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Btrfs: add btrfs_compare_trees function

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This function is used to find the differences between
two trees. The tree compare skips whole subtrees if it
detects shared tree blocks and thus is pretty fast.

Signed-off-by: Alexander Block <ablock84@googlemail.com>
Reviewed-by: David Sterba <dave@jikos.cz>
Reviewed-by: Arne Jansen <sensille@gmx.net>
Reviewed-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
Reviewed-by: Alex Lyakas <alex.bolshoy.btrfs@gmail.com>
This commit is contained in:
Alexander Block 2012-06-05 21:07:48 +02:00
parent 8ea05e3a42
commit 7069830a9e
2 changed files with 440 additions and 0 deletions
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425
fs/btrfs/ctree.c
View File

@ -5005,6 +5005,431 @@ out:
return ret;
}
static void tree_move_down(struct btrfs_root *root,
struct btrfs_path *path,
int *level, int root_level)
{
path->nodes[*level - 1] = read_node_slot(root, path->nodes[*level],
path->slots[*level]);
path->slots[*level - 1] = 0;
(*level)--;
}
static int tree_move_next_or_upnext(struct btrfs_root *root,
struct btrfs_path *path,
int *level, int root_level)
{
int ret = 0;
int nritems;
nritems = btrfs_header_nritems(path->nodes[*level]);
path->slots[*level]++;
while (path->slots[*level] == nritems) {
if (*level == root_level)
return -1;
/* move upnext */
path->slots[*level] = 0;
free_extent_buffer(path->nodes[*level]);
path->nodes[*level] = NULL;
(*level)++;
path->slots[*level]++;
nritems = btrfs_header_nritems(path->nodes[*level]);
ret = 1;
}
return ret;
}
/*
* Returns 1 if it had to move up and next. 0 is returned if it moved only next
* or down.
*/
static int tree_advance(struct btrfs_root *root,
struct btrfs_path *path,
int *level, int root_level,
int allow_down,
struct btrfs_key *key)
{
int ret;
if (*level == 0 || !allow_down) {
ret = tree_move_next_or_upnext(root, path, level, root_level);
} else {
tree_move_down(root, path, level, root_level);
ret = 0;
}
if (ret >= 0) {
if (*level == 0)
btrfs_item_key_to_cpu(path->nodes[*level], key,
path->slots[*level]);
else
btrfs_node_key_to_cpu(path->nodes[*level], key,
path->slots[*level]);
}
return ret;
}
static int tree_compare_item(struct btrfs_root *left_root,
struct btrfs_path *left_path,
struct btrfs_path *right_path,
char *tmp_buf)
{
int cmp;
int len1, len2;
unsigned long off1, off2;
len1 = btrfs_item_size_nr(left_path->nodes[0], left_path->slots[0]);
len2 = btrfs_item_size_nr(right_path->nodes[0], right_path->slots[0]);
if (len1 != len2)
return 1;
off1 = btrfs_item_ptr_offset(left_path->nodes[0], left_path->slots[0]);
off2 = btrfs_item_ptr_offset(right_path->nodes[0],
right_path->slots[0]);
read_extent_buffer(left_path->nodes[0], tmp_buf, off1, len1);
cmp = memcmp_extent_buffer(right_path->nodes[0], tmp_buf, off2, len1);
if (cmp)
return 1;
return 0;
}
#define ADVANCE 1
#define ADVANCE_ONLY_NEXT -1
/*
* This function compares two trees and calls the provided callback for
* every changed/new/deleted item it finds.
* If shared tree blocks are encountered, whole subtrees are skipped, making
* the compare pretty fast on snapshotted subvolumes.
*
* This currently works on commit roots only. As commit roots are read only,
* we don't do any locking. The commit roots are protected with transactions.
* Transactions are ended and rejoined when a commit is tried in between.
*
* This function checks for modifications done to the trees while comparing.
* If it detects a change, it aborts immediately.
*/
int btrfs_compare_trees(struct btrfs_root *left_root,
struct btrfs_root *right_root,
btrfs_changed_cb_t changed_cb, void *ctx)
{
int ret;
int cmp;
struct btrfs_trans_handle *trans = NULL;
struct btrfs_path *left_path = NULL;
struct btrfs_path *right_path = NULL;
struct btrfs_key left_key;
struct btrfs_key right_key;
char *tmp_buf = NULL;
int left_root_level;
int right_root_level;
int left_level;
int right_level;
int left_end_reached;
int right_end_reached;
int advance_left;
int advance_right;
u64 left_blockptr;
u64 right_blockptr;
