netlink: make the maximum allowed netlink socket buffer runtime tunable.

Dumping large routng tables (>1M paths with multipath) require the socket
 buffer which is larger than the currently defined limit.
Allow the limit to be set in runtime, similar to kern.ipc.maxsockbuf.

Reported by:	Marek Zarychta <zarychtam@plan-b.pwste.edu.pl>
MFC after:	1 day

2 files changed, 27 insertions, 0 deletions

diff --git a/share/man/man4/netlink.4 b/share/man/man4/netlink.4
index fdcc823b01a6..ece4892f481e 100644
--- a/share/man/man4/netlink.4
+++ b/share/man/man4/netlink.4
@@ -280,6 +280,12 @@ Default receive buffer for the netlink socket.
 Note that the socket recvspace has to be least as long as the longest
 message that can be received from this socket.
 .El
+.Bl -tag -width indent
+.It Va net.netlink.nl_maxsockbuf
+Maximum receive buffer for the netlink socket that can be set via
+.Dv SO_RCVBUF
+socket option.
+.El
 .Sh DEBUGGING
 Netlink implements per-functional-unit debugging, with different severities
 controllable via the
diff --git a/sys/netlink/netlink_domain.c b/sys/netlink/netlink_domain.c
index 5f9120f14308..01023f7244b6 100644
--- a/sys/netlink/netlink_domain.c
+++ b/sys/netlink/netlink_domain.c
@@ -77,6 +77,11 @@ SYSCTL_ULONG(_net_netlink, OID_AUTO, recvspace, CTLFLAG_RW, &nl_recvspace, 0,
 
 extern u_long sb_max_adj;
 static u_long nl_maxsockbuf = 512 * 1024 * 1024; /* 512M, XXX: init based on physmem */
+static int sysctl_handle_nl_maxsockbuf(SYSCTL_HANDLER_ARGS);
+SYSCTL_OID(_net_netlink, OID_AUTO, nl_maxsockbuf,
+    CTLTYPE_ULONG | CTLFLAG_RW | CTLFLAG_MPSAFE, &nl_maxsockbuf, 0,
+    sysctl_handle_nl_maxsockbuf, "LU",
+    "Maximum Netlink socket buffer size");
 
 uint32_t
 nlp_get_pid(const struct nlpcb *nlp)
@@ -676,6 +681,22 @@ nl_ctloutput(struct socket *so, struct sockopt *sopt)
 }
 
 static int
+sysctl_handle_nl_maxsockbuf(SYSCTL_HANDLER_ARGS)
+{
+	int error = 0;
+	u_long tmp_maxsockbuf = nl_maxsockbuf;
+
+	error = sysctl_handle_long(oidp, &tmp_maxsockbuf, arg2, req);
+	if (error || !req->newptr)
+		return (error);
+	if (tmp_maxsockbuf < MSIZE + MCLBYTES)
+		return (EINVAL);
+	nl_maxsockbuf = tmp_maxsockbuf;
+
+	return (0);
+}
+
+static int
 nl_setsbopt(struct socket *so, struct sockopt *sopt)
 {
 	int error, optval;