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Date: Sun, 18 Jun 2017 09:12:50 +0800
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Tejun Heo <tj@kernel.org>, linux-fsdevel@vger.kernel.org
Subject: Re: odd sysfs find behavior, was: Re: [PATCH v6 00/10] Implement
 NVMe Namespace Descriptor Identification
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On Sat, Jun 17, 2017 at 02:08:14PM +0200, Christoph Hellwig wrote:
> On Fri, Jun 16, 2017 at 10:28:28PM +0900, Linus Torvalds wrote:
> > Hmm. The *traditional* reason for this particular 'find' oddity is
> > that find has an optimization which will look at the nlink count of a
> > directory to decide how many subdirectories it can have.
> 
> It looks like sysfs maintains i_nlink properly as far as I can tell.
> But I noticed another things that's even more weird:
> 
> root@testvm:~/nvmetcli# find /sys -name uuid
> root@testvm:~/nvmetcli# find /sys -name uuid
> /sys/devices/virtual/nvme-fabrics/ctl/nvme2/nvme2n1/uuid
> 
> so just repeating the find a second time makes it work!  Looks like
> there is some sort of lazy population scheme in sysfs..

There is a lazy population scheme in sysfs, but that means that things
are only populated in memory when we actually look for them, not the
second time around only :)

I just tried this on my laptop which does have a nvme block device in
it, and it worked just fine both times.

As Linus said, a strace would be great.

thanks,

greg k-h