lib: Add unix_msg

This is a messaging layer based on unix domain datagram sockets.

Sending to an idle socket is just one single nonblocking sendmsg call. If the
recv queue is full, we start a background thread to do a blocking call. The
source4 based imessaging uses a polling fallback. In a situation where
thousands of senders beat one single blocked socket, this will generate load on
the system due to the constant polling. This does not happen with a threaded
blocking send call.

The threaded approach has another advantage: We save become_root() calls on the
retries. The access checks are done when the blocking socket is connected, the
threaded blocking send call does not check permissions anymore.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

source3/lib/unix_msg/test_source.c

@@ -0,0 +1,79 @@
+#include "replace.h"
+#include "unix_msg.h"
+#include "poll_funcs/poll_funcs_tevent.h"
+#include "tevent.h"
+
+int main(int argc, const char *argv[])
+{
+	struct poll_funcs funcs;
+	struct unix_msg_ctx **ctxs;
+	struct tevent_context *ev;
+	struct iovec iov;
+	int ret;
+	unsigned i;
+	unsigned num_ctxs = 1;
+
+	if (argc < 2) {
+		fprintf(stderr, "Usage: %s <sockname> [num_contexts]\n", argv[0]);
+		return 1;
+	}
+	if (argc > 2) {
+		num_ctxs = atoi(argv[2]);
+	}
+
+	ev = tevent_context_init(NULL);
+	if (ev == NULL) {
+		perror("tevent_context_init failed");
+		return 1;
+	}
+	poll_funcs_init_tevent(&funcs, ev);
+
+	ctxs = talloc_array(ev, struct unix_msg_ctx *, num_ctxs);
+	if (ctxs == NULL) {
+		fprintf(stderr, "talloc failed\n");
+		return 1;
+	}
+
+	for (i=0; i<num_ctxs; i++) {
+		ret = unix_msg_init(NULL, &funcs, 256, 1, NULL, NULL,
+				    &ctxs[i]);
+		if (ret != 0) {
+			fprintf(stderr, "unix_msg_init failed: %s\n",
+				strerror(ret));
+			return 1;
+		}
+	}
+
+	iov.iov_base = &i;
+	iov.iov_len = sizeof(i);
+
+	for (i=0; i<num_ctxs; i++) {
+		unsigned j;
+
+		for (j=0; j<100000; j++) {
+			ret = unix_msg_send(ctxs[i], argv[1], &iov, 1);
+			if (ret != 0) {
+				fprintf(stderr, "unix_msg_send failed: %s\n",
+					strerror(ret));
+				return 1;
+			}
+		}
+	}
+
+	while (true) {
+		ret = tevent_loop_once(ev);
+		if (ret == -1) {
+			fprintf(stderr, "tevent_loop_once failed: %s\n",
+				strerror(errno));
+			exit(1);
+		}
+	}
+
+	for (i=0; i<num_ctxs; i++) {
+		unix_msg_free(ctxs[i]);
+	}
+
+	talloc_free(ev);
+
+	return 0;
+}