Adding upstream version 1:10.5.12.upstream/1%10.5.12upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2030 insertions, 0 deletions

diff --git a/storage/myisam/mi_dynrec.c b/storage/myisam/mi_dynrec.c
new file mode 100644
index 00000000..09c10040
--- /dev/null
+++ b/storage/myisam/mi_dynrec.c
@@ -0,0 +1,2030 @@
+/*
+   Copyright (c) 2000, 2011, Oracle and/or its affiliates
+
+   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 02110-1335  USA */
+
+/*
+  Functions to handle space-packed-records and blobs
+ 
+  A row may be stored in one or more linked blocks.
+  The block size is between MI_MIN_BLOCK_LENGTH and MI_MAX_BLOCK_LENGTH.
+  Each block is aligned on MI_DYN_ALIGN_SIZE.
+  The reson for the max block size is to not have too many different types
+  of blocks.  For the differnet block types, look at _mi_get_block_info()
+*/
+
+#include "myisamdef.h"
+
+/* Enough for comparing if number is zero */
+static char zero_string[]={0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
+
+static int write_dynamic_record(MI_INFO *info,const uchar *record,
+				ulong reclength);
+static int _mi_find_writepos(MI_INFO *info,ulong reclength,my_off_t *filepos,
+			     ulong *length);
+static int update_dynamic_record(MI_INFO *info,my_off_t filepos,uchar *record,
+				 ulong reclength);
+static int delete_dynamic_record(MI_INFO *info,my_off_t filepos,
+				 uint second_read);
+static int _mi_cmp_buffer(File file, const uchar *buff, my_off_t filepos,
+			  uint length);
+
+/* Play it safe; We have a small stack when using threads */
+#undef my_alloca
+#undef my_afree
+#define my_alloca(A) my_malloc(PSI_NOT_INSTRUMENTED, (A),MYF(0))
+#define my_afree(A) my_free((A))
+
+	/* Interface function from MI_INFO */
+
+#ifdef HAVE_MMAP
+
+/*
+  Create mmaped area for MyISAM handler
+
+  SYNOPSIS
+    mi_dynmap_file()
+    info		MyISAM handler
+
+  RETURN
+    0  ok
+    1  error.
+*/
+
+my_bool mi_dynmap_file(MI_INFO *info, my_off_t size)
+{
+  DBUG_ENTER("mi_dynmap_file");
+  if (size == 0 || size > (my_off_t) (~((size_t) 0)))
+  {
+    if (size)
+      DBUG_PRINT("warning", ("File is too large for mmap"));
+    else
+      DBUG_PRINT("warning", ("Do not mmap zero-length"));
+    DBUG_RETURN(1);
+  }
+  /*
+    I wonder if it is good to use MAP_NORESERVE. From the Linux man page:
+    MAP_NORESERVE
+      Do not reserve swap space for this mapping. When swap space is
+      reserved, one has the guarantee that it is possible to modify the
+      mapping. When swap space is not reserved one might get SIGSEGV
+      upon a write if no physical memory is available.
+  */
+  info->s->file_map= (uchar*)
+                  my_mmap(0, (size_t) size,
+                          info->s->mode==O_RDONLY ? PROT_READ :
+                          PROT_READ | PROT_WRITE,
+                          MAP_SHARED | MAP_NORESERVE,
+                          info->dfile, 0L);
+  if (info->s->file_map == (uchar*) MAP_FAILED)
+  {
+    info->s->file_map= NULL;
+    DBUG_RETURN(1);
+  }
+#if defined(HAVE_MADVISE)
+  madvise((char*) info->s->file_map, size, MADV_RANDOM);
+#endif
+  info->s->mmaped_length= (size_t) size;
+  info->s->file_read= mi_mmap_pread;
+  info->s->file_write= mi_mmap_pwrite;
+  DBUG_RETURN(0);
+}
+
+
+/*
+  Destroy mmaped area for MyISAM handler
+
+  SYNOPSIS
+    mi_munmap_file()
+    info                  MyISAM handler
+
+  RETURN
+    0  ok
+   !0  error.
+*/
+
+int mi_munmap_file(MI_INFO *info)
+{
+  int ret;
+  DBUG_ENTER("mi_unmap_file");
+  if ((ret= my_munmap((void*) info->s->file_map, info->s->mmaped_length)))
+    DBUG_RETURN(ret);
+  info->s->file_read= mi_nommap_pread;
+  info->s->file_write= mi_nommap_pwrite;
+  info->s->file_map= 0;
+  info->s->mmaped_length= 0;
+  DBUG_RETURN(0);
+}
+
+
+/*
+  Resize mmaped area for MyISAM handler
+
+  SYNOPSIS
+    mi_remap_file()
+    info		MyISAM handler
+
+  RETURN
+*/
+
+void mi_remap_file(MI_INFO *info, my_off_t size)
+{
+  if (info->s->file_map)
+  {
+    mi_munmap_file(info);
+    mi_dynmap_file(info, size);
+  }
+}
+#endif
+
+
+/*
+  Read bytes from MySAM handler, using mmap or pread
+
+  SYNOPSIS
+    mi_mmap_pread()
+    info		MyISAM handler
+    Buffer              Input buffer
+    Count               Count of bytes for read
+    offset              Start position
+    MyFlags             
+
+  RETURN
+    0  ok
+*/
+
+size_t mi_mmap_pread(MI_INFO *info, uchar *Buffer,
+                    size_t Count, my_off_t offset, myf MyFlags)
+{
+  DBUG_PRINT("info", ("mi_read with mmap %d\n", info->dfile));
+  if (info->s->concurrent_insert)
+    mysql_rwlock_rdlock(&info->s->mmap_lock);
+
+  /*
+    The following test may fail in the following cases:
+    - We failed to remap a memory area (fragmented memory?)
+    - This thread has done some writes, but not yet extended the
+    memory mapped area.
+  */
+
+  if (info->s->mmaped_length >= offset + Count)
+  {
+    memcpy(Buffer, info->s->file_map + offset, Count);
+    if (info->s->concurrent_insert)
+      mysql_rwlock_unlock(&info->s->mmap_lock);
+    return 0;
+  }
+  else
+  {
+    if (info->s->concurrent_insert)
+      mysql_rwlock_unlock(&info->s->mmap_lock);
+    return mysql_file_pread(info->dfile, Buffer, Count, offset, MyFlags);
+  }
+}
+
+
+        /* wrapper for mysql_file_pread in case if mmap isn't used */
+
+size_t mi_nommap_pread(MI_INFO *info, uchar *Buffer,
+                       size_t Count, my_off_t offset, myf MyFlags)
+{
+  return mysql_file_pread(info->dfile, Buffer, Count, offset, MyFlags);
+}
+
+
+/*
+  Write bytes to MySAM handler, using mmap or pwrite
+
+  SYNOPSIS
+    mi_mmap_pwrite()
+    info		MyISAM handler
+    Buffer              Output buffer
+    Count               Count of bytes for write
+    offset              Start position
+    MyFlags             
+
+  RETURN
+    0  ok
+    !=0  error.  In this case return error from pwrite
+*/
+
+size_t mi_mmap_pwrite(MI_INFO *info, const uchar *Buffer,
+                      size_t Count, my_off_t offset, myf MyFlags)
+{
+  DBUG_PRINT("info", ("mi_write with mmap %d\n", info->dfile));
+  if (info->s->concurrent_insert)
+    mysql_rwlock_rdlock(&info->s->mmap_lock);
+
+  /*
+    The following test may fail in the following cases:
+    - We failed to remap a memory area (fragmented memory?)
+    - This thread has done some writes, but not yet extended the
+    memory mapped area.
