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/*
* linux/fs/hfs/bdelete.c
*
* Copyright (C) 1995-1997 Paul H. Hargrove
* This file may be distributed under the terms of the GNU General Public License.
*
* This file contains the code to delete 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"
/*================ Variable-like macros ================*/
#define FULL (HFS_SECTOR_SIZE - sizeof(struct NodeDescriptor))
#define NO_SPACE (HFS_SECTOR_SIZE+1)
/*================ File-local functions ================*/
/*
* bdelete_nonempty()
*
* Description:
* Deletes a record from a given bnode without regard to it becoming empty.
* Input Variable(s):
* struct hfs_brec* brec: pointer to the brec for the deletion
* struct hfs_belem* belem: which node in 'brec' to delete from
* 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'.
* Postconditions:
* The record has been inserted in the position indicated by 'brec'.
*/
static void bdelete_nonempty(struct hfs_brec *brec, struct hfs_belem *belem)
{
int i, rec, nrecs, tomove;
hfs_u16 size;
hfs_u8 *start;
struct hfs_bnode *bnode = belem->bnr.bn;
rec = belem->record;
nrecs = bnode->ndNRecs;
size = bnode_rsize(bnode, rec);
tomove = bnode_offset(bnode, nrecs+1) - bnode_offset(bnode, rec+1);
/* adjust the record table */
for (i = rec+1; i <= nrecs; ++i) {
hfs_put_hs(bnode_offset(bnode,i+1) - size, RECTBL(bnode,i));
}
/* move it down */
start = bnode_key(bnode, rec);
memmove(start, start + size, tomove);
/* update record count */
--bnode->ndNRecs;
}
/*
* del_root()
*
* Description:
* Delete the current root bnode.
* Input Variable(s):
* struct hfs_bnode_ref *root: reference to the root bnode
* Output Variable(s):
* NONE
* Returns:
* int: 0 on success, error code on failure
* Preconditions:
* 'root' refers to the root bnode with HFS_LOCK_WRITE access.
* None of 'root's children are held with HFS_LOCK_WRITE access.
* Postconditions:
* The current 'root' node is removed from the tree and the depth
* of the tree is reduced by one.
* If 'root' is an index node with exactly one child, then that
* child becomes the new root of the tree.
* If 'root' is an empty leaf node the tree becomes empty.
* Upon return access to 'root' is relinquished.
*/
static int del_root(struct hfs_bnode_ref *root)
{
struct hfs_btree *tree = root->bn->tree;
struct hfs_bnode_ref child;
hfs_u32 node;
if (root->bn->ndNRecs > 1) {
return 0;
} else if (root->bn->ndNRecs == 0) {
/* tree is empty */
tree->bthRoot = 0;
tree->root = NULL;
tree->bthRoot = 0;
tree->bthFNode = 0;
tree->bthLNode = 0;
--tree->bthDepth;
tree->dirt = 1;
if (tree->bthDepth) {
hfs_warn("hfs_bdelete: empty tree with bthDepth=%d\n",
tree->bthDepth);
goto bail;
}
return hfs_bnode_free(root);
} else if (root->bn->ndType == ndIndxNode) {
/* tree is non-empty */
node = hfs_get_hl(bkey_record(bnode_datastart(root->bn)));
child = hfs_bnode_find(tree, node, HFS_LOCK_READ);
if (!child.bn) {
hfs_warn("hfs_bdelete: can't read child node.\n");
goto bail;
}
child.bn->sticky = HFS_STICKY;
if (child.bn->next) {
child.bn->next->prev = child.bn->prev;
}
if (child.bn->prev) {
child.bn->prev->next = child.bn->next;
}
if (bhash(tree, child.bn->node) == child.bn) {
bhash(tree, child.bn->node) = child.bn->next;
}
child.bn->next = NULL;
child.bn->prev = NULL;
tree->bthRoot = child.bn->node;
tree->root = child.bn;
/* re-assign bthFNode and bthLNode if the new root is
a leaf node. */
if (child.bn->ndType == ndLeafNode) {
tree->bthFNode = node;
tree->bthLNode = node;
}
hfs_bnode_relse(&child);
tree->bthRoot = node;
--tree->bthDepth;
tree->dirt = 1;
if (!tree->bthDepth) {
hfs_warn("hfs_bdelete: non-empty tree with "
"bthDepth == 0\n");
goto bail;
}
return hfs_bnode_free(root); /* marks tree dirty */
}
hfs_bnode_relse(root);
return 0;
bail:
hfs_bnode_relse(root);
return -EIO;
}
/*
* delete_empty_bnode()
*
* Description:
* Removes an empty non-root bnode from between 'left' and 'right'
* Input Variable(s):
* hfs_u32 left_node: node number of 'left' or zero if 'left' is invalid
* struct hfs_bnode_ref *left: reference to the left neighbor of the
* bnode to remove, or invalid if no such neighbor exists.