u64 left_start_ctransid;
u64 right_start_ctransid;
u64 ctransid;
left_path = btrfs_alloc_path();
if (!left_path) {
ret = -ENOMEM;
goto out;
}
right_path = btrfs_alloc_path();
if (!right_path) {
ret = -ENOMEM;
goto out;
}
tmp_buf = kmalloc(left_root->leafsize, GFP_NOFS);
if (!tmp_buf) {
ret = -ENOMEM;
goto out;
}
left_path->search_commit_root = 1;
left_path->skip_locking = 1;
right_path->search_commit_root = 1;
right_path->skip_locking = 1;
spin_lock(&left_root->root_times_lock);
left_start_ctransid = btrfs_root_ctransid(&left_root->root_item);
spin_unlock(&left_root->root_times_lock);
spin_lock(&right_root->root_times_lock);
right_start_ctransid = btrfs_root_ctransid(&right_root->root_item);
spin_unlock(&right_root->root_times_lock);
trans = btrfs_join_transaction(left_root);
if (IS_ERR(trans)) {
ret = PTR_ERR(trans);
trans = NULL;
goto out;
}
/*
* Strategy: Go to the first items of both trees. Then do
*
* If both trees are at level 0
* Compare keys of current items
* If left < right treat left item as new, advance left tree
* and repeat
* If left > right treat right item as deleted, advance right tree
* and repeat
* If left == right do deep compare of items, treat as changed if
* needed, advance both trees and repeat
* If both trees are at the same level but not at level 0
* Compare keys of current nodes/leafs
* If left < right advance left tree and repeat
* If left > right advance right tree and repeat
* If left == right compare blockptrs of the next nodes/leafs
* If they match advance both trees but stay at the same level
* and repeat
* If they don't match advance both trees while allowing to go
* deeper and repeat
* If tree levels are different
* Advance the tree that needs it and repeat
*
* Advancing a tree means:
* If we are at level 0, try to go to the next slot. If that's not
* possible, go one level up and repeat. Stop when we found a level
* where we could go to the next slot. We may at this point be on a
* node or a leaf.
*
* If we are not at level 0 and not on shared tree blocks, go one
* level deeper.
*
* If we are not at level 0 and on shared tree blocks, go one slot to
* the right if possible or go up and right.
*/
left_level = btrfs_header_level(left_root->commit_root);
left_root_level = left_level;
left_path->nodes[left_level] = left_root->commit_root;
extent_buffer_get(left_path->nodes[left_level]);
right_level = btrfs_header_level(right_root->commit_root);
right_root_level = right_level;
right_path->nodes[right_level] = right_root->commit_root;
extent_buffer_get(right_path->nodes[right_level]);
if (left_level == 0)
btrfs_item_key_to_cpu(left_path->nodes[left_level],
&left_key, left_path->slots[left_level]);
else
btrfs_node_key_to_cpu(left_path->nodes[left_level],
&left_key, left_path->slots[left_level]);
if (right_level == 0)
btrfs_item_key_to_cpu(right_path->nodes[right_level],
&right_key, right_path->slots[right_level]);
else
btrfs_node_key_to_cpu(right_path->nodes[right_level],
&right_key, right_path->slots[right_level]);
left_end_reached = right_end_reached = 0;
advance_left = advance_right = 0;
while (1) {
/*
* We need to make sure the transaction does not get committed
* while we do anything on commit roots. This means, we need to
* join and leave transactions for every item that we process.
*/
if (trans && btrfs_should_end_transaction(trans, left_root)) {
btrfs_release_path(left_path);
btrfs_release_path(right_path);
ret = btrfs_end_transaction(trans, left_root);
trans = NULL;
if (ret < 0)
goto out;
}
/* now rejoin the transaction */
if (!trans) {
trans = btrfs_join_transaction(left_root);
if (IS_ERR(trans)) {
ret = PTR_ERR(trans);
trans = NULL;
goto out;
}
spin_lock(&left_root->root_times_lock);
ctransid = btrfs_root_ctransid(&left_root->root_item);
spin_unlock(&left_root->root_times_lock);
if (ctransid != left_start_ctransid)
left_start_ctransid = 0;
spin_lock(&right_root->root_times_lock);
ctransid = btrfs_root_ctransid(&right_root->root_item);
spin_unlock(&right_root->root_times_lock);
if (ctransid != right_start_ctransid)
right_start_ctransid = 0;
if (!left_start_ctransid || !right_start_ctransid) {