+  */
+
+  if (info->s->mmaped_length >= offset + Count)
+  {
+    memcpy(info->s->file_map + offset, Buffer, Count); 
+    if (info->s->concurrent_insert)
+      mysql_rwlock_unlock(&info->s->mmap_lock);
+    return 0;
+  }
+  else
+  {
+    info->s->nonmmaped_inserts++;
+    if (info->s->concurrent_insert)
+      mysql_rwlock_unlock(&info->s->mmap_lock);
+    return mysql_file_pwrite(info->dfile, Buffer, Count, offset, MyFlags);
+  }
+
+}
+
+
+        /* wrapper for mysql_file_pwrite in case if mmap isn't used */
+
+size_t mi_nommap_pwrite(MI_INFO *info, const uchar *Buffer,
+                      size_t Count, my_off_t offset, myf MyFlags)
+{
+  return mysql_file_pwrite(info->dfile, Buffer, Count, offset, MyFlags);
+}
+
+
+int _mi_write_dynamic_record(MI_INFO *info, const uchar *record)
+{
+  ulong reclength=_mi_rec_pack(info,info->rec_buff,record);
+  return (write_dynamic_record(info,info->rec_buff,reclength));
+}
+
+int _mi_update_dynamic_record(MI_INFO *info, my_off_t pos, const uchar *record)
+{
+  uint length=_mi_rec_pack(info,info->rec_buff,record);
+  return (update_dynamic_record(info,pos,info->rec_buff,length));
+}
+
+int _mi_write_blob_record(MI_INFO *info, const uchar *record)
+{
+  uchar *rec_buff;
+  int error;
+  ulong reclength,reclength2,extra;
+
+  extra= (ALIGN_SIZE(MI_MAX_DYN_BLOCK_HEADER)+MI_SPLIT_LENGTH+
+	  MI_DYN_DELETE_BLOCK_HEADER+1);
+  reclength= (info->s->base.pack_reclength +
+	      _mi_calc_total_blob_length(info,record)+ extra);
+  if (!(rec_buff=(uchar*) my_alloca(reclength)))
+  {
+    my_errno= HA_ERR_OUT_OF_MEM; /* purecov: inspected */
+    return(-1);
+  }
+  reclength2= _mi_rec_pack(info,rec_buff+ALIGN_SIZE(MI_MAX_DYN_BLOCK_HEADER),
+			   record);
+  DBUG_PRINT("info",("reclength: %lu  reclength2: %lu",
+		     reclength, reclength2));
+  DBUG_ASSERT(reclength2 <= reclength);
+  error=write_dynamic_record(info,rec_buff+ALIGN_SIZE(MI_MAX_DYN_BLOCK_HEADER),
+			     reclength2);
+  my_afree(rec_buff);
+  return(error);
+}
+
+
+int _mi_update_blob_record(MI_INFO *info, my_off_t pos, const uchar *record)
+{
+  uchar *rec_buff;
+  int error;
+  ulong reclength,extra;
+
+  extra= (ALIGN_SIZE(MI_MAX_DYN_BLOCK_HEADER)+MI_SPLIT_LENGTH+
+	  MI_DYN_DELETE_BLOCK_HEADER);
+  reclength= (info->s->base.pack_reclength+
+	      _mi_calc_total_blob_length(info,record)+ extra);
+  if (!(rec_buff=(uchar*) my_alloca(reclength)))
+  {
+    my_errno= HA_ERR_OUT_OF_MEM; /* purecov: inspected */
+    return(-1);
+  }
+  reclength=_mi_rec_pack(info,rec_buff+ALIGN_SIZE(MI_MAX_DYN_BLOCK_HEADER),
+			 record);
+  error=update_dynamic_record(info,pos,
+			      rec_buff+ALIGN_SIZE(MI_MAX_DYN_BLOCK_HEADER),
+			      reclength);
+  my_afree(rec_buff);
+  return(error);
+}
+
+
+int _mi_delete_dynamic_record(MI_INFO *info)
+{
+  return delete_dynamic_record(info,info->lastpos,0);
+}
+
+
+	/* Write record to data-file */
+
+static int write_dynamic_record(MI_INFO *info, const uchar *record,
+				ulong reclength)
+{
+  int flag;
+  ulong length;
+  my_off_t filepos;
+  DBUG_ENTER("write_dynamic_record");
+
+  flag=0;
+
+  /*
+    Check if we have enough room for the new record.
+    First we do simplified check to make usual case faster.
+    Then we do more precise check for the space left.
+    Though it still is not absolutely precise, as
+    we always use MI_MAX_DYN_BLOCK_HEADER while it can be
+    less in the most of the cases.
+  */
+
+  if (unlikely(info->s->base.max_data_file_length -
+               info->state->data_file_length <
+               reclength + MI_MAX_DYN_BLOCK_HEADER))
+  {
+    if (info->s->base.max_data_file_length - info->state->data_file_length +
+        info->state->empty - info->state->del * MI_MAX_DYN_BLOCK_HEADER <
+        reclength + MI_MAX_DYN_BLOCK_HEADER)
+    {
+      my_errno=HA_ERR_RECORD_FILE_FULL;
+      DBUG_RETURN(1);
+    }
+  }
+
+  do
+  {
+    if (_mi_find_writepos(info,reclength,&filepos,&length))
+      goto err;
+    if (_mi_write_part_record(info,filepos,length,
+                              (info->append_insert_at_end ?
+                               HA_OFFSET_ERROR : info->s->state.dellink),
+			      (uchar**) &record,&reclength,&flag))
+      goto err;
+  } while (reclength);
+
+  DBUG_RETURN(0);
+err:
+  DBUG_RETURN(1);
+}
+
+
+	/* Get a block for data ; The given data-area must be used !! */
+
+static int _mi_find_writepos(MI_INFO *info,
+			     ulong reclength, /* record length */
+			     my_off_t *filepos, /* Return file pos */
+			     ulong *length)   /* length of block at filepos */
+{
+  MI_BLOCK_INFO block_info;
+  ulong tmp;
+  DBUG_ENTER("_mi_find_writepos");
+
+  if (info->s->state.dellink != HA_OFFSET_ERROR &&
+      !info->append_insert_at_end)
+  {
+    /* Deleted blocks exists;  Get last used block */
+    *filepos=info->s->state.dellink;
+    block_info.second_read=0;
+    info->rec_cache.seek_not_done=1;
+    if (!(_mi_get_block_info(&block_info,info->dfile,info->s->state.dellink) &
+	   BLOCK_DELETED))
+    {
+      DBUG_PRINT("error",("Delete link crashed"));
+      my_errno=HA_ERR_WRONG_IN_RECORD;
+      DBUG_RETURN(-1);
+    }
+    info->s->state.dellink=block_info.next_filepos;
+    info->state->del--;
+    info->state->empty-= block_info.block_len;
+    *length= block_info.block_len;
+  }
+  else
+  {
+    /* No deleted blocks;  Allocate a new block */
+    *filepos=info->state->data_file_length;
+    if ((tmp= reclength + 3 + MY_TEST(reclength >= (65520 - 3))) <
+	info->s->base.min_block_length)
+      tmp= info->s->base.min_block_length;
+    else
+      tmp= ((tmp+MI_DYN_ALIGN_SIZE-1) &
+	    (~ (ulong) (MI_DYN_ALIGN_SIZE-1)));
+    if (info->state->data_file_length >
+	(info->s->base.max_data_file_length - tmp))
+    {
+      my_errno=HA_ERR_RECORD_FILE_FULL;
+      DBUG_RETURN(-1);
+    }
+    if (tmp > MI_MAX_BLOCK_LENGTH)
+      tmp=MI_MAX_BLOCK_LENGTH;
+    *length= tmp;
+    info->state->data_file_length+= tmp;
+    info->s->state.split++;
+    info->update|=HA_STATE_WRITE_AT_END;
+  }
+  DBUG_RETURN(0);
+} /* _mi_find_writepos */
+
+
+
+/*
+  Unlink a deleted block from the deleted list.
+  This block will be combined with the preceding or next block to form
+  a big block.
+*/
+
+static my_bool unlink_deleted_block(MI_INFO *info, MI_BLOCK_INFO *block_info)
+{
+  DBUG_ENTER("unlink_deleted_block");
+  if (block_info->filepos == info->s->state.dellink)
+  {
+    /* First deleted block;  We can just use this ! */
+    info->s->state.dellink=block_info->next_filepos;
+  }
+  else
+  {
+    MI_BLOCK_INFO tmp;
+    tmp.second_read=0;
+    /* Unlink block from the previous block */
+    if (!(_mi_get_block_info(&tmp,info->dfile,block_info->prev_filepos)
+	  & BLOCK_DELETED))
+      DBUG_RETURN(1);				/* Something is wrong */
+    mi_sizestore(tmp.header+4,block_info->next_filepos);
+    if (info->s->file_write(info, tmp.header+4,8,
+		  block_info->prev_filepos+4, MYF(MY_NABP)))
+      DBUG_RETURN(1);
+    /* Unlink block from next block */
+    if (block_info->next_filepos != HA_OFFSET_ERROR)
+    {
+      if (!(_mi_get_block_info(&tmp,info->dfile,block_info->next_filepos)
+	    & BLOCK_DELETED))
+	DBUG_RETURN(1);				/* Something is wrong */
+      mi_sizestore(tmp.header+12,block_info->prev_filepos);
+      if (info->s->file_write(info, tmp.header+12,8,
+		    block_info->next_filepos+12,
+		    MYF(MY_NABP)))
+	DBUG_RETURN(1);
+    }
+  }
+  /* We now have one less deleted block */
+  info->state->del--;
+  info->state->empty-= block_info->block_len;
+  info->s->state.split--;
+
+  /*
+    If this was a block that we where accessing through table scan
+    (mi_rrnd() or mi_scan(), then ensure that we skip over this block
+    when doing next mi_rrnd() or mi_scan().
+  */
+  if (info->nextpos == block_info->filepos)
+    info->nextpos+=block_info->block_len;
+  DBUG_RETURN(0);
+}
+
+
+/*
+  Add a backward link to delete block
+
+  SYNOPSIS
+    update_backward_delete_link()
+    info		MyISAM handler
+    delete_block	Position to delete block to update.
+			If this is 'HA_OFFSET_ERROR', nothing will be done
+    filepos		Position to block that 'delete_block' should point to
+
+  RETURN
+    0  ok
+    1  error.  In this case my_error is set.
