Wed, Apr 12, 2017 at 02:34:06PM CEST, johannes@xxxxxxxxxxxxxxxx wrote:
>From: Johannes Berg <johannes.berg@xxxxxxxxx>
>
>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 <johannes.berg@xxxxxxxxx>
Reviewed-by: Jiri Pirko <jiri@xxxxxxxxxxxx>
[...]
>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)
