[dpdk-dev] [PATCH v2] Fixes: 57f90f894588("net/virtio: reuse packed ring functions")

[Xia, Chenbo]

Hi Vipul,

> -----Original Message-----
> From: Vipul Ashri <vipul.ashri at oracle.com>
> Sent: Wednesday, August 12, 2020 5:23 PM
> To: dev at dpdk.org
> Cc: Xia, Chenbo <chenbo.xia at intel.com>; vipul.ashri at oracle.com;
> edwin.leung at oracle.com
> Subject: [PATCH v2] Fixes: 57f90f894588("net/virtio: reuse packed ring
> functions")
> 
> Problem - Standard Tx packets are not going out and found broken
>  due to cleanup malfunctioning whereever below mentioned macro is
>  used.
> 
> RootCause - Here inside Macro 'ASSIGN_UNLESS_EQUAL(var, val)'
>  assignment to 'var' argument passed is always failing as assignment
>  done using 'var_' having local scope only.
> 
> Signed-off-by: Vipul Ashri <vipul.ashri at oracle.com>

I understand now. Your patch makes sense. But your commit title/msg is still
wrong. An example commit message should be (you could use this):

net/virtio: fix wrong variable assignment in helper macro

Inside Macro ASSIGN_UNLESS_EQUAL(var, val), assignment to var is always failing
as assignment done using var_ having local scope only. This leads to TX packets
not going out and found broken due to cleanup malfunctioning. This patch fixes
the wrong variable assignment.

Fixes: 57f90f894588("net/virtio: reuse packed ring functions")
Cc: stable at dpdk.org

Signed-off-by: Vipul Ashri <vipul.ashri at oracle.com>

> ---
>  drivers/net/virtio/virtqueue.h | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/virtio/virtqueue.h
> b/drivers/net/virtio/virtqueue.h
> index 105a9c00c..20c95471e 100644
> --- a/drivers/net/virtio/virtqueue.h
> +++ b/drivers/net/virtio/virtqueue.h
> @@ -607,10 +607,8 @@ virtqueue_notify(struct virtqueue *vq)
> 
>  /* avoid write operation when necessary, to lessen cache issues */
>  #define ASSIGN_UNLESS_EQUAL(var, val) do {	\
> -	typeof(var) var_ = (var);		\
> -	typeof(val) val_ = (val);		\
> -	if ((var_) != (val_))			\
> -		(var_) = (val_);		\
> +	if ((var) != (val))			\
> +		(var) = (val);			\
>  } while (0)
> 
>  #define virtqueue_clear_net_hdr(hdr) do {		\
> --
> 2.28.0.windows.1