[PATCH RFC iproute2] libnetlink: allow reading more than one message from extack

[Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>]

This patch introduces support for reading more than one message from
extack's and to adjust their level (warning/error) accordingly.

Yes, there is a FIXME tag in the callback call for now.

Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
---
 lib/libnetlink.c | 55 ++++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 40 insertions(+), 15 deletions(-)

diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index 928de1dd16d84b7802c06d0a659f5d73e1bbcb4b..7c4c81e11e02ea857888190eb5e7a9e99d159bb3 100644
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -43,9 +43,16 @@ static const enum mnl_attr_data_type extack_policy[NLMSGERR_ATTR_MAX + 1] = {
 	[NLMSGERR_ATTR_OFFS]	= MNL_TYPE_U32,
 };
 
+#define NETLINK_MAX_EXTACK_MSGS 8
+struct extack_args {
+	const struct nlattr *msg[NETLINK_MAX_EXTACK_MSGS];
+	const struct nlattr *offs;
+	int msg_count;
+};
+
 static int err_attr_cb(const struct nlattr *attr, void *data)
 {
-	const struct nlattr **tb = data;
+	struct extack_args *tb = data;
 	uint16_t type;
 
 	if (mnl_attr_type_valid(attr, NLMSGERR_ATTR_MAX) < 0) {
@@ -60,19 +67,23 @@ static int err_attr_cb(const struct nlattr *attr, void *data)
 		return MNL_CB_ERROR;
 	}
 
-	tb[type] = attr;
+	if (type == NLMSGERR_ATTR_OFFS)
+		tb->offs = attr;
+	else if (tb->msg_count < NETLINK_MAX_EXTACK_MSGS)
+		tb->msg[tb->msg_count++] = attr;
 	return MNL_CB_OK;
 }
 
 /* dump netlink extended ack error message */
 int nl_dump_ext_ack(const struct nlmsghdr *nlh, nl_ext_ack_fn_t errfn)
 {
-	struct nlattr *tb[NLMSGERR_ATTR_MAX + 1] = {};
+	struct extack_args tb = {};
 	const struct nlmsgerr *err = mnl_nlmsg_get_payload(nlh);
 	const struct nlmsghdr *err_nlh = NULL;
 	unsigned int hlen = sizeof(*err);
-	const char *msg = NULL;
+	const char *msg[NETLINK_MAX_EXTACK_MSGS] = {};
 	uint32_t off = 0;
+	int ret, i;
 
 	/* no TLVs, nothing to do here */
 	if (!(nlh->nlmsg_flags & NLM_F_ACK_TLVS))
@@ -82,14 +93,14 @@ int nl_dump_ext_ack(const struct nlmsghdr *nlh, nl_ext_ack_fn_t errfn)
 	if (!(nlh->nlmsg_flags & NLM_F_CAPPED))
 		hlen += mnl_nlmsg_get_payload_len(&err->msg);
 
-	if (mnl_attr_parse(nlh, hlen, err_attr_cb, tb) != MNL_CB_OK)
+	if (mnl_attr_parse(nlh, hlen, err_attr_cb, &tb) != MNL_CB_OK)
 		return 0;
 
-	if (tb[NLMSGERR_ATTR_MSG])
-		msg = mnl_attr_get_str(tb[NLMSGERR_ATTR_MSG]);
+	for (i = 0; i < NETLINK_MAX_EXTACK_MSGS && tb.msg[i]; i++)
+		msg[i] = mnl_attr_get_str(tb.msg[i]);
 
-	if (tb[NLMSGERR_ATTR_OFFS]) {
-		off = mnl_attr_get_u32(tb[NLMSGERR_ATTR_OFFS]);
+	if (tb.offs) {
+		off = mnl_attr_get_u32(tb.offs);
 
 		if (off > nlh->nlmsg_len) {
 			fprintf(stderr,
@@ -100,21 +111,35 @@ int nl_dump_ext_ack(const struct nlmsghdr *nlh, nl_ext_ack_fn_t errfn)
 	}
 
 	if (errfn)
-		return errfn(msg, off, err_nlh);
+		return errfn(*msg, off, err_nlh); /* FIXME */
 
-	if (msg && *msg != '\0') {
+	ret = 0;
+	for (i = 0; i < NETLINK_MAX_EXTACK_MSGS && msg[i]; i++) {
 		bool is_err = !!err->error;
+		const char *_msg = msg[i];
+
+		/* Message tagging has precedence.
+		 * KERN_WARNING = ASCII Start Of Header ('\001') + '4'
+		 */
+		if (!strncmp(_msg, "\0014", 2)) {
+			is_err = false;
+			_msg += 2;
+		}
+		/* But we can't have Error if it didn't fail. */
+		if (is_err && !err->error)
+			is_err = 0;
 
 		fprintf(stderr, "%s: %s",
-			is_err ? "Error" : "Warning", msg);
-		if (msg[strlen(msg) - 1] != '.')
+			is_err ? "Error" : "Warning", _msg);
+		if (_msg[strlen(_msg) - 1] != '.')
 			fprintf(stderr, ".");
 		fprintf(stderr, "\n");
 
-		return is_err ? 1 : 0;
+		if (is_err)
+			ret = 1;
 	}
 
-	return 0;
+	return ret;
 }
 #else
 #warning "libmnl required for error support"
-- 
2.14.3