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

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

On Fri, May 18, 2018 at 02:48:11PM +0000, guido@kiener-muenchen.de wrote:
> 
> Zitat von Greg KH <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];
> > ?
> > 
> 
> Oh yes, I should know that from another project. Indead we did not test it
> with 32 bit applications on 64 platforms.
> 
> When we use your proposal then we just can use
> #define USBTMC_IOCTL_WRITE _IO(USBTMC_IOC_NR, 13)?

Why 13?  Use the structure please, that way you know you always get it
right.

thanks,

greg k-h
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