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path: root/src/bucket.c
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/* bucket.c - The routines for playing with hash buckets. */

/* This file is part of GDBM, the GNU data base manager.
   Copyright (C) 1990-2021 Free Software Foundation, Inc.

   GDBM 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 3, or (at your option)
   any later version.

   GDBM 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 GDBM. If not, see <http://www.gnu.org/licenses/>.   */

#include "autoconf.h"
#include "gdbmdefs.h"
#include <limits.h>

#define GDBM_MAX_DIR_SIZE INT_MAX
#define GDBM_MAX_DIR_HALF (GDBM_MAX_DIR_SIZE / 2)

/* Initializing a new hash buckets sets all bucket entries to -1 hash value. */
void
_gdbm_new_bucket (GDBM_FILE dbf, hash_bucket *bucket, int bits)
{
  int index;

  /* Initialize the avail block. */
  bucket->av_count = 0;

  /* Set the information fields first. */
  bucket->bucket_bits = bits;
  bucket->count = 0;
  
  /* Initialize all bucket elements. */
  for (index = 0; index < dbf->header->bucket_elems; index++)
    bucket->h_table[index].hash_value = -1;
}

/* Return true if the directory entry at DIR_INDEX can be considered
   valid. This means that DIR_INDEX is in the valid range for addressing
   the dir array, and the offset stored in dir[DIR_INDEX] points past
   first two blocks in file. This does not necessarily mean that there's
   a valid bucket or data block at that offset. All this implies is that
   it is safe to use the offset for look up in the bucket cache and to
   attempt to read a block at that offset. */
int
gdbm_dir_entry_valid_p (GDBM_FILE dbf, int dir_index)
{
  return dir_index >= 0
         && dir_index < GDBM_DIR_COUNT (dbf)
         && dbf->dir[dir_index] >= dbf->header->block_size;
}

static void
set_cache_entry (GDBM_FILE dbf, cache_elem *elem)
{
  dbf->cache_entry = elem;
  dbf->bucket = dbf->cache_entry->ca_bucket;
}


/* LRU list management */

/* Link ELEM after REF in DBF cache.  If REF is NULL, link at head */
static void
lru_link_elem (GDBM_FILE dbf, cache_elem *elem, cache_elem *ref)
{
  if (!ref)
    {
      elem->ca_prev = NULL;
      elem->ca_next = dbf->cache_mru;
      if (dbf->cache_mru)
	dbf->cache_mru->ca_prev = elem;
      else
	dbf->cache_lru = elem;
      dbf->cache_mru = elem;
    }
  else
    {
      cache_elem *x;

      elem->ca_prev = ref;
      elem->ca_next = ref->ca_next;
      if ((x = ref->ca_next))
	x->ca_prev = elem;
      else
	dbf->cache_lru = elem;
      ref->ca_next = elem;
    }
}

/* Unlink ELEM from the list of cache elements in DBF. */
static void
lru_unlink_elem (GDBM_FILE dbf, cache_elem *elem)
{
  cache_elem *x;

  if ((x = elem->ca_prev))
    x->ca_next = elem->ca_next;
  else
    dbf->cache_mru = elem->ca_next;
  if ((x = elem->ca_next))
    x->ca_prev = elem->ca_prev;
  else
    dbf->cache_lru = elem->ca_prev;
  elem->ca_prev = elem->ca_next = NULL;
}

enum
  {
    elem_failure = -1,
    elem_new,
    elem_found
  };

static int
cache_idx_lookup (GDBM_FILE dbf, off_t adr, size_t *idx)
{
  if (dbf->cache_num == 0)
    {
      *idx = 0;
    }
  else
    {
      size_t l, r, m;
  
      l = 0;
      r = dbf->cache_num;
  
      while (l < r)
	{
	  m = (l + r) / 2;
	  if (dbf->cache_idx[m].elem->ca_adr < adr)
	    l = m + 1;
	  else
	    r = m;
	}

      *idx = l;
      if (l < dbf->cache_num && dbf->cache_idx[l].elem->ca_adr == adr)
	return elem_found;
    }
  return elem_new;
}

