netlink: refactor writer initialization KPI

o Allow callers to initialize a writer that will malloc(9) with M_WAITOK.
o Use size_t for expected malloc size.
o Use correct types to initialize a group writer.
o Rename functions into nl_writer_ namespace instead of nlmsg_, cause
  they are working on nl_writer, not on nlmsg.
o Make the KPI responsible to sparsely initialize the writer structure.
o Garbage collect chain writer.  Fixes 17083b94a915.

All current consumers are left as is, however some may benefit from
M_WAITOK allocation as well as supplying a correct expected size.

Reviewed by:		melifaro
Differential Revision:	https://reviews.freebsd.org/D47549

1 files changed, 7 insertions, 5 deletions

diff --git a/sys/netlink/netlink_generic.c b/sys/netlink/netlink_generic.c
index 28f9fe108ef4..4a3c83da57e1 100644
--- a/sys/netlink/netlink_generic.c
+++ b/sys/netlink/netlink_generic.c
@@ -256,14 +256,16 @@ nlctrl_notify(void *arg __unused, const struct genl_family *gf, int cmd)
 {
 	struct nlmsghdr hdr = {.nlmsg_type = NETLINK_GENERIC };
 	struct genlmsghdr ghdr = { .cmd = cmd };
-	struct nl_writer nw = {};
+	struct nl_writer nw;
 
-	if (nlmsg_get_group_writer(&nw, NLMSG_SMALL, NETLINK_GENERIC, ctrl_group_id)) {
-		dump_family(&hdr, &ghdr, gf, &nw);
-		nlmsg_flush(&nw);
+	if (!nl_writer_group(&nw, NLMSG_SMALL, NETLINK_GENERIC, ctrl_group_id,
+	    false)) {
+		NL_LOG(LOG_DEBUG, "error allocating group writer");
 		return;
 	}
-	NL_LOG(LOG_DEBUG, "error allocating group writer");
+
+	dump_family(&hdr, &ghdr, gf, &nw);
+	nlmsg_flush(&nw);
 }
 
 static const struct genl_cmd nlctrl_cmds[] = {