From 65f1eaeac0efc968797f3ac955b85ba3f5d4f9c8 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Thu, 30 Oct 2008 16:55:34 +1100 Subject: [XFS] add helpers for addressing entities inside a btree block Add new helpers in xfs_btree.c to find the record, key and block pointer entries inside a btree block. To implement this genericly the ->get_maxrecs methods and two new xfs_btree_ops entries for the key and record sizes are used. Also add a big comment describing how the addressing inside a btree block works. Note that these helpers are unused until users are introduced in the next patches and this patch will thus cause some harmless compiler warnings. SGI-PV: 985583 SGI-Modid: xfs-linux-melb:xfs-kern:32189a Signed-off-by: Christoph Hellwig Signed-off-by: Lachlan McIlroy Signed-off-by: Bill O'Donnell Signed-off-by: David Chinner --- fs/xfs/xfs_btree.c | 130 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 130 insertions(+) (limited to 'fs/xfs/xfs_btree.c') diff --git a/fs/xfs/xfs_btree.c b/fs/xfs/xfs_btree.c index 893e86f..4aec7c7 100644 --- a/fs/xfs/xfs_btree.c +++ b/fs/xfs/xfs_btree.c @@ -403,6 +403,136 @@ xfs_btree_dup_cursor( } /* + * XFS btree block layout and addressing: + * + * There are two types of blocks in the btree: leaf and non-leaf blocks. + * + * The leaf record start with a header then followed by records containing + * the values. A non-leaf block also starts with the same header, and + * then first contains lookup keys followed by an equal number of pointers + * to the btree blocks at the previous level. + * + * +--------+-------+-------+-------+-------+-------+-------+ + * Leaf: | header | rec 1 | rec 2 | rec 3 | rec 4 | rec 5 | rec N | + * +--------+-------+-------+-------+-------+-------+-------+ + * + * +--------+-------+-------+-------+-------+-------+-------+ + * Non-Leaf: | header | key 1 | key 2 | key N | ptr 1 | ptr 2 | ptr N | + * +--------+-------+-------+-------+-------+-------+-------+ + * + * The header is called struct xfs_btree_block for reasons better left unknown + * and comes in different versions for short (32bit) and long (64bit) block + * pointers. The record and key structures are defined by the btree instances + * and opaque to the btree core. The block pointers are simple disk endian + * integers, available in a short (32bit) and long (64bit) variant. + * + * The helpers below calculate the offset of a given record, key or pointer + * into a btree block (xfs_btree_*_offset) or return a pointer to the given + * record, key or pointer (xfs_btree_*_addr). Note that all addressing + * inside the btree block is done using indices starting at one, not zero! + */ + +/* + * Return size of the btree block header for this btree instance. + */ +static inline size_t xfs_btree_block_len(struct xfs_btree_cur *cur) +{ + return (cur->bc_flags & XFS_BTREE_LONG_PTRS) ? + sizeof(struct xfs_btree_lblock) : + sizeof(struct xfs_btree_sblock); +} + +/* + * Return size of btree block pointers for this btree instance. + */ +static inline size_t xfs_btree_ptr_len(struct xfs_btree_cur *cur) +{ + return (cur->bc_flags & XFS_BTREE_LONG_PTRS) ? + sizeof(__be64) : sizeof(__be32); +} + +/* + * Calculate offset of the n-th record in a btree block. + */ +STATIC size_t +xfs_btree_rec_offset( + struct xfs_btree_cur *cur, + int n) +{ + return xfs_btree_block_len(cur) + + (n - 1) * cur->bc_ops->rec_len; +} + +/* + * Calculate offset of the n-th key in a btree block. + */ +STATIC size_t +xfs_btree_key_offset( + struct xfs_btree_cur *cur, + int n) +{ + return xfs_btree_block_len(cur) + + (n - 1) * cur->bc_ops->key_len; +} + +/* + * Calculate offset of the n-th block pointer in a btree block. + */ +STATIC size_t +xfs_btree_ptr_offset( + struct xfs_btree_cur *cur, + int n, + int level) +{ + return xfs_btree_block_len(cur) + + cur->bc_ops->get_maxrecs(cur, level) * cur->bc_ops->key_len + + (n - 1) * xfs_btree_ptr_len(cur); +} + +/* + * Return a pointer to the n-th record in the btree block. + */ +STATIC union xfs_btree_rec * +xfs_btree_rec_addr( + struct xfs_btree_cur *cur, + int n, + struct xfs_btree_block *block) +{ + return (union xfs_btree_rec *) + ((char *)block + xfs_btree_rec_offset(cur, n)); +} + +/* + * Return a pointer to the n-th key in the btree block. + */ +STATIC union xfs_btree_key * +xfs_btree_key_addr( + struct xfs_btree_cur *cur, + int n, + struct xfs_btree_block *block) +{ + return (union xfs_btree_key *) + ((char *)block + xfs_btree_key_offset(cur, n)); +} + +/* + * Return a pointer to the n-th block pointer in the btree block. + */ +STATIC union xfs_btree_ptr * +xfs_btree_ptr_addr( + struct xfs_btree_cur *cur, + int n, + struct xfs_btree_block *block) +{ + int level = xfs_btree_get_level(block); + + ASSERT(block->bb_level != 0); + + return (union xfs_btree_ptr *) + ((char *)block + xfs_btree_ptr_offset(cur, n, level)); +} + +/* * Get a the root block which is stored in the inode. * * For now this btree implementation assumes the btree root is always -- cgit v1.1