Re: [PATCH v6 06/18] nvme: Rapid Path Failure Recovery read controller identify fields

[Mohamed Khalfella <mkhalfella@purestorage.com>]

On Mon 2026-10-19 14:18:53 -0700, Mohamed Khalfella wrote:
> On Mon 2026-10-19 18:56:04 +0200, Daniel Wagner wrote:
> > > TP8028 Rapid Path Failure added new fields to controller identify
> > > response. Read CIU (Controller Instance Uniquifier), CIRN (Controller
> > > Instance Random Number), and CCRL (Cross-Controller Reset Limit) from
> > > controller identify response. Expose CIU and CIRN as sysfs attributes
> > > so the values can be used directly by user if needed.
> > 
> > What's the use case for it? This is an public/stable interface,
> > it needs a justification and documentation
> 
> CIU and CIRN identify an instance of an NVMe controller. For a given
> CNTLID different values of CIU and CIRN identify different controller
> instances of the same controller. The justification is that the values
> allow the user to identify a specific controller instance.
> 
> host# grep . /sys/class/nvme/nvme0/{cntlid,cirn,ciu}
> /sys/class/nvme/nvme0/cntlid:1
> /sys/class/nvme/nvme0/cirn:42541d24813bb536
> /sys/class/nvme/nvme0/ciu:57
> host# nvme admin-passthru \
>   --opcode 0x38 \
>   --cdw10=$(( 0x1 | 0x57<<16 )) \
>   --cdw12=$(( 0x42541d24813bb536 & 0xffffffff )) \
>   --cdw13=$(( ( 0x42541d24813bb536 >> 32 ) & 0xffffffff )) \
>   /dev/nvme1
> Admin Command Vendor Specific is Success and result: 0x00000000
> host#
> 
> One usecase is to use the values to issue CCR command manually. Not that
> I imagine one would want to do that, but if they want to do it they need
> this information. CIU is also present in CCR log page. Someone reading
> the log page might want to correlate a log page entry with a specific
> controller, so they need the information to be exported somehow.
> 
> diff --git a/Documentation/ABI/stable/sysfs-nvme b/Documentation/ABI/stable/sysfs-nvme
> index a2f5d0710db4..ebc3634c1a96 100644
> --- a/Documentation/ABI/stable/sysfs-nvme
> +++ b/Documentation/ABI/stable/sysfs-nvme
> @@ -9,6 +9,17 @@ Description:
>  		of the NVMe controller, as reported in the Identify
>  		Controller data structure.
>  
> +What:		/sys/class/nvme/nvmeX/cirn
> +What:		/sys/class/nvme/nvmeX/ciu
> +Date:		October 2026
> +KernelVersion:	7.5
> +Contact:	Mohamed Khalfella <mkhalfella@purestorage.com>
> +Description:
> +		Shows CIRN (Controller Instance Random Number) and CIU
> +		(Controller Instance Uniquifier) of the current instance
> +		of the NVMe controller as reported by Identify Controller
> +		data structure.
> +
>  What:		/sys/class/nvme/nvmeX/cntlid
>  Date:		February 2016
>  KernelVersion:	4.6
> 
> How about a diff like the one above for a documentation? I can add
> something similar to the one above assuming the change will be merged in
> 7.5. Or I can add it later on? Maybe in an -rc after the change is
> merged?
> 
> What do you think?

Added the diff above to the patch. Let me know if you want me to modify
it.

> 
> > 
> > > Also add the nvme_fence_timeout_ms() helper that derives a fencing
> > > timeout from the controller keep-alive timeout (kato).
> > 
> > There is no user in this patch, introduce it when you use it.
> 
> Moved the hunk to patch "nvme: Implement cross-controller reset recovery"
> where the function is actually used.
> 
> > 
> > -- 
> > Daniel Wagner <wagi@kernel.org>