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

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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: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo 2020-02-24 09:19:02 +08:00 committed by David Sterba
parent 4d81ea8bb4
commit 2a979612d5
1 changed files with 41 additions and 20 deletions
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61
fs/btrfs/relocation.c
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@ -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;
};
/*
* present a block pointer in the backref cache
*/
struct backref_edge {
struct list_head list[2];
struct backref_node *node[2];
};
#define LOWER 0
#define UPPER 1
#define RELOCATION_RESERVED_NODES 256
/*
* 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];
};
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);