[iproute2 net-next 1/3] netlink: Add flag to suppress print of nlmsg error

[David Ahern <dsa@cumulusnetworks.com>]

Allow callers of the dump API to handle nlmsg errors (e.g., an
unsupported feature). Setting RTNL_HANDLE_F_SUPPRESS_NLERR in the
rtnl_handle avoids unnecessary messages to the users in some case.
For example,

  RTNETLINK answers: Operation not supported

when probing for support of a new feature.

Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
---
 include/libnetlink.h | 1 +
 lib/libnetlink.c     | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/libnetlink.h b/include/libnetlink.h
index bd0267dfcc02..c43ab0a2d9d9 100644
--- a/include/libnetlink.h
+++ b/include/libnetlink.h
@@ -21,6 +21,7 @@ struct rtnl_handle {
 	int			proto;
 	FILE		       *dump_fp;
 #define RTNL_HANDLE_F_LISTEN_ALL_NSID		0x01
+#define RTNL_HANDLE_F_SUPPRESS_NLERR		0x02
 	int			flags;
 };
 
diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index 9303b6686e2c..5b75b2db4e0b 100644
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -299,7 +299,8 @@ static void rtnl_dump_error(const struct rtnl_handle *rth,
 		     errno == EOPNOTSUPP))
 			return;
 
-		perror("RTNETLINK answers");
+		if (!(rth->flags & RTNL_HANDLE_F_SUPPRESS_NLERR))
+			perror("RTNETLINK answers");
 	}
 }
 
-- 
2.1.4