[PATCH v7 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

v7: -Modified DHCP advertisement eligibility criteria IPv4 addresses:
     We now permit link local addresses to be eligible if they were
     configured by the user.
    -Adapted to previous changes in this series
---
 conf.c    |  5 +++--
 dhcp.c    | 14 +++++++++-----
 fwd.c     |  8 ++++++++
 migrate.c |  5 +++++
 passt.h   |  1 +
 5 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/conf.c b/conf.c
index 3cb3553..612df07 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"
@@ -1181,8 +1182,8 @@ 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) {
+		a = fwd_get_addr(c, AF_INET, CONF_ADDR_DHCP, 0);
+		if (a) {
 			uint32_t mask;
 
 			mask = IN4_MASK(inany_prefix_len(&a->addr,
diff --git a/dhcp.c b/dhcp.c
index f0fa212..0f98cfc 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"
 
 /**
@@ -302,19 +304,18 @@ static void opt_set_dns_search(const struct ctx *c, size_t max_len)
  */
 int dhcp(const struct ctx *c, struct iov_tail *data)
 {
+	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 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;
 
@@ -346,8 +347,11 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
 	    m->op != BOOTREQUEST)
 		return -1;
 
-	a = fwd_get_addr(c, AF_INET, 0, 0);
-	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/fwd.c b/fwd.c
index b177be9..39e52c4 100644
--- a/fwd.c
+++ b/fwd.c
@@ -293,6 +293,14 @@ void fwd_set_addr(struct ctx *c, const union inany_addr *addr,
 		return;
 	}
 
+	/* Determine advertisement eligibility */
+	if (inany_v4(addr)) {
+		if ((flags & CONF_ADDR_USER) ||
+		    (flags & CONF_ADDR_HOST && !(flags & CONF_ADDR_LINKLOCAL)))
+			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 93f67ae..afdc8b4 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 - Migration format for a single address entry
@@ -83,6 +84,8 @@ static uint8_t flags_to_migration(uint8_t flags)
 		migration |= MIGRATE_ADDR_LINKLOCAL;
 	if (flags & CONF_ADDR_OBSERVED)
 		migration |= MIGRATE_ADDR_OBSERVED;
+	if (flags & CONF_ADDR_DHCP)
+		migration |= MIGRATE_ADDR_DHCP;
 
 	return migration;
 }
@@ -105,6 +108,8 @@ static uint8_t flags_from_migration(uint8_t migration)
 		flags |= CONF_ADDR_LINKLOCAL;
 	if (migration & MIGRATE_ADDR_OBSERVED)
 		flags |= CONF_ADDR_OBSERVED;
+	if (migration & MIGRATE_ADDR_DHCP)
+		flags |= CONF_ADDR_DHCP;
 
 	return flags;
 }
diff --git a/passt.h b/passt.h
index 3ef84eb..9508c2a 100644
--- a/passt.h
+++ b/passt.h
@@ -83,6 +83,7 @@ struct guest_addr {
 #define CONF_ADDR_GENERATED	BIT(2)		/* Generated by PASST/PASTA */
 #define CONF_ADDR_LINKLOCAL	BIT(3)		/* Link-local address */
 #define CONF_ADDR_OBSERVED	BIT(4)		/* Seen in guest traffic */
+#define CONF_ADDR_DHCP		BIT(5)		/* Advertise via DHCP (IPv4) */
 };
 
 /**
-- 
2.52.0