On 07/18/2012 06:02 PM, Alex Lyakas wrote:

Hi Liu,
can you pls explain this a bit more to me.
I see in my fs that there are (FREE_SPACE,0, offset) items in the root
tree. It seems that offset here is the objectid of the appropriate
BLOCK_GROUP_ITEM. Also, I see that each FREE_SPACE points at some
INODE_ITEM within the root tree, and this INODE_ITEM also has extents.
I presume that these extents contain the free space cache in some
format, is that correct?

More or less.

As its name shows, a free space inode's data (you name it extents) consists of
free space info, meanwhile, a free space inode is issued to a block group,
so the free space info actually stands for free space in the block group:

|<-    a block group len    ->|
|----vvv----vvv-------vvv-----|

'v' : occupied.
'-' : available. (free space)

these free space info are indexed in a rbtree in memory, and each entry has [start, len].

However, I don't see any FREE_INO entries, what are they? Are they
perhaps used only when "inode_cache" mount option is used, so inode
numbers are not always incremented in btrfs_find_free_ino(), but
smaller unused numbers are reused?

Yes, that's what it is used for.

Also, I don't see anywhere BTRFS_BTREE_INODE_OBJECTID in the tree root
tree. So what is this "btree inode" that you mention?

The code refers to disk_io.c, in the function 'open_ctree()' you can see the definition.

Basically btree inode's data stands for btrfs's metadata, I think you can find something
in btrfs's wiki page?


And thanks for your energy on btrfs! :)

thanks,
liubo

Thanks,
Alex.


On Tue, Jul 10, 2012 at 2:28 PM, Liu Bo [off-list ref] wrote:

quoted

For btree inode, its root is also 'tree root', so btree inode can be
misunderstood as a free space inode.

We should add one more check for btree inode.

Signed-off-by: Liu Bo <redacted>
---
 fs/btrfs/btrfs_inode.h |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 12394a9..b168238 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h

@@ -194,8 +194,10 @@ static inline void btrfs_i_size_write(struct inode *inode, u64 size)
 static inline bool btrfs_is_free_space_inode(struct btrfs_root *root,
                                       struct inode *inode)
 {
-       if (root == root->fs_info->tree_root ||
-           BTRFS_I(inode)->location.objectid == BTRFS_FREE_INO_OBJECTID)
+       if (root == root->fs_info->tree_root &&
+           btrfs_ino(inode) != BTRFS_BTREE_INODE_OBJECTID)
+               return true;
+       if (BTRFS_I(inode)->location.objectid == BTRFS_FREE_INO_OBJECTID)
                return true;
        return false;
 }
--

1.6.5.2

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