fwd_rule: Move forwarding rule formatting

In order to be shared with the upcoming configuration client, we want to
split code which deals with forwarding rules as standalone objects from
those which deal with forwarding rules as they're actually used to
implement forwarding in passt/pasta.

Create fwd_rule.c to contain code from the first category, and start off
by moving code to format rules into text for human display into it.  While
we're at it, we rework that formatting code a little to make it more
flexible.

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

6 files changed, 113 insertions, 55 deletions

diff --git a/Makefile b/Makefile
index dd647b1..f697c12 100644
--- a/Makefile
+++ b/Makefile
@@ -38,11 +38,11 @@ FLAGS += -DVERSION=\"$(VERSION)\"
 FLAGS += -DDUAL_STACK_SOCKETS=$(DUAL_STACK_SOCKETS)
 
 PASST_SRCS = arch.c arp.c bitmap.c checksum.c conf.c dhcp.c dhcpv6.c \
-	epoll_ctl.c flow.c fwd.c icmp.c igmp.c inany.c iov.c ip.c isolation.c \
-	lineread.c log.c mld.c ndp.c netlink.c migrate.c packet.c passt.c \
-	pasta.c pcap.c pif.c repair.c serialise.c tap.c tcp.c tcp_buf.c \
-	tcp_splice.c tcp_vu.c udp.c udp_flow.c udp_vu.c util.c vhost_user.c \
-	virtio.c vu_common.c
+	epoll_ctl.c flow.c fwd.c fwd_rule.c icmp.c igmp.c inany.c iov.c ip.c \
+	isolation.c lineread.c log.c mld.c ndp.c netlink.c migrate.c packet.c \
+	passt.c pasta.c pcap.c pif.c repair.c serialise.c tap.c tcp.c \
+	tcp_buf.c tcp_splice.c tcp_vu.c udp.c udp_flow.c udp_vu.c util.c \
+	vhost_user.c virtio.c vu_common.c
 QRAP_SRCS = qrap.c
 PASST_REPAIR_SRCS = passt-repair.c
 SRCS = $(PASST_SRCS) $(QRAP_SRCS) $(PASST_REPAIR_SRCS)
diff --git a/conf.c b/conf.c
index 03e0fe5..10e8fb2 100644
--- a/conf.c
+++ b/conf.c
@@ -1269,7 +1269,7 @@ dns6:
 			dir = "Inbound";
 
 		info("%s forwarding rules (%s):", dir, pif_name(i));
-		fwd_rules_print(c->fwd[i]);
+		fwd_rules_info(c->fwd[i]->rules, c->fwd[i]->count);
 	}
 }
 
diff --git a/fwd.c b/fwd.c
index 7e0edc3..39a14c4 100644
--- a/fwd.c
+++ b/fwd.c
@@ -305,20 +305,6 @@ parse_err:
 }
 
 /**
- * fwd_rule_addr() - Return match address for a rule
- * @rule:	Forwarding rule
- *
- * Return: matching address for rule, NULL if it matches all addresses
- */
-static const union inany_addr *fwd_rule_addr(const struct fwd_rule *rule)
-{
-	if (rule->flags & FWD_DUAL_STACK_ANY)
-		return NULL;
-
-	return &rule->addr;
-}
-
-/**
  * fwd_port_map_ephemeral() - Mark ephemeral ports in a bitmap
  * @map:	Bitmap to update
  */
@@ -487,40 +473,6 @@ const struct fwd_rule *fwd_rule_search(const struct fwd_table *fwd,
 	return NULL;
 }
 
-/**
- * fwd_rules_print() - Print forwarding rules for debugging
- * @fwd:	Table to print
- */
-void fwd_rules_print(const struct fwd_table *fwd)
-{
-	unsigned i;
-
-	for (i = 0; i < fwd->count; i++) {
-		const struct fwd_rule *rule = &fwd->rules[i];
-		const char *percent = *rule->ifname ? "%" : "";
-		const char *weak = "", *scan = "";
-		char addr[INANY_ADDRSTRLEN];
-
-		inany_ntop(fwd_rule_addr(rule), addr, sizeof(addr));
-		if (rule->flags & FWD_WEAK)
-			weak = " (best effort)";
-		if (rule->flags & FWD_SCAN)
-			scan = " (auto-scan)";
-
-		if (rule->first == rule->last) {
-			info("    %s [%s]%s%s:%hu  =>  %hu %s%s",
-			     ipproto_name(rule->proto), addr, percent,
-			     rule->ifname, rule->first, rule->to, weak, scan);
-		} else {
-			info("    %s [%s]%s%s:%hu-%hu  =>  %hu-%hu %s%s",
-			     ipproto_name(rule->proto), addr, percent,
-			     rule->ifname, rule->first, rule->last,
-			     rule->to, rule->last - rule->first + rule->to,
-			     weak, scan);
-		}
-	}
-}
-
 /** fwd_sync_one() - Create or remove listening sockets for a forward entry
  * @c:		Execution context
  * @pif:	Interface to create listening sockets for
diff --git a/fwd.h b/fwd.h
index 7e9ec49..805fabd 100644
--- a/fwd.h
+++ b/fwd.h
@@ -91,7 +91,6 @@ void fwd_rule_add(struct fwd_table *fwd, uint8_t proto, uint8_t flags,
 const struct fwd_rule *fwd_rule_search(const struct fwd_table *fwd,
 				       const struct flowside *ini,
 				       uint8_t proto, int hint);
-void fwd_rules_print(const struct fwd_table *fwd);
 