+*/
+
+static int update_backward_delete_link(MI_INFO *info, my_off_t delete_block,
+				       my_off_t filepos)
+{
+  MI_BLOCK_INFO block_info;
+  DBUG_ENTER("update_backward_delete_link");
+
+  if (delete_block != HA_OFFSET_ERROR)
+  {
+    block_info.second_read=0;
+    if (_mi_get_block_info(&block_info,info->dfile,delete_block)
+	& BLOCK_DELETED)
+    {
+      uchar buff[8];
+      mi_sizestore(buff,filepos);
+      if (info->s->file_write(info,buff, 8, delete_block+12, MYF(MY_NABP)))
+	DBUG_RETURN(1);				/* Error on write */
+    }
+    else
+    {
+      my_errno=HA_ERR_WRONG_IN_RECORD;
+      DBUG_RETURN(1);				/* Wrong delete link */
+    }
+  }
+  DBUG_RETURN(0);
+}
+
+	/* Delete datarecord from database */
+	/* info->rec_cache.seek_not_done is updated in cmp_record */
+
+static int delete_dynamic_record(MI_INFO *info, my_off_t filepos,
+				 uint second_read)
+{
+  uint length,b_type;
+  MI_BLOCK_INFO block_info,del_block;
+  int error;
+  my_bool remove_next_block;
+  DBUG_ENTER("delete_dynamic_record");
+
+  /* First add a link from the last block to the new one */
+  error= update_backward_delete_link(info, info->s->state.dellink, filepos);
+
+  block_info.second_read=second_read;
+  do
+  {
+    /* Remove block at 'filepos' */
+    if ((b_type=_mi_get_block_info(&block_info,info->dfile,filepos))
+	& (BLOCK_DELETED | BLOCK_ERROR | BLOCK_SYNC_ERROR |
+	   BLOCK_FATAL_ERROR) ||
+	(length=(uint) (block_info.filepos-filepos) +block_info.block_len) <
+	MI_MIN_BLOCK_LENGTH)
+    {
+      my_errno=HA_ERR_WRONG_IN_RECORD;
+      DBUG_RETURN(1);
+    }
+    /* Check if next block is a delete block */
+    del_block.second_read=0;
+    remove_next_block=0;
+    if (_mi_get_block_info(&del_block,info->dfile,filepos+length) &
+	BLOCK_DELETED && del_block.block_len+length < MI_DYN_MAX_BLOCK_LENGTH)
+    {
+      /* We can't remove this yet as this block may be the head block */
+      remove_next_block=1;
+      length+=del_block.block_len;
+    }
+
+    block_info.header[0]=0;
+    mi_int3store(block_info.header+1,length);
+    mi_sizestore(block_info.header+4,info->s->state.dellink);
+    if (b_type & BLOCK_LAST)
+      bfill(block_info.header+12,8,255);
+    else
+      mi_sizestore(block_info.header+12,block_info.next_filepos);
+    if (info->s->file_write(info,(uchar*) block_info.header,20,filepos,
+		  MYF(MY_NABP)))
+      DBUG_RETURN(1);
+    info->s->state.dellink = filepos;
+    info->state->del++;
+    info->state->empty+=length;
+    filepos=block_info.next_filepos;
+
+    /* Now it's safe to unlink the deleted block directly after this one */
+    if (remove_next_block && unlink_deleted_block(info,&del_block))
+      error=1;
+  } while (!(b_type & BLOCK_LAST));
+
+  DBUG_RETURN(error);
+}
+
+
+	/* Write a block to datafile */
+
+int _mi_write_part_record(MI_INFO *info,
+			  my_off_t filepos,	/* points at empty block */
+			  ulong length,		/* length of block */
+			  my_off_t next_filepos,/* Next empty block */
+			  uchar **record,	/* pointer to record ptr */
+			  ulong *reclength,	/* length of *record */
+			  int *flag)		/* *flag == 0 if header */
+{
+  ulong head_length,res_length,extra_length,long_block,del_length;
+  uchar *pos,*record_end;
+  my_off_t  next_delete_block;
+  uchar temp[MI_SPLIT_LENGTH+MI_DYN_DELETE_BLOCK_HEADER];
+  DBUG_ENTER("_mi_write_part_record");
+
+  next_delete_block=HA_OFFSET_ERROR;
+
+  res_length=extra_length=0;
+  if (length > *reclength + MI_SPLIT_LENGTH)
+  {						/* Splitt big block */
+    res_length=MY_ALIGN(length- *reclength - MI_EXTEND_BLOCK_LENGTH,
+			MI_DYN_ALIGN_SIZE);
+    length-= res_length;			/* Use this for first part */
+  }
+  long_block= (length < 65520L && *reclength < 65520L) ? 0 : 1;
+  if (length == *reclength+ 3 + long_block)
+  {
+    /* Block is exactly of the right length */
+    temp[0]=(uchar) (1+ *flag)+(uchar) long_block;	/* Flag is 0 or 6 */
+    if (long_block)
+    {
+      mi_int3store(temp+1,*reclength);
+      head_length=4;
+    }
+    else
+    {
+      mi_int2store(temp+1,*reclength);
+      head_length=3;
+    }
+  }
+  else if (length-long_block < *reclength+4)
+  {						/* To short block */
+    if (next_filepos == HA_OFFSET_ERROR)
+      next_filepos= (info->s->state.dellink != HA_OFFSET_ERROR &&
+                     !info->append_insert_at_end ?
+                     info->s->state.dellink : info->state->data_file_length);
+    if (*flag == 0)				/* First block */
+    {
+      if (*reclength > MI_MAX_BLOCK_LENGTH)
+      {
+	head_length= 16;
+	temp[0]=13;
+	mi_int4store(temp+1,*reclength);
+	mi_int3store(temp+5,length-head_length);
+	mi_sizestore((uchar*) temp+8,next_filepos);
+      }
+      else
+      {
+	head_length=5+8+long_block*2;
+	temp[0]=5+(uchar) long_block;
+	if (long_block)
+	{
+	  mi_int3store(temp+1,*reclength);
+	  mi_int3store(temp+4,length-head_length);
+	  mi_sizestore((uchar*) temp+7,next_filepos);
+	}
+	else
+	{
+	  mi_int2store(temp+1,*reclength);
+	  mi_int2store(temp+3,length-head_length);
+	  mi_sizestore((uchar*) temp+5,next_filepos);
+	}
+      }
+    }
+    else
+    {
+      head_length=3+8+long_block;
+      temp[0]=11+(uchar) long_block;
+      if (long_block)
+      {
+	mi_int3store(temp+1,length-head_length);
+	mi_sizestore((uchar*) temp+4,next_filepos);
+      }
+      else
+      {
+	mi_int2store(temp+1,length-head_length);
+	mi_sizestore((uchar*) temp+3,next_filepos);
+      }
+    }
+  }
+  else
+  {					/* Block with empty info last */
+    head_length=4+long_block;
+    extra_length= length- *reclength-head_length;
+    temp[0]= (uchar) (3+ *flag)+(uchar) long_block; /* 3,4 or 9,10 */
+    if (long_block)
+    {
+      mi_int3store(temp+1,*reclength);
+      temp[4]= (uchar) (extra_length);
+    }
+    else
+    {
+      mi_int2store(temp+1,*reclength);
+      temp[3]= (uchar) (extra_length);
+    }
+    length=	  *reclength+head_length;	/* Write only what is needed */
+  }
+  DBUG_DUMP("header",(uchar*) temp,head_length);
+
+	/* Make a long block for one write */
+  record_end= *record+length-head_length;
+  del_length=(res_length ? MI_DYN_DELETE_BLOCK_HEADER : 0);
+  bmove((uchar*) (*record-head_length),(uchar*) temp,head_length);
+  memcpy(temp,record_end,(size_t) (extra_length+del_length));
+  bzero((uchar*) record_end,extra_length);
+
+  if (res_length)
+  {
+    /* Check first if we can join this block with the next one */
+    MI_BLOCK_INFO del_block;
+    my_off_t next_block=filepos+length+extra_length+res_length;
+
+    del_block.second_read=0;
+    if (next_block < info->state->data_file_length &&
+	info->s->state.dellink != HA_OFFSET_ERROR)
+    {
+      if ((_mi_get_block_info(&del_block,info->dfile,next_block)
+	   & BLOCK_DELETED) &&
+	  res_length + del_block.block_len < MI_DYN_MAX_BLOCK_LENGTH)
+      {
+	if (unlink_deleted_block(info,&del_block))
+	  goto err;
+	res_length+=del_block.block_len;
+      }
+    }
+
+    /* Create a delete link of the last part of the block */
+    pos=record_end+extra_length;
+    pos[0]= '\0';
+    mi_int3store(pos+1,res_length);
+    mi_sizestore(pos+4,info->s->state.dellink);
+    bfill(pos+12,8,255);			/* End link */
+    next_delete_block=info->s->state.dellink;
+    info->s->state.dellink= filepos+length+extra_length;
+    info->state->del++;
+    info->state->empty+=res_length;
+    info->s->state.split++;
+  }
+  if (info->opt_flag & WRITE_CACHE_USED &&
+      info->update & HA_STATE_WRITE_AT_END)
+  {
+    if (info->update & HA_STATE_EXTEND_BLOCK)
+    {
+      info->update&= ~HA_STATE_EXTEND_BLOCK;
+      if (my_block_write(&info->rec_cache,(uchar*) *record-head_length,
+			 length+extra_length+del_length,filepos))
+      goto err;
+    }
+    else if (my_b_write(&info->rec_cache,(uchar*) *record-head_length,
+			length+extra_length+del_length))
+      goto err;
+  }
+  else
+  {
+    info->rec_cache.seek_not_done=1;
+    if (info->s->file_write(info,(uchar*) *record-head_length,length+extra_length+
+		  del_length,filepos,info->s->write_flag))
+      goto err;
+  }
+  memcpy(record_end,temp,(size_t) (extra_length+del_length));
+  *record=record_end;
+  *reclength-=(length-head_length);
+  *flag=6;
+
+  if (del_length)
+  {
+    /* link the next delete block to this */
+    if (update_backward_delete_link(info, next_delete_block,
+				    info->s->state.dellink))
+      goto err;
+  }
+
+  DBUG_RETURN(0);
+err:
+  DBUG_PRINT("exit",("errno: %d",my_errno));
+  DBUG_RETURN(1);
+} /*_mi_write_part_record */
+
+
+	/* update record from datafile */
+
+static int update_dynamic_record(MI_INFO *info, my_off_t filepos, uchar *record,
+				 ulong reclength)
+{
+  int flag;
+  uint error;
+  ulong length;
+  MI_BLOCK_INFO block_info;
+  DBUG_ENTER("update_dynamic_record");
+
+  flag=block_info.second_read=0;
+  /*
+     Check if we have enough room for the record.
