Re: [RFC][PATH 4/4] ovl: relax lock_rename when moving files between work and upper dir

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On Fri, Nov 11, 2016 at 1:05 AM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> On Thu, Nov 10, 2016 at 11:02:21PM +0000, Al Viro wrote:
>> On Fri, Nov 11, 2016 at 12:44:43AM +0200, Amir Goldstein wrote:
>> > If work dir and upper dir have a common parent, then it
>> > is safe to move files between them without taking the super block
>> > s_vfs_rename_mutex.
>> >
>> > Since both upper dir and work dir (as well as $workdir/work)
>> > are delete locked on overlay mount, they cannot be moved.
>>
>> Do explain.  What do you mean, "delete locked" and why exactly can't they
>> be moved?
>

That is explained in commit message of the first 2 patches, but
foremost I would like to say that the name "delete locked" is just the
best of all the bad choices for names I came up with, so I am expecting
better name suggestions.

The concept is to pin the entry so that it cannot be moved, so can have
certain guaranties about the stability of the directories topology.

> More specifically, what makes you think that may_delete() is called before
> any change of parent?

Because it is checked at the beginning of vfs_rename()
and in order to change a parent, an entry needs to be renamed. no?
What am I missing?
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