/* Frees element ELEM.  Unlinks it from the cache tree and LRU list. */
static void
cache_elem_free (GDBM_FILE dbf, cache_elem *elem)
{
  size_t n;

  if (cache_idx_lookup (dbf, elem->ca_adr, &n) != elem_found)
    abort (); //FIXME
  memmove (&dbf->cache_idx[n], &dbf->cache_idx[n + 1],
	   (dbf->cache_num - n - 1) * sizeof (dbf->cache_idx[0]));

  lru_unlink_elem (dbf, elem);
  elem->ca_next = dbf->cache_avail;
  dbf->cache_avail = elem;
  dbf->cache_num--;
}

/* Free the least recently used cache entry. */
static inline int
cache_lru_free (GDBM_FILE dbf)
{
  cache_elem *last = dbf->cache_lru;
  
  if (last->ca_changed)
    {
      if (_gdbm_write_bucket (dbf, last))
	return -1;
    }
  cache_elem_free (dbf, last);
  return 0;
}
  
static int
cache_lookup (GDBM_FILE dbf, off_t adr, cache_elem *ref, cache_elem **ret_elem)
{
  int rc;
  size_t n;
  cache_elem *elem;
  int retrying = 0;
  
  dbf->cache_access_count++;
  rc = cache_idx_lookup (dbf, adr, &n);
  switch (rc)
    {
    case elem_found:
      elem = dbf->cache_idx[n].elem;
      elem->ca_hits++;
      lru_unlink_elem (dbf, elem);
      break;
      
    case elem_new:
      if (!dbf->cache_avail)
	{
	  if (dbf->cache_lru->ca_adr < adr)
	    n--;
	  if (cache_lru_free (dbf))
	    return elem_failure;
	}
      elem = dbf->cache_avail;

      if (elem->ca_bucket == NULL)
	{
	  if ((elem->ca_bucket = calloc (1, dbf->header->bucket_size)) == NULL)
	    return elem_failure;
	}
      dbf->cache_avail = elem->ca_next;
      
      if (n < dbf->cache_num)
	memmove (&dbf->cache_idx[n + 1], &dbf->cache_idx[n],
		 (dbf->cache_num - n) * sizeof (dbf->cache_idx[0]));
      else if (n == dbf->cache_size)
	n--;

      dbf->cache_idx[n].elem = elem;

      elem->ca_adr = adr;
      elem->ca_changed = FALSE;
      elem->ca_data.hash_val = -1;
      elem->ca_data.elem_loc = -1;

      elem->ca_prev = elem->ca_next = NULL;
      elem->ca_hits = 0;
  
      dbf->cache_num++;
      
      break;

    default:
      abort ();
    }
  
  lru_link_elem (dbf, elem, ref);
  *ret_elem = elem;
  return rc;
}

/* Find a bucket for DBF that is pointed to by the bucket directory from
   location DIR_INDEX.   The bucket cache is first checked to see if it
   is already in memory.  If not, a bucket may be tossed to read the new
   bucket.  On success, the requested bucket becomes the "current" bucket
   and dbf->bucket points to the correct bucket. On error, the current
   bucket remains unchanged. */

int
_gdbm_get_bucket (GDBM_FILE dbf, int dir_index)
{
  int rc;
  off_t bucket_adr;	/* The address of the correct hash bucket.  */
  off_t	file_pos;	/* The return address for lseek. */
  hash_bucket *bucket;
  cache_elem *elem;
  
  if (!gdbm_dir_entry_valid_p (dbf, dir_index))
    {
      /* FIXME: negative caching? */
      GDBM_SET_ERRNO (dbf, GDBM_BAD_DIR_ENTRY, TRUE);
      return -1;
    }
  
  /* Initial set up. */
  dbf->bucket_dir = dir_index;
  bucket_adr = dbf->dir[dir_index];

  switch (cache_lookup (dbf, bucket_adr, NULL, &elem))
    {
    case elem_found:
      break;
      
    case elem_new:
      /* Position the file pointer */
      file_pos = gdbm_file_seek (dbf, bucket_adr, SEEK_SET);
      if (file_pos != bucket_adr)
	{
	  GDBM_SET_ERRNO (dbf, GDBM_FILE_SEEK_ERROR, TRUE);
	  cache_elem_free (dbf, elem);
	  _gdbm_fatal (dbf, _("lseek error"));
	  return -1;
	}

