Re: PATCH] firewire: add padding to some struct

From: Stefan Richter
Date: Fri Jul 18 2008 - 07:39:16 EST

JiSheng Zhang wrote:
> If p is a pointer to struct fw_cdev_event_response), p->data will point to the
> padding data rather than the right place, it will cause problem under some
> platforms. For example, in the function handle_device_event of libraw1394(ported
> to juju stack):
> .....
> rc = u64_to_ptr(u->response.closure);
> if (rc->data != NULL)
> memcpy(rc->data, u->, rc->length);//here it will lost the last four
> bytes
> errcode = juju_to_raw1394_errcode(u->response.rcode);
> .....
> Although this problem can be solved by add the offset to the pointer, but the
> member:__u32 data[0] lost its original meaning.

I don't understand what the problem is. As long as both kernel and
library use "" or "&response + offsetof(typeof(response),
data)", they will write and read at the correct location.

There would be a problem if one of the two used "&response +
sizeof(response)" instead. Does this happen anywhere? If so, then
these places need to be fixed, not the struct definition.
Stefan Richter
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