Re: odd sysfs find behavior, was: Re: [PATCH v6 00/10] Implement NVMe Namespace Descriptor Identification

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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