[PATCH v6 10/13] migrate: Update protocol to v3 for multi-address support

[Jon Maloy <jmaloy@redhat.com>]

We update the migration protocol to version 3 to support distributing
multiple addresses from the unified address array. The new protocol
migrates all address entries in the array, along with their prefix
lengths and flags, and leaves it to the receiver to filter which
ones he wants to apply.

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

---
v4: - Broke out as separate commit
    - Made number of transferable addresses variable

v6: - Separated internal and wire transfer format
---
 migrate.c | 178 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 178 insertions(+)

diff --git a/migrate.c b/migrate.c
index a92301b..7b9a2f6 100644
--- a/migrate.c
+++ b/migrate.c
@@ -44,6 +44,71 @@ struct migrate_seen_addrs_v2 {
 	unsigned char mac[ETH_ALEN];
 } __attribute__((packed));
 
+/**
+ * Wire format flags for address migration (v3)
+ * These are stable values - do not change existing assignments
+ */
+#define MIGRATE_ADDR_USER	BIT(0)
+#define MIGRATE_ADDR_HOST	BIT(1)
+#define MIGRATE_ADDR_LINKLOCAL	BIT(2)
+#define MIGRATE_ADDR_OBSERVED	BIT(3)
+
+/**
+ * struct migrate_addr_v3 - Wire format for a single address entry
+ * @addr:	IPv6 or IPv4-mapped address (16 bytes)
+ * @prefix_len:	Prefix length
+ * @flags:	MIGRATE_ADDR_* flags (wire format)
+ */
+struct migrate_addr_v3 {
+	struct in6_addr addr;
+	uint8_t prefix_len;
+	uint8_t flags;
+} __attribute__((__packed__));
+
+/**
+ * flags_to_wire() - Convert internal flags to stable wire format
+ * @flags:	Internal CONF_ADDR_* flags
+ *
+ * Return: Wire format MIGRATE_ADDR_* flags
+ */
+static uint8_t flags_to_wire(uint8_t flags)
+{
+	uint8_t wire = 0;
+
+	if (flags & CONF_ADDR_USER)
+		wire |= MIGRATE_ADDR_USER;
+	if (flags & CONF_ADDR_HOST)
+		wire |= MIGRATE_ADDR_HOST;
+	if (flags & CONF_ADDR_LINKLOCAL)
+		wire |= MIGRATE_ADDR_LINKLOCAL;
+	if (flags & CONF_ADDR_OBSERVED)
+		wire |= MIGRATE_ADDR_OBSERVED;
+
+	return wire;
+}
+
+/**
+ * flags_from_wire() - Convert wire format flags to internal format
+ * @wire:	Wire format MIGRATE_ADDR_* flags
+ *
+ * Return: Internal CONF_ADDR_* flags
+ */
+static uint8_t flags_from_wire(uint8_t wire)
+{
+	uint8_t flags = 0;
+
+	if (wire & MIGRATE_ADDR_USER)
+		flags |= CONF_ADDR_USER;
+	if (wire & MIGRATE_ADDR_HOST)
+		flags |= CONF_ADDR_HOST;
+	if (wire & MIGRATE_ADDR_LINKLOCAL)
+		flags |= CONF_ADDR_LINKLOCAL;
+	if (wire & MIGRATE_ADDR_OBSERVED)
+		flags |= CONF_ADDR_OBSERVED;
+
+	return flags;
+}
+
 /**
  * seen_addrs_source_v2() - Copy and send guest observed addresses from source
  * @c:		Execution context
@@ -126,6 +191,98 @@ static int seen_addrs_target_v2(struct ctx *c,
 	return 0;
 }
 