      /* Read the bucket. */
      rc = _gdbm_full_read (dbf, elem->ca_bucket, dbf->header->bucket_size);
      if (rc)
	{
	  GDBM_DEBUG (GDBM_DEBUG_ERR,
		      "%s: error reading bucket: %s",
		      dbf->name, gdbm_db_strerror (dbf));
	  dbf->need_recovery = TRUE;
	  cache_elem_free (dbf, elem);
	  _gdbm_fatal (dbf, gdbm_db_strerror (dbf));
	  return -1;
	}

      /* Validate the bucket */
      bucket = elem->ca_bucket;
      if (!(bucket->count >= 0
	    && bucket->count <= dbf->header->bucket_elems
	    && bucket->bucket_bits >= 0
	    && bucket->bucket_bits <= dbf->header->dir_bits))
	{
	  GDBM_SET_ERRNO (dbf, GDBM_BAD_BUCKET, TRUE);
	  cache_elem_free (dbf, elem);
	  return -1;
	}
      /* Validate bucket_avail table */
      if (gdbm_bucket_avail_table_validate (dbf, bucket))
	{
	  cache_elem_free (dbf, elem);
	  return -1;
	}
      
      /* Update the cache */
      elem->ca_adr = bucket_adr;
      elem->ca_data.elem_loc = -1;
      elem->ca_changed = FALSE;
      
      break;
      
    case elem_failure:
      return -1;
    }
  set_cache_entry (dbf, elem);
  
  return 0;
}

/* Split the current bucket.  This includes moving all items in the bucket to
   a new bucket.  This doesn't require any disk reads because all hash values
   are stored in the buckets.  Splitting the current bucket may require
   doubling the size of the hash directory.  */
int
_gdbm_split_bucket (GDBM_FILE dbf, int next_insert)
{
  off_t        old_adr[GDBM_HASH_BITS];  /* Address of the old directories. */
  int          old_size[GDBM_HASH_BITS]; /* Size of the old directories. */
  int	       old_count;	/* Number of old directories. */

  int          index;		/* Used in array indexing. */
  int          index1;		/* Used in array indexing. */
  
  /* No directories are yet old. */
  old_count = 0;
  while (dbf->bucket->count == dbf->header->bucket_elems)
    {
      int          new_bits;	/* The number of bits for the new buckets. */
      cache_elem  *newcache[2]; /* Location in the cache for the buckets. */
      off_t        adr_0;	/* File address of the new bucket 0. */
      off_t        adr_1;	/* File address of the new bucket 1. */
      avail_elem   old_bucket;	/* Avail Struct for the old bucket. */
      
      off_t        dir_start0;	/* Used in updating the directory. */
      off_t        dir_start1;
      off_t        dir_end;

      new_bits = dbf->bucket->bucket_bits + 1;
      /* Allocate two new buckets */
      adr_0 = _gdbm_alloc (dbf, dbf->header->bucket_size);
      switch (cache_lookup (dbf, adr_0, dbf->cache_mru, &newcache[0]))
	{
	case elem_new:
	  break;

	case elem_found:
	  /* should not happen */
	  GDBM_DEBUG (GDBM_DEBUG_ERR,
		      "%s: bucket found where it should not",
		      dbf->name);
	  GDBM_SET_ERRNO (dbf, GDBM_BUCKET_CACHE_CORRUPTED, TRUE);
	  return -1;

	case elem_failure:
	  return -1;
	}
      _gdbm_new_bucket (dbf, newcache[0]->ca_bucket, new_bits);

      adr_1 = _gdbm_alloc (dbf, dbf->header->bucket_size);
      switch (cache_lookup (dbf, adr_1, newcache[0], &newcache[1]))
	{
	case elem_new:
	  break;

	case elem_found:
	  /* should not happen */
	  GDBM_DEBUG (GDBM_DEBUG_ERR,
		      "%s: bucket found where it should not",
		      dbf->name);
	  GDBM_SET_ERRNO (dbf, GDBM_BUCKET_CACHE_CORRUPTED, TRUE);
	  return -1;

	case elem_failure:
	  return -1;
	}
      _gdbm_new_bucket (dbf, newcache[1]->ca_bucket, new_bits);

