On Mar 10, 2016, at 2:59 PM, Al Viro wrote:
> On Thu, Mar 10, 2016 at 02:20:42AM +0000, Al Viro wrote:
>
>> I'll pick it. Mind if I fold it into the one I'd posted (with credits,
>> obviously)?
>
> Actually, it's still racy - there's a window between d_obtain_alias() and
> ll_d_init() where it can be picked by d_splice_alias().
>
> Sigh... I'm really tempted to just add ->d_init() and let d_alloc() call it
> if non-NULL.
In fact I was surprised this was not the case already and so people
needed to call it by hand in every possible case where a new dentry is possibly
originated leading to a bit of a mess (and some bugs).
The downside is that we do the allocation at all times even if the dentry is
going to be promptly destroyed because we found a better alias.
In this way calling it just like we do today, after d_exact_alias + d_splice_alias
is another option, I guess and saves us some alloc + free trouble and a minuscle
overhead reduction for filesystems (majority of the in-kerel ones) that don't
really need this init at all.
> The question is what should it get and what should it be the method of...
>
> How about
> int (*d_init)(struct dentry *);
> in dentry_operations, with __d_alloc() ending with
> d_set_d_op(dentry, dentry->d_sb->s_d_op);
> if (unlikely(dentry->d_op && dentry->d_op->d_init)) {
> int err = dentry->d_op->d_init(dentry);
> if (unlikely(err)) {
> dentry_free(dentry);
> return ERR_PTR(err);
> }
> }
> this_cpu_inc(nr_dentry);
>
> return dentry;
> }
>
> Then lustre would simply have
>
> int ll_d_init(struct dentry *de)
> {
> struct ll_dentry_data *lld = kzalloc(sizeof(*lld), GFP_NOFS);
> if (unlikely(!lld))
> return -ENOMEM;
> lld->lld_invalid = 1;
> smp_wmb(); /* read barrier in whatever will find us */
> de->d_fsdata = lld;
> return 0;
> }
>
> as its ->d_init() and forget about all that mess.
>
> Objections, better ideas?
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