+     First we do simplified check to make usual case faster.
+     Then we do more precise check for the space left.
+     Though it still is not absolutely precise, as
+     we always use MI_MAX_DYN_BLOCK_HEADER while it can be
+     less in the most of the cases.
+  */
+
+  /*
+    compare with just the reclength as we're going
+    to get some space from the old replaced record
+  */
+  if (unlikely(info->s->base.max_data_file_length -
+        info->state->data_file_length < reclength))
+  {
+    /*
+       let's read the old record's block to find out the length of the
+       old record
+    */
+    if ((error=_mi_get_block_info(&block_info,info->dfile,filepos))
+        & (BLOCK_DELETED | BLOCK_ERROR | BLOCK_SYNC_ERROR | BLOCK_FATAL_ERROR))
+    {
+      DBUG_PRINT("error",("Got wrong block info"));
+      if (!(error & BLOCK_FATAL_ERROR))
+        my_errno=HA_ERR_WRONG_IN_RECORD;
+      goto err;
+    }
+
+    /*
+      if new record isn't longer, we can go on safely
+    */
+    if (block_info.rec_len < reclength)
+    {
+      if (info->s->base.max_data_file_length - info->state->data_file_length +
+          info->state->empty - info->state->del * MI_MAX_DYN_BLOCK_HEADER <
+          reclength - block_info.rec_len + MI_MAX_DYN_BLOCK_HEADER)
+      {
+        my_errno=HA_ERR_RECORD_FILE_FULL;
+        goto err;
+      }
+    }
+    block_info.second_read=0;
+  }
+
+  while (reclength > 0)
+  {
+    if (filepos != info->s->state.dellink)
+    {
+      block_info.next_filepos= HA_OFFSET_ERROR;
+      if ((error=_mi_get_block_info(&block_info,info->dfile,filepos))
+	  & (BLOCK_DELETED | BLOCK_ERROR | BLOCK_SYNC_ERROR |
+	     BLOCK_FATAL_ERROR))
+      {
+	DBUG_PRINT("error",("Got wrong block info"));
+	if (!(error & BLOCK_FATAL_ERROR))
+	  my_errno=HA_ERR_WRONG_IN_RECORD;
+	goto err;
+      }
+      length=(ulong) (block_info.filepos-filepos) + block_info.block_len;
+      if (length < reclength)
+      {
+	uint tmp=MY_ALIGN(reclength - length + 3 +
+                          MY_TEST(reclength >= 65520L), MI_DYN_ALIGN_SIZE);
+	/* Don't create a block bigger than MI_MAX_BLOCK_LENGTH */
+	tmp= MY_MIN(length+tmp, MI_MAX_BLOCK_LENGTH)-length;
+	/* Check if we can extend this block */
+	if (block_info.filepos + block_info.block_len ==
+	    info->state->data_file_length &&
+	    info->state->data_file_length <
+	    info->s->base.max_data_file_length-tmp)
+	{
+	  /* extend file */
+	  DBUG_PRINT("info",("Extending file with %d bytes",tmp));
+	  if (info->nextpos == info->state->data_file_length)
+	    info->nextpos+= tmp;
+	  info->state->data_file_length+= tmp;
+	  info->update|= HA_STATE_WRITE_AT_END | HA_STATE_EXTEND_BLOCK;
+	  length+=tmp;
+	}
+	else if (length < MI_MAX_BLOCK_LENGTH - MI_MIN_BLOCK_LENGTH)
+	{
+	  /*
+	    Check if next block is a deleted block
+	    Above we have MI_MIN_BLOCK_LENGTH to avoid the problem where
+	    the next block is so small it can't be split which could
+	    cause problems
+	  */
+
+	  MI_BLOCK_INFO del_block;
+	  del_block.second_read=0;
+	  if (_mi_get_block_info(&del_block,info->dfile,
+				 block_info.filepos + block_info.block_len) &
+	      BLOCK_DELETED)
+	  {
+	    /* Use; Unlink it and extend the current block */
+	    DBUG_PRINT("info",("Extending current block"));
+	    if (unlink_deleted_block(info,&del_block))
+	      goto err;
+	    if ((length+=del_block.block_len) > MI_MAX_BLOCK_LENGTH)
+	    {
+	      /*
+		New block was too big, link overflow part back to
+		delete list
+	      */
+	      my_off_t next_pos;
+	      ulong rest_length= length-MI_MAX_BLOCK_LENGTH;
+	      set_if_bigger(rest_length, MI_MIN_BLOCK_LENGTH);
+	      next_pos= del_block.filepos+ del_block.block_len - rest_length;
+
+	      if (update_backward_delete_link(info, info->s->state.dellink,
+					      next_pos))
+		DBUG_RETURN(1);
+
+	      /* create delete link for data that didn't fit into the page */
+	      del_block.header[0]=0;
+	      mi_int3store(del_block.header+1, rest_length);
+	      mi_sizestore(del_block.header+4,info->s->state.dellink);
+	      bfill(del_block.header+12,8,255);
+	      if (info->s->file_write(info,(uchar*) del_block.header,20, next_pos,
+			    MYF(MY_NABP)))
+		DBUG_RETURN(1);
+	      info->s->state.dellink= next_pos;
+	      info->s->state.split++;
+	      info->state->del++;
+	      info->state->empty+= rest_length;
+	      length-= rest_length;
+	    }
+	  }
+	}
+      }
+    }
+    else
+    {
+      if (_mi_find_writepos(info,reclength,&filepos,&length))
+	goto err;
+    }
+    if (_mi_write_part_record(info,filepos,length,block_info.next_filepos,
+			      &record,&reclength,&flag))
+      goto err;
+    if ((filepos=block_info.next_filepos) == HA_OFFSET_ERROR)
+    {
+      /* Start writing data on deleted blocks */
+      filepos=info->s->state.dellink;
+    }
+  }
+
+  if (block_info.next_filepos != HA_OFFSET_ERROR)
+  {
+    /*
+      delete_dynamic_record() may change data file position.
+      IO cache must be notified as it may still have cached
+      data, which has to be flushed later.
