Re: [PATCH 06/14] sysfs: Rewrite sysfs_get_dentry

[Tejun Heo <htejun-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Eric W. Biederman wrote:
> Tejun Heo <htejun-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> writes:
> 
>> Hmmm... I think we can live with a bit of complexity in
>> sysfs_get_dentry().  It's very well localized and not even long.  I have
>> been trying hard to untangle sysfs internals from vfs and have a bit of
>> resistance against going back.  But, then again, if we can achieve
>> something better and simpler, why not?
> 
> Right now my real challenge is untangling sysfs_move_dir.  In the
> case of multiple mounts of the sysfs tree.

OIC.  Yeah, I guess moving a sd with multiple dentries attached could be
pretty difficult.

> My practical problem is that I need to hold a lock for the sysfs
> dirents and while that lock is held I need to call sysfs_get_dentry
> for the destination directory once for each superblock.
> 
> It might be that some kind of reader-writer lock strategy is what
> I need to untangle this mess.  Rather then making changing to i_mutex.
> All I know is at the moment it is taking a lot of code reading and
> brain storm to come of with something that is easy to maintain.

Just in case, sysfs used to have sysfs_rename_rwsem to protect
move/rename against tree walking, which became unnecessary after i_mutex
-> sysfs_mutex conversion.  Move/rename can use stupid big fat locks if
that helps.

Good luck.

-- 
tejun