tools: hv: ignore ENOBUFS and ENOMEM in the KVP daemon

Under high memory pressure and very high KVP R/W test pressure, the netlink
recvfrom() may transiently return ENOBUFS to the daemon -- we found this
during a 2-week stress test.

We'd better not terminate the daemon on the failure, because a typical KVP
user will re-try the R/W and hopefully it will succeed next time.

We can also ignore the errors on sending.

Cc: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tools/hv/hv_kvp_daemon.c

@@ -1559,8 +1559,15 @@ int main(int argc, char *argv[])
 				addr_p, &addr_l);
 
 		if (len < 0) {
+			int saved_errno = errno;
 			syslog(LOG_ERR, "recvfrom failed; pid:%u error:%d %s",
 					addr.nl_pid, errno, strerror(errno));
+
+			if (saved_errno == ENOBUFS) {
+				syslog(LOG_ERR, "receive error: ignored");
+				continue;
+			}
+
 			close(fd);
 			return -1;
 		}
@@ -1763,8 +1770,15 @@ kvp_done:
 
 		len = netlink_send(fd, incoming_cn_msg);
 		if (len < 0) {
+			int saved_errno = errno;
 			syslog(LOG_ERR, "net_link send failed; error: %d %s", errno,
 					strerror(errno));
+
+			if (saved_errno == ENOMEM || saved_errno == ENOBUFS) {
+				syslog(LOG_ERR, "send error: ignored");
+				continue;
+			}
+
 			exit(EXIT_FAILURE);
 		}
 	}