+/**
+ * addrs_source_v3() - Send all addresses with flags from source
+ * @c:		Execution context
+ * @stage:	Migration stage, unused
+ * @fd:		File descriptor for state transfer
+ *
+ * Send all address entries using a stable wire format. Each field is
+ * serialized explicitly to avoid coupling the wire format to internal
+ * structure layout or flag bit assignments.
+ *
+ * Return: 0 on success, positive error code on failure
+ */
+/* cppcheck-suppress [constParameterCallback, unmatchedSuppression] */
+static int addrs_source_v3(struct ctx *c,
+			   const struct migrate_stage *stage, int fd)
+{
+	uint8_t addr_count = c->addr_count;
+	const struct guest_addr *a;
+
+	(void)stage;
+
+	/* Send count first */
+	if (write_all_buf(fd, &addr_count, sizeof(addr_count)))
+		return errno;
+
+	/* Send each address in stable wire format */
+	for_each_addr(a, c, 0) {
+		struct migrate_addr_v3 wire = {
+			.addr = a->addr.a6,
+			.prefix_len = a->prefix_len,
+			.flags = flags_to_wire(a->flags),
+		};
+
+		if (write_all_buf(fd, &wire, sizeof(wire)))
+			return errno;
+	}
+
+	/* Send MAC */
+	if (write_all_buf(fd, c->guest_mac, ETH_ALEN))
+		return errno;
+
+	return 0;
+}
+
+/**
+ * addrs_target_v3() - Receive addresses on target
+ * @c:		Execution context
+ * @stage:	Migration stage, unused
+ * @fd:		File descriptor for state transfer
+ *
+ * Receive address entries from the stable wire format and merge only
+ * observed addresses into local array. Source sends all addresses for
+ * forward compatibility, but target only applies those marked as observed.
+ *
+ * Return: 0 on success, positive error code on failure
+ */
+static int addrs_target_v3(struct ctx *c,
+			   const struct migrate_stage *stage, int fd)
+{
+	uint8_t addr_count, i;
+
+	(void)stage;
+
+	if (read_all_buf(fd, &addr_count, sizeof(addr_count)))
+		return errno;
+
+	if (addr_count > MAX_GUEST_ADDRS)
+		addr_count = MAX_GUEST_ADDRS;
+
+	/* Read each address from stable wire format */
+	for (i = 0; i < addr_count; i++) {
+		struct migrate_addr_v3 wire;
+		struct guest_addr addr;
+
+		if (read_all_buf(fd, &wire, sizeof(wire)))
+			return errno;
+
+		addr.addr.a6 = wire.addr;
+		addr.prefix_len = wire.prefix_len;
+		addr.flags = flags_from_wire(wire.flags);
+
+		if (addr.flags & CONF_ADDR_OBSERVED)
+			fwd_set_addr(c, &addr.addr, addr.flags,
+				     addr.prefix_len);
+	}
+
+	if (read_all_buf(fd, c->guest_mac, ETH_ALEN))
+		return errno;
+
+	return 0;
+}
+
 /* Stages for version 2 */
 static const struct migrate_stage stages_v2[] = {
 	{
@@ -146,8 +303,29 @@ static const struct migrate_stage stages_v2[] = {
 	{ 0 },
 };
 
+/* Stages for version 3 (multiple observed IPv4 addresses) */
+static const struct migrate_stage stages_v3[] = {
+	{
+		.name = "addresses",
+		.source = addrs_source_v3,
+		.target = addrs_target_v3,
+	},
+	{
+		.name = "prepare flows",
+		.source = flow_migrate_source_pre,
+		.target = NULL,
+	},
+	{
+		.name = "transfer flows",
+		.source = flow_migrate_source,
+		.target = flow_migrate_target,
+	},
+	{ 0 },
+};
+
 /* Supported encoding versions, from latest (most preferred) to oldest */
 static const struct migrate_version versions[] = {
+	{ 3,	stages_v3, },
 	{ 2,	stages_v2, },
 	/* v1 was released, but not widely used.  It had bad endianness for the
 	 * MSS and omitted timestamps, which meant it usually wouldn't work.
-- 
2.52.0