* struct hfs_bnode_ref *center: reference to the bnode to remove
* hfs_u32 right_node: node number of 'right' or zero if 'right' is invalid
* struct hfs_bnode_ref *right: reference to the right neighbor of the
* bnode to remove, or invalid if no such neighbor exists.
* Output Variable(s):
* NONE
* Returns:
* void
* Preconditions:
* 'left_node' is as described above.
* 'left' points to a valid (struct hfs_bnode_ref) having HFS_LOCK_WRITE
* access and referring to the left neighbor of 'center' if such a
* neighbor exists, or invalid if no such neighbor exists.
* 'center' points to a valid (struct hfs_bnode_ref) having HFS_LOCK_WRITE
* access and referring to the bnode to delete.
* 'right_node' is as described above.
* 'right' points to a valid (struct hfs_bnode_ref) having HFS_LOCK_WRITE
* access and referring to the right neighbor of 'center' if such a
* neighbor exists, or invalid if no such neighbor exists.
* Postconditions:
* If 'left' is valid its 'ndFLink' field becomes 'right_node'.
* If 'right' is valid its 'ndBLink' field becomes 'left_node'.
* If 'center' was the first leaf node then the tree's 'bthFNode'
* field becomes 'right_node'
* If 'center' was the last leaf node then the tree's 'bthLNode'
* field becomes 'left_node'
* 'center' is NOT freed and access to the nodes is NOT relinquished.
*/
static void delete_empty_bnode(hfs_u32 left_node, struct hfs_bnode_ref *left,
struct hfs_bnode_ref *center,
hfs_u32 right_node, struct hfs_bnode_ref *right)
{
struct hfs_bnode *bnode = center->bn;
if (left_node) {
left->bn->ndFLink = right_node;
} else if (bnode->ndType == ndLeafNode) {
bnode->tree->bthFNode = right_node;
bnode->tree->dirt = 1;
}
if (right_node) {
right->bn->ndBLink = left_node;
} else if (bnode->ndType == ndLeafNode) {
bnode->tree->bthLNode = left_node;
bnode->tree->dirt = 1;
}
}
/*
* balance()
*
* Description:
* Attempt to equalize space usage in neighboring bnodes.
* Input Variable(s):
* struct hfs_bnode *left: the left bnode.
* struct hfs_bnode *right: the right bnode.
* Output Variable(s):
* NONE
* Returns:
* void
* Preconditions:
* 'left' and 'right' point to valid (struct hfs_bnode)s obtained
* with HFS_LOCK_WRITE access, and are neighbors.
* Postconditions:
* Records are shifted either left or right to make the space usage
* nearly equal. When exact equality is not possible the break
* point is chosen to reduce data movement.
* The key corresponding to 'right' in its parent is NOT updated.
*/
static void balance(struct hfs_bnode *left, struct hfs_bnode *right)
{
int index, left_free, right_free, half;
left_free = bnode_freespace(left);
right_free = bnode_freespace(right);
half = (left_free + right_free)/2;
if (left_free < right_free) {
/* shift right to balance */
index = left->ndNRecs + 1;
while (right_free >= half) {
--index;
right_free -= bnode_rsize(left,index)+sizeof(hfs_u16);
}
if (index < left->ndNRecs) {
#if defined(DEBUG_ALL) || defined(DEBUG_BALANCE)
hfs_warn("shifting %d of %d recs right to balance: ",
left->ndNRecs - index, left->ndNRecs);
#endif
hfs_bnode_shift_right(left, right, index+1);
#if defined(DEBUG_ALL) || defined(DEBUG_BALANCE)
hfs_warn("%d,%d\n", left->ndNRecs, right->ndNRecs);
#endif
}
} else {
/* shift left to balance */
index = 0;
while (left_free >= half) {
++index;
left_free -= bnode_rsize(right,index)+sizeof(hfs_u16);
}
if (index > 1) {
#if defined(DEBUG_ALL) || defined(DEBUG_BALANCE)
hfs_warn("shifting %d of %d recs left to balance: ",
index-1, right->ndNRecs);
#endif
hfs_bnode_shift_left(left, right, index-1);
#if defined(DEBUG_ALL) || defined(DEBUG_BALANCE)
hfs_warn("%d,%d\n", left->ndNRecs, right->ndNRecs);
#endif
}
}
}
/*
* bdelete()
*
* Delete the given record from a B-tree.
