[XFS] implement generic xfs_btree_lookup
From: Dave Chinner <dgc@sgi.com>
[hch: split out from bigger patch and minor adaptions]
SGI-PV: 985583
SGI-Modid: xfs-linux-melb:xfs-kern:32192a
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Bill O'Donnell <billodo@sgi.com>
Signed-off-by: David Chinner <david@fromorbit.com>
diff --git a/fs/xfs/xfs_btree.c b/fs/xfs/xfs_btree.c
index 3d561f8..41912a0 100644
--- a/fs/xfs/xfs_btree.c
+++ b/fs/xfs/xfs_btree.c
@@ -1270,3 +1270,222 @@
return error;
}
+
+STATIC int
+xfs_btree_lookup_get_block(
+ struct xfs_btree_cur *cur, /* btree cursor */
+ int level, /* level in the btree */
+ union xfs_btree_ptr *pp, /* ptr to btree block */
+ struct xfs_btree_block **blkp) /* return btree block */
+{
+ struct xfs_buf *bp; /* buffer pointer for btree block */
+ int error = 0;
+
+ /* special case the root block if in an inode */
+ if ((cur->bc_flags & XFS_BTREE_ROOT_IN_INODE) &&
+ (level == cur->bc_nlevels - 1)) {
+ *blkp = xfs_btree_get_iroot(cur);
+ return 0;
+ }
+
+ /*
+ * If the old buffer at this level for the disk address we are
+ * looking for re-use it.
+ *
+ * Otherwise throw it away and get a new one.
+ */
+ bp = cur->bc_bufs[level];
+ if (bp && XFS_BUF_ADDR(bp) == xfs_btree_ptr_to_daddr(cur, pp)) {
+ *blkp = XFS_BUF_TO_BLOCK(bp);
+ return 0;
+ }
+
+ error = xfs_btree_read_buf_block(cur, pp, level, 0, blkp, &bp);
+ if (error)
+ return error;
+
+ xfs_btree_setbuf(cur, level, bp);
+ return 0;
+}
+
+/*
+ * Get current search key. For level 0 we don't actually have a key
+ * structure so we make one up from the record. For all other levels
+ * we just return the right key.
+ */
+STATIC union xfs_btree_key *
+xfs_lookup_get_search_key(
+ struct xfs_btree_cur *cur,
+ int level,
+ int keyno,
+ struct xfs_btree_block *block,
+ union xfs_btree_key *kp)
+{
+ if (level == 0) {
+ cur->bc_ops->init_key_from_rec(kp,
+ xfs_btree_rec_addr(cur, keyno, block));
+ return kp;
+ }
+
+ return xfs_btree_key_addr(cur, keyno, block);
+}
+
+/*
+ * Lookup the record. The cursor is made to point to it, based on dir.
+ * Return 0 if can't find any such record, 1 for success.
+ */
+int /* error */
+xfs_btree_lookup(
+ struct xfs_btree_cur *cur, /* btree cursor */
+ xfs_lookup_t dir, /* <=, ==, or >= */
+ int *stat) /* success/failure */
+{
+ struct xfs_btree_block *block; /* current btree block */
+ __int64_t diff; /* difference for the current key */
+ int error; /* error return value */
+ int keyno; /* current key number */
+ int level; /* level in the btree */
+ union xfs_btree_ptr *pp; /* ptr to btree block */
+ union xfs_btree_ptr ptr; /* ptr to btree block */
+
+ XFS_BTREE_TRACE_CURSOR(cur, XBT_ENTRY);
+ XFS_BTREE_TRACE_ARGI(cur, dir);
+
+ XFS_BTREE_STATS_INC(cur, lookup);
+
+ block = NULL;
+ keyno = 0;
+
+ /* initialise start pointer from cursor */
+ cur->bc_ops->init_ptr_from_cur(cur, &ptr);
+ pp = &ptr;
+
+ /*
+ * Iterate over each level in the btree, starting at the root.
+ * For each level above the leaves, find the key we need, based
+ * on the lookup record, then follow the corresponding block
+ * pointer down to the next level.
+ */
+ for (level = cur->bc_nlevels - 1, diff = 1; level >= 0; level--) {
+ /* Get the block we need to do the lookup on. */
+ error = xfs_btree_lookup_get_block(cur, level, pp, &block);
+ if (error)
+ goto error0;
+
+ if (diff == 0) {
+ /*
+ * If we already had a key match at a higher level, we
+ * know we need to use the first entry in this block.
+ */
+ keyno = 1;
+ } else {
+ /* Otherwise search this block. Do a binary search. */
+
+ int high; /* high entry number */
+ int low; /* low entry number */
+
+ /* Set low and high entry numbers, 1-based. */
+ low = 1;
+ high = xfs_btree_get_numrecs(block);
+ if (!high) {
+ /* Block is empty, must be an empty leaf. */
+ ASSERT(level == 0 && cur->bc_nlevels == 1);
+
+ cur->bc_ptrs[0] = dir != XFS_LOOKUP_LE;
+ XFS_BTREE_TRACE_CURSOR(cur, XBT_EXIT);
+ *stat = 0;
+ return 0;
+ }
+
+ /* Binary search the block. */
+ while (low <= high) {
+ union xfs_btree_key key;
+ union xfs_btree_key *kp;
+
+ XFS_BTREE_STATS_INC(cur, compare);
+
+ /* keyno is average of low and high. */
+ keyno = (low + high) >> 1;
+
+ /* Get current search key */
+ kp = xfs_lookup_get_search_key(cur, level,
+ keyno, block, &key);
+
+ /*
+ * Compute difference to get next direction:
+ * - less than, move right
+ * - greater than, move left
+ * - equal, we're done
+ */
+ diff = cur->bc_ops->key_diff(cur, kp);
+ if (diff < 0)
+ low = keyno + 1;
+ else if (diff > 0)
+ high = keyno - 1;
+ else
+ break;
+ }
+ }
+
+ /*
+ * If there are more levels, set up for the next level
+ * by getting the block number and filling in the cursor.
+ */
+ if (level > 0) {
+ /*
+ * If we moved left, need the previous key number,
+ * unless there isn't one.
+ */
+ if (diff > 0 && --keyno < 1)
+ keyno = 1;
+ pp = xfs_btree_ptr_addr(cur, keyno, block);
+
+#ifdef DEBUG
+ error = xfs_btree_check_ptr(cur, pp, 0, level);
+ if (error)
+ goto error0;
+#endif
+ cur->bc_ptrs[level] = keyno;
+ }
+ }
+
+ /* Done with the search. See if we need to adjust the results. */
+ if (dir != XFS_LOOKUP_LE && diff < 0) {
+ keyno++;
+ /*
+ * If ge search and we went off the end of the block, but it's
+ * not the last block, we're in the wrong block.
+ */
+ xfs_btree_get_sibling(cur, block, &ptr, XFS_BB_RIGHTSIB);
+ if (dir == XFS_LOOKUP_GE &&
+ keyno > xfs_btree_get_numrecs(block) &&
+ !xfs_btree_ptr_is_null(cur, &ptr)) {
+ int i;
+
+ cur->bc_ptrs[0] = keyno;
+ error = xfs_btree_increment(cur, 0, &i);
+ if (error)
+ goto error0;
+ XFS_WANT_CORRUPTED_RETURN(i == 1);
+ XFS_BTREE_TRACE_CURSOR(cur, XBT_EXIT);
+ *stat = 1;
+ return 0;
+ }
+ } else if (dir == XFS_LOOKUP_LE && diff > 0)
+ keyno--;
+ cur->bc_ptrs[0] = keyno;
+
+ /* Return if we succeeded or not. */
+ if (keyno == 0 || keyno > xfs_btree_get_numrecs(block))
+ *stat = 0;
+ else if (dir != XFS_LOOKUP_EQ || diff == 0)
+ *stat = 1;
+ else
+ *stat = 0;
+ XFS_BTREE_TRACE_CURSOR(cur, XBT_EXIT);
+ return 0;
+
+error0:
+ XFS_BTREE_TRACE_CURSOR(cur, XBT_ERROR);
+ return error;
+}