linux-kernel - Re: sysfs regression: wrong link counts

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Date:	Mon, 30 Jan 2012 19:45:10 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Greg KH <greg@...ah.com>, Jiri Slaby <jslaby@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>,
	systemd-devel@...ts.freedesktop.org
Subject: Re: sysfs regression: wrong link counts

Alan Cox <alan@...rguk.ukuu.org.uk> writes:

>> Isn't there some other "proper" way of doing this in userspace, or is
>> this really the correct way?
>
> You can look at the S_IFMT bits and stuff however link count indicating
> number of subdirectories is a standard Unix thing and used by many quite
> mundane tools as an optimisation.

Those tools for a decade or better all know to treat nlink == 1 as the
case where the optimization does not apply.

On a traditional unix filesytem the most common place you will see nlink
== 1 is when the link count overflows.  extN with > 65536 subdirectories
as I recall.


Eric
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