+    */
+    info->rec_cache.seek_not_done= 1;
+    if (delete_dynamic_record(info,block_info.next_filepos,1))
+      goto err;
+  }
+  DBUG_RETURN(0);
+err:
+  DBUG_RETURN(1);
+}
+
+
+	/* Pack a record. Return new reclength */
+
+uint _mi_rec_pack(MI_INFO *info, register uchar *to,
+                  register const uchar *from)
+{
+  uint		length,new_length,flag,bit,i;
+  uchar		*pos,*end,*startpos,*packpos;
+  enum en_fieldtype type;
+  reg3 MI_COLUMNDEF *rec;
+  MI_BLOB	*blob;
+  DBUG_ENTER("_mi_rec_pack");
+
+  flag=0 ; bit=1;
+  startpos=packpos=to; to+= info->s->base.pack_bits; blob=info->blobs;
+  rec=info->s->rec;
+
+  for (i=info->s->base.fields ; i-- > 0; from+= length,rec++)
+  {
+    length=(uint) rec->length;
+    if ((type = (enum en_fieldtype) rec->type) != FIELD_NORMAL)
+    {
+      if (type == FIELD_BLOB)
+      {
+	if (!blob->length)
+	  flag|=bit;
+	else
+	{
+	  char *temp_pos;
+	  size_t tmp_length=length-portable_sizeof_char_ptr;
+	  memcpy((uchar*) to,from,tmp_length);
+	  memcpy(&temp_pos,from+tmp_length,sizeof(char*));
+	  memcpy(to+tmp_length,temp_pos,(size_t) blob->length);
+	  to+=tmp_length+blob->length;
+	}
+	blob++;
+      }
+      else if (type == FIELD_SKIP_ZERO)
+      {
+	if (memcmp((uchar*) from,zero_string,length) == 0)
+	  flag|=bit;
+	else
+	{
+	  memcpy((uchar*) to,from,(size_t) length); to+=length;
+	}
+      }
+      else if (type == FIELD_SKIP_ENDSPACE ||
+	       type == FIELD_SKIP_PRESPACE)
+      {
+	pos= (uchar*) from; end= (uchar*) from + length;
+	if (type == FIELD_SKIP_ENDSPACE)
+	{					/* Pack trailing spaces */
+	  while (end > from && *(end-1) == ' ')
+	    end--;
+	}
+	else
+	{					/* Pack pref-spaces */
+	  while (pos < end && *pos == ' ')
+	    pos++;
+	}
+	new_length=(uint) (end-pos);
+        if (new_length + 1 + MY_TEST(rec->length > 255 && new_length > 127)
+	    < length)
+	{
+	  if (rec->length > 255 && new_length > 127)
+	  {
+            to[0]= (uchar) ((new_length & 127) + 128);
+            to[1]= (uchar) (new_length >> 7);
+            to+=2;
+          }
+          else
+            *to++= (uchar) new_length;
+	  memcpy((uchar*) to,pos,(size_t) new_length); to+=new_length;
+	  flag|=bit;
+	}
+	else
+	{
+	  memcpy(to,from,(size_t) length); to+=length;
+	}
+      }
+      else if (type == FIELD_VARCHAR)
+      {
+        uint pack_length= HA_VARCHAR_PACKLENGTH(rec->length -1);
+	uint tmp_length;
+        if (pack_length == 1)
+        {
+          tmp_length= (uint) *(uchar*) from;
+          *to++= *from;
+        }
+        else
+        {
+          tmp_length= uint2korr(from);
+          store_key_length_inc(to,tmp_length);
+        }
+        memcpy(to, from+pack_length,tmp_length);
+        to+= tmp_length;
+        continue;
+      }
+      else
+      {
+	memcpy(to,from,(size_t) length); to+=length;
+	continue;				/* Normal field */
+      }
+      if ((bit= bit << 1) >= 256)
+      {
+        *packpos++= (uchar) flag;
+	bit=1; flag=0;
+      }
+    }
+    else
+    {
+      memcpy(to,from,(size_t) length); to+=length;
+    }
+  }
+  if (bit != 1)
+    *packpos= (uchar) flag;
+  if (info->s->calc_checksum)
+    *to++= (uchar) info->checksum;
+  DBUG_PRINT("exit",("packed length: %d",(int) (to-startpos)));
+  DBUG_RETURN((uint) (to-startpos));
+} /* _mi_rec_pack */
+
+
+
+/*
+  Check if a record was correctly packed. Used only by myisamchk
+  Returns 0 if record is ok.
+*/
+
+my_bool _mi_rec_check(MI_INFO *info,const uchar *record, uchar *rec_buff,
+                      ulong packed_length, my_bool with_checksum)
+{
+  uint		length,new_length,flag,bit,i;
+  uchar		*pos,*end,*packpos,*to;
+  enum en_fieldtype type;
+  reg3 MI_COLUMNDEF *rec;
+  DBUG_ENTER("_mi_rec_check");
+
+  packpos=rec_buff; to= rec_buff+info->s->base.pack_bits;
+  rec=info->s->rec;
+  flag= *packpos; bit=1;
+
+  for (i=info->s->base.fields ; i-- > 0; record+= length, rec++)
+  {
+    length=(uint) rec->length;
+    if ((type = (enum en_fieldtype) rec->type) != FIELD_NORMAL)
+    {
+      if (type == FIELD_BLOB)
+      {
+	uint blob_length=
+	  _mi_calc_blob_length(length-portable_sizeof_char_ptr,record);
+	if (!blob_length && !(flag & bit))
+	  goto err;
+	if (blob_length)
+	  to+=length - portable_sizeof_char_ptr+ blob_length;
+      }
+      else if (type == FIELD_SKIP_ZERO)
+      {
+	if (memcmp((uchar*) record,zero_string,length) == 0)
+	{
+	  if (!(flag & bit))
+	    goto err;
+	}
+	else
+	  to+=length;
+      }
+      else if (type == FIELD_SKIP_ENDSPACE ||
+	       type == FIELD_SKIP_PRESPACE)
+      {
+	pos= (uchar*) record; end= (uchar*) record + length;
+	if (type == FIELD_SKIP_ENDSPACE)
+	{					/* Pack trailing spaces */
+	  while (end > record && *(end-1) == ' ')
+	    end--;
+	}
+	else
+	{					/* Pack pre-spaces */
+	  while (pos < end && *pos == ' ')
+	    pos++;
+	}
+	new_length=(uint) (end-pos);
+        if (new_length + 1 + MY_TEST(rec->length > 255 && new_length > 127)
+	    < length)
+	{
+	  if (!(flag & bit))
+	    goto err;
+	  if (rec->length > 255 && new_length > 127)
+	  {
+            /* purecov: begin inspected */
+            if (to[0] != (uchar) ((new_length & 127) + 128) ||
+                to[1] != (uchar) (new_length >> 7))
+              goto err;
+            to+=2;
+            /* purecov: end */
+          }
+          else if (*to++ != (uchar) new_length)
+	    goto err;
+	  to+=new_length;
+	}
+	else
+	  to+=length;
+      }
+      else if (type == FIELD_VARCHAR)
+      {
+        uint pack_length= HA_VARCHAR_PACKLENGTH(rec->length -1);
+	uint tmp_length;
+        if (pack_length == 1)
+        {
+          tmp_length= (uint) *(uchar*) record;
+          to+= 1+ tmp_length;
+          continue;
+        }
+        else
+        {
+          tmp_length= uint2korr(record);
+          to+= get_pack_length(tmp_length)+tmp_length;
+        }
+        continue;
+      }
+      else
+      {
+	to+=length;
+	continue;				/* Normal field */
+      }
+      if ((bit= bit << 1) >= 256)
+      {
+	flag= *++packpos;
+	bit=1;
+      }
+    }
+    else
+      to+= length;
+  }
+  if (packed_length != (uint) (to - rec_buff) + MY_TEST(info->s->calc_checksum) ||
+      (bit != 1 && (flag & ~(bit - 1))))
+    goto err;
+  if (with_checksum && ((uchar) info->checksum != (uchar) *to))
+  {
+    DBUG_PRINT("error",("wrong checksum for row"));
+    goto err;
+  }
+  DBUG_RETURN(0);
+
+err:
+  DBUG_RETURN(1);
+}
+
+
+
+	/* Unpacks a record */
+	/* Returns -1 and my_errno =HA_ERR_RECORD_DELETED if reclength isn't */
+	/* right. Returns reclength (>0) if ok */
+
+size_t _mi_rec_unpack(register MI_INFO *info, register uchar *to, uchar *from,
+		     ulong found_length)
+{
+  uint flag,bit,length,rec_length,min_pack_length;
+  enum en_fieldtype type;
+  uchar *from_end,*to_end,*packpos;
+  reg3 MI_COLUMNDEF *rec,*end_field;
+  DBUG_ENTER("_mi_rec_unpack");
+
+  to_end=to + info->s->base.reclength;
+  from_end=from+found_length;
+  flag= (uchar) *from; bit=1; packpos=from;
+  if (found_length < info->s->base.min_pack_length)
+    goto err;
+  from+= info->s->base.pack_bits;
+  min_pack_length=info->s->base.min_pack_length - info->s->base.pack_bits;
+
+  for (rec=info->s->rec , end_field=rec+info->s->base.fields ;
+       rec < end_field ; to+= rec_length, rec++)
+  {
+    rec_length=rec->length;
+    if ((type = (enum en_fieldtype) rec->type) != FIELD_NORMAL &&
+	(type != FIELD_CHECK))
+    {
+      if (type == FIELD_VARCHAR)
+      {
+        uint pack_length= HA_VARCHAR_PACKLENGTH(rec_length-1);
+        if (pack_length == 1)
+        {
+          length= (uint) *(uchar*) from;
+          if (length > rec_length-1)
+            goto err;
+          *to= *from++;
+        }
+        else
+        {
+          get_key_length(length, from);
+          if (length > rec_length-2)
+            goto err;
+          int2store(to,length);
