Re: [PATCH] ethdev: remove useless parameter in callback process

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 11/28/2017 2:09 PM, Thomas Monjalon wrote:
> The pointer to the user parameter of the callback registration is
> automatically pass to the callback function.
> There is no point to allow changing this user parameter by a caller.
> That's why this parameter is always set to NULL by PMDs and set only
> in ethdev layer before calling the callback function.

It can be helpful to mention a little from history:

user cb_arg overwrite introduced by [1], to enable driver pass a pointer to user
callback function and carry some information back from app to driver.

Later to prevent usage of cb_arg as both input and output, an explicit output
(ret_param) added [2] to _rte_eth_dev_callback_process() but previous cb_arg
overwriting kept without any user.

[1]: c1ceaf3ad056 ("ethdev: add an argument to internal callback function")

[2]: d6af1a13d7a1 ("ethdev: add return values to callback process API")

> 
> The NULL parameter in the internal callback processing function
> is now removed. It makes clear that the callback parameter is user
> managed and opaque from a DPDK point of view.
> 
> Signed-off-by: Thomas Monjalon <thomas@monjalon.net>

Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>