[iproute PATCH] ip: add error reporting when RTM_GETNSID failed

[Jan Engelhardt <jengelh@inai.de>]

`ip addr` when run under qemu-user-riscv64, fails. This likely is due
to qemu-5.1 not doing translation of RTM_GETNSID calls. Aborting ip
completely is not helpful for the user however. This patch reworks
the error handling.

Before:

rtest:/ # ip a
2: host0@if4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
request send failed: Operation not supported
    link/ether 46:3f:2d:88:3d:db brd ff:ff:ff:ff:ff:ffrtest:/ #

Afterwards:

rtest:/ # ip a
2: host0@if4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
rtnl_send(RTM_GETNSID): Operation not supported. Continuing anyway.
    link/ether 46:3f:2d:88:3d:db brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 192.168.72.147/28 brd 192.168.72.159 scope global host0
       valid_lft forever preferred_lft forever
    inet6 fe80::443f:2dff:fe88:3ddb/64 scope link
       valid_lft forever preferred_lft forever
rtest:/ #

Signed-off-by: Jan Engelhardt <jengelh@inai.de>
---
 ip/ipnetns.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/ip/ipnetns.c b/ip/ipnetns.c
index 46cc235b..e7a45653 100644
--- a/ip/ipnetns.c
+++ b/ip/ipnetns.c
@@ -78,6 +78,8 @@ static int ipnetns_have_nsid(void)
 	if (have_rtnl_getnsid < 0) {
 		fd = open("/proc/self/ns/net", O_RDONLY);
 		if (fd < 0) {
+			fprintf(stderr, "/proc/self/ns/net: %s. "
+				"Continuing anyway.\n", strerror(errno));
 			have_rtnl_getnsid = 0;
 			return 0;
 		}
@@ -85,8 +87,11 @@ static int ipnetns_have_nsid(void)
 		addattr32(&req.n, 1024, NETNSA_FD, fd);
 
 		if (rtnl_send(&rth, &req.n, req.n.nlmsg_len) < 0) {
-			perror("request send failed");
-			exit(1);
+			fprintf(stderr, "rtnl_send(RTM_GETNSID): %s. "
+				"Continuing anyway.\n", strerror(errno));
+			have_rtnl_getnsid = 0;
+			close(fd);
+			return 0;
 		}
 		rtnl_listen(&rth, ipnetns_accept_msg, NULL);
 		close(fd);
-- 
2.28.0