devlink: mnlg: Catch returned error value of dumpit commands

Devlink commands which implements the dumpit callback may return error.
The netlink function netlink_dump() sends the errno value as the payload
of the message, while answering user space with NLMSG_DONE.
To enable receiving errno value for dumpit commands we have to check for
it in the message. If it is a negative value then the dump returned an
error so we should set errno accordingly and check for ext_ack in case
it was set.

Fixes: 049c58539f ("devlink: mnlg: Add support for extended ack")
Signed-off-by: Moshe Shemesh <moshe@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

devlink/mnlg.c

@@ -85,6 +85,13 @@ static int mnlg_cb_error(const struct nlmsghdr *nlh, void *data)
 
 static int mnlg_cb_stop(const struct nlmsghdr *nlh, void *data)
 {
+	int len = *(int *)NLMSG_DATA(nlh);
+
+	if (len < 0) {
+		errno = -len;
+		nl_dump_ext_ack_done(nlh, len);
+		return MNL_CB_ERROR;
+	}
 	return MNL_CB_STOP;
 }
 

include/libnetlink.h

@@ -129,6 +129,7 @@ int rtnl_send(struct rtnl_handle *rth, const void *buf, int)
 int rtnl_send_check(struct rtnl_handle *rth, const void *buf, int)
 	__attribute__((warn_unused_result));
 int nl_dump_ext_ack(const struct nlmsghdr *nlh, nl_ext_ack_fn_t errfn);
+int nl_dump_ext_ack_done(const struct nlmsghdr *nlh, int error);
 
 int addattr(struct nlmsghdr *n, int maxlen, int type);
 int addattr8(struct nlmsghdr *n, int maxlen, int type, __u8 data);

lib/libnetlink.c

@@ -125,7 +125,7 @@ int nl_dump_ext_ack(const struct nlmsghdr *nlh, nl_ext_ack_fn_t errfn)
 	return 0;
 }
 
-static int nl_dump_ext_ack_done(const struct nlmsghdr *nlh, int error)
+int nl_dump_ext_ack_done(const struct nlmsghdr *nlh, int error)
 {
 	struct nlattr *tb[NLMSGERR_ATTR_MAX + 1] = {};
 	unsigned int hlen = sizeof(int);
@@ -155,7 +155,7 @@ int nl_dump_ext_ack(const struct nlmsghdr *nlh, nl_ext_ack_fn_t errfn)
 	return 0;
 }
 
-static int nl_dump_ext_ack_done(const struct nlmsghdr *nlh, int error)
+int nl_dump_ext_ack_done(const struct nlmsghdr *nlh, int error)
 {
 	return 0;
 }