Re: changing d_parent

[Jan Hudec <bulb@ucw.cz>]

On Sun, May 18, 2003 at 07:42:29PM +0200, Jerome de Vivie wrote:
> 
> I would like to change the "d_parent" field of a dentry. This is for
> shrinking entry equivalent to a "./" in my filesystem namespace.
> 
> The dentry has just been allocated and has no child. I'm new to the 
> dcache and i would like to know if thoses lines are is safe:
> 
>     spin_lock(&dcache_lock);
>     list_del(&dentry->d_child);
>     dput(dentry->d_parent);
>     dentry->d_parent = dget(newparent);
>     list_add(&dentry->d_child, &newparent->d_subdirs);
>     spin_unlock(&dcache_lock);

One thing that comes to mind, the dentry must not be hashed and you need
to hash it at some point (d_rehash()) (IIRC it does not work on hashed
dentries).

Another thing is, that dput may lock dcache_lock, so it must be only
called after you release it.

Also note the difference of dget and dget_locked. None of them locks
dcache_lock, but dget only gets a dentry you already hold (remember, you
are not expected to hold dcache_lock), while dget_locked can get
a dentry you just found in child list/hash.

I wonder what you are really doing. You should never ever need to mess
with . and .., since lookup deals with them for you.

-------------------------------------------------------------------------------
						 Jan 'Bulb' Hudec <bulb@ucw.cz>