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btrbk: add documentation on caching in btr_tree()

pull/208/head
Axel Burri 2018-01-30 13:20:44 +01:00
parent 84bac59ab4
commit 753d68b2ed
1 changed files with 7 additions and 1 deletions
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@ -2058,8 +2058,14 @@ sub btr_tree($$)
TRACE "btr_tree: processing subvolume list of: $vol->{PRINT}";
# check if we already know this tree
# return a reference to the cached root if we already know the tree
# (making sure every tree is only stored once).
# die if duplicate UUID exist on different file systems (no matter
# if local or remote).
# note: this relies on subvolume UUID's to be "universally unique"
# (which is why cloning btrfs filesystems using "dd" is a bad idea)
if((scalar @$node_list) && $uuid_cache{$node_list->[0]->{uuid}}) {
# first uuid of $node_list is already known
TRACE "uuid_cache HIT: $node_list->[0]->{uuid}";
$vol_root = $uuid_cache{$node_list->[0]->{uuid}}->{TREE_ROOT}->{ID_HASH}->{$vol_root_id};
die "Duplicate UUID on different file systems" unless($vol_root);