[06/12] usb: usbtmc: Add vendor specific/asynchronous read/write ioctls

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, May 17, 2018 at 07:03:30PM +0200, Guido Kiener wrote:
> +/*
> + * usbtmc_message->flags:
> + */
> +#define USBTMC_FLAG_ASYNC		0x0001
> +#define USBTMC_FLAG_APPEND		0x0002
> +#define USBTMC_FLAG_IGNORE_TRAILER	0x0004
> +
> +struct usbtmc_message {
> +	void __user *message; /* pointer to header and data */
> +	__u64 transfer_size; /* size of bytes to transfer */
> +	__u64 transferred; /* size of received/written bytes */
> +	__u32 flags; /* bit 0: 0 = synchronous; 1 = asynchronous */
> +} __attribute__ ((packed));

Very odd structure.  Your userspace pointer is going to be totally out
of alignment on 32bit systems running on a 64bit kernel.  Why have a
separate pointer at all?  Why not just put the mesage at the end of this
structure directly with something like:
	__u8 message[0];
?

Much easier and you don't have to mess with the whole compatible ioctl
thunking layer (which I think you ignored here, which means you all
didn't test it...)

thanks,

greg k-h
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