On Mon, 2008-08-18 at 21:20 +0100, David Woodhouse wrote:
> On Mon, 2008-08-18 at 15:47 -0400, Chris Mason wrote:
> > Lets pretend I had put in commments something like the code below.
> > The important part is that directories have only one link, so they
> > have only one backref.
>
> OK. Now can I rip that code out anyway? The VFS will never call
> btrfs_lookup() for ".." -- not since the 2.2 kernel :)
>
> I'm still a little confused about precisely what btrfs_search_slot()
> returns when it doesn't find a match -- that's probably where the
> documentation would be more useful.
>
if btrfs_search_slot returns < 0, there was an error
if btrfs_search_slot returns > 1, path->slots[0] is the spot in the tree
where you'd want to insert the item.
In this case, if path->slots[0] == 0, there are no keys in the tree
smaller than your search key.
If path->slots[0] == btrfs_header_nritems(path->nodes[0]), there are no
items in this node that have a key > than your search key.
> What I have in btrfs_get_parent() is correct, I think -- but could
> probably be simplified to your version, searching for (u64)-1 and then
> not needing to call btrfs_next_leaf().
Yes.
>
> Something like this?
>
> (And am I fixing a use-after-free bug by moving that btrfs_free_path()
> down by a line, at the end?)
>
Most definitely ;) One comment inline below
> diff --git a/export.c b/export.c
> index 797b4cb..830e87a 100644
> --- a/export.c
> +++ b/export.c
> @@ -156,27 +156,27 @@ static struct dentry *btrfs_get_parent(struct dentry *child)
>
> key.objectid = dir->i_ino;
> btrfs_set_key_type(&key, BTRFS_INODE_REF_KEY);
> - key.offset = 0;
> + key.offset = (u64)-1;
> ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
> - BUG_ON(ret == 0);
> - ret = 0;
>
> leaf = path->nodes[0];
> slot = path->slots[0];
> - nritems = btrfs_header_nritems(leaf);
> - if (slot >= nritems) {
> - ret = btrfs_next_leaf(root, path);
> - if (ret) {
> - btrfs_free_path(path);
> - goto out;
> - }
> - leaf = path->nodes[0];
> - slot = path->slots[0];
> + if (ret < 0 && slot == 0) {
^^^^^^^^^^^^^ should be ||, and should set ret to
something bad if slot == 0
> + btrfs_free_path(path);
> + goto out;
> }
> + /*
> + This will be in the slot _before_ the one that btrfs_search_slot()
> + returns. And for some reason which dwmw2 doesn't quite understand,
> + that'll definitely be in the same leaf that btrfs_search_slot()
> + returned -- even if btrfs_search_slot() had to look in the _next_
> + leaf to find the first key which is greater than what we asked for
> + */
> + slot--;
>
> + btrfs_item_key_to_cpu(leaf, &key, slot);
> btrfs_free_path(path);
>
> - btrfs_item_key_to_cpu(leaf, &key, slot);
> if (key.objectid != dir->i_ino || key.type != BTRFS_INODE_REF_KEY)
> goto out;
>
>
>
-chris
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