Commit 2a979612 authored by Qu Wenruo's avatar Qu Wenruo Committed by David Sterba
Browse files

btrfs: reloc: use wrapper to replace open-coded edge linking 



Since backref_edge is used to connect upper and lower backref nodes, and
needs to access both nodes, some code can look pretty nasty:

		list_add_tail(&edge->list[LOWER], &cur->upper);

The above code will link @cur to the LOWER side of the edge, while both
"LOWER" and "upper" words show up.  This can sometimes be very confusing
for reader to grasp.

This patch introduces a new wrapper, link_backref_edge(), to handle the
linking behavior.  Which also has extra ASSERT() to ensure caller won't
pass wrong nodes.

Also, this updates the comment of related lists of backref_node and
backref_edge, to make it more clear that each list points to what.

Reviewed-by: default avatarJosef Bacik <josef@toxicpanda.com>
Reviewed-by: default avatarNikolay Borisov <nborisov@suse.com>
Signed-off-by: default avatarQu Wenruo <wqu@suse.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 4d81ea8b

fs/btrfs/relocation.c

+37 −16
Original line number Diff line number Diff line
@@ -92,10 +92,12 @@ struct backref_node { 
	u64 owner;

	/* link to pending, changed or detached list */

	struct list_head list;

	/* list of upper level blocks reference this block */



	/* List of upper level edges, which link this node to its parents */

	struct list_head upper;

	/* list of child blocks in the cache */

	/* List of lower level edges, which link this node to its children */

	struct list_head lower;



	/* NULL if this node is not tree root */

	struct btrfs_root *root;

	/* extent buffer got by COW the block */
@@ -130,17 +132,26 @@ struct backref_node { 
	unsigned int is_reloc_root:1;

};



#define LOWER	0

#define UPPER	1

#define RELOCATION_RESERVED_NODES	256

/*

 * present a block pointer in the backref cache

 * present an edge connecting upper and lower backref nodes.

 */

struct backref_edge {

	/*

	 * list[LOWER] is linked to backref_node::upper of lower level node,

	 * and list[UPPER] is linked to backref_node::lower of upper level node.

	 *

	 * Also, build_backref_tree() uses list[UPPER] for pending edges, before

	 * linking list[UPPER] to its upper level nodes.

	 */

	struct list_head list[2];



	/* Two related nodes */

	struct backref_node *node[2];

};



#define LOWER	0

#define UPPER	1

#define RELOCATION_RESERVED_NODES	256



struct backref_cache {

	/* red black tree of all backref nodes in the cache */
@@ -363,6 +374,22 @@ static struct backref_edge *alloc_backref_edge(struct backref_cache *cache) 
	return edge;

}



#define		LINK_LOWER	(1 << 0)

#define		LINK_UPPER	(1 << 1)

static void link_backref_edge(struct backref_edge *edge,

			      struct backref_node *lower,

			      struct backref_node *upper,

			      int link_which)

{

	ASSERT(upper && lower && upper->level == lower->level + 1);

	edge->node[LOWER] = lower;

	edge->node[UPPER] = upper;

	if (link_which & LINK_LOWER)

		list_add_tail(&edge->list[LOWER], &lower->upper);

	if (link_which & LINK_UPPER)

		list_add_tail(&edge->list[UPPER], &upper->lower);

}



static void free_backref_edge(struct backref_cache *cache,

			      struct backref_edge *edge)

{
@@ -767,9 +794,7 @@ static int handle_direct_tree_backref(struct backref_cache *cache, 
		ASSERT(upper->checked);

		INIT_LIST_HEAD(&edge->list[UPPER]);

	}

	list_add_tail(&edge->list[LOWER], &cur->upper);

	edge->node[LOWER] = cur;

	edge->node[UPPER] = upper;

	link_backref_edge(edge, cur, upper, LINK_LOWER);

	return 0;

}
@@ -914,9 +939,7 @@ static int handle_indirect_tree_backref(struct backref_cache *cache, 
			if (!upper->owner)

				upper->owner = btrfs_header_owner(eb);

		}

		list_add_tail(&edge->list[LOWER], &lower->upper);

		edge->node[LOWER] = lower;

		edge->node[UPPER] = upper;

		link_backref_edge(edge, lower, upper, LINK_LOWER);



		if (rb_node) {

			btrfs_put_root(root);
@@ -1340,10 +1363,8 @@ static int clone_backref_node(struct btrfs_trans_handle *trans, 
			if (!new_edge)

				goto fail;



			new_edge->node[UPPER] = new_node;

			new_edge->node[LOWER] = edge->node[LOWER];

			list_add_tail(&new_edge->list[UPPER],

				      &new_node->lower);

			link_backref_edge(new_edge, edge->node[LOWER], new_node,

					  LINK_UPPER);

		}

	} else {

		list_add_tail(&new_node->lower, &cache->leaves);

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