Re: [PATCh v2 8/9] btrfs: tree-checker: Verify inode item

[Qu Wenruo]

On 2019/3/28 下午9:57, David Sterba wrote:
> On Thu, Mar 28, 2019 at 09:42:59PM +0800, Qu Wenruo wrote:
>>
>>
>> On 2019/3/28 下午9:38, David Sterba wrote:
>>> On Wed, Mar 20, 2019 at 02:37:16PM +0800, Qu Wenruo wrote:
>>>> +  if (S_ISDIR(mode) && btrfs_inode_nlink(leaf, iitem) > 1) {
>>>> +          inode_item_err(fs_info, leaf, slot,
>>>> +                         "invalid nlink: has %u expect no more than 1 for 
>>>> dir",
>>>> +                  btrfs_inode_nlink(leaf, iitem));
>>>> +          goto error;
>>>> +  }
>>>
>>> I'm not sure about this check, the number of links for a directory is 1,
>>> but the exact count could be implemented (there's a project idea for
>>> that). I don't know if this will require an incompat bit or not.
>>
>> That means we have hard link for directories.
> 
> Yes, hard links of directories are forbidden by VFS but that's not the
> point here:
> 
> https://btrfs.wiki.kernel.org/index.php/Project_ideas#Track_link_count_for_directories
> 
> "The link count for directories is traditionally used to count the number
> of subdirectores iff the link count is >= 2."

Oh, got it.

But for that case, it would be much better to go for things like nbytes
or size, as by all means, those two members are less meaningful than
nlinks for directory.

Thanks,
Qu

>