linux-kernel - Re: [PATCH v5 05/21] libnvdimm: control (ioctl) messages for libnvdimm bus and dimm devices

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Message-ID: <CAPcyv4jmHpg4YrseBWH-k=achv4N-V8n2X0CkFw+-AFsiRuH8A@mail.gmail.com>
Date:	Mon, 8 Jun 2015 23:57:42 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Christoph Hellwig <hch@....de>
Cc:	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	Jens Axboe <axboe@...nel.dk>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Neil Brown <neilb@...e.de>,
	Greg KH <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	jmoyer <jmoyer@...hat.com>, linux-api@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v5 05/21] libnvdimm: control (ioctl) messages for
 libnvdimm bus and dimm devices

On Mon, Jun 8, 2015 at 11:34 PM, Christoph Hellwig <hch@....de> wrote:
> On Mon, Jun 01, 2015 at 08:14:35PM -0400, Dan Williams wrote:
>> Most discovery/configuration of the libnvdimm-subsystem is done via
>> sysfs attributes.  However, some libnvdimm buses, particularly the
>> ACPI.NFIT bus, define a small set of messages that can be passed to the
>> platform.  For convenience we derive the initial libnvdimm-ioctl command
>> formats directly from the NFIT DSM Interface Example formats.
>
> Why not merge these into the extensive sysfs interface?

Data payload size for one, these commands transfer more than a page
worth of data at a time.

Even if we killed the ioctl interface to userspace we still need all
the ugly data marshaling code in the kernel to craft properly
formatted ACPI _DSM messages.  I try to share as much common
infrastructure from the ACPI _DSM implementation to the ioctl
interface (nd_cmd_dimm_desc() + nd_cmd_bus_desc()).
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