linux-kernel - Re: [PATCH v2 0/3] nvdimm: Add an IOCTL pass thru for DSM calls

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Date:	Mon, 16 Nov 2015 11:00:20 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Jerry Hoemann <jerry.hoemann@....com>
Cc:	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>,
	"Elliott, Robert (Persistent Memory)" <elliott@....com>,
	jmoyer <jmoyer@...hat.com>,
	Dmitry Krivenok <krivenok.dmitry@...il.com>,
	Linda Knippers <linda.knippers@....com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/3] nvdimm: Add an IOCTL pass thru for DSM calls

On Mon, Nov 16, 2015 at 10:38 AM, Jerry Hoemann <jerry.hoemann@....com> wrote:
>
> The NVDIMM code in the kernel supports an IOCTL interface to user
> space based upon the Intel Example DSM:
>
>         http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf
>
> This interface cannot be used by other NVDIMM DSMs that support
> incompatible functions.
>
> This patch set adds a generic "passthru" IOCTL interface which
> is not tied to a particular DSM.
>
> A new _IOC_NR ND_CMD_PASSTHRU == "100" is added for the pass thru call.
>
> The new data structure nd_passthru_pkg serves as a wrapper for the passthru
> calls.  This wrapper supplies the data that the kernel needs to
> make the _DSM call.
>
> Unlike the definitions of the _DSM functions themselves, the nd_passthru_pkg
> provides the calling information (input/output sizes) in an uniform
> manner making the kernel marshaling of the arguments straight
> forward.
>
> This shifts the marshaling burden from the kernel to the user
> space application while still permitting the kernel to internally
> call _DSM functions.
>
> To make the resultant kernel code easier to understand the existing
> functions acpi_nfit_ctl and __nd_ioctl were renamed to .*_intel to
> denote calling mechanism as in 4.3 tailored to the Intel Example DSM.
> New functions acpi_nfit_ctl_passthru and __nd_ioctl_passthru were
> created to supply the pass thru interface.

Let's not do the _intel vs _passthru split.  I want to convert the
existing commands over to this new interface and deprecate the old
ioctl-command formats.  I.e. it isn't the case that this will be a
always be a blind "passthru" mechanism, the kernel will need to crack
open this payload in some circumstances.
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