nilfs2: add bmap function to seek a valid key

Add a new bmap function, nilfs_bmap_seek_key(), which seeks a valid
entry and returns its key starting from a given key.  This function
can be used to skip hole blocks efficiently.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 63 insertions, 0 deletions

diff --git a/fs/nilfs2/btree.c b/fs/nilfs2/btree.c
index ecdbae19a766..059f37137f9a 100644
--- a/fs/nilfs2/btree.c
+++ b/fs/nilfs2/btree.c
@@ -633,6 +633,44 @@ static int nilfs_btree_do_lookup_last(const struct nilfs_bmap *btree,
 	return 0;
 }
 
+/**
+ * nilfs_btree_get_next_key - get next valid key from btree path array
+ * @btree: bmap struct of btree
+ * @path: array of nilfs_btree_path struct
+ * @minlevel: start level
+ * @nextkey: place to store the next valid key
+ *
+ * Return Value: If a next key was found, 0 is returned. Otherwise,
+ * -ENOENT is returned.
+ */
+static int nilfs_btree_get_next_key(const struct nilfs_bmap *btree,
+				    const struct nilfs_btree_path *path,
+				    int minlevel, __u64 *nextkey)
+{
+	struct nilfs_btree_node *node;
+	int maxlevel = nilfs_btree_height(btree) - 1;
+	int index, next_adj, level;
+
+	/* Next index is already set to bp_index for leaf nodes. */
+	next_adj = 0;
+	for (level = minlevel; level <= maxlevel; level++) {
+		if (level == maxlevel)
+			node = nilfs_btree_get_root(btree);
+		else
+			node = nilfs_btree_get_nonroot_node(path, level);
+
+		index = path[level].bp_index + next_adj;
+		if (index < nilfs_btree_node_get_nchildren(node)) {
+			/* Next key is in this node */
+			*nextkey = nilfs_btree_node_get_key(node, index);
+			return 0;
+		}
+		/* For non-leaf nodes, next index is stored at bp_index + 1. */
+		next_adj = 1;
+	}
+	return -ENOENT;
+}
+
 static int nilfs_btree_lookup(const struct nilfs_bmap *btree,
 			      __u64 key, int level, __u64 *ptrp)
 {
@@ -1563,6 +1601,27 @@ out:
 	return ret;
 }
 
+static int nilfs_btree_seek_key(const struct nilfs_bmap *btree, __u64 start,
+				__u64 *keyp)
+{
+	struct nilfs_btree_path *path;
+	const int minlevel = NILFS_BTREE_LEVEL_NODE_MIN;
+	int ret;
+
+	path = nilfs_btree_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	ret = nilfs_btree_do_lookup(btree, path, start, NULL, minlevel, 0);
+	if (!ret)
+		*keyp = start;
+	else if (ret == -ENOENT)
+		ret = nilfs_btree_get_next_key(btree, path, minlevel, keyp);
+
+	nilfs_btree_free_path(path);
+	return ret;
+}
+
 static int nilfs_btree_last_key(const struct nilfs_bmap *btree, __u64 *keyp)
 {
 	struct nilfs_btree_path *path;
@@ -2298,7 +2357,9 @@ static const struct nilfs_bmap_operations nilfs_btree_ops = {
 	.bop_assign		=	nilfs_btree_assign,
 	.bop_mark		=	nilfs_btree_mark,
 
+	.bop_seek_key		=	nilfs_btree_seek_key,
 	.bop_last_key		=	nilfs_btree_last_key,
+
 	.bop_check_insert	=	NULL,
 	.bop_check_delete	=	nilfs_btree_check_delete,
 	.bop_gather_data	=	nilfs_btree_gather_data,
@@ -2318,7 +2379,9 @@ static const struct nilfs_bmap_operations nilfs_btree_ops_gc = {
 	.bop_assign		=	nilfs_btree_assign_gc,
 	.bop_mark		=	NULL,
 
+	.bop_seek_key		=	NULL,
 	.bop_last_key		=	NULL,
+
 	.bop_check_insert	=	NULL,
 	.bop_check_delete	=	NULL,
 	.bop_gather_data	=	NULL,