      /* Double the directory size if necessary. */
      if (dbf->header->dir_bits == dbf->bucket->bucket_bits)
	{
	  off_t       *new_dir;		/* Pointer to the new directory. */
	  int          dir_size;	/* Size of the new directory. */
	  off_t        dir_adr; 	/* Address of the new directory. */
	  
	  if (dbf->header->dir_size >= GDBM_MAX_DIR_HALF)
	    {
	      GDBM_SET_ERRNO (dbf, GDBM_DIR_OVERFLOW, TRUE);
	      _gdbm_fatal (dbf, _("directory overflow"));
	      return -1;
	    }
	  dir_size = dbf->header->dir_size * 2;
	  dir_adr  = _gdbm_alloc (dbf, dir_size);
	  if (dir_adr == 0)
	    return -1;
	  new_dir = malloc (dir_size);
	  if (new_dir == NULL)
	    {
	      GDBM_SET_ERRNO (dbf, GDBM_MALLOC_ERROR, TRUE);
	      _gdbm_fatal (dbf, _("malloc error"));
	      return -1;
	    }

	  for (index = 0; index < GDBM_DIR_COUNT (dbf); index++)
	    {
	      new_dir[2*index]   = dbf->dir[index];
	      new_dir[2*index+1] = dbf->dir[index];
	    }
	  
	  /* Update header. */
	  old_adr[old_count] = dbf->header->dir;
	  dbf->header->dir = dir_adr;
	  old_size[old_count] = dbf->header->dir_size;
	  dbf->header->dir_size = dir_size;
	  dbf->header->dir_bits = new_bits;
	  old_count++;
	  
	  /* Now update dbf.  */
	  dbf->header_changed = TRUE;
	  dbf->bucket_dir *= 2;
	  free (dbf->dir);
	  dbf->dir = new_dir;
	}

      /* Copy all elements in dbf->bucket into the new buckets. */
      for (index = 0; index < dbf->header->bucket_elems; index++)
	{
	  bucket_element *old_el = &dbf->bucket->h_table[index];
	  hash_bucket *bucket =
	    newcache[(old_el->hash_value >> (GDBM_HASH_BITS - new_bits)) & 1]->ca_bucket;
	  int elem_loc = old_el->hash_value % dbf->header->bucket_elems;
	  while (bucket->h_table[elem_loc].hash_value != -1)
	    elem_loc = (elem_loc + 1) % dbf->header->bucket_elems;
	  bucket->h_table[elem_loc] = *old_el;
	  bucket->count++;
	}
      
      /* Allocate avail space for the newcache[1]->ca_bucket. */
      newcache[1]->ca_bucket->bucket_avail[0].av_adr
	= _gdbm_alloc (dbf, dbf->header->block_size);
      if (newcache[1]->ca_bucket->bucket_avail[0].av_adr == 0)
	return -1;
      newcache[1]->ca_bucket->bucket_avail[0].av_size
	= dbf->header->block_size;
      newcache[1]->ca_bucket->av_count = 1;
      
      /* Copy the avail elements in dbf->bucket to newcache[0]->ca_bucket. */
      newcache[0]->ca_bucket->av_count = dbf->bucket->av_count;
      index = 0;
      if (newcache[0]->ca_bucket->av_count == BUCKET_AVAIL)
	{
	  /* The avail is full, move the first one to newcache[1]->ca_bucket.*/
	  _gdbm_put_av_elem (dbf->bucket->bucket_avail[0],
			     newcache[1]->ca_bucket->bucket_avail,
			     &newcache[1]->ca_bucket->av_count, 
                             dbf->coalesce_blocks);
	  index = 1;
	  newcache[0]->ca_bucket->av_count--;
	}

      index1 = 0;
      for (; index < dbf->bucket->av_count; index++)
	{
	  newcache[0]->ca_bucket->bucket_avail[index1++]
	    = dbf->bucket->bucket_avail[index];
	}
      