+        }
+        if (from+length > from_end)
+          goto err;
+        memcpy(to+pack_length, from, length);
+        from+= length;
+        min_pack_length--;
+        continue;
+      }
+      if (flag & bit)
+      {
+	if (type == FIELD_BLOB || type == FIELD_SKIP_ZERO)
+	  bzero((uchar*) to,rec_length);
+	else if (type == FIELD_SKIP_ENDSPACE ||
+		 type == FIELD_SKIP_PRESPACE)
+	{
+	  if (rec->length > 255 && *from & 128)
+	  {
+	    if (from + 1 >= from_end)
+	      goto err;
+	    length= (*from & 127)+ ((uint) (uchar) *(from+1) << 7); from+=2;
+	  }
+	  else
+	  {
+	    if (from == from_end)
+	      goto err;
+	    length= (uchar) *from++;
+	  }
+	  min_pack_length--;
+	  if (length >= rec_length ||
+	      min_pack_length + length > (uint) (from_end - from))
+	    goto err;
+	  if (type == FIELD_SKIP_ENDSPACE)
+	  {
+	    memcpy(to,(uchar*) from,(size_t) length);
+	    bfill((uchar*) to+length,rec_length-length,' ');
+	  }
+	  else
+	  {
+	    bfill((uchar*) to,rec_length-length,' ');
+	    memcpy(to+rec_length-length,(uchar*) from,(size_t) length);
+	  }
+	  from+=length;
+	}
+      }
+      else if (type == FIELD_BLOB)
+      {
+	uint size_length=rec_length- portable_sizeof_char_ptr;
+	ulong blob_length=_mi_calc_blob_length(size_length,from);
+        ulong from_left= (ulong) (from_end - from);
+        if (from_left < size_length ||
+            from_left - size_length < blob_length ||
+            from_left - size_length - blob_length < min_pack_length)
+          goto err;
+	memcpy(to, from, (size_t) size_length);
+	from+=size_length;
+	memcpy(to+size_length, &from, sizeof(char*));
+	from+=blob_length;
+      }
+      else
+      {
+	if (type == FIELD_SKIP_ENDSPACE || type == FIELD_SKIP_PRESPACE)
+	  min_pack_length--;
+	if (min_pack_length + rec_length > (uint) (from_end - from))
+	  goto err;
+	memcpy(to,(uchar*) from,(size_t) rec_length); from+=rec_length;
+      }
+      if ((bit= bit << 1) >= 256)
+      {
+	flag= (uchar) *++packpos; bit=1;
+      }
+    }
+    else
+    {
+      if (min_pack_length > (uint) (from_end - from))
+	goto err;
+      min_pack_length-=rec_length;
+      memcpy(to, (uchar*) from, (size_t) rec_length);
+      from+=rec_length;
+    }
+  }
+  if (info->s->calc_checksum)
+    from++;
+  if (to == to_end && from == from_end && (bit == 1 || !(flag & ~(bit-1))))
+    DBUG_RETURN(found_length);
+
+err:
+  my_errno= HA_ERR_WRONG_IN_RECORD;
+  DBUG_PRINT("error",("to_end: %p -> %p  from_end: %p -> %p",
+		      to, to_end, from, from_end));
+  DBUG_DUMP("from",(uchar*) info->rec_buff,info->s->base.min_pack_length);
+  DBUG_RETURN(MY_FILE_ERROR);
+} /* _mi_rec_unpack */
+
+
+	/* Calc length of blob. Update info in blobs->length */
+
+ulong _mi_calc_total_blob_length(MI_INFO *info, const uchar *record)
+{
+  ulong length;
+  MI_BLOB *blob,*end;
+
+  for (length=0, blob= info->blobs, end=blob+info->s->base.blobs ;
+       blob != end;
+       blob++)
+  {
+    blob->length=_mi_calc_blob_length(blob->pack_length,record + blob->offset);
+    length+=blob->length;
+  }
+  return length;
+}
+
+
+ulong _mi_calc_blob_length(uint length, const uchar *pos)
+{
+  switch (length) {
+  case 1:
+    return (uint) (uchar) *pos;
+  case 2:
+    return (uint) uint2korr(pos);
+  case 3:
+    return uint3korr(pos);
+  case 4:
+    return uint4korr(pos);
+  default:
+    break;
+  }
+  return 0; /* Impossible */
+}
+
+
+void _mi_store_blob_length(uchar *pos,uint pack_length,uint length)
+{
+  switch (pack_length) {
+  case 1:
+    *pos= (uchar) length;
+    break;
+  case 2:
+    int2store(pos,length);
+    break;
+  case 3:
+    int3store(pos,length);
+    break;
+  case 4:
+    int4store(pos,length);
+  default:
+    break;
+  }
+  return;
+}
+
+
+/*
+  Read record from datafile.
+
+  SYNOPSIS
+    _mi_read_dynamic_record()
+      info                      MI_INFO pointer to table.
+      filepos                   From where to read the record.
+      buf                       Destination for record.
+
+  NOTE
+
+    If a write buffer is active, it needs to be flushed if its contents
+    intersects with the record to read. We always check if the position
+    of the first byte of the write buffer is lower than the position
+    past the last byte to read. In theory this is also true if the write
+    buffer is completely below the read segment. That is, if there is no
+    intersection. But this case is unusual. We flush anyway. Only if the
+    first byte in the write buffer is above the last byte to read, we do
+    not flush.
+
+    A dynamic record may need several reads. So this check must be done
+    before every read. Reading a dynamic record starts with reading the
+    block header. If the record does not fit into the free space of the
+    header, the block may be longer than the header. In this case a
+    second read is necessary. These one or two reads repeat for every
+    part of the record.
+
+  RETURN
+    0           OK
+    -1          Error
+*/
+
+int _mi_read_dynamic_record(MI_INFO *info, my_off_t filepos, uchar *buf)
+{
+  int block_of_record;
+  uint b_type,UNINIT_VAR(left_length);
+  uchar *UNINIT_VAR(to);
+  MI_BLOCK_INFO block_info;
+  File file;
+  DBUG_ENTER("mi_read_dynamic_record");
+
+  if (filepos != HA_OFFSET_ERROR)
+  {
+    file=info->dfile;
+    block_of_record= 0;   /* First block of record is numbered as zero. */
+    block_info.second_read= 0;
+    do
+    {
+      /* A corrupted table can have wrong pointers. (Bug# 19835) */
+      if (filepos == HA_OFFSET_ERROR)
+        goto panic;
+      if (info->opt_flag & WRITE_CACHE_USED &&
+	  info->rec_cache.pos_in_file < filepos + MI_BLOCK_INFO_HEADER_LENGTH &&
+	  flush_io_cache(&info->rec_cache))
+	goto err;
+      info->rec_cache.seek_not_done=1;
+      if ((b_type= _mi_get_block_info(&block_info, file, filepos))
+	  & (BLOCK_DELETED | BLOCK_ERROR | BLOCK_SYNC_ERROR |
+	     BLOCK_FATAL_ERROR))
+      {
+	if (b_type & (BLOCK_SYNC_ERROR | BLOCK_DELETED))
+	  my_errno=HA_ERR_RECORD_DELETED;
+	goto err;
+      }
+      if (block_of_record++ == 0)			/* First block */
+      {
+	if (block_info.rec_len > (uint) info->s->base.max_pack_length)
+	  goto panic;
+	if (info->s->base.blobs)
+	{
+	  if (!(to=mi_alloc_rec_buff(info, block_info.rec_len,
+				     &info->rec_buff)))
+	    goto err;
+	}
+	else
+	  to= info->rec_buff;
+	left_length=block_info.rec_len;
+      }
+      if (left_length < block_info.data_len || ! block_info.data_len)
+	goto panic;			/* Wrong linked record */
+      /* copy information that is already read */
+      {
+        uint offset= (uint) (block_info.filepos - filepos);
+        uint prefetch_len= (sizeof(block_info.header) - offset);
+        filepos+= sizeof(block_info.header);
+
+        if (prefetch_len > block_info.data_len)
+          prefetch_len= block_info.data_len;
+        if (prefetch_len)
+        {
+          memcpy((uchar*) to, block_info.header + offset, prefetch_len);
+          block_info.data_len-= prefetch_len;
+          left_length-= prefetch_len;
+          to+= prefetch_len;
+        }
+      }
+      /* read rest of record from file */
+      if (block_info.data_len)
+      {
+        if (info->opt_flag & WRITE_CACHE_USED &&
+            info->rec_cache.pos_in_file < filepos + block_info.data_len &&
+            flush_io_cache(&info->rec_cache))
+          goto err;
+        /*
+          What a pity that this method is not called 'file_pread' and that
+          there is no equivalent without seeking. We are at the right
+          position already. :(
+        */
+        if (info->s->file_read(info, (uchar*) to, block_info.data_len,
+                               filepos, MYF(MY_NABP)))
+          goto panic;
+        left_length-=block_info.data_len;
+        to+=block_info.data_len;
+      }
+      filepos= block_info.next_filepos;
