The rtnetlink rtmsg rtm_table variable can hold route table IDs no
higher than UCHAR_MAX.

Use the rtnetlink RTA_TABLE route attribute for table IDs larger
than UCHAR_MAX, which can represent a 32 bit integer worth of
route tables.

While RTA_TABLE support was added to the kernel in commit [0] and
has been supported since 2006 starting from v2.6.19, we retain
a backward compatible approach for consistency with the existing
code for reading route table back from the kernel [1].

0: 
https://github.com/torvalds/linux/commit/9e762a4a89b302cb3b26a1f9bb33eff459eaeca9
1: 
https://github.com/openvswitch/ovs/blob/8b7f1eb8db1aa99ccf7b542662129450caff65e0/lib/route-table.c#L284-L287
Signed-off-by: Frode Nordahl <[email protected]>
---
 lib/route-table.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/lib/route-table.c b/lib/route-table.c
index 1703b69b4..180da1632 100644
--- a/lib/route-table.c
+++ b/lib/route-table.c
@@ -198,7 +198,7 @@ route_table_wait(void)
 }
 
 static bool
-route_table_dump_one_table(unsigned char id)
+route_table_dump_one_table(uint32_t id)
 {
     uint64_t reply_stub[NL_DUMP_BUFSIZE / 8];
     struct ofpbuf request, reply, buf;
@@ -212,7 +212,13 @@ route_table_dump_one_table(unsigned char id)
 
     rq_msg = ofpbuf_put_zeros(&request, sizeof *rq_msg);
     rq_msg->rtm_family = AF_UNSPEC;
-    rq_msg->rtm_table = id;
+
+    if (id > UCHAR_MAX) {
+        rq_msg->rtm_table = RT_TABLE_UNSPEC;
+        nl_msg_put_u32(&request, RTA_TABLE, id);
+    } else {
+        rq_msg->rtm_table = id;
+    }
 
     nl_dump_start(&dump, NETLINK_ROUTE, &request);
     ofpbuf_uninit(&request);
@@ -241,7 +247,7 @@ route_table_dump_one_table(unsigned char id)
 static void
 route_table_reset(void)
 {
-    unsigned char tables[] = {
+    uint32_t tables[] = {
         RT_TABLE_DEFAULT,
         RT_TABLE_MAIN,
         RT_TABLE_LOCAL,
-- 
2.47.1

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