NVMe controller reset

[Busch, Keith]

You could do remove + rescan with sysfs if you don't have
open references on your drive.

Here's a different proposal from 18 months ago:

http://lists.infradead.org/pipermail/linux-nvme/2013-September/000391.html

I still think it's a good idea.

On Tue, 17 Mar 2015, Brandon Schulz wrote:
> I see.  Thanks for the response.
> 
> So this won't work for the back-ports to 2.6.32-ish kernels, as you mentioned, so does anyone have
> a preference for how it is done there?
> 
> We're going to have to implement a mechanism, and if there are strong opinions against
> implementing it as an ioctl, I'd like to hear them before we go write the code and submit the
> patches.
> 
> My objective here is to find an acceptable mechanism that can eventually be pulled into the older
> distro kernels.  If I'm going about this the wrong way, please let me know.
> 
> Thanks,
> Brandon
> 
> 
> 
> -----Original Message-----
> From: Keith Busch [mailto:keith.busch at intel.com]
> Sent: Tuesday, March 17, 2015 3:30 PM
> To: Brandon Schulz
> Cc: linux-nvme at lists.infradead.org
> Subject: Re: NVMe controller reset
> 
> On Tue, 17 Mar 2015, Brandon Schulz wrote:
> > What is the preferred way (if there is one) to force a controller reset from user-space?
> >
> > If, for example, a user-space tool was going to do a firmware activate that required a
> controller reset, how would one trigger the reset?  I do not see an ioctl defined for this today,
> or am I missing something?
> 
> Like this:
> 
>    # echo 1 > /sys/class/nvme/nvme<#>/device/reset
> 
> This assumes you're using kernel >= 4.0. Before that'd, the entry was under "class/misc" instead
> of "class/nvme". It was moved to a new class because 'misc' wasn't giving us enough minors to have
> more than several dozen NVMe drives in a system, but I want hundreds.
> 
> It also assumes you're using a kernel >= 3.15. While the sysfs entry exists pre-3.15, it wasn't
> safe to use because there was no notification callback for drivers to subscribe to.
> 
> Had I known what a pain it was to back-port the pci callback to older kernels (it apparently
> breaks kABI), I would have used an nvme specific sysfs entry, but that's where we are today.