# Re: \[PATCH 12/15\] driver core: Implement tagged directory support for device classes.

- From: Tejun Heo \<hidden\>
- Date: 2008-07-16 05:50:48 
- List: netdev
- Page: https://ratatoskr.run/netdev/2008/07/1125988
- Thread: https://ratatoskr.run/netdev/2008/07/1125986/t.md

```text
Hello,

Eric W. Biederman wrote:
>> Eric, with the multiple superblocks, sysfs now uses inode from the
>> default sysfs_sb with dentries from other sb's.  Is this okay?  Are
>> there any other filesystems which do this?
> 
> I don't know of any other filesystems where this unique challenge arises.
> /proc almost qualifies but it never needs to be modified.
> 
> It is certainly ok to go from multiple dentries to a single inode.
> I'm trying to remember why I choose to do that.  I think both because it simplifies
> the locking and keeps us more efficient in the icache.

It's a bit scary tho.  Working inode->i_dentry or dentry->d_alias
crosses multiple sb's.  sysfs isn't too greedy about dcache/icache.
Only open files and directories hold them and only single copy of
sysfs_dirent is there for most nodes.  Wouldn't it be better to stay on
the safer side and use separate inode hierarchy?

Thanks.

-- 
tejun
```