*/
static int bdelete(struct hfs_brec *brec)
{
struct hfs_btree *tree = brec->tree;
struct hfs_belem *belem = brec->bottom;
struct hfs_belem *parent = (belem-1);
struct hfs_bnode *bnode;
hfs_u32 left_node, right_node;
struct hfs_bnode_ref left, right;
int left_space, right_space, min_space;
int fix_right_key;
int fix_key;
while ((belem > brec->top) &&
(belem->flags & (HFS_BPATH_UNDERFLOW | HFS_BPATH_FIRST))) {
bnode = belem->bnr.bn;
fix_key = belem->flags & HFS_BPATH_FIRST;
fix_right_key = 0;
bdelete_nonempty(brec, belem);
if (bnode->node == tree->root->node) {
del_root(&belem->bnr);
--brec->bottom;
goto done;
}
/* check for btree corruption which could lead to deadlock */
left_node = bnode->ndBLink;
right_node = bnode->ndFLink;
if ((left_node && hfs_bnode_in_brec(left_node, brec)) ||
(right_node && hfs_bnode_in_brec(right_node, brec)) ||
(left_node == right_node)) {
hfs_warn("hfs_bdelete: corrupt btree\n");
hfs_brec_relse(brec, NULL);
return -EIO;
}
/* grab the left neighbor if it exists */
if (left_node) {
hfs_bnode_lock(&belem->bnr, HFS_LOCK_RESRV);
left = hfs_bnode_find(tree,left_node,HFS_LOCK_WRITE);
if (!left.bn) {
hfs_warn("hfs_bdelete: unable to read left "
"neighbor.\n");
hfs_brec_relse(brec, NULL);
return -EIO;
}
hfs_bnode_lock(&belem->bnr, HFS_LOCK_WRITE);
if (parent->record != 1) {
left_space = bnode_freespace(left.bn);
} else {
left_space = NO_SPACE;
}
} else {
left.bn = NULL;
left_space = NO_SPACE;
}
/* grab the right neighbor if it exists */
if (right_node) {
right = hfs_bnode_find(tree,right_node,HFS_LOCK_WRITE);
if (!right.bn) {
hfs_warn("hfs_bdelete: unable to read right "
"neighbor.\n");
hfs_bnode_relse(&left);
hfs_brec_relse(brec, NULL);
return -EIO;
}
if (parent->record < parent->bnr.bn->ndNRecs) {
right_space = bnode_freespace(right.bn);
} else {
right_space = NO_SPACE;
}
} else {
right.bn = NULL;
right_space = NO_SPACE;
}
if (left_space < right_space) {
min_space = left_space;
} else {
min_space = right_space;
}
if (min_space == NO_SPACE) {
hfs_warn("hfs_bdelete: no siblings?\n");
hfs_brec_relse(brec, NULL);
return -EIO;
}
if (bnode->ndNRecs == 0) {
delete_empty_bnode(left_node, &left, &belem->bnr,
right_node, &right);
} else if (min_space + bnode_freespace(bnode) >= FULL) {
if ((right_space == NO_SPACE) ||
((right_space == min_space) &&
(left_space != NO_SPACE))) {
hfs_bnode_shift_left(left.bn, bnode,
bnode->ndNRecs);
} else {
hfs_bnode_shift_right(bnode, right.bn, 1);
fix_right_key = 1;
}
delete_empty_bnode(left_node, &left, &belem->bnr,
right_node, &right);
} else if (min_space == right_space) {
balance(bnode, right.bn);
fix_right_key = 1;
} else {
balance(left.bn, bnode);
fix_key = 1;
}
if (fix_right_key) {
hfs_bnode_update_key(brec, belem, right.bn, 1);
}
hfs_bnode_relse(&left);
hfs_bnode_relse(&right);
if (bnode->ndNRecs) {
if (fix_key) {
hfs_bnode_update_key(brec, belem, bnode, 0);
}
goto done;
}
hfs_bnode_free(&belem->bnr);
--brec->bottom;
belem = parent;
--parent;
}
if (belem < brec->top) {
hfs_warn("hfs_bdelete: Missing parent.\n");
hfs_brec_relse(brec, NULL);
return -EIO;
}
bdelete_nonempty(brec, belem);
done:
hfs_brec_relse(brec, NULL);
return 0;
}
/*================ Global functions ================*/
/*
* hfs_bdelete()
*
* Delete the requested record from a B-tree.
*/
int hfs_bdelete(struct hfs_btree *tree, const struct hfs_bkey *key)
{
struct hfs_belem *belem;
struct hfs_bnode *bnode;
struct hfs_brec brec;
int retval;
if (!tree || (tree->magic != HFS_BTREE_MAGIC) || !key) {
hfs_warn("hfs_bdelete: invalid arguments.\n");
return -EINVAL;
}
retval = hfs_bfind(&brec, tree, key, HFS_BFIND_DELETE);
if (!retval) {
belem = brec.bottom;
bnode = belem->bnr.bn;
belem->flags = 0;
if ((bnode->ndNRecs * sizeof(hfs_u16) + bnode_end(bnode) -
bnode_rsize(bnode, belem->record)) < FULL/2) {
belem->flags |= HFS_BPATH_UNDERFLOW;
}
if (belem->record == 1) {
belem->flags |= HFS_BPATH_FIRST;
}
if (!belem->flags) {
hfs_brec_lock(&brec, brec.bottom);
} else {
hfs_brec_lock(&brec, NULL);
}
retval = bdelete(&brec);
if (!retval) {
--brec.tree->bthNRecs;
brec.tree->dirt = 1;
}
hfs_brec_relse(&brec, NULL);
}
return retval;
}
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