linux-kernel - Re: [PATCH 06/21] nd: ndctl class device, and nd bus attributes

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Date:	Sat, 18 Apr 2015 13:08:01 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	Neil Brown <neilb@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 06/21] nd: ndctl class device, and nd bus attributes

On Sat, Apr 18, 2015 at 1:07 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
> On Fri, Apr 17, 2015 at 09:35:46PM -0400, Dan Williams wrote:
>> This is the position (device topology) independent method to find all
>> the NFIT-defined buses in the system.  The expectation is that there
>> will only ever be one "nd" bus discovered via /sys/class/nd/ndctl0.
>> However, we allow for the possibility of multiple buses and they will
>> listed in discovery order as ndctl0...ndctlN.  This character device
>> hosts the ioctl for passing control messages (as defined by the NFIT
>> spec).  The "format" and "revision" attributes of this device identify
>> the format of the messages.  In the event an NFIT is registered with an
>> unknown/unsupported control message format then the "format" attribute
>> will not be visible.
>>
>> Cc: Greg KH <gregkh@...uxfoundation.org>
>> Cc: Neil Brown <neilb@...e.de>
>> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
>> ---
>>  drivers/block/nd/Makefile     |    1
>>  drivers/block/nd/bus.c        |   84 +++++++++++++++++++++++++++++++++++++++++
>>  drivers/block/nd/core.c       |   71 ++++++++++++++++++++++++++++++++++-
>>  drivers/block/nd/nd-private.h |    5 ++
>>  4 files changed, 160 insertions(+), 1 deletion(-)
>>  create mode 100644 drivers/block/nd/bus.c
>>
>> diff --git a/drivers/block/nd/Makefile b/drivers/block/nd/Makefile
>> index c6bec0c185c5..7772fb599809 100644
>> --- a/drivers/block/nd/Makefile
>> +++ b/drivers/block/nd/Makefile
>> @@ -20,3 +20,4 @@ obj-$(CONFIG_NFIT_ACPI) += nd_acpi.o
>>  nd_acpi-y := acpi.o
>>
>>  nd-y := core.o
>> +nd-y += bus.o
>> diff --git a/drivers/block/nd/bus.c b/drivers/block/nd/bus.c
>> new file mode 100644
>> index 000000000000..c27db50511f2
>> --- /dev/null
>> +++ b/drivers/block/nd/bus.c
>> @@ -0,0 +1,84 @@
>> +/*
>> + * Copyright(c) 2013-2015 Intel Corporation. All rights reserved.
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of version 2 of the GNU General Public License as
>> + * published by the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope that it will be useful, but
>> + * WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> + * General Public License for more details.
>> + */
>> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>> +#include <linux/uaccess.h>
>> +#include <linux/fcntl.h>
>> +#include <linux/slab.h>
>> +#include <linux/fs.h>
>> +#include <linux/io.h>
>> +#include "nd-private.h"
>> +#include "nfit.h"
>> +
>> +static int nd_major;
>> +static struct class *nd_class;
>> +
>> +int nd_bus_create_ndctl(struct nd_bus *nd_bus)
>> +{
>> +     dev_t devt = MKDEV(nd_major, nd_bus->id);
>> +     struct device *dev;
>> +
>> +     dev = device_create(nd_class, &nd_bus->dev, devt, nd_bus, "ndctl%d",
>> +                     nd_bus->id);
>> +
>> +     if (IS_ERR(dev)) {
>> +             dev_dbg(&nd_bus->dev, "failed to register ndctl%d: %ld\n",
>> +                             nd_bus->id, PTR_ERR(dev));
>> +             return PTR_ERR(dev);
>> +     }
>> +     return 0;
>> +}
>> +
>> +void nd_bus_destroy_ndctl(struct nd_bus *nd_bus)
>> +{
>> +     device_destroy(nd_class, MKDEV(nd_major, nd_bus->id));
>> +}
>> +
>> +static long nd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>> +{
>> +     return -ENXIO;
>> +}
>
> There is no ioctl call here, so why even have this character device?

Our management library finds nd buses by /sys/class/nd.  The
nd_ioctl() gets filled out in "[PATCH 08/21] nd: ndctl.h, the nd ioctl
abi".
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