 void fwd_scan_ports_init(struct ctx *c);
 void fwd_scan_ports_timer(struct ctx * c, const struct timespec *now);
diff --git a/fwd_rule.c b/fwd_rule.c
new file mode 100644
index 0000000..a034d5d
--- /dev/null
+++ b/fwd_rule.c
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0-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
+ *
+ * PESTO - Programmable Extensible Socket Translation Orchestrator
+ *  front-end for passt(1) and pasta(1) forwarding configuration
+ *
+ * fwd_rule.c - Helpers for working with forwarding rule specifications
+ *
+ * Copyright Red Hat
+ * Author: David Gibson <david@gibson.dropbear.id.au>
+ */
+
+#include <stdio.h>
+
+#include "fwd_rule.h"
+
+/**
+ * fwd_rule_addr() - Return match address for a rule
+ * @rule:	Forwarding rule
+ *
+ * Return: matching address for rule, NULL if it matches all addresses
+ */
+const union inany_addr *fwd_rule_addr(const struct fwd_rule *rule)
+{
+	if (rule->flags & FWD_DUAL_STACK_ANY)
+		return NULL;
+
+	return &rule->addr;
+}
+
+/**
+ * fwd_rule_fmt() - Prettily format forwarding rule as a string
+ * @rule:	Rule to format
+ * @dst:	Buffer to store output (should have FWD_RULE_STRLEN bytes)
+ * @size:	Size of @dst
+ */
+#if defined(__GNUC__) && __GNUC__ < 15
+/* Workaround bug in gcc 12, 13 & 14 (at least) which gives a false positive
+ * -Wformat-overflow message if this function is inlined.
+ */
+__attribute__((noinline))
+#endif
+static const char *fwd_rule_fmt(const struct fwd_rule *rule,
+				char *dst, size_t size)
+{
+	const char *percent = *rule->ifname ? "%" : "";
+	const char *weak = "", *scan = "";
+	char addr[INANY_ADDRSTRLEN];
+	int len;
+
+	inany_ntop(fwd_rule_addr(rule), addr, sizeof(addr));
+	if (rule->flags & FWD_WEAK)
+		weak = " (best effort)";
+	if (rule->flags & FWD_SCAN)
+		scan = " (auto-scan)";
+
+	if (rule->first == rule->last) {
+		len = snprintf(dst, size,
+			       "%s [%s]%s%s:%hu  =>  %hu %s%s",
+			       ipproto_name(rule->proto), addr, percent,
+			       rule->ifname, rule->first, rule->to, weak, scan);
+	} else {
+		in_port_t tolast = rule->last - rule->first + rule->to;
+		len = snprintf(dst, size,
+			       "%s [%s]%s%s:%hu-%hu  =>  %hu-%hu %s%s",
+			       ipproto_name(rule->proto), addr, percent,
+			       rule->ifname, rule->first, rule->last,
+			       rule->to, tolast, weak, scan);
+	}
+
+	if (len < 0 || (size_t)len >= size)
+		return NULL;
+
+	return dst;
+}
+
+/**
+ * fwd_rules_info() - Print forwarding rules for debugging
+ * @fwd:	Table to print
+ */
+void fwd_rules_info(const struct fwd_rule *rules, size_t count)
+{
+	unsigned i;
+
+	for (i = 0; i < count; i++) {
+		char buf[FWD_RULE_STRLEN];
+
+		info("    %s", fwd_rule_fmt(&rules[i], buf, sizeof(buf)));
+	}
+}
diff --git a/fwd_rule.h b/fwd_rule.h
index ae0e1d6..e92efb6 100644
--- a/fwd_rule.h
+++ b/fwd_rule.h
@@ -13,7 +13,9 @@
 #include <net/if.h>
 #include <netinet/in.h>
 
+#include "ip.h"
 #include "inany.h"
+#include "bitmap.h"
 
 /**
  * struct fwd_rule - Forwarding rule governing a range of ports
@@ -41,4 +43,14 @@ struct fwd_rule {
 	uint8_t flags;
 };
 
+#define FWD_RULE_STRLEN					    \
+	(IPPROTO_STRLEN - 1				    \
+	 + INANY_ADDRSTRLEN - 1				    \
+	 + IFNAMSIZ - 1					    \
+	 + 4 * (UINT16_STRLEN - 1)			    \
+	 + sizeof(" []%:-  =>  - (best effort) (auto-scan)"))
+
+const union inany_addr *fwd_rule_addr(const struct fwd_rule *rule);
+void fwd_rules_info(const struct fwd_rule *rules, size_t count);
+
 #endif /* FWD_RULE_H */