+    } while (left_length);
+
+    info->update|= HA_STATE_AKTIV;	/* We have a aktive record */
+    fast_mi_writeinfo(info);
+    DBUG_RETURN(_mi_rec_unpack(info,buf,info->rec_buff,block_info.rec_len) !=
+		MY_FILE_ERROR ? 0 : -1);
+  }
+  fast_mi_writeinfo(info);
+  DBUG_RETURN(-1);			/* Wrong data to read */
+
+panic:
+  my_errno=HA_ERR_WRONG_IN_RECORD;
+err:
+  (void) _mi_writeinfo(info,0);
+  DBUG_RETURN(-1);
+}
+
+	/* compare unique constraint between stored rows */
+
+int _mi_cmp_dynamic_unique(MI_INFO *info, MI_UNIQUEDEF *def,
+			   const uchar *record, my_off_t pos)
+{
+  uchar *rec_buff,*old_record;
+  int error;
+  DBUG_ENTER("_mi_cmp_dynamic_unique");
+
+  if (!(old_record=my_alloca(info->s->base.reclength)))
+    DBUG_RETURN(1);
+
+  /* Don't let the compare destroy blobs that may be in use */
+  rec_buff=info->rec_buff;
+  if (info->s->base.blobs)
+    info->rec_buff=0;
+  error=_mi_read_dynamic_record(info,pos,old_record);
+  if (!error)
+    error=mi_unique_comp(def, record, old_record, def->null_are_equal);
+  if (info->s->base.blobs)
+  {
+    my_free(mi_get_rec_buff_ptr(info, info->rec_buff));
+    info->rec_buff=rec_buff;
+  }
+  my_afree(old_record);
+  DBUG_RETURN(error);
+}
+
+
+	/* Compare of record one disk with packed record in memory */
+
+int _mi_cmp_dynamic_record(register MI_INFO *info, register const uchar *record)
+{
+  uint flag,reclength,b_type;
+  my_off_t filepos;
+  uchar *buffer;
+  MI_BLOCK_INFO block_info;
+  DBUG_ENTER("_mi_cmp_dynamic_record");
+
+  if (info->opt_flag & WRITE_CACHE_USED)
+  {
+    info->update&= ~(HA_STATE_WRITE_AT_END | HA_STATE_EXTEND_BLOCK);
+    if (flush_io_cache(&info->rec_cache))
+      DBUG_RETURN(-1);
+  }
+  info->rec_cache.seek_not_done=1;
+
+	/* If nobody have touched the database we don't have to test rec */
+
+  buffer=info->rec_buff;
+  if ((info->opt_flag & READ_CHECK_USED))
+  {						/* If check isn't disabled  */
+    if (info->s->base.blobs)
+    {
+      if (!(buffer=(uchar*) my_alloca(info->s->base.pack_reclength+
+				     _mi_calc_total_blob_length(info,record))))
+	DBUG_RETURN(-1);
+    }
+    reclength=_mi_rec_pack(info,buffer,record);
+    record= buffer;
+
+    filepos=info->lastpos;
+    flag=block_info.second_read=0;
+    block_info.next_filepos=filepos;
+    while (reclength > 0)
+    {
+      if ((b_type=_mi_get_block_info(&block_info,info->dfile,
+				    block_info.next_filepos))
+	  & (BLOCK_DELETED | BLOCK_ERROR | BLOCK_SYNC_ERROR |
+	     BLOCK_FATAL_ERROR))
+      {
+	if (b_type & (BLOCK_SYNC_ERROR | BLOCK_DELETED))
+	  my_errno=HA_ERR_RECORD_CHANGED;
+	goto err;
+      }
+      if (flag == 0)				/* First block */
+      {
+	flag=1;
+	if (reclength != block_info.rec_len)
+	{
+	  my_errno=HA_ERR_RECORD_CHANGED;
+	  goto err;
+	}
+      } else if (reclength < block_info.data_len)
+      {
+	my_errno=HA_ERR_WRONG_IN_RECORD;
+	goto err;
+      }
+      reclength-=block_info.data_len;
+      if (_mi_cmp_buffer(info->dfile,record,block_info.filepos,
+			 block_info.data_len))
+      {
+	my_errno=HA_ERR_RECORD_CHANGED;
+	goto err;
+      }
+      flag=1;
+      record+=block_info.data_len;
+    }
+  }
+  my_errno=0;
+err:
+  if (buffer != info->rec_buff)
+    my_afree((uchar*) buffer);
+  DBUG_RETURN(my_errno);
+}
+
+
+	/* Compare file to buffert */
+
+static int _mi_cmp_buffer(File file, const uchar *buff, my_off_t filepos,
+			  uint length)
+{
+  uint next_length;
+  uchar temp_buff[IO_SIZE*2];
+  DBUG_ENTER("_mi_cmp_buffer");
+
+  next_length= IO_SIZE*2 - (uint) (filepos & (IO_SIZE-1));
+
+  while (length > IO_SIZE*2)
+  {
+    if (mysql_file_pread(file, temp_buff, next_length, filepos, MYF(MY_NABP)) ||
+	memcmp(buff, temp_buff, next_length))
+      goto err;
+    filepos+=next_length;
+    buff+=next_length;
+    length-= next_length;
+    next_length=IO_SIZE*2;
+  }
+  if (mysql_file_pread(file, temp_buff, length, filepos, MYF(MY_NABP)))
+    goto err;
+  DBUG_RETURN(memcmp(buff,temp_buff,length));
+err:
+  DBUG_RETURN(1);
+}
+
+
+/*
+  Read record from datafile.
+
+  SYNOPSIS
+    _mi_read_rnd_dynamic_record()
+      info                      MI_INFO pointer to table.
+      buf                       Destination for record.
+      filepos                   From where to read the record.
+      skip_deleted_blocks       If to repeat reading until a non-deleted
+                                record is found.
+
+  NOTE
+
+    If a write buffer is active, it needs to be flushed if its contents
+    intersects with the record to read. We always check if the position
+    of the first byte of the write buffer is lower than the position
+    past the last byte to read. In theory this is also true if the write
+    buffer is completely below the read segment. That is, if there is no
+    intersection. But this case is unusual. We flush anyway. Only if the
+    first byte in the write buffer is above the last byte to read, we do
+    not flush.
+
+    A dynamic record may need several reads. So this check must be done
+    before every read. Reading a dynamic record starts with reading the
+    block header. If the record does not fit into the free space of the
+    header, the block may be longer than the header. In this case a
+    second read is necessary. These one or two reads repeat for every
+    part of the record.
+
+  RETURN
+    0           OK
+    != 0        Error
+*/
+
+int _mi_read_rnd_dynamic_record(MI_INFO *info, uchar *buf,
+				register my_off_t filepos,
+				my_bool skip_deleted_blocks)
+{
+  int block_of_record, info_read, save_errno;
+  uint left_len,b_type;
+  uchar *UNINIT_VAR(to);
+  MI_BLOCK_INFO block_info;
+  MYISAM_SHARE *share=info->s;
+  DBUG_ENTER("_mi_read_rnd_dynamic_record");
+
+  info_read=0;
+
+  if (info->lock_type == F_UNLCK)
+  {
+#ifndef UNSAFE_LOCKING
+    if (share->tot_locks == 0)
+    {
+      if (my_lock(share->kfile,F_RDLCK,0L,F_TO_EOF,
+		  MYF(MY_SEEK_NOT_DONE) | info->lock_wait))
+	DBUG_RETURN(my_errno);
+    }
+#else
+    info->tmp_lock_type=F_RDLCK;
+#endif
+  }
+  else
+    info_read=1;				/* memory-keyinfoblock is ok */
+
+  block_of_record= 0;   /* First block of record is numbered as zero. */
+  block_info.second_read= 0;
+  left_len=1;
+  do
+  {
+    if (filepos >= info->state->data_file_length)
+    {
+      if (!info_read)
+      {						/* Check if changed */
+	info_read=1;
+	info->rec_cache.seek_not_done=1;
+	if (mi_state_info_read_dsk(share->kfile,&share->state,1))
+	  goto panic;
+      }
+      if (filepos >= info->state->data_file_length)
+      {
+	my_errno= HA_ERR_END_OF_FILE;
+	goto err;
+      }
+    }
+    if (info->opt_flag & READ_CACHE_USED)
+    {
+      if (_mi_read_cache(&info->rec_cache,(uchar*) block_info.header,filepos,
+			 sizeof(block_info.header),
+			 (!block_of_record && skip_deleted_blocks ?
+                          READING_NEXT : 0) | READING_HEADER))
+	goto panic;
+      b_type=_mi_get_block_info(&block_info,-1,filepos);
+    }
+    else
+    {
+      if (info->opt_flag & WRITE_CACHE_USED &&
+	  info->rec_cache.pos_in_file < filepos + MI_BLOCK_INFO_HEADER_LENGTH &&
+	  flush_io_cache(&info->rec_cache))
+	DBUG_RETURN(my_errno);
+      info->rec_cache.seek_not_done=1;
+      b_type=_mi_get_block_info(&block_info,info->dfile,filepos);
+    }
+
+    if (b_type & (BLOCK_DELETED | BLOCK_ERROR | BLOCK_SYNC_ERROR |
+		  BLOCK_FATAL_ERROR))
+    {
+      if ((b_type & (BLOCK_DELETED | BLOCK_SYNC_ERROR)))
+      {
+        if (skip_deleted_blocks)
+        {
+          filepos=block_info.filepos+block_info.block_len;
+          block_info.second_read=0;
+          continue;		/* Search after next_record */
+        }
+        /*
+          If we're not on the first block of a record and
+          the block is marked as deleted or out of sync,
+          something's gone wrong: the record is damaged.
