linux-kernel - Re: [PATCH v9 00/19] DCD: Add support for Dynamic Capacity Devices (DCD)

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Message-ID: <67fde05cdc323_71fe29420@dwillia2-xfh.jf.intel.com.notmuch>
Date: Mon, 14 Apr 2025 21:28:12 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Ira Weiny <ira.weiny@...el.com>, Fan Ni <nifan.cxl@...il.com>
CC: Dave Jiang <dave.jiang@...el.com>, Jonathan Cameron
	<Jonathan.Cameron@...wei.com>, Dan Williams <dan.j.williams@...el.com>,
	Davidlohr Bueso <dave@...olabs.net>, Alison Schofield
	<alison.schofield@...el.com>, Vishal Verma <vishal.l.verma@...el.com>,
	<linux-cxl@...r.kernel.org>, <nvdimm@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, Li Ming <ming.li@...omail.com>
Subject: Re: [PATCH v9 00/19] DCD: Add support for Dynamic Capacity Devices
 (DCD)

Ira Weiny wrote:
[..]
> > However, after that, I tried to create a dax device as below, it failed.
> > 
> > root@...ian:~# daxctl create-device -r region0 -v
> > libdaxctl: __dax_regions_init: no dax regions found via: /sys/class/dax

Note that /sys/class/dax support was removed from the kernel back in
v5.17:

83762cb5c7c4 dax: Kill DEV_DAX_PMEM_COMPAT

daxctl still supports pre-v5.17 kernels and always checks both subsystem
types. This is a debug message just confirming that it is running on a
new kernel, see dax_regions_init() in daxctl.

> > error creating devices: No such device or address
> > created 0 devices
> > root@...ian:~# 
> > 
> > root@...ian:~# ls /sys/class/dax 
> > ls: cannot access '/sys/class/dax': No such file or directory
> 
> Have you update daxctl with cxl-cli?
> 
> I was confused by this lack of /sys/class/dax and checked with Vishal.  He
> says this is legacy.
> 
> I have /sys/bus/dax and that works fine for me with the latest daxctl
> built from the ndctl code I sent out:
> 
> https://github.com/weiny2/ndctl/tree/dcd-region3-2025-04-13
> 
> Could you build and use the executables from that version?

The same debug message still exists in that version and will fire every
time when debug is enabled.