Re: [PATCH] ceph: is_root_ceph_dentry() cleanup

[Al Viro <viro@zeniv.linux.org.uk>]

On Tue, Feb 11, 2025 at 06:01:21PM +0000, Viacheslav Dubeyko wrote:

> After some considerations, I believe we can follow such simple logic.
> Correct me if I will be wrong here. The ceph_lookup() method's responsibility is
> to "look up a single dir entry". It sounds for me that if we have positive
> dentry,
> then it doesn't make sense to call the ceph_lookup(). And if ceph_lookup() has
> been
> called for the positive dentry, then something wrong is happening.

VFS never calls it that way; ceph itself might, if ceph_handle_notrace_create()
is called with positive dentry.

> But all this logic is not about negative dentry, it's about local check
> before sending request to MDS server. So, I think we need to change the logic
> in likewise way:
> 
> if (<we can check locally>) {
>     <do check locally>
>     if (-ENOENT)
>         return NULL;
> } else {
>    <send request to MDS server>
> }
> 
> Am I right here? :) Let me change the logic in this way and to test it.

First of all, returning NULL does *not* mean "it's negative"; d_add(dentry, NULL)
does that.  What would "we can check locally" be?  AFAICS, the checks in
__ceph_dir_is_complete() and near it are doing just that...

The really unpleasant question is whether ceph_handle_notrace_create() could
end up feeding an already-positive dentry to direct call of ceph_lookup()...