+        */
+        if (block_of_record != 0)
+          goto panic;
+	my_errno=HA_ERR_RECORD_DELETED;
+	info->lastpos=block_info.filepos;
+	info->nextpos=block_info.filepos+block_info.block_len;
+      }
+      goto err;
+    }
+    if (block_of_record == 0)				/* First block */
+    {
+      if (block_info.rec_len > (uint) share->base.max_pack_length)
+	goto panic;
+      info->lastpos=filepos;
+      if (share->base.blobs)
+      {
+	if (!(to= mi_alloc_rec_buff(info, block_info.rec_len,
+				    &info->rec_buff)))
+	  goto err;
+      }
+      else
+	to= info->rec_buff;
+      left_len=block_info.rec_len;
+    }
+    if (left_len < block_info.data_len)
+      goto panic;				/* Wrong linked record */
+
+    /* copy information that is already read */
+    {
+      uint offset=(uint) (block_info.filepos - filepos);
+      uint tmp_length= (sizeof(block_info.header) - offset);
+      filepos=block_info.filepos;
+
+      if (tmp_length > block_info.data_len)
+	tmp_length= block_info.data_len;
+      if (tmp_length)
+      {
+	memcpy((uchar*) to, block_info.header+offset,tmp_length);
+	block_info.data_len-=tmp_length;
+	left_len-=tmp_length;
+	to+=tmp_length;
+	filepos+=tmp_length;
+      }
+    }
+    /* read rest of record from file */
+    if (block_info.data_len)
+    {
+      if (info->opt_flag & READ_CACHE_USED)
+      {
+	if (_mi_read_cache(&info->rec_cache,(uchar*) to,filepos,
+			   block_info.data_len,
+			   (!block_of_record && skip_deleted_blocks) ?
+                           READING_NEXT : 0))
+	  goto panic;
+      }
+      else
+      {
+        if (info->opt_flag & WRITE_CACHE_USED &&
+            info->rec_cache.pos_in_file <
+            block_info.filepos + block_info.data_len &&
+            flush_io_cache(&info->rec_cache))
+          goto err;
+        /* mysql_file_seek(info->dfile, filepos, MY_SEEK_SET, MYF(0)); */
+        if (mysql_file_read(info->dfile, (uchar*) to, block_info.data_len,
+                            MYF(MY_NABP)))
+	{
+	  if (my_errno == HA_ERR_FILE_TOO_SHORT)
+	    my_errno= HA_ERR_WRONG_IN_RECORD;	/* Unexpected end of file */
+	  goto err;
+	}
+      }
+    }
+    /*
+      Increment block-of-record counter. If it was the first block,
+      remember the position behind the block for the next call.
+    */
+    if (block_of_record++ == 0)
+    {
+      info->nextpos= block_info.filepos + block_info.block_len;
+      skip_deleted_blocks= 0;
+    }
+    left_len-=block_info.data_len;
+    to+=block_info.data_len;
+    filepos=block_info.next_filepos;
+  } while (left_len);
+
+  info->update|= HA_STATE_AKTIV | HA_STATE_KEY_CHANGED;
+  fast_mi_writeinfo(info);
+  if (_mi_rec_unpack(info,buf,info->rec_buff,block_info.rec_len) !=
+      MY_FILE_ERROR)
+    DBUG_RETURN(0);
+  DBUG_RETURN(my_errno);			/* Wrong record */
+
+panic:
+  my_errno=HA_ERR_WRONG_IN_RECORD;		/* Something is fatal wrong */
+err:
+  save_errno=my_errno;
+  (void) _mi_writeinfo(info,0);
+  DBUG_RETURN(my_errno=save_errno);
+}
+
+
+	/* Read and process header from a dynamic-record-file */
+
+uint _mi_get_block_info(MI_BLOCK_INFO *info, File file, my_off_t filepos)
+{
+  uint return_val=0;
+  uchar *header=info->header;
+
+  if (file >= 0)
+  {
+    /*
+      We do not use mysql_file_pread() here because we want to have the file
+      pointer set to the end of the header after this function.
+      mysql_file_pread() may leave the file pointer untouched.
+    */
+    mysql_file_seek(file, filepos, MY_SEEK_SET, MYF(0));
+    if (mysql_file_read(file, header, sizeof(info->header), MYF(0)) !=
+	sizeof(info->header))
+      goto err;
+  }
+  DBUG_DUMP("header",header,MI_BLOCK_INFO_HEADER_LENGTH);
+  if (info->second_read)
+  {
+    if (info->header[0] <= 6 || info->header[0] == 13)
+      return_val=BLOCK_SYNC_ERROR;
+  }
+  else
+  {
+    if (info->header[0] > 6 && info->header[0] != 13)
+      return_val=BLOCK_SYNC_ERROR;
+  }
+  info->next_filepos= HA_OFFSET_ERROR; /* Dummy if no next block */
+
+  switch (info->header[0]) {
+  case 0:
+    if ((info->block_len=(uint) mi_uint3korr(header+1)) <
+	MI_MIN_BLOCK_LENGTH ||
+	(info->block_len & (MI_DYN_ALIGN_SIZE -1)))
+      goto err;
+    info->filepos=filepos;
+    info->next_filepos=mi_sizekorr(header+4);
+    info->prev_filepos=mi_sizekorr(header+12);
+#if SIZEOF_OFF_T == 4
+    if ((mi_uint4korr(header+4) != 0 &&
+	 (mi_uint4korr(header+4) != (ulong) ~0 ||
+	  info->next_filepos != (ulong) ~0)) ||
+	(mi_uint4korr(header+12) != 0 &&
+	 (mi_uint4korr(header+12) != (ulong) ~0 ||
+	  info->prev_filepos != (ulong) ~0)))
+      goto err;
+#endif
+    return return_val | BLOCK_DELETED;		/* Deleted block */
+
+  case 1:
+    info->rec_len=info->data_len=info->block_len=mi_uint2korr(header+1);
+    info->filepos=filepos+3;
+    return return_val | BLOCK_FIRST | BLOCK_LAST;
+  case 2:
+    info->rec_len=info->data_len=info->block_len=mi_uint3korr(header+1);
+    info->filepos=filepos+4;
+    return return_val | BLOCK_FIRST | BLOCK_LAST;
+
+  case 13:
+    info->rec_len=mi_uint4korr(header+1);
+    info->block_len=info->data_len=mi_uint3korr(header+5);
+    info->next_filepos=mi_sizekorr(header+8);
+    info->second_read=1;
+    info->filepos=filepos+16;
+    return return_val | BLOCK_FIRST;
+
+  case 3:
+    info->rec_len=info->data_len=mi_uint2korr(header+1);
+    info->block_len=info->rec_len+ (uint) header[3];
+    info->filepos=filepos+4;
+    return return_val | BLOCK_FIRST | BLOCK_LAST;
+  case 4:
+    info->rec_len=info->data_len=mi_uint3korr(header+1);
+    info->block_len=info->rec_len+ (uint) header[4];
+    info->filepos=filepos+5;
+    return return_val | BLOCK_FIRST | BLOCK_LAST;
+
+  case 5:
+    info->rec_len=mi_uint2korr(header+1);
+    info->block_len=info->data_len=mi_uint2korr(header+3);
+    info->next_filepos=mi_sizekorr(header+5);
+    info->second_read=1;
+    info->filepos=filepos+13;
+    return return_val | BLOCK_FIRST;
+  case 6:
+    info->rec_len=mi_uint3korr(header+1);
+    info->block_len=info->data_len=mi_uint3korr(header+4);
+    info->next_filepos=mi_sizekorr(header+7);
+    info->second_read=1;
+    info->filepos=filepos+15;
+    return return_val | BLOCK_FIRST;
+
+    /* The following blocks are identical to 1-6 without rec_len */
+  case 7:
+    info->data_len=info->block_len=mi_uint2korr(header+1);
+    info->filepos=filepos+3;
+    return return_val | BLOCK_LAST;
+  case 8:
+    info->data_len=info->block_len=mi_uint3korr(header+1);
+    info->filepos=filepos+4;
+    return return_val | BLOCK_LAST;
+
+  case 9:
+    info->data_len=mi_uint2korr(header+1);
+    info->block_len=info->data_len+ (uint) header[3];
+    info->filepos=filepos+4;
+    return return_val | BLOCK_LAST;
+  case 10:
+    info->data_len=mi_uint3korr(header+1);
+    info->block_len=info->data_len+ (uint) header[4];
+    info->filepos=filepos+5;
+    return return_val | BLOCK_LAST;
+
+  case 11:
+    info->data_len=info->block_len=mi_uint2korr(header+1);
+    info->next_filepos=mi_sizekorr(header+3);
+    info->second_read=1;
+    info->filepos=filepos+11;
+    return return_val;
+  case 12:
+    info->data_len=info->block_len=mi_uint3korr(header+1);
+    info->next_filepos=mi_sizekorr(header+4);
+    info->second_read=1;
+    info->filepos=filepos+12;
+    return return_val;
+  }
+
+err:
+  my_errno=HA_ERR_WRONG_IN_RECORD;	 /* Garbage */
+  return BLOCK_ERROR;
+}