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    Length: 10960 (0x2ad0)
    Types: TextFile
    Names: »falloc.c«

└─⟦a05ed705a⟧ Bits:30007078 DKUUG GNU 2/12/89
    └─⟦847972ed9⟧ »./gdbm0.9.tar.Z« 
        └─⟦e41d67701⟧ 
            └─⟦this⟧ »gdbm/falloc.c« 

TextFile

/* falloc.c - The file space management routines for dbm. */

/*  GNU DBM  - DataBase Manager (database subroutines) by Philip A. Nelson
    Copyright (C) 1989  Free Software Foundation, Inc.

    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.

    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., 675 Mass Ave, Cambridge, MA 02139, USA.

    You may contact the author by:
       e-mail:  phil@wwu.edu
      us-mail:  Philip A. Nelson
                Computer Science Department
                Western Washington University
                Bellingham, WA 98226
        phone:  (206) 676-3035
       
*************************************************************************/

#include <stdio.h>
#include <sys/types.h>
#include <sys/file.h>
#include <sys/stat.h>
#include "gdbmdefs.h"
#include "systems.h"


static avail_elem get_elem();	/* Get avail_elems from a list. */
static avail_elem get_block();
static push_avail_block();
static pop_avail_block();
static adjust_bucket_avail();

/* Allocate space in the file DBF for a block NUM_BYTES in length.  Return
   the file address of the start of the block.  Allocation is done on a
   first fit basis from the entries in the file header avail block.  If 
   nothing is there that has enough space, another block at the end of the
   file is allocated and the unused portion is returned to the avail block.
   This routine "guarantees" that an allocation does not cross a block
   boundary unless the size is larger than a single block.
   The avail structure is changed by this routine if a  change is needed.
   If an error occurs, the value of 0 will be returned.  */

int
_gdbm_alloc (dbf, num_bytes)
     gdbm_file_info *dbf;
     int num_bytes;
{
  int file_adr;			/* The address of the block. */
  int temp;			/* For temporary storage.  */
  avail_elem av_el;		/* For temporary use. */

  /* The current bucket is the first place to look for space. */
  av_el = get_elem (num_bytes, dbf->bucket->bucket_avail,
		    &dbf->bucket->av_count);

  /* If we did not find some space, we have more work to do. */
  if (av_el.av_size == 0)
    {
     /* Is the header avail block empty and there is something on the stack. */
      if (dbf->header->avail.count == 0 && dbf->header->avail.next_block != 0)
	pop_avail_block (dbf);
      
      /* Get another full block from end of file. */
      av_el = get_block (num_bytes, dbf);

      dbf->header_changed = TRUE;
    }

  /* We now have the place from which we will allocate the new space. */
  file_adr = av_el.av_adr;

  /* Put the unused space back in the avail block. */
  av_el.av_adr += num_bytes;
  av_el.av_size -= num_bytes;
  _gdbm_free (dbf, av_el.av_adr, av_el.av_size);

  /* Return the address. */
  return file_adr;
  
}



/* Free space of size NUM_BYTES in the file DBF at file address FILE_ADR.  Make
   it avaliable for reuse through _gdbm_alloc.  This routine changes the
   avail structure.  The value TRUE is returned if there were errors.  If no
   errors occured, the value FALSE is returned. */

_gdbm_free (dbf, file_adr, num_bytes)
     gdbm_file_info *dbf;
     int file_adr;
     int num_bytes;
{
  avail_elem temp;
  avail_elem temp1;
  

  /* Is it too small to worry about? */
  if (num_bytes <= IGNORE_SIZE)
    return;

  /* Initialize the avail element. */
  temp.av_size = num_bytes;
  temp.av_adr = file_adr;

  /* Is the freed space large or small? */
  if (num_bytes >= dbf->header->block_size)
    {
      _gdbm_put_av_elem (temp, dbf->header->avail.av_table,
			 &dbf->header->avail.count);
      dbf->header_changed = TRUE;
    }
  else
    {
      /* Try to put into the current bucket. */
      if (dbf->bucket->av_count < BUCKET_AVAIL)
	_gdbm_put_av_elem (temp, dbf->bucket->bucket_avail,
			   &dbf->bucket->av_count);
      else
	{
	  _gdbm_put_av_elem (temp, dbf->header->avail.av_table,
			     &dbf->header->avail.count);
	  dbf->header_changed = TRUE;
	}
    }

  if (dbf->header_changed)
    adjust_bucket_avail (dbf);

  /* All work is done. */
  return;
}




/* The following are all utility routines needed by the previous two. */


/* Gets the avail block at the top of the stack and loads it into the
   active avail block.  It does a "free" for itself! */

static
pop_avail_block (dbf)
     gdbm_file_info *dbf;
{
  int num_bytes;		/* For reading. */
  avail_elem temp;

  /* Set up variables. */
  temp.av_adr = dbf->header->avail.next_block;
  temp.av_size = (dbf->header->avail.size * sizeof(avail_elem)) >> 1
                 + sizeof(avail_block);

  /* Read the block. */
  num_bytes = lseek (dbf->desc, temp.av_adr, L_SET);
  if (num_bytes != temp.av_adr)  _gdbm_fatal(dbf, "lseek error");
  num_bytes = read (dbf->desc, &dbf->header->avail, temp.av_size);
  if (num_bytes != temp.av_size) _gdbm_fatal(dbf, "read error");

  /* We changed the header. */
  dbf->header_changed = TRUE;

  /* Free the previous avail block. */
  _gdbm_put_av_elem (temp, dbf->header->avail.av_table,
		     &dbf->header->avail.count);
}


/* Splits the header avail block and pushes on onto the stack. */

static
push_avail_block (dbf, up_adr, up_size)
     gdbm_file_info *dbf;
     int up_adr;
     int up_size;
{
  int num_bytes;
  int av_size;
  int av_adr;
  int index;
  avail_block *temp;
  avail_elem  new_loc;
 

  /* Caclulate the size of the split block. */
  av_size = ((dbf->header->avail.size * sizeof(avail_elem)) >> 1)
            + sizeof(avail_block);

  /* Get address in file for new av_size bytes. */
  new_loc = get_elem (av_size, dbf->header->avail.av_table,
		      &dbf->header->avail.count);
  if (new_loc.av_size == 0)
    new_loc = get_block (av_size, dbf);
  av_adr = new_loc.av_adr;


  /* Split the header block. */
  temp = (avail_block *) alloca (av_size);
  temp->size = dbf->header->avail.size;
  temp->count = 0;
  temp->next_block = dbf->header->avail.next_block;
  for (index = 1; index < dbf->header->avail.count; index++)
    if ((index & 0x1) == 1 )	/* Index is odd. */
      temp->av_table[temp->count++] = dbf->header->avail.av_table[index];
    else
      dbf->header->avail.av_table[index>>1] =
	dbf->header->avail.av_table[index];


  /* Free the unneeded space. */
  new_loc.av_adr += av_size;
  new_loc.av_size -= av_size;
  _gdbm_free (dbf, new_loc.av_adr, new_loc.av_size);

  /* To reduce I/O, add the UPDATE STUFF HERE. */
/*      dbf->header->upd_param1 = up_adr;
        dbf->header->upd_param2 = up_size; */

  /* Update the disk. */
  num_bytes = lseek (dbf->desc, av_adr, L_SET);
  if (num_bytes != av_adr) _gdbm_fatal(dbf, "lseek error");
  num_bytes = write (dbf->desc, temp, av_size);
  if (num_bytes != av_size) _gdbm_fatal(dbf, "write error");

}



/* Get_elem returns an elements in the AV_TABLE block which is
   larger than SIZE.  It extracts that element from the AVAIL_ELEM block
   and keeps track of that extraction.  If no block is found larger than
   SIZE, find_size returns a size of zero.  This routine does no I/O. */

static avail_elem
get_elem (size, av_table, av_count)
     int size;
     avail_elem av_table[];
     int *av_count;
{
  int index;			/* For searching through the avail block. */
  avail_elem val;		/* The default return value. */

  /* Initialize default return value. */
  val.av_adr = 0;
  val.av_size = 0;

  /* Search for element.  List is sorted by size. */
  index = 0;
  while ( index < *av_count && av_table[index].av_size < size)
    {
      index++;
    }

  /* Did we find one of the right size? */
  if (index >= *av_count)
    return val;

  /* Ok, save that element and move all others up one. */
  val = av_table[index];
  *av_count -= 1;
  while (index < *av_count)
    {
      av_table[index] = av_table[index+1];
      index++;
    }

  return val;
}


/* This routine inserts a single NEW_EL into the AV_TABLE block in
   sorted order. This routine does no I/O. */

_gdbm_put_av_elem (new_el, av_table, av_count)
     avail_elem new_el;
     avail_elem av_table[];
     int *av_count;
{
  int index;			/* For searching through the avail block. */
  int index1;

  /* Is it too small to deal with? */
  if (new_el.av_size <= IGNORE_SIZE)
    return FALSE; 

  /* Search for place to put element.  List is sorted by size. */
  index = 0;
  while ( index < *av_count && av_table[index].av_size < new_el.av_size)
    {
      index++;
    }

  /* Move all others up one. */
  index1 = *av_count-1;
  while (index1 >= index)
    {
      av_table[index1+1] = av_table[index1];
      index1--;
    }
  
  /* Add the new element. */
  av_table[index] = new_el;

  /* Increment the number of elements. */
  *av_count += 1;  

  return TRUE;
}



/* Get_block "allocates" new file space and the end of the file.  This is
   done in integral block sizes.  (This helps insure that data smaller than
   one block size is in a single block.)  Enough blocks are allocated to
   make sure the allocated number of blocks is larger than SIZE.  DBF 
   contains the file header that needs updating.  This routine does no I/O.  */

static avail_elem
get_block (size, dbf)
     int size;
     gdbm_file_info *dbf;
{
  avail_elem val;

  /* Need at least one block. */
  val.av_adr  = dbf->header->next_block;
  val.av_size = dbf->header->block_size;

  /* Get enough blocks to fit the need. */
  while (val.av_size < size)
    val.av_size += dbf->header->block_size;

  /* Update the header and return. */
  dbf->header->next_block += val.av_size;

  /* We changed the header. */
  dbf->header_changed = TRUE;

  return val;
  
}


/*  When the header already needs writing, we can make sure the current
    bucket has its avail block as close to 1/2 full as possible. */
static
adjust_bucket_avail (dbf)
     gdbm_file_info *dbf;
{
  int third = BUCKET_AVAIL / 3;
  avail_elem av_el;

  /* Can we add more entries to the bucket? */
  if (dbf->bucket->av_count < third)
    {
      if (dbf->header->avail.count > 0)
	{
	  dbf->header->avail.count -= 1;
	  av_el = dbf->header->avail.av_table[dbf->header->avail.count];
	  _gdbm_put_av_elem (av_el, dbf->bucket->bucket_avail,
			     &dbf->bucket->av_count);
	  dbf->bucket_changed = TRUE;
	}
      return;
    }

  /* Is there too much in the bucket? */
  while (dbf->bucket->av_count > BUCKET_AVAIL-third
	 & dbf->header->avail.count < dbf->header->avail.size)
    {
      av_el = get_elem (0, dbf->bucket->bucket_avail, &dbf->bucket->av_count);
      _gdbm_put_av_elem (av_el, dbf->header->avail.av_table,
			 &dbf->header->avail.count);
      dbf->bucket_changed = TRUE;
    }
}