linux-kernel - Re: kdbus: add header file

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Date:	Thu, 30 Oct 2014 09:20:20 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
	john.stultz@...aro.org, tj@...nel.org, marcel@...tmann.org,
	desrt@...rt.ca, hadess@...ess.net, dh.herrmann@...il.com,
	tixxdz@...ndz.org, simon.mcvittie@...labora.co.uk,
	daniel@...que.org, alban.crequy@...labora.co.uk,
	javier.martinez@...labora.co.uk, teg@...m.no
Subject: Re: kdbus: add header file

On Wednesday 29 October 2014 15:00:46 Greg Kroah-Hartman wrote:
> +enum kdbus_ioctl_type {
> +       KDBUS_CMD_BUS_MAKE =            _IOW(KDBUS_IOCTL_MAGIC, 0x00,
> +                                            struct kdbus_cmd_make),
> +       KDBUS_CMD_DOMAIN_MAKE =         _IOW(KDBUS_IOCTL_MAGIC, 0x10,
> +                                            struct kdbus_cmd_make),
> +       KDBUS_CMD_ENDPOINT_MAKE =       _IOW(KDBUS_IOCTL_MAGIC, 0x20,
> +                                            struct kdbus_cmd_make),
> +
> +       KDBUS_CMD_HELLO =               _IOWR(KDBUS_IOCTL_MAGIC, 0x30,
> +                                             struct kdbus_cmd_hello),
> +       KDBUS_CMD_BYEBYE =              _IO(KDBUS_IOCTL_MAGIC, 0x31),
> +
> +       KDBUS_CMD_MSG_SEND =            _IOWR(KDBUS_IOCTL_MAGIC, 0x40,
> +                                             struct kdbus_msg),
> +       KDBUS_CMD_MSG_RECV =            _IOWR(KDBUS_IOCTL_MAGIC, 0x41,
> +                                             struct kdbus_cmd_recv),
> +       KDBUS_CMD_MSG_CANCEL =          _IOW(KDBUS_IOCTL_MAGIC, 0x42,
> +                                            struct kdbus_cmd_cancel),
> +       KDBUS_CMD_FREE =                _IOW(KDBUS_IOCTL_MAGIC, 0x43,
> +                                            struct kdbus_cmd_free),
> 

I think in general, using enum is great, but for ioctl command numbers,
we probably want to have defines so the user space implementation can
use #ifdef to see if the kernel version that it is being built for
knows a particular command.

You could do that using 

#define KDBUS_CMD_BUS_MAKE KDBUS_CMD_BUS_MAKE

while keeping the enum, or do it like everybody else using

#define KDBUS_CMD_BUS_MAKE _IOW(KDBUS_IOCTL_MAGIC, 0x00, struct kdbus_cmd_make)

which might in fact help some tools that try to do automated parsing
of header files to find ioctl commands.

	Arnd
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