Linux Cross Reference
Linux/fs/hfs/bins_del.c

   /*
    * linux/fs/hfs/bins_del.c
    *
    * Copyright (C) 1995-1997  Paul H. Hargrove
    * This file may be distributed under the terms of the GNU Public License.
    *
    * This file contains the code common to inserting and deleting records
    * in a B-tree.
    *
   * "XXX" in a comment is a note to myself to consider changing something.
   *
   * In function preconditions the term "valid" applied to a pointer to
   * a structure means that the pointer is non-NULL and the structure it
   * points to has all fields initialized to consistent values.
   */
  
  #include "hfs_btree.h"
  
  /*================ File-local functions ================*/
  
  /*
   * hfs_bnode_update_key()
   *
   * Description:
   *   Updates the key for a bnode in its parent.
   *   The key change is propagated up the tree as necessary.
   * Input Variable(s):
   *   struct hfs_brec *brec: the search path to update keys in
   *   struct hfs_belem *belem: the search path element with the changed key
   *   struct hfs_bnode *bnode: the bnode with the changed key
   *   int offset: the "distance" from 'belem->bn' to 'bnode':
   *    0 if the change is in 'belem->bn',
   *    1 if the change is in its right sibling, etc.
   * Output Variable(s):
   *   NONE
   * Returns:
   *   void
   * Preconditions:
   *   'brec' points to a valid (struct hfs_brec)
   *   'belem' points to a valid (struct hfs_belem) in 'brec'.
   *   'bnode' points to a valid (struct hfs_bnode) which is non-empty
   *    and is 'belem->bn' or one of its siblings.
   *   'offset' is as described above.
   * Postconditions:
   *   The key change is propagated up the tree as necessary.
   */
  void hfs_bnode_update_key(struct hfs_brec *brec, struct hfs_belem *belem,
                            struct hfs_bnode *bnode, int offset)
  {
          int record = (--belem)->record + offset;
          void *key = bnode_datastart(bnode) + 1;
          int keysize = brec->tree->bthKeyLen;
          struct hfs_belem *limit;
  
          memcpy(1+bnode_key(belem->bnr.bn, record), key, keysize);
  
          /* don't trash the header */
          if (brec->top > &brec->elem[1]) {
                  limit = brec->top;
          } else {
                  limit = &brec->elem[1];
          }
  
          while ((belem > limit) && (record == 1)) {
                  record = (--belem)->record;
                  memcpy(1+belem_key(belem), key, keysize);
          }
  }
  
  /*
   * hfs_bnode_shift_right()
   *
   * Description:
   *   Shifts some records from a node to its right neighbor.
   * Input Variable(s):
   *   struct hfs_bnode* left: the node to shift records from
   *   struct hfs_bnode* right: the node to shift records to
   *   hfs_u16 first: the number of the first record in 'left' to move to 'right'
   * Output Variable(s):
   *   NONE
   * Returns:
   *   void
   * Preconditions:
   *   'left' and 'right' point to valid (struct hfs_bnode)s.
   *   'left' contains at least 'first' records.
   *   'right' has enough free space to hold the records to be moved from 'left'
   * Postconditions:
   *   The record numbered 'first' and all records after it in 'left' are
   *   placed at the beginning of 'right'.
   *   The key corresponding to 'right' in its parent is NOT updated.
   */
  void hfs_bnode_shift_right(struct hfs_bnode *left, struct hfs_bnode *right,
                             int first)
  {
          int i, adjust, nrecs;
          unsigned size;
          hfs_u16 *to, *from;
  
          if ((first <= 0) || (first > left->ndNRecs)) {
                 hfs_warn("bad argument to shift_right: first=%d, nrecs=%d\n",
                        first, left->ndNRecs);
                 return;
         }
 
         /* initialize variables */
         nrecs = left->ndNRecs + 1 - first;
         size = bnode_end(left) - bnode_offset(left, first);
 
         /* move (possibly empty) contents of right node forward */
         memmove(bnode_datastart(right) + size,
                 bnode_datastart(right), 
                 bnode_end(right) - sizeof(struct NodeDescriptor));
 