WARN(1, KERN_WARNING
"btrfs: btrfs_compare_tree detected "
"a change in one of the trees while "
"iterating. This is probably a "
"bug.\n");
ret = -EIO;
goto out;
}
/*
* the commit root may have changed, so start again
* where we stopped
*/
left_path->lowest_level = left_level;
right_path->lowest_level = right_level;
ret = btrfs_search_slot(NULL, left_root,
&left_key, left_path, 0, 0);
if (ret < 0)
goto out;
ret = btrfs_search_slot(NULL, right_root,
&right_key, right_path, 0, 0);
if (ret < 0)
goto out;
}
if (advance_left && !left_end_reached) {
ret = tree_advance(left_root, left_path, &left_level,
left_root_level,
advance_left != ADVANCE_ONLY_NEXT,
&left_key);
if (ret < 0)
left_end_reached = ADVANCE;
advance_left = 0;
}
if (advance_right && !right_end_reached) {
ret = tree_advance(right_root, right_path, &right_level,
right_root_level,
advance_right != ADVANCE_ONLY_NEXT,
&right_key);
if (ret < 0)
right_end_reached = ADVANCE;
advance_right = 0;
}
if (left_end_reached && right_end_reached) {
ret = 0;
goto out;
} else if (left_end_reached) {
if (right_level == 0) {
ret = changed_cb(left_root, right_root,
left_path, right_path,
&right_key,
BTRFS_COMPARE_TREE_DELETED,
ctx);
if (ret < 0)
goto out;
}
advance_right = ADVANCE;
continue;
} else if (right_end_reached) {
if (left_level == 0) {
ret = changed_cb(left_root, right_root,
left_path, right_path,
&left_key,
BTRFS_COMPARE_TREE_NEW,
ctx);
if (ret < 0)
goto out;
}
advance_left = ADVANCE;
continue;
}
if (left_level == 0 && right_level == 0) {
cmp = btrfs_comp_cpu_keys(&left_key, &right_key);
if (cmp < 0) {
ret = changed_cb(left_root, right_root,
left_path, right_path,
&left_key,
BTRFS_COMPARE_TREE_NEW,
ctx);
if (ret < 0)
goto out;
advance_left = ADVANCE;
} else if (cmp > 0) {
ret = changed_cb(left_root, right_root,
left_path, right_path,
&right_key,
BTRFS_COMPARE_TREE_DELETED,
ctx);
if (ret < 0)
goto out;
advance_right = ADVANCE;
} else {
ret = tree_compare_item(left_root, left_path,
right_path, tmp_buf);
if (ret) {
ret = changed_cb(left_root, right_root,
left_path, right_path,
&left_key,
BTRFS_COMPARE_TREE_CHANGED,
ctx);
if (ret < 0)
goto out;
}
advance_left = ADVANCE;
advance_right = ADVANCE;
}
} else if (left_level == right_level) {
cmp = btrfs_comp_cpu_keys(&left_key, &right_key);
if (cmp < 0) {
advance_left = ADVANCE;
} else if (cmp > 0) {
advance_right = ADVANCE;
} else {
left_blockptr = btrfs_node_blockptr(
left_path->nodes[left_level],
left_path->slots[left_level]);
right_blockptr = btrfs_node_blockptr(
right_path->nodes[right_level],
right_path->slots[right_level]);
if (left_blockptr == right_blockptr) {
/*
* As we're on a shared block, don't
* allow to go deeper.
*/
advance_left = ADVANCE_ONLY_NEXT;
advance_right = ADVANCE_ONLY_NEXT;
} else {
advance_left = ADVANCE;
advance_right = ADVANCE;
}
}
} else if (left_level < right_level) {
advance_right = ADVANCE;
} else {
advance_left = ADVANCE;
}
}
out:
btrfs_free_path(left_path);
btrfs_free_path(right_path);
kfree(tmp_buf);
if (trans) {
if (!ret)
ret = btrfs_end_transaction(trans, left_root);
else
btrfs_end_transaction(trans, left_root);
}
return ret;
}
/*
* this is similar to btrfs_next_leaf, but does not try to preserve
* and fixup the path. It looks for and returns the next key in the

15
fs/btrfs/ctree.h
View File

@ -2722,6 +2722,21 @@ int btrfs_search_forward(struct btrfs_root *root, struct btrfs_key *min_key,
struct btrfs_key *max_key,
struct btrfs_path *path, int cache_only,
u64 min_trans);
enum btrfs_compare_tree_result {
BTRFS_COMPARE_TREE_NEW,
BTRFS_COMPARE_TREE_DELETED,
BTRFS_COMPARE_TREE_CHANGED,
};
typedef int (*btrfs_changed_cb_t)(struct btrfs_root *left_root,
struct btrfs_root *right_root,
struct btrfs_path *left_path,
struct btrfs_path *right_path,
struct btrfs_key *key,
enum btrfs_compare_tree_result result,
void *ctx);
int btrfs_compare_trees(struct btrfs_root *left_root,
struct btrfs_root *right_root,
btrfs_changed_cb_t cb, void *ctx);
int btrfs_cow_block(struct btrfs_trans_handle *trans,
struct btrfs_root *root, struct extent_buffer *buf,
struct extent_buffer *parent, int parent_slot,