      /* Update the directory.  We have new file addresses for both buckets. */
      dir_start1 = (dbf->bucket_dir >> (dbf->header->dir_bits - new_bits)) | 1;
      dir_end = (dir_start1 + 1) << (dbf->header->dir_bits - new_bits);
      dir_start1 = dir_start1 << (dbf->header->dir_bits - new_bits);
      dir_start0 = dir_start1 - (dir_end - dir_start1);
      for (index = dir_start0; index < dir_start1; index++)
	dbf->dir[index] = adr_0;
      for (index = dir_start1; index < dir_end; index++)
	dbf->dir[index] = adr_1;
      
      /* Set changed flags. */
      newcache[0]->ca_changed = TRUE;
      newcache[1]->ca_changed = TRUE;
      dbf->bucket_changed = TRUE;
      dbf->directory_changed = TRUE;
      dbf->second_changed = TRUE;
      
      /* Update the cache! */
      dbf->bucket_dir = _gdbm_bucket_dir (dbf, next_insert);
      
      /* Invalidate old cache entry. */
      old_bucket.av_adr  = dbf->cache_entry->ca_adr;
      old_bucket.av_size = dbf->header->bucket_size;
      cache_elem_free (dbf, dbf->cache_entry);
      
      /* Set dbf->bucket to the proper bucket. */
      if (dbf->dir[dbf->bucket_dir] != adr_0)
	{
	  cache_elem *t = newcache[0];
	  newcache[0] = newcache[1];
	  newcache[1] = t;
	}

      _gdbm_put_av_elem (old_bucket,
			 newcache[1]->ca_bucket->bucket_avail,
			 &newcache[1]->ca_bucket->av_count, 
			 dbf->coalesce_blocks);
      lru_unlink_elem (dbf, newcache[0]);
      lru_link_elem (dbf, newcache[0], NULL);
      set_cache_entry (dbf, newcache[0]);
    }

  /* Get rid of old directories. */
  for (index = 0; index < old_count; index++)
    if (_gdbm_free (dbf, old_adr[index], old_size[index]))
      return -1;

  return 0;
}


/* The only place where a bucket is written.  CA_ENTRY is the
   cache entry containing the bucket to be written. */

int
_gdbm_write_bucket (GDBM_FILE dbf, cache_elem *ca_entry)
{
  int rc;
  off_t file_pos;	/* The return value for lseek. */

  file_pos = gdbm_file_seek (dbf, ca_entry->ca_adr, SEEK_SET);
  if (file_pos != ca_entry->ca_adr)
    {
      GDBM_SET_ERRNO (dbf, GDBM_FILE_SEEK_ERROR, TRUE);
      _gdbm_fatal (dbf, _("lseek error"));
      return -1;
    }
  rc = _gdbm_full_write (dbf, ca_entry->ca_bucket, dbf->header->bucket_size);
  if (rc)
    {
      GDBM_DEBUG (GDBM_DEBUG_STORE|GDBM_DEBUG_ERR,
		  "%s: error writing bucket: %s",
		  dbf->name, gdbm_db_strerror (dbf));	  
      _gdbm_fatal (dbf, gdbm_strerror (rc));
      return -1;
    }

  ca_entry->ca_changed = FALSE;
  ca_entry->ca_data.hash_val = -1;
  ca_entry->ca_data.elem_loc = -1;
  return 0;
}