         /* copy in new records */
         memcpy(bnode_datastart(right), bnode_key(left,first), size);
 
         /* fix up offsets in right node */
         i = right->ndNRecs + 1;
         from = RECTBL(right, i);
         to = from - nrecs;
         while (i--) {
                 hfs_put_hs(hfs_get_hs(from++) + size, to++);
         }
         adjust = sizeof(struct NodeDescriptor) - bnode_offset(left, first);
         i = nrecs-1;
         from = RECTBL(left, first+i);
         while (i--) {
                 hfs_put_hs(hfs_get_hs(from++) + adjust, to++);
         }
 
         /* fix record counts */
         left->ndNRecs -= nrecs;
         right->ndNRecs += nrecs;
 }
 
 /*
  * hfs_bnode_shift_left()
  *
  * Description:
  *   Shifts some records from a node to its left neighbor.
  * Input Variable(s):
  *   struct hfs_bnode* left: the node to shift records to
  *   struct hfs_bnode* right: the node to shift records from
  *   hfs_u16 last: the number of the last record in 'right' to move to 'left'
  * Output Variable(s):
  *   NONE
  * Returns:
  *   void
  * Preconditions:
  *   'left' and 'right' point to valid (struct hfs_bnode)s.
  *   'right' contains at least 'last' records.
  *   'left' has enough free space to hold the records to be moved from 'right'
  * Postconditions:
  *   The record numbered 'last' and all records before it in 'right' are
  *   placed at the end of 'left'.
  *   The key corresponding to 'right' in its parent is NOT updated.
  */
 void hfs_bnode_shift_left(struct hfs_bnode *left, struct hfs_bnode *right,
                           int last)
 {
         int i, adjust, nrecs;
         unsigned size;
         hfs_u16 *to, *from;
 
         if ((last <= 0) || (last > right->ndNRecs)) {
                 hfs_warn("bad argument to shift_left: last=%d, nrecs=%d\n",
                        last, right->ndNRecs);
                 return;
         }
 
         /* initialize variables */
         size = bnode_offset(right, last + 1) - sizeof(struct NodeDescriptor);
 
         /* copy records to left node */
         memcpy(bnode_dataend(left), bnode_datastart(right), size);
 
         /* move (possibly empty) remainder of right node backward */
         memmove(bnode_datastart(right), bnode_datastart(right) + size, 
                         bnode_end(right) - bnode_offset(right, last + 1));
 
         /* fix up offsets */
         nrecs = left->ndNRecs;
         i = last;
         from = RECTBL(right, 2);
         to = RECTBL(left, nrecs + 2);
         adjust = bnode_offset(left, nrecs + 1) - sizeof(struct NodeDescriptor);
         while (i--) {
                 hfs_put_hs(hfs_get_hs(from--) + adjust, to--);
         }
         i = right->ndNRecs + 1 - last;
         ++from;
         to = RECTBL(right, 1);
         while (i--) {
                 hfs_put_hs(hfs_get_hs(from--) - size, to--);
         }
 
         /* fix record counts */
         left->ndNRecs += last;
         right->ndNRecs -= last;
 }
 
 /*
  * hfs_bnode_in_brec()
  *
  * Description:
  *   Determines whethet a given bnode is part of a given brec.
  *   This is used to avoid deadlock in the case of a corrupted b-tree.
  * Input Variable(s):
  *   hfs_u32 node: the number of the node to check for.
  *   struct hfs_brec* brec: the brec to check in.
  * Output Variable(s):
  *   NONE
  * Returns:
  *   int: 1 it found, 0 if not
  * Preconditions:
  *   'brec' points to a valid struct hfs_brec.
  * Postconditions:
  *   'brec' is unchanged.
  */
 int hfs_bnode_in_brec(hfs_u32 node, const struct hfs_brec *brec)
 {
         const struct hfs_belem *belem = brec->bottom;
 
         while (belem && (belem >= brec->top)) {
                 if (belem->bnr.bn && (belem->bnr.bn->node == node)) {
                         return 1;
                 }
                 --belem;
         }
         return 0;
 }