netlink: Change rtnl_dump_done to always show error

The original code which became rtnl_dump_done only shows netlink errors
if the protocol is NETLINK_SOCK_DIAG, but netlink dumps always appends
the length which contains any error encountered during the dump. Update
rtnl_dump_done to always show the error if there is one.

As an *example* without this patch, dumping a route object that exceeds
the internal buffer size terminates with no message to the user -- the
dump just ends because the NLMSG_DONE attribute was received. With this
patch the user at least gets a message that the dump was aborted.

$ ip ro ls
default via 10.0.2.2 dev eth0
10.0.2.0/24 dev eth0 proto kernel scope link src 10.0.2.15
10.10.0.0/16 dev veth1 proto kernel scope link src 10.10.0.1
172.16.1.0/24 dev br0.11 proto kernel scope link src 172.16.1.1
Error: Buffer too small for object
Dump terminated

The point of this patch is to notify the user of a failure versus
silently exiting on a partial dump. Because the NLMSG_DONE attribute
was received, the entire dump needs to be restarted to use a larger
buffer for EMSGSIZE errors. That could be done automatically but it
has other user impacts (e.g., duplicate output if the dump is
restarted) and should be the subject of a different patch.

Signed-off-by: David Ahern <dsahern@gmail.com>

diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index 5b75b2db4e0b4cfd603d9b9d0edc4cdde5ed8a7d..d4b831f67ea223bb18861bacea03eac2c40e3cee 100644 (file)
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -266,21 +266,27 @@ static int rtnl_dump_done(const struct rtnl_handle *rth,
 {
        int len = *(int *)NLMSG_DATA(h);
 
-       if (rth->proto == NETLINK_SOCK_DIAG) {
-               if (h->nlmsg_len < NLMSG_LENGTH(sizeof(int))) {
-                       fprintf(stderr, "DONE truncated\n");
-                       return -1;
-               }
-
+       if (h->nlmsg_len < NLMSG_LENGTH(sizeof(int))) {
+               fprintf(stderr, "DONE truncated\n");
+               return -1;
+       }
 
-               if (len < 0) {
-                       errno = -len;
-                       if (errno == ENOENT || errno == EOPNOTSUPP)
-                               return -1;
+       if (len < 0) {
+               errno = -len;
+               switch (errno) {
+               case ENOENT:
+               case EOPNOTSUPP:
+                       return -1;
+               case EMSGSIZE:
+                       fprintf(stderr,
+                               "Error: Buffer too small for object.\n");
+                       break;
+               default:
                        perror("RTNETLINK answers");
-                       return len;
                }
+               return len;
        }
+
        return 0;
 }