lib: allow recirculating/relaying log messages

This is primarily intended for ldpd with its split-process architecture.
The LDE/LDPE subprocesses currently lose the extended zlog
functionality.

The zlog_live target already encapsulates all necessary bits for vtysh.
Reuse it for a relay function to be used in the main ldpd process.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>

1 files changed, 56 insertions, 0 deletions

diff --git a/lib/zlog_recirculate.c b/lib/zlog_recirculate.c
new file mode 100644
index 0000000000..abc73eeed0
--- /dev/null
+++ b/lib/zlog_recirculate.c
@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: ISC
+/*
+ * Copyright (c) 2024  David Lamparter, for NetDEF, Inc.
+ */
+
+#include "zebra.h"
+
+#include "log.h"
+#include "frrevent.h"
+
+#include "zlog_recirculate.h"
+
+/* This is only the event loop part;  it's split off from
+ * zlog_recirculate_live_msg since there's an integration boundary;  this
+ * half deals with events, the other half with zlog interna.
+ *
+ * As of writing, this runs in ldpd in the *parent* process and receives log
+ * messages from the lde/ldpe subprocesses.  It is not used anywhere else
+ * (yet?)
+ */
+static void zlog_recirculate_recv(struct event *ev)
+{
+	uint8_t rxbuf[4096];
+	ssize_t n_rd;
+	int fd = EVENT_FD(ev);
+
+	/* see below for -2, "\n\0" are added */
+	n_rd = read(fd, rxbuf, sizeof(rxbuf) - 2);
+	if (n_rd == 0) {
+		/* EOF */
+		close(fd);
+		/* event_add_read not called yet, nothing to cancel */
+		return;
+	}
+	if (n_rd < 0 && (errno != EAGAIN) && (errno != EWOULDBLOCK)) {
+		/* error */
+		zlog_warn("error on log relay socket %d: %m", fd);
+		close(fd);
+		/* event_add_read not called yet, nothing to cancel */
+		return;
+	}
+
+	event_add_read(ev->master, zlog_recirculate_recv, NULL, fd, NULL);
+	if (n_rd < 0)
+		return;
+
+	/* log infrastructure has an implicit \n\0 at the end */
+	rxbuf[n_rd] = '\n';
+	rxbuf[n_rd + 1] = '\0';
+	zlog_recirculate_live_msg(rxbuf, n_rd);
+}
+
+void zlog_recirculate_subscribe(struct event_loop *el, int fd)
+{
+	event_add_read(el, zlog_recirculate_recv, NULL, fd, NULL);
+}