Subject: Re: [PATCH net-next v5 3/5] netlink: allow sending extended ACK with cookie on success

From: Jiri Pirko <[email-masked]>
Date: Wed, 12 Apr 2017 15:47:09 +0200

Wed, Apr 12, 2017 at 02:34:06PM CEST, [email-masked] wrote:
>From: Johannes Berg <[email-masked]>
>
>Now that we have extended error reporting and a new message format
>for netlink ACK messages, also extend this to be able to return
>arbitrary cookie data on success.
>
>This will allow, for example, nl80211 to not send an extra message
>for cookies identifying newly created objects, but return those
>directly in the ACK message.
>
>The cookie data size is currently limited to 20 bytes (since Jamal
>talked about using SHA1 for identifiers.)
>
>Thanks to Jamal Hadi Salim for bringing up this idea during the
>discussions.
>
>Signed-off-by: Johannes Berg <[email-masked]>

Reviewed-by: Jiri Pirko <jiri-VPRAkNaXOzVWk0Htik3J/[email-masked]>

[...]

>diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
>index 7df88770e029..f86127a46cfc 100644
>--- a/include/uapi/linux/netlink.h
>+++ b/include/uapi/linux/netlink.h
>@@ -122,6 +122,9 @@ struct nlmsgerr {
>  * @NLMSGERR_ATTR_MSG: error message string (string)
>  * @NLMSGERR_ATTR_OFFS: offset of the invalid attribute in the original
>  *	 message, counting from the beginning of the header (u32)
>+ * @NLMSGERR_ATTR_COOKIE: arbitrary subsystem specific cookie to
>+ *	be used - in the success case - to identify a created
>+ *	object or operation or similar (binary)
>  * @__NLMSGERR_ATTR_MAX: number of attributes
>  * @NLMSGERR_ATTR_MAX: highest attribute number
>  */
>@@ -129,6 +132,7 @@ enum nlmsgerr_attrs {
> 	NLMSGERR_ATTR_UNUSED,
> 	NLMSGERR_ATTR_MSG,
> 	NLMSGERR_ATTR_OFFS,
>+	NLMSGERR_ATTR_COOKIE,
> 
> 	__NLMSGERR_ATTR_MAX,
> 	NLMSGERR_ATTR_MAX = __NLMSGERR_ATTR_MAX - 1
>diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
>index c1564768000e..ee841f00a6ec 100644
>--- a/net/netlink/af_netlink.c
>+++ b/net/netlink/af_netlink.c
>@@ -2311,6 +2311,10 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
> 		}
> 	} else {
> 		flags |= NLM_F_CAPPED;
>+
>+		if (nlk->flags & NETLINK_F_EXT_ACK &&
>+		    extack && extack->cookie_len)
>+			tlvlen += nla_total_size(extack->cookie_len);
> 	}
> 

Now I see why you have "if (tlvlen)" where you have it :)

> 	if (tlvlen)