Re: Difference between invalidating and deleting dentry

[Nikolaus Rath <Nikolaus@rath.org>]

On Oct 19 2016, Miklos Szeredi <miklos-sUDqSbJrdHQHWmgEVkV9KA@public.gmane.org> wrote:
> On Wed, Oct 19, 2016 at 10:32 AM, Amir Goldstein <amir73il-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>> On Wed, Oct 19, 2016 at 11:01 AM, Miklos Szeredi <miklos-sUDqSbJrdHQHWmgEVkV9KA@public.gmane.org> wrote:
>>> On Wed, Oct 19, 2016 at 7:53 AM, Amir Goldstein <amir73il-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>>>> On Wed, Oct 19, 2016 at 4:51 AM, Nikolaus Rath <Nikolaus-BTH8mxji4b0@public.gmane.org> wrote:
>>>
>>>>> Really no one able to clarify the difference between the FUSE invalidate
>>>>> and delete dentry requests?
>>>>
>>>> It may sound strange to you, but I think the documentation is clear enough.
>>>> The difference is that in delete case, you *know* that the entry has
>>>> been deleted
>>>> and in invalidate case, you may not know what happened to the entry.
>>>> The specific use cases are implementation specific, but maybe you lost
>>>> contact with remote server or maybe the remote protocol imposes a timeout
>>>> for validity or maybe you do not have enough information
>>>> to figure out if the entry has been deleted and re-created.
>>>> Invalidate simply means that you no longer know that the entry is valid.
>>>
>>> That was the intent, yes.  However 'invalidate' + 'lookup negative'
>>> should be equivalent to 'delete'.  And it is.
>>>
>>> The reason why 'delete' was introduced by commit 451d0f599934 ("FUSE:
>>> Notifying the kernel of deletion.") is that 'invalidate' wasn't able
>>> to remove in-use subtrees.
>>>
>>> Commit bafc9b754f75 ("vfs: More precise tests in d_invalidate")
>>> changed that, so now 'notify_delete' is superfluous and AFAICS the
>>> effect of it is exactly the same as 'notify_invalidate'.
>>>
>>
>> Minus fsnotify_nameremove() for whatever it is worth.
>
> Ah, right.  But fuse lacks proper fsnotify support for remote fs
> anyway, so it's not worth much.

Thanks Miklos!

So I'll extend the documentation to say that both _invalidate() and
_delete() drop the dentry from the cache (so the next lookup attempt)
will be passed to the fuse file sysem), but that _delete() will also
inform any inotify watchers that the entry has disappeared.


Best,
-Nikolaus

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