linux-kernel - Re: [RFC] st_nlink after rmdir() and rename()

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Date:	Fri, 04 Mar 2011 06:37:15 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] st_nlink after rmdir() and rename()

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Thu, Mar 3, 2011 at 12:46 PM, OGAWA Hirofumi
> <hirofumi@...l.parknet.co.jp> wrote:
>>
>> But, some commands see i_nlink (IIRC, it's checking i_nlink == 2, to
>> know empty dir or not).
>
> Actually, that would be a serious bug in the application.
>
> The traditional rule of thumb is that a directory with i_nlink==1 has
> a "I'm not counting at all".
>
> For example, I think that's the rule that 'find' uses to decide if a
> directory can have subdirectories (and when it could try to stop
> scanning early): i_nlink == 1 means that yes, it _can_ have
> subdirectories, we just don't know how many.

Yes. I think it is.

> So checking i_nlink==2 is actually a user-level bug.

We can call it's the user-level bug, but like you know, we will receive
many complain if old behavior was broken. If you are saying i_nlink == 2
is meaning the undefine, it sounds strange. (I was thinking it's why
isofs is using i_nlink == 1 always. I.e. i_nlink >= 2 is defined
behavior. Actually the reason would be "find" was checking i_nlink == 2
though)

>> So we have to simulate some levels. I guess you
>> are not saying we don't need to care it at all though.
>
> I'm saying that it should just work to set i_nlink=1 and not do
> anything at all. Ever. It's a valid model for directory counts.
>
> Seriously - that's what isofs does, for example. It does mean that
> 'find' for certain cases gets bit more expensive, but on the other
> hand, other operations are a lot _less_ expensive.
>
> We might well try that as a FAT mount option, to let people decide
> whether they really do want the "scan directories all the time" or
> only the "let 'find' scan directories when it needs to" behavior.

Yes. i_nlink == 1 is ok, IIRC (I checked last time at least. And I used
i_nlink == 1 for exFAT).  And I agree with you almost all, but isofs is
read-only, the read-only is why I was not really sure.

And I can't only see is why you refuse to make consistent behavior (if
you are saying it). It's why I said if it's _really easy_.

Thanks
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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