Change Details

Netlink has a confirmation/error reporting mechanism for the sent messages. Kernel explicitly acks each messages if requested (NLM_F_ACK) or if message processing results in an error. Similarly, for multipart messages - typically dumps, where each message represents a single object like an interface or a route - another message, NLMSG_DONE is used to indicate the end of dump and the resulting status. As a result, successfull dump ends with both NLMSG_DONE and NLMSG_ERROR messages. RFC 3549 does not say anything specific about such case. Linux adopted an optimisation which suppresses NLMSG_ERROR message when NLMSG_DONE is already sent. Certain libraries/applications like libnl depends on such behavior. Suppress sending NLMSG_ERROR if NLMSG_DONE is already sent, by setting newly-added 'suppress_ack' flag in the writer and checking this flag when generating ack. This change restores libnl compatibility. Before: ``` ~ nl-link-list Error: Unable to allocate link cache: Message sequence number mismatch ```` After: ``` ~ nl-link-list vtnet0 ether 52:54:00:14:e3:19 <broadcast,multicast,up,running> lo0 ieee1394 <loopback,multicast,up,running> ```

Netlink has a confirmation/error reporting mechanism for the sent messages. Kernel explicitly acks each messages if requested (NLM_F_ACK) or if message processing results in an error. Similarly, for multipart messages - typically dumps, where each message represents a single object like an interface or a route - another message, NLMSG_DONE is used to indicate the end of dump and the resulting status. As a result, successfull dump ends with both NLMSG_DONE and NLMSG_ERROR messages. RFC 3549 does not say anything specific about such case. Linux adopted an optimisation which suppresses NLMSG_ERROR message when NLMSG_DONE is already sent. Certain libraries/applications like libnl depends on such behavior. Suppress sending NLMSG_ERROR if NLMSG_DONE is already sent, by setting newly-added 'suppress_ack' flag in the writer and checking this flag when generating ack. This change restores libnl compatibility.

Netlink has a confirmation/error reporting mechanism for the sent messages. Kernel explicitly acks each messages if requested (NLM_F_ACK) or if message processing results in an error. Similarly, for multipart messages - typically dumps, where each message represents a single object like an interface or a route - another message, NLMSG_DONE is used to indicate the end of dump and the resulting status. As a result, successfull dump ends with both NLMSG_DONE and NLMSG_ERROR messages. RFC 3549 does not say anything specific about such case. Linux adopted an optimisation which suppresses NLMSG_ERROR message when NLMSG_DONE is already sent. Certain libraries/applications like libnl depends on such behavior. Suppress sending NLMSG_ERROR if NLMSG_DONE is already sent, by setting newly-added 'suppress_ack' flag in the writer and checking this flag when generating ack. This change restores libnl compatibility. Before: ``` ~ nl-link-list Error: Unable to allocate link cache: Message sequence number mismatch ```` After: ``` ~ nl-link-list vtnet0 ether 52:54:00:14:e3:19 <broadcast,multicast,up,running> lo0 ieee1394 <loopback,multicast,up,running> ```