[PATCH v6 11/13] dhcp: Select address for DHCP distribution

[Jon Maloy <jmaloy@redhat.com>]

We introduce a CONF_ADDR_DHCP flag to mark if an added address is
eligible for DHCP advertisement. By doing this once and for all
in the fwd_set_addr() function, the DHCP code only needs to check
for this flag to know that all criteria for advertisement are
fulfilled. Hence, we update the code in dhcp.c correspondingly.

We also let the conf_print() function use this flag to determine
and print the selected address.

Signed-off-by: Jon Maloy <jmaloy@redhat.com>

---
v6: Split off from a commit handling both DHCP and DHCPv6
---
 conf.c    |  9 ++++-----
 dhcp.c    | 21 +++++++++++++--------
 dhcp.h    |  2 +-
 fwd.c     |  9 +++++++++
 migrate.c |  5 +++++
 passt.h   |  1 +
 6 files changed, 33 insertions(+), 14 deletions(-)

diff --git a/conf.c b/conf.c
index 320a9e4..512fa38 100644
--- a/conf.c
+++ b/conf.c
@@ -46,6 +46,7 @@
 #include "lineread.h"
 #include "isolation.h"
 #include "log.h"
+#include "fwd.h"
 #include "vhost_user.h"
 
 #define NETNS_RUN_DIR	"/run/netns"
@@ -1182,11 +1183,9 @@ static void conf_print(const struct ctx *c)
 			     inet_ntop(AF_INET, &c->ip4.map_host_loopback,
 				       buf, sizeof(buf)));
 
-		a = fwd_get_addr(c, AF_INET, 0, 0);
-		if (a && !c->no_dhcp) {
-			uint32_t mask;
-
-			mask = IN4_MASK(inany_prefix_len(a));
+		a = fwd_get_addr(c, AF_INET, CONF_ADDR_DHCP, 0);
+		if (a) {
+			uint32_t mask = IN4_MASK(inany_prefix_len(a));
 
 			info("DHCP:");
 			inany_ntop(&a->addr, buf, sizeof(buf));
diff --git a/dhcp.c b/dhcp.c
index 6d9def5..cdb3afb 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -31,6 +31,8 @@
 #include "passt.h"
 #include "tap.h"
 #include "log.h"
+#include "fwd.h"
+#include "conf.h"
 #include "dhcp.h"
 
 /**
@@ -300,23 +302,22 @@ static void opt_set_dns_search(const struct ctx *c, size_t max_len)
  *
  * Return: 0 if it's not a DHCP message, 1 if handled, -1 on failure
  */
-int dhcp(const struct ctx *c, struct iov_tail *data)
+int dhcp(struct ctx *c, struct iov_tail *data)
 {
-	const struct guest_addr *a = fwd_get_addr(c, AF_INET, 0, 0);
+	struct in_addr addr, mask, dst;
 	char macstr[ETH_ADDRSTRLEN];
+	const struct guest_addr *a;
 	size_t mlen, dlen, opt_len;
-	struct in_addr mask, dst;
+	struct udphdr uh_storage;
 	struct ethhdr eh_storage;
 	struct iphdr iph_storage;
-	struct udphdr uh_storage;
+	const struct udphdr *uh;
 	const struct ethhdr *eh;
 	const struct iphdr *iph;
-	const struct udphdr *uh;
 	struct msg m_storage;
 	struct msg const *m;
-	struct in_addr addr;
 	struct msg reply;
-	unsigned int i;
+	int i;
 
 	eh = IOV_REMOVE_HEADER(data, eh_storage);
 	iph = IOV_PEEK_HEADER(data, iph_storage);
@@ -346,7 +347,11 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
 	    m->op != BOOTREQUEST)
 		return -1;
 
-	ASSERT(a);
+	/* Select address to offer */
+	a = fwd_get_addr(c, AF_INET, CONF_ADDR_DHCP, 0);
+	if (!a)
+		return -1;
+
 	addr = *inany_v4(&a->addr);
 
 	reply.op		= BOOTREPLY;
diff --git a/dhcp.h b/dhcp.h
index cd50c99..7326c7d 100644
--- a/dhcp.h
+++ b/dhcp.h
@@ -6,7 +6,7 @@
 #ifndef DHCP_H
 #define DHCP_H
 
-int dhcp(const struct ctx *c, struct iov_tail *data);
+int dhcp(struct ctx *c, struct iov_tail *data);
 void dhcp_init(void);
 
 #endif /* DHCP_H */
diff --git a/fwd.c b/fwd.c
index b3f5dc0..e1c85dd 100644
--- a/fwd.c
+++ b/fwd.c
@@ -295,6 +295,15 @@ void fwd_set_addr(struct ctx *c, const union inany_addr *addr,
 		return;
 	}
 
+	/* Determine advertisement eligibility */
+	if ((flags & (CONF_ADDR_HOST | CONF_ADDR_USER)) &&
+	    !(flags & CONF_ADDR_LINKLOCAL)) {
+		if (inany_v4(addr)) {
+			if (!c->no_dhcp)
+				flags |= CONF_ADDR_DHCP;
+		}
+	}
+
 	/* Add to head or tail, depending on flag */
 	if (flags & CONF_ADDR_OBSERVED) {
 		a = &arr[0];
diff --git a/migrate.c b/migrate.c
index 7b9a2f6..1d1e0e6 100644
--- a/migrate.c
+++ b/migrate.c
@@ -52,6 +52,7 @@ struct migrate_seen_addrs_v2 {
 #define MIGRATE_ADDR_HOST	BIT(1)
 #define MIGRATE_ADDR_LINKLOCAL	BIT(2)
 #define MIGRATE_ADDR_OBSERVED	BIT(3)
+#define MIGRATE_ADDR_DHCP	BIT(4)
 
 /**
  * struct migrate_addr_v3 - Wire format for a single address entry
@@ -83,6 +84,8 @@ static uint8_t flags_to_wire(uint8_t flags)
 		wire |= MIGRATE_ADDR_LINKLOCAL;
 	if (flags & CONF_ADDR_OBSERVED)
 		wire |= MIGRATE_ADDR_OBSERVED;
+	if (flags & CONF_ADDR_DHCP)
+		wire |= MIGRATE_ADDR_DHCP;
 
 	return wire;
 }
@@ -105,6 +108,8 @@ static uint8_t flags_from_wire(uint8_t wire)
 		flags |= CONF_ADDR_LINKLOCAL;
 	if (wire & MIGRATE_ADDR_OBSERVED)
 		flags |= CONF_ADDR_OBSERVED;
+	if (wire & MIGRATE_ADDR_DHCP)
+		flags |= CONF_ADDR_DHCP;
 
 	return flags;
 }
diff --git a/passt.h b/passt.h
index db2f10d..5ea1715 100644
--- a/passt.h
+++ b/passt.h
@@ -75,6 +75,7 @@ enum passt_modes {
 #define CONF_ADDR_HOST		BIT(1)		/* From host interface */
 #define CONF_ADDR_LINKLOCAL	BIT(2)		/* Link-local address */
 #define CONF_ADDR_OBSERVED	BIT(3)		/* Seen in guest traffic */
+#define CONF_ADDR_DHCP		BIT(4)		/* Advertise via DHCP (IPv4) */
 
 /**
  * struct guest_addr - Unified IPv4/IPv6 address entry
-- 
2.52.0