[PATCH wireguard-tools v4 1/3] ipc: linux: filter netdevices kernel-side

[Asbjørn Sloth Tønnesen]

Tell the kernel that we are only interested in wireguard netdevices,
so the kernel don't have to dump all the other netdevices.

Kernel-side support for this was added in Linux v4.6 in
commit dc599f76c22b ("net: Add support for filtering link dump by
master device and kind").

Tested with 10000 netdevices (common with ISP BNG setups), and a
single wireguard netdevice.

Baseline:
  # time ./src/wg show
  real    0m0.342s
  user    0m0.013s
  sys     0m0.290s

With patch:
  # time ./src/wg show
  real    0m0.006s
  user    0m0.000s
  sys     0m0.005s

Despite the subject prefix, this patch also applies to the
embeddable C library, so the two implementations stay in sync.

Signed-off-by: Asbjørn Sloth Tønnesen <ast at fiberby.net>
---
 contrib/embeddable-wg-library/wireguard.c | 6 ++++++
 src/ipc-linux.h                           | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/contrib/embeddable-wg-library/wireguard.c b/contrib/embeddable-wg-library/wireguard.c
index 4941549..7ac0d6c 100644
--- a/contrib/embeddable-wg-library/wireguard.c
+++ b/contrib/embeddable-wg-library/wireguard.c
@@ -943,6 +943,7 @@ static int fetch_device_names(struct string_list *list)
 	int ret = 0;
 	struct nlmsghdr *nlh;
 	struct ifinfomsg *ifm;
+	struct nlattr *linkinfo_nest;
 
 	ret = -ENOMEM;
 	rtnl_buffer = calloc(mnl_ideal_socket_buffer_size(), 1);
@@ -968,6 +969,11 @@ static int fetch_device_names(struct string_list *list)
 	nlh->nlmsg_seq = seq;
 	ifm = mnl_nlmsg_put_extra_header(nlh, sizeof(*ifm));
 	ifm->ifi_family = AF_UNSPEC;
+
+	linkinfo_nest = mnl_attr_nest_start(nlh, IFLA_LINKINFO);
+	mnl_attr_put_strz(nlh, IFLA_INFO_KIND, WG_GENL_NAME);
+	mnl_attr_nest_end(nlh, linkinfo_nest);
+
 	message_len = nlh->nlmsg_len;
 
 	if (mnl_socket_sendto(nl, rtnl_buffer, message_len) < 0) {
diff --git a/src/ipc-linux.h b/src/ipc-linux.h
index 01247f1..c56fede 100644
--- a/src/ipc-linux.h
+++ b/src/ipc-linux.h
@@ -80,6 +80,7 @@ static int kernel_get_wireguard_interfaces(struct string_list *list)
 	int ret = 0;
 	struct nlmsghdr *nlh;
 	struct ifinfomsg *ifm;
+	struct nlattr *linkinfo_nest;
 
 	ret = -ENOMEM;
 	rtnl_buffer = calloc(SOCKET_BUFFER_SIZE, 1);
@@ -105,6 +106,11 @@ static int kernel_get_wireguard_interfaces(struct string_list *list)
 	nlh->nlmsg_seq = seq;
 	ifm = mnl_nlmsg_put_extra_header(nlh, sizeof(*ifm));
 	ifm->ifi_family = AF_UNSPEC;
+
+	linkinfo_nest = mnl_attr_nest_start(nlh, IFLA_LINKINFO);
+	mnl_attr_put_strz(nlh, IFLA_INFO_KIND, WG_GENL_NAME);
+	mnl_attr_nest_end(nlh, linkinfo_nest);
+
 	message_len = nlh->nlmsg_len;
 
 	if (mnl_socket_sendto(nl, rtnl_buffer, message_len) < 0) {
-- 
2.53.0