linux-kernel - Re: [PATCH 7/7] [v2] drivers/misc: introduce Freescale hypervisor management driver

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Message-Id: <201106012340.14237.arnd@arndb.de>
Date:	Wed, 1 Jun 2011 23:40:14 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Timur Tabi <timur@...escale.com>
Cc:	kumar.gala@...escale.com, benh@...nel.crashing.org, greg@...ah.com,
	akpm@...nel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, linux-console@...r.kernel.org
Subject: Re: [PATCH 7/7] [v2] drivers/misc: introduce Freescale hypervisor management driver

On Wednesday 01 June 2011, Timur Tabi wrote:
> The Freescale hypervisor management driver provides several services to
> drivers and applications related to the Freescale hypervisor:
> 
> 1. An ioctl interface for querying and managing partitions
> 
> 2. A file interface to reading incoming doorbells
> 
> 3. An interrupt handler for shutting down the partition upon receiving the
>    shutdown doorbell from a manager partition
> 
> 4. An interface for receiving callbacks when a managed partition shuts down.
> 
> Signed-off-by: Timur Tabi <timur@...escale.com>
> ---
>  drivers/misc/Kconfig           |    7 +
>  drivers/misc/Makefile          |    1 +
>  drivers/misc/fsl_hypervisor.c  |  941 ++++++++++++++++++++++++++++++++++++++++
>  include/linux/Kbuild           |    1 +
>  include/linux/fsl_hypervisor.h |  203 +++++++++
>  5 files changed, 1153 insertions(+), 0 deletions(-)
>  create mode 100644 drivers/misc/fsl_hypervisor.c
>  create mode 100644 include/linux/fsl_hypervisor.h

I think drivers/misc is not the right place for this, but I'm not completely
sure what is. drivers/firmware would be better at least, but virt/fsl might
also be ok.

> +static long ioctl_dtprop(struct fsl_hv_ioctl_prop __user *p, int set)
> +{
> +	struct fsl_hv_ioctl_prop param;
> +	char __user *upath, *upropname;
> +	void __user *upropval;
> +	char *path = NULL, *propname = NULL;
> +	void *propval = NULL;
> +	int ret = 0;
> +

I'm not convinced that an ioctl interface is the right way to work with
device tree properties. A more natural way would be to export it as
a file system, or maybe as a flattened device tree blob (the latter option
would require changing the hypervisor interface, which might not be
possible).

> +/**
> + * fsl_hv_ioctl: ioctl main entry point
> + */
> +static long fsl_hv_ioctl(struct file *file, unsigned int cmd,
> +			 unsigned long argaddr)
> +{
> +	union fsl_hv_ioctl_param __user *arg =
> +		(union fsl_hv_ioctl_param __user *)argaddr;
> +	long ret;
> +

For an ioctl, please follow the normal pattern of defining a separate
structure for each case, no union.

You can use a void __user * in the common ioctl function, and pass that
to the typed argument list in the specific functions.

	Arnd
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