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netlink: avoid putting empty mbufs on the socket queue
When processing incoming Netlink messages in nl_process_nbuf() kernel always allocates a writer with a buffer to put generated reply to. However, certain messages aren't replied. That makes nlmsg_flush() to put an empty buffer to the socket. Avoid doing that because avoiding is much easier than dealing with empty buffers on the receiver side.
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@ -740,12 +740,7 @@ nl_soreceive(struct socket *so, struct sockaddr **psa, struct uio *uio,
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TAILQ_FOREACH(nb, &sb->nl_queue, tailq) {
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u_int offset;
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/*
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* XXXGL: zero length buffer may be at the tail of a queue
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* when a writer overflows socket buffer. When this is
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* improved, use MPASS(nb->offset < nb->datalen).
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*/
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MPASS(nb->offset <= nb->datalen);
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MPASS(nb->offset < nb->datalen);
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offset = nb->offset;
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while (offset < nb->datalen) {
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hdr = (struct nlmsghdr *)&nb->data[offset];
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@ -201,6 +201,8 @@ nl_send(struct nl_writer *nw, struct nlpcb *nlp)
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struct nl_buf *nb;
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MPASS(nw->hdr == NULL);
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MPASS(nw->buf != NULL);
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MPASS(nw->buf->datalen > 0);
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IF_DEBUG_LEVEL(LOG_DEBUG2) {
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struct nlmsghdr *hdr = (struct nlmsghdr *)nw->buf->data;
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@ -100,6 +100,7 @@ _nlmsg_ignore_limit(struct nl_writer *nw)
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bool
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_nlmsg_flush(struct nl_writer *nw)
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{
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bool result;
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if (__predict_false(nw->hdr != NULL)) {
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/* Last message has not been completed, skip it. */
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@ -109,8 +110,14 @@ _nlmsg_flush(struct nl_writer *nw)
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nw->hdr = NULL;
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}
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NL_LOG(LOG_DEBUG2, "OUT");
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bool result = nw->cb(nw);
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if (nw->buf->datalen == 0) {
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MPASS(nw->num_messages == 0);
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nl_buf_free(nw->buf);
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nw->buf = NULL;
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return (true);
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}
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result = nw->cb(nw);
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nw->num_messages = 0;
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if (!result) {
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