Re: [PATCH 12/15] driver core: Implement tagged directory supportfor device classes.

From: Tejun Heo
Date: Wed Jul 16 2008 - 03:03:25 EST

Tejun Heo wrote:
> Hello, Eric.
> Eric W. Biederman wrote:
>> Tejun Heo <htejun@xxxxxxxxx> 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.

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