netdev - [PATCH iproute2-next 2/4] lib: iplink: print warnings for missing data

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Date:   Fri, 22 Jan 2021 20:53:49 -0800
From:   Edwin Peer <edwin.peer@...adcom.com>
To:     netdev@...r.kernel.org
Cc:     Edwin Peer <edwin.peer@...adcom.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Andrew Gospodarek <andrew.gospodarek@...adcom.com>,
        Michael Chan <michael.chan@...adcom.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Michal Kubecek <mkubecek@...e.cz>,
        David Ahern <dsahern@...il.com>
Subject: [PATCH iproute2-next 2/4] lib: iplink: print warnings for missing data

The kernel might truncate VF info in IFLA_VFINFO_LIST. Sufficiently new
kernels will provide NLM_F_NEST_TRUNCATED in these cases, but this flag
has limited resolution, as it pertains to the entire netlink message. A
better approach is to compare the expected number of VFs in IFLA_NUM_VF
to how many were found in the list and warn accordingly.

Signed-off-by: Edwin Peer <edwin.peer@...adcom.com>
---
 ip/ipaddress.c   |  9 ++++++++-
 lib/libnetlink.c | 12 ++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/ip/ipaddress.c b/ip/ipaddress.c
index 571346b15cc3..0bbcee2b3bb2 100644
--- a/ip/ipaddress.c
+++ b/ip/ipaddress.c
@@ -922,6 +922,7 @@ int print_linkinfo(struct nlmsghdr *n, void *arg)
 	const char *name;
 	unsigned int m_flag = 0;
 	SPRINT_BUF(b1);
+	bool truncated_vfs = false;
 
 	if (n->nlmsg_type != RTM_NEWLINK && n->nlmsg_type != RTM_DELLINK)
 		return 0;
@@ -1199,15 +1200,18 @@ int print_linkinfo(struct nlmsghdr *n, void *arg)
 
 	if ((do_link || show_details) && tb[IFLA_VFINFO_LIST] && tb[IFLA_NUM_VF]) {
 		struct rtattr *i, *vflist = tb[IFLA_VFINFO_LIST];
-		int rem = RTA_PAYLOAD(vflist);
+		int rem = RTA_PAYLOAD(vflist), count = 0;
 
 		open_json_array(PRINT_JSON, "vfinfo_list");
 		for (i = RTA_DATA(vflist); RTA_OK(i, rem); i = RTA_NEXT(i, rem)) {
 			open_json_object(NULL);
 			print_vfinfo(fp, ifi, i);
 			close_json_object();
+			count++;
 		}
 		close_json_array(PRINT_JSON, NULL);
+		if (count != rta_getattr_u32(tb[IFLA_NUM_VF]))
+			truncated_vfs = true;
 	}
 
 	if (tb[IFLA_PROP_LIST]) {
@@ -1228,6 +1232,9 @@ int print_linkinfo(struct nlmsghdr *n, void *arg)
 
 	print_string(PRINT_FP, NULL, "%s", "\n");
 	fflush(fp);
+	/* prettier here if stderr and stdout go to the same place */
+	if (truncated_vfs)
+		fprintf(stderr, "Truncated VF list: %s\n", name);
 	return 1;
 }
 
diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index c958aa57d0cd..b1f07d4570cf 100644
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -833,6 +833,9 @@ static int rtnl_dump_filter_l(struct rtnl_handle *rth,
 				if (h->nlmsg_flags & NLM_F_DUMP_INTR)
 					dump_intr = 1;
 
+				if (h->nlmsg_flags & NLM_F_NEST_TRUNCATED)
+					fprintf(stderr, "Incomplete data: truncated attribute list\n");
+
 				if (h->nlmsg_type == NLMSG_DONE) {
 					err = rtnl_dump_done(h);
 					if (err < 0) {
@@ -978,6 +981,9 @@ next:
 				continue;
 			}
 
+			if (h->nlmsg_flags & NLM_F_NEST_TRUNCATED)
+				fprintf(stderr, "Incomplete data: truncated attribute list\n");
+
 			if (h->nlmsg_type == NLMSG_ERROR) {
 				struct nlmsgerr *err = (struct nlmsgerr *)NLMSG_DATA(h);
 				int error = err->error;
@@ -1156,6 +1162,9 @@ int rtnl_listen(struct rtnl_handle *rtnl,
 				exit(1);
 			}
 
+			if (h->nlmsg_flags & NLM_F_NEST_TRUNCATED)
+				fprintf(stderr, "Incomplete data: truncated attribute list\n");
+
 			err = handler(&ctrl, h, jarg);
 			if (err < 0)
 				return err;
@@ -1206,6 +1215,9 @@ int rtnl_from_file(FILE *rtnl, rtnl_listen_filter_t handler,
 			return -1;
 		}
 
+		if (h->nlmsg_flags & NLM_F_NEST_TRUNCATED)
+			fprintf(stderr, "Incomplete data: truncated attribute list\n");
+
 		status = fread(NLMSG_DATA(h), 1, NLMSG_ALIGN(l), rtnl);
 
 		if (status != NLMSG_ALIGN(l)) {
-- 
2.30.0


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