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

Jean Delvare
2012-10-27T14:32:24Z

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:
> > 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