Re: [PATCH 1/2] Btrfs: fix btrfs_is_free_space_inode to recognize btree inode

[Liu Bo <liubo2009@cn.fujitsu.com>]

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 <liubo2009@cn.fujitsu.com> wrote:
>> 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 <liubo2009@cn.fujitsu.com>
>> ---
>>  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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