[PATCH iproute2-next v2 3/3] Improve batch and dump times by caching link lookups

[David Ahern <dsahern@kernel.org>]

From: David Ahern <dsahern@gmail.com>

ip route uses ll_name_to_index and ll_index_to_name to convert between
device names and indices. At the moment both use for the ioctl based glibc
functions if_nametoindex and if_indextoname and does not cache the result.
When using a batch file or dumping large number of routes this means the
same device lookups can be done repeatedly adding unnecessary overhead
(socket + ioctl + close for each device lookup).

Add a new function, ll_link_get, to send a netlink based RTM_GETLINK. If
successful, cache the result in idx_head and name_head so future lookups
can re-use the entry. Update ll_name_to_index and ll_index_to_name to use
ll_link_get and only fallback to the glibc functions if it fails.

With this change the time to install 720,022 routes with 2 ecmp nexthops
where the nexthop device is given is reduced from 31.4 seconds to 19.2
seconds. A dump of those routes drops from 13.3 to 2.8 seconds.

Signed-off-by: David Ahern <dsahern@gmail.com>
---
 lib/ll_map.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 51 insertions(+), 1 deletion(-)

diff --git a/lib/ll_map.c b/lib/ll_map.c
index 8e8a0b1e9c9d..2d7b65dcb8f7 100644
--- a/lib/ll_map.c
+++ b/lib/ll_map.c
@@ -152,6 +152,48 @@ static unsigned int ll_idx_a2n(const char *name)
 	return idx;
 }
 
+static int ll_link_get(const char *name, int index)
+{
+	struct {
+		struct nlmsghdr		n;
+		struct ifinfomsg	ifm;
+		char			buf[1024];
+	} req = {
+		.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg)),
+		.n.nlmsg_flags = NLM_F_REQUEST,
+		.n.nlmsg_type = RTM_GETLINK,
+		.ifm.ifi_index = index,
+	};
+	__u32 filt_mask = RTEXT_FILTER_VF | RTEXT_FILTER_SKIP_STATS;
+	struct rtnl_handle rth = {};
+	struct nlmsghdr *answer;
+	int rc = 0;
+
+	if (rtnl_open(&rth, 0) < 0)
+		return 0;
+
+	addattr32(&req.n, sizeof(req), IFLA_EXT_MASK, filt_mask);
+	if (name)
+		addattr_l(&req.n, sizeof(req), IFLA_IFNAME, name,
+			  strlen(name) + 1);
+
+	if (rtnl_talk(&rth, &req.n, &answer) < 0)
+		goto out;
+
+	/* add entry to cache */
+	rc  = ll_remember_index(answer, NULL);
+	if (!rc) {
+		struct ifinfomsg *ifm = NLMSG_DATA(answer);
+
+		rc = ifm->ifi_index;
+	}
+
+	free(answer);
+out:
+	rtnl_close(&rth);
+	return rc;
+}
+
 const char *ll_index_to_name(unsigned int idx)
 {
 	static char buf[IFNAMSIZ];
@@ -164,6 +206,12 @@ const char *ll_index_to_name(unsigned int idx)
 	if (im)
 		return im->name;
 
+	if (ll_link_get(NULL, idx) == idx) {
+		im = ll_get_by_index(idx);
+		if (im)
+			return im->name;
+	}
+
 	if (if_indextoname(idx, buf) == NULL)
 		snprintf(buf, IFNAMSIZ, "if%u", idx);
 
@@ -204,7 +252,9 @@ unsigned ll_name_to_index(const char *name)
 	if (im)
 		return im->index;
 
-	idx = if_nametoindex(name);
+	idx = ll_link_get(name, 0);
+	if (idx == 0)
+		idx = if_nametoindex(name);
 	if (idx == 0)
 		idx = ll_idx_a2n(name);
 	return idx;
-- 
2.11.0