packet: Add support for multi-vector packetsHEADmaster

The packet pool was previously limited to handling packets contained
within a single buffer.

This patch extends the packet pool to support iovec array,
allowing a single logical packet to be composed of multiple iovec.

To accommodate this, the storage format within the pool is modified.
For a multi-vector packet, a header entry is now stored first with
iov_base = NULL and iov_len holding the number of subsequent
vectors. The actual data vectors are then stored in the following
pool slots.

The packet_add_do() and packet_get_do() functions are updated to
manage this new format for storing and retrieving packets. The
pool_full() check is also adjusted to ensure there is enough
space for all vectors of a new packet before adding it.

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

3 files changed, 39 insertions, 21 deletions

diff --git a/packet.c b/packet.c
index 27693c5..890561b 100644
--- a/packet.c
+++ b/packet.c
@@ -91,14 +91,17 @@ static int packet_check_range(const struct pool *p, const char *ptr, size_t len,
 	return 0;
 }
 /**
- * pool_full() - Is a packet pool full?
+ * pool_can_fit() - Can a new packet fit in the pool?
  * @p:		Pointer to packet pool
+ * @data:	check data can fit in the pool
  *
- * Return: true if the pool is full, false if more packets can be added
+ * Return: true if @data can be added, false otherwise
  */
-bool pool_full(const struct pool *p)
+bool pool_can_fit(const struct pool *p, struct iov_tail *data)
 {
-	return p->count >= p->size;
+	iov_tail_prune(data);
+
+	return p->count + data->cnt  + (data->cnt > 1) <= p->size;
 }
 
 /**
@@ -111,11 +114,9 @@ bool pool_full(const struct pool *p)
 void packet_add_do(struct pool *p, struct iov_tail *data,
 		   const char *func, int line)
 {
-	size_t idx = p->count;
-	const char *start;
-	size_t len;
+	size_t idx = p->count, i, offset;
 
-	if (pool_full(p)) {
+	if (!pool_can_fit(p, data)) {
 		debug("add packet index %zu to pool with size %zu, %s:%i",
 		      idx, p->size, func, line);
 		return;
@@ -124,18 +125,30 @@ void packet_add_do(struct pool *p, struct iov_tail *data,
 	if (!iov_tail_prune(data))
 		return;
 
-	ASSERT(data->cnt == 1); /* we don't support iovec */
+	if (data->cnt > 1) {
+		p->pkt[idx].iov_base = NULL;
+		p->pkt[idx].iov_len = data->cnt;
+		idx++;
+	}
 
-	len = data->iov[0].iov_len - data->off;
-	start = (char *)data->iov[0].iov_base + data->off;
+	offset = data->off;
+	for (i = 0; i < data->cnt; i++) {
+		const char *start;
+		size_t len;
 
-	if (packet_check_range(p, start, len, func, line))
-		return;
+		len = data->iov[i].iov_len - offset;
+		start = (char *)data->iov[i].iov_base + offset;
+		offset = 0;
 
-	p->pkt[idx].iov_base = (void *)start;
-	p->pkt[idx].iov_len = len;
+		if (packet_check_range(p, start, len, func, line))
+			return;
 
-	p->count++;
+		p->pkt[idx].iov_base = (void *)start;
+		p->pkt[idx].iov_len = len;
+		idx++;
+	}
+
+	p->count = idx;
 }
 
 /**
@@ -165,9 +178,14 @@ bool packet_get_do(const struct pool *p, size_t idx,
 		return false;
 	}
 
-	data->cnt = 1;
+	if (p->pkt[idx].iov_base) {
+		data->cnt = 1;
+		data->iov = &p->pkt[idx];
+	} else {
+		data->cnt = p->pkt[idx].iov_len;
+		data->iov = &p->pkt[idx + 1];
+	}
 	data->off = 0;
-	data->iov = &p->pkt[idx];
 
 	for (i = 0; i < data->cnt; i++) {
 		