/* Cache manipulation functions. */

/* Initialize the bucket cache. */
int
_gdbm_cache_init (GDBM_FILE dbf, size_t size)
{
  size_t i;
  
  if (size == 0)
    size = 1;

  if (dbf->cache_size)
    {
      _gdbm_cache_flush (dbf);
      _gdbm_cache_free (dbf);
    }
  
  dbf->cache_storage = calloc (size, sizeof (dbf->cache_storage[0]));
  if (!dbf->cache_storage)
    return -1;
  dbf->cache_avail = &dbf->cache_storage[0];
  for (i = 0; i < size - 1; i++)
    dbf->cache_storage[i].ca_next = &dbf->cache_storage[i+1];
  dbf->cache_storage[i].ca_next = NULL;
  
  dbf->cache_idx = calloc (size, sizeof (dbf->cache_idx[0]));
  if (!dbf->cache_idx)
    {
      free (dbf->cache_storage);
      dbf->cache_storage = NULL;
      dbf->cache_avail = NULL;
      return -1;
    }
  
  dbf->cache_size = size;

  return 0;
}

/* Free the bucket cache */
void
_gdbm_cache_free (GDBM_FILE dbf)
{
  size_t i;
  
  for (i = 0; i < dbf->cache_size; i++)
    {
      free (dbf->cache_storage[i].ca_data.dptr);
      free (dbf->cache_storage[i].ca_bucket);
    }
  free (dbf->cache_storage);
  free (dbf->cache_idx);
}

/* Flush cache content to disk. */
int
_gdbm_cache_flush (GDBM_FILE dbf)
{
  cache_elem *elem;
  for (elem = dbf->cache_lru; elem; elem = elem->ca_prev)
    {
      if (elem->ca_changed)
	{
	  if (_gdbm_write_bucket (dbf, elem))
	    return -1;
	}
    }
  return 0;
}

int
_gdbm_fetch_data (GDBM_FILE dbf, off_t off, size_t size, void *buf)
{
  off_t bucket_adr;
  off_t file_pos;
  int rc;
  cache_elem *elem;
  char *dst = buf;

  bucket_adr = (off / dbf->header->bucket_size)
                 * dbf->header->bucket_size;
  off -= bucket_adr;
  while (size)
    {
      size_t nbytes;
      
      switch (cache_lookup (dbf, bucket_adr, dbf->cache_mru, &elem))
	{
	case elem_found:
	  break;
	  
	case elem_new:
	  /* Position the file pointer */
	  file_pos = gdbm_file_seek (dbf, bucket_adr, SEEK_SET);
	  if (file_pos != bucket_adr)
	    {
	      GDBM_SET_ERRNO (dbf, GDBM_FILE_SEEK_ERROR, TRUE);
	      cache_elem_free (dbf, elem);
	      _gdbm_fatal (dbf, _("lseek error"));
	      return -1;
	    }

	  /* Read the bucket. */
	  rc = _gdbm_full_read (dbf, elem->ca_bucket,
				dbf->header->bucket_size);
	  if (rc)
	    {
	      GDBM_DEBUG (GDBM_DEBUG_ERR,
			  "%s: error reading data bucket: %s",
			  dbf->name, gdbm_db_strerror (dbf));
	      dbf->need_recovery = TRUE;
	      cache_elem_free (dbf, elem);
	      _gdbm_fatal (dbf, gdbm_db_strerror (dbf));
	      return -1;
	    }
	  break;
	  
	case elem_failure:
	  return -1;
	}

      nbytes = dbf->header->bucket_size - off;
      if (nbytes > size)
	nbytes = size;
      memcpy (dst, (char*) elem->ca_bucket + off, nbytes);
      dst += nbytes;
      size -= nbytes;
      bucket_adr++;
      off = 0;
    }
  return 0;
}

void
gdbm_get_cache_stats (GDBM_FILE dbf,
		      size_t *access_count,
		      size_t *cache_count,
		      struct gdbm_cache_stat *bstat,
		      size_t nstat)
{
  if (access_count)
    *access_count = dbf->cache_access_count;
  if (cache_count)
    *cache_count = dbf->cache_num;
  if (bstat)
    {
      size_t i;
      cache_elem *elem;

      if (nstat > dbf->cache_num)
	nstat = dbf->cache_num;
      
      for (i = 0, elem = dbf->cache_mru; i < nstat; i++, elem = elem->ca_next)
	{
	  bstat[i].adr = elem->ca_adr;
	  bstat[i].hits = elem->ca_hits;
	}
    }
}

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