From dc566127dd161b6c997466a2349ac179527ea89b Mon Sep 17 00:00:00 2001 From: Wu Fengguang Date: Tue, 16 Jun 2009 15:31:32 -0700 Subject: radix-tree: add radix_tree_prev_hole() The counterpart of radix_tree_next_hole(). To be used by context readahead. Signed-off-by: Wu Fengguang Cc: Vladislav Bolkhovitin Cc: Jens Axboe Cc: Jeff Moyer Cc: Nick Piggin Cc: Ying Han Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/radix-tree.c | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) (limited to 'lib') diff --git a/lib/radix-tree.c b/lib/radix-tree.c index 4bb42a0344ec..5301a52cdb4d 100644 --- a/lib/radix-tree.c +++ b/lib/radix-tree.c @@ -666,6 +666,43 @@ unsigned long radix_tree_next_hole(struct radix_tree_root *root, } EXPORT_SYMBOL(radix_tree_next_hole); +/** + * radix_tree_prev_hole - find the prev hole (not-present entry) + * @root: tree root + * @index: index key + * @max_scan: maximum range to search + * + * Search backwards in the range [max(index-max_scan+1, 0), index] + * for the first hole. + * + * Returns: the index of the hole if found, otherwise returns an index + * outside of the set specified (in which case 'index - return >= max_scan' + * will be true). In rare cases of wrap-around, LONG_MAX will be returned. + * + * radix_tree_next_hole may be called under rcu_read_lock. However, like + * radix_tree_gang_lookup, this will not atomically search a snapshot of + * the tree at a single point in time. For example, if a hole is created + * at index 10, then subsequently a hole is created at index 5, + * radix_tree_prev_hole covering both indexes may return 5 if called under + * rcu_read_lock. + */ +unsigned long radix_tree_prev_hole(struct radix_tree_root *root, + unsigned long index, unsigned long max_scan) +{ + unsigned long i; + + for (i = 0; i < max_scan; i++) { + if (!radix_tree_lookup(root, index)) + break; + index--; + if (index == LONG_MAX) + break; + } + + return index; +} +EXPORT_SYMBOL(radix_tree_prev_hole); + static unsigned int __lookup(struct radix_tree_node *slot, void ***results, unsigned long index, unsigned int max_items, unsigned long *next_index) -- cgit v1.2.3-59-g8ed1b