[PATCH 7/8] i2c: add 'transferred' field to struct i2c_msg

On Thu, 25 Oct 2012 15:18:00 +0100, Russell King - ARM Linux wrote:

On Thu, Oct 25, 2012 at 03:56:33PM +0200, Jean Delvare wrote:

quoted

The original idea of using the hole in the i2c_msg structure is from
David Brownell, who was apparently familiar with such practice, so I
assumed it was OK. Actually I still assume it is, until someone comes
with an supported architecture where it is not.

According to Al Viro, that would be m68k.

OK... So to make things clear, let me ask Al directly about it. Al, can
you please tell us if:

--- a/include/uapi/linux/i2c.h
+++ b/include/uapi/linux/i2c.h
 struct i2c_msg {
 	__u16 addr;		/* slave address			*/
 	__u16 flags;
 	__u16 len;		/* msg length				*/
+	__u16 transferred;	/* actual bytes transferred             */
 	__u8 *buf;		/* pointer to msg data			*/
 };
 

would break binary compatibility on m68k or any other architecture you
are familiar with? Note that struct i2c_msg isn't declared with
attribute packed, so my assumption was that pointer "buf" was align on
at least 4 bytes, leaving a hole between len and buf. Am I wrong?

Thanks,
-- 
Jean Delvare