complete boot failure in 4.5-rc1 caused by nvme: make SG_IO support optional

[James.Bottomley@HansenPartnership.com (James Bottomley)]

On Mon, 2016-02-08@08:32 +0100, Hannes Reinecke wrote:
> On 02/08/2016 12:07 AM, James Bottomley wrote:
> > On Sun, 2016-02-07@15:28 -0700, Jens Axboe wrote:
> > > On 02/07/2016 09:04 AM, James Bottomley wrote:
> > > > On Sun, 2016-02-07@10:22 +0100, Christoph Hellwig wrote:
> > > > > Keith said it should be on by default, and I promised him to
> > > > > change
> > > > > it once we run into problems, which I guess this counts as.
> > > > > 
> > > > > But just curious:  what distro are you using?  Upstream
> > > > > systemd
> > > > > explicitly rejected using scsi_id for NVMe here:
> > > > > 
> > > > > 	https://github.com/systemd/systemd/issues/1453
> > > > > 
> > > > > and all my test systems don't do this either.
> > > > 
> > > > This was SUSE (in my case, openSUSE Leap).  I just checked the
> > > > source
> > > > package; they patch the by-id rules back in for NVME:
> > > > 
> > > > # PATCH-FIX-SUSE 1101-rules-persistent-device-names-for-NVMe
> > > > -devices.patch (bsc#944132)
> > > > Patch1101:      1101-rules-persistent-device-names-for-NVMe
> > > > -devices.patch
> > > > 
> > > > The bugzilla is giving access denied for bug id 944132, so it's
> > > > likely
> > > > some proprietary vendor problem.  The patch has no preamble, so
> > > > it's
> > > > hard to tell what they were thinking.
> > > 
> > > I run root-on-nvme on my laptop, and I haven't observed any
> > > problems.
> > 
> > Me too apparently.  It looks like this problem may be SUSE specific
> > unless another distro has enabled this.  I can see why they would:
> > you
> > do need persistent names for devices, even NVMe ones.
> > 
> > > Generally I hate for options to default y unless absolutely 
> > > necessary, it's a sure fire way to feature creep your kernel
> > > without 
> > > noticing. I don't think getting all hot about this issue is fair,
> > > if 
> > > the only known case is suse.
> > 
> > Well, OK, I'm annoyed because it was a systemd system which means
> > debugging boot failures are excruciatingly difficult so it took me
> > a
> > week and a half to find out what the problem was.  Perhaps I was a
> > bit
> > rash to label this as an easily foreseen problem.
> > 
> > I opened a bug against SUSE to tell them to turn it on:
> > 
> > https://bugzilla.opensuse.org/show_bug.cgi?id=965497
> > 
> > The second problem is that there's currently no way to transition
> > to
> > using the serial attribute the way the udev 60-persistent
> > -storage.rules
> > are written, so if distros have some by-id hack, it will have to be
> > maintained for a while.  I annotated the already closed bug on this
> > in
> > systemd with the rules that work for me.
> > 
> Why, but you can.
> That's precisely what I did with the transition to sg_inq; I've
> added a new set of rules (55-sg_inq.rules and 59-sg-symlinks.rules)
> which will override the values from 60-persistent-storage.rules.
> 
> Do we have defined sysfs attributes for NVMe devices nowadays?
> If so I'd be willing to create/send some sysfs rules for them.

This is the one I finally settled on (for 60-persistent-storage) for
SUSE.  It keeps everything working across old and new kernels.

# nvme
SUBSYSTEMS=="nvme", ATTRS{serial}=="?*", PROGRAM="/usr/bin/echo $attr{serial}", ENV{ID_SERIAL}="%c", ENV{ID_BUS}="nvme"

I already complained to Keith that the echo is required to strip the
leading whitespace which I don't think should be in the serial
attribute.

James