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

[hare@suse.de (Hannes Reinecke)]

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.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare at suse.de			               +49 911 74053 688
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