Move logging functions to a new file, log.c

Logging to file is going to add some further complexity that we don't
want to squeeze into util.c.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

log.c

@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+/* PASST - Plug A Simple Socket Transport
+ *  for qemu/UNIX domain socket mode
+ *
+ * PASTA - Pack A Subtle Tap Abstraction
+ *  for network namespace/tap device mode
+ *
+ * log.c - Logging functions
+ *
+ * Copyright (c) 2020-2022 Red Hat GmbH
+ * Author: Stefano Brivio <sbrivio@redhat.com>
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <time.h>
+#include <syslog.h>
+#include <stdarg.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+
+#include "log.h"
+
+/* For __openlog() and __setlogmask() wrappers, and passt_vsyslog() */
+static int	log_mask;
+static int	log_sock = -1;
+static char	log_ident[BUFSIZ];
+static int	log_opt;
+static time_t	log_debug_start;
+int		log_trace;
+
+#define logfn(name, level)						\
+void name(const char *format, ...) {					\
+	struct timespec tp;						\
+	va_list args;							\
+									\
+	if (setlogmask(0) & LOG_MASK(LOG_DEBUG)) {			\
+		clock_gettime(CLOCK_REALTIME, &tp);			\
+		fprintf(stderr, "%li.%04li: ",				\
+			tp.tv_sec - log_debug_start,			\
+			tp.tv_nsec / (100L * 1000));			\
+	} else {							\
+		va_start(args, format);					\
+		passt_vsyslog(level, format, args);			\
+		va_end(args);						\
+	}								\
+									\
+	if (setlogmask(0) & LOG_MASK(LOG_DEBUG) ||			\
+	    setlogmask(0) == LOG_MASK(LOG_EMERG)) {			\
+		va_start(args, format);					\
+		(void)vfprintf(stderr, format, args); 			\
+		va_end(args);						\
+		if (format[strlen(format)] != '\n')			\
+			fprintf(stderr, "\n");				\
+	}								\
+}
+
+logfn(err,   LOG_ERR)
+logfn(warn,  LOG_WARNING)
+logfn(info,  LOG_INFO)
+logfn(debug, LOG_DEBUG)
+
+void trace_init(int enable)
+{
+	log_trace = enable;
+}
+
+/**
+ * __openlog() - Non-optional openlog() wrapper, to allow custom vsyslog()
+ * @ident:	openlog() identity (program name)
+ * @option:	openlog() options
+ * @facility:	openlog() facility (LOG_DAEMON)
+ */
+void __openlog(const char *ident, int option, int facility)
+{
+	struct timespec tp;
+
+	clock_gettime(CLOCK_REALTIME, &tp);
+	log_debug_start = tp.tv_sec;
+
+	if (log_sock < 0) {
+		struct sockaddr_un a = { .sun_family = AF_UNIX, };
+
+		log_sock = socket(AF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC, 0);
+		if (log_sock < 0)
+			return;
+
+		strncpy(a.sun_path, _PATH_LOG, sizeof(a.sun_path));
+		if (connect(log_sock, (const struct sockaddr *)&a, sizeof(a))) {
+			close(log_sock);
+			log_sock = -1;
+			return;
+		}
+	}
+
+	log_mask |= facility;
+	strncpy(log_ident, ident, sizeof(log_ident) - 1);
+	log_opt = option;
+
+	openlog(ident, option, facility);
+}
+
+/**
+ * __setlogmask() - setlogmask() wrapper, to allow custom vsyslog()
+ * @mask:	Same as setlogmask() mask
+ */
+void __setlogmask(int mask)
+{
+	log_mask = mask;
+	setlogmask(mask);
+}
+
+/**
+ * passt_vsyslog() - vsyslog() implementation not using heap memory
+ * @pri:	Facility and level map, same as priority for vsyslog()
+ * @format:	Same as vsyslog() format
+ * @ap:		Same as vsyslog() ap
+ */
+void passt_vsyslog(int pri, const char *format, va_list ap)
+{
+	char buf[BUFSIZ];
+	int n;
+
+	if (!(LOG_MASK(LOG_PRI(pri)) & log_mask))
+		return;
+
+	/* Send without name and timestamp, the system logger should add them */
+	n = snprintf(buf, BUFSIZ, "<%i> ", pri);
+
+	n += vsnprintf(buf + n, BUFSIZ - n, format, ap);
+
+	if (format[strlen(format)] != '\n')
+		n += snprintf(buf + n, BUFSIZ - n, "\n");
+
+	if (log_opt & LOG_PERROR)
+		fprintf(stderr, "%s", buf + sizeof("<0>"));
+
+	if (send(log_sock, buf, n, 0) != n)
+		fprintf(stderr, "Failed to send %i bytes to syslog\n", n);
+}