0)) &&
      my_delete(fname,MYF(MY_WME)))
    {
      die("Delete of %s failed, aborting", fname);
    }
  open_file(fname,&sra_cache, cache_size);
  for (i = 0; i < num_loops; i++)
  {
    char buf[4];
    int block_size = abs(rand() % max_block);
    int4store(buf, block_size);
    if (my_b_append(&sra_cache,buf,4) ||
	my_b_append(&sra_cache, block, block_size))
      die("write failed");
    total_bytes += 4+block_size;
  }
  close_file(&sra_cache);
  my_free(block,MYF(MY_WME));
  if (!my_stat(fname,&status,MYF(MY_WME)))
    die("%s failed to stat, but I had just closed it,\
 wonder how that happened");
  printf("Final size of %s is %s, wrote %d bytes\n",fname,
	 llstr(status.st_size,llstr_buf),
	 total_bytes);
  my_delete(fname, MYF(MY_WME));
  /* check correctness of tests */
  if (total_bytes != status.st_size)
  {
    fprintf(stderr,"Not the same number of bytes acutally  in file as bytes \
supposedly written\n");
    error=1;
  }
  exit(error);
  return 0;
}
#endif