In recent Linux kernels, there is support for extended acknowledgement
to netlink messages. This is quite useful for diagnosing errors
in configuration in the kernel with TAP.
Signed-off-by: Stephen Hemminger <step...@networkplumber.org>
---
drivers/net/tap/tap_netlink.c | 78 +++++++++++++++++++++++++++++++++++
1 file changed, 78 insertions(+)
diff --git a/drivers/net/tap/tap_netlink.c b/drivers/net/tap/tap_netlink.c
index 64220178a6ba..2365678a9c13 100644
--- a/drivers/net/tap/tap_netlink.c
+++ b/drivers/net/tap/tap_netlink.c
@@ -9,10 +9,12 @@
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>
+#include <stdbool.h>
#include <rte_malloc.h>
#include <tap_netlink.h>
#include <rte_random.h>
+
#include "tap_log.h"
/* Must be quite large to support dumping a huge list of QDISC or filters. */
@@ -43,6 +45,7 @@ tap_nl_init(uint32_t nl_groups)
.nl_family = AF_NETLINK,
.nl_groups = nl_groups,
};
+ int one = 1;
fd = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE);
if (fd < 0) {
@@ -59,6 +62,12 @@ tap_nl_init(uint32_t nl_groups)
close(fd);
return -1;
}
+
+#ifdef NETLINK_EXT_ACK
+ /* Ask for extended ACK response. on older kernel will ignore request.
*/
+ setsockopt(fd, SOL_NETLINK, NETLINK_EXT_ACK, &one, sizeof(one));
+#endif
+
if (bind(fd, (struct sockaddr *)&local, sizeof(local)) < 0) {
TAP_LOG(ERR, "Unable to bind to the netlink socket");
close(fd);
@@ -119,6 +128,74 @@ tap_nl_send(int nlsk_fd, struct nlmsghdr *nh)
return send_bytes;
}
+#ifdef NETLINK_EXT_ACK
+static const struct nlattr *
+tap_nl_attr_first(const struct nlmsghdr *nh, size_t offset)
+{
+ return (const struct nlattr *)((const char *)nh + NLMSG_SPACE(offset));
+}
+
+static const struct nlattr *
+tap_nl_attr_next(const struct nlattr *attr)
+{
+ return (const struct nlattr *)((const char *)attr
+ + NLMSG_ALIGN(attr->nla_len));
+}
+
+static bool
+tap_nl_attr_ok(const struct nlattr *attr, int len)
+{
+ if (len < (int)sizeof(struct nlattr))
+ return false; /* missing header */
+ if (attr->nla_len < sizeof(struct nlattr))
+ return false; /* attribute length should include itself */
+ if ((int)attr->nla_len > len)
+ return false; /* attribute is truncated */
+ return true;
+}
+
+
+/* Decode extended errors from kernel */
+static void
+tap_nl_dump_ext_ack(const struct nlmsghdr *nh, const struct nlmsgerr *err)
+{
+ const struct nlattr *attr;
+ const char *tail = (const char *)nh + NLMSG_ALIGN(nh->nlmsg_len);
+ size_t hlen = sizeof(*err);
+
+ /* no TLVs, no extended response */
+ if (!(nh->nlmsg_flags & NLM_F_ACK_TLVS))
+ return;
+
+ if (!(nh->nlmsg_flags & NLM_F_CAPPED))
+ hlen += err->msg.nlmsg_len - NLMSG_HDRLEN;
+
+ for (attr = tap_nl_attr_first(nh, hlen);
+ tap_nl_attr_ok(attr, tail - (const char *)attr);
+ attr = tap_nl_attr_next(attr)) {
+ uint16_t type = attr->nla_type & NLA_TYPE_MASK;
+
+ if (type == NLMSGERR_ATTR_MSG) {
+ const char *msg = (const char *)attr
+ + NLMSG_ALIGN(sizeof(*attr));
+
+ if (err->error)
+ TAP_LOG(ERR, "%s", msg);
+ else
+
+ TAP_LOG(WARNING, "%s", msg);
+ break;
+ }
+ }
+}
+#else
+/*
+ * External ACK support was added in Linux kernel 4.17
+ * on older kernels, just ignore that part of message
+ */
+#define tap_nl_dump_ext_ack(nh, err) do { } while();
+#endif
+
/**
* Check that the kernel sends an appropriate ACK in response
* to an tap_nl_send().
@@ -174,6 +251,7 @@ tap_nl_recv(int nlsk_fd, int (*cb)(struct nlmsghdr *, void
*arg), void *arg)
if (nh->nlmsg_type == NLMSG_ERROR) {
struct nlmsgerr *err_data = NLMSG_DATA(nh);
+ tap_nl_dump_ext_ack(nh, err_data);
if (err_data->error < 0) {
errno = -err_data->error;
return -1;
--
2.20.1
