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

[Christoph Hellwig <hch@lst.de>]

On Sun, Jun 18, 2017 at 09:12:50AM +0800, Greg Kroah-Hartman wrote:
> > 
> > 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.

Note that the search is for an attribute in the sysfs dir, but trying
to search for the device it doesn't make any difference.

> As Linus said, a strace would be great.

Both straces attached (gzipped due to size).  Note that this on a system
with four NVMe devices, two of which are nvme-loop devices that have the
uuid attribute.