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

- List: netdev
- 3 messages, 3 authors
- Page: https://ratatoskr.run/netdev/2008/07/1126002/t

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

- From: Eric W. Biederman \<hidden\>
- Date: 2008-07-16 06:42:27 
- Message: https://ratatoskr.run/netdev/2008/07/1126002.md

```text
Tejun Heo [ref] writes:

> 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?

To do that I believe we would need to ensure sysfs does not use 
the inode->i_mutex lock except to keep the VFS layer out.  Allowing us
to safely change the directory structure, without holding it.

You raise a good point about inode->i_dentry and dentry->d_alias.
Generally they are used by fat like filesystems but I am starting to
see uses in generic pieces of code.  I don't see any problems today
but yes it would be good to do the refactoring to allow us to duplicate
the inodes. 

Eric

```

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

- From: Tejun Heo \<hidden\>
- Date: 2008-07-16 06:49:24 
- Message: https://ratatoskr.run/netdev/2008/07/1126003.md

```text
Hello, Eric.

Eric W. Biederman wrote:
> Tejun Heo [ref] writes:
> 
>> 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?
> 
> To do that I believe we would need to ensure sysfs does not use 
> the inode->i_mutex lock except to keep the VFS layer out.  Allowing us
> to safely change the directory structure, without holding it.

I don't think sysfs is depending on i_mutex anymore but I need to go
through the code to make sure.

> You raise a good point about inode->i_dentry and dentry->d_alias.
> Generally they are used by fat like filesystems but I am starting to
> see uses in generic pieces of code.  I don't see any problems today
> but yes it would be good to do the refactoring to allow us to duplicate
> the inodes. 

Yeah, I can't spot any place which can cause actual problem yet but it's
still scary as we're breaking a vfs assumption and even if it's not a
problem now, future seemingly unrelated changes can break things subtly.

Thanks.

-- 
tejun
```

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

- From: Tejun Heo \<hidden\>
- Date: 2008-07-16 07:03:24 
- Message: https://ratatoskr.run/netdev/2008/07/1126006.md

```text
Tejun Heo wrote:
> Hello, Eric.
> 
> Eric W. Biederman wrote:
>> Tejun Heo [ref] writes:
>>
>>> 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?
>> To do that I believe we would need to ensure sysfs does not use 
>> the inode->i_mutex lock except to keep the VFS layer out.  Allowing us
>> to safely change the directory structure, without holding it.
> 
> I don't think sysfs is depending on i_mutex anymore but I need to go
> through the code to make sure.
> 
>> You raise a good point about inode->i_dentry and dentry->d_alias.
>> Generally they are used by fat like filesystems but I am starting to
>> see uses in generic pieces of code.  I don't see any problems today
>> but yes it would be good to do the refactoring to allow us to duplicate
>> the inodes. 
> 
> Yeah, I can't spot any place which can cause actual problem yet but it's
> still scary as we're breaking a vfs assumption and even if it's not a
> problem now, future seemingly unrelated changes can break things subtly.

Okay, one small problem spotted.  It seems invalidate_inodes() can fail
which will make generic_shutdown_super() complain.  It's not a fatal
failure tho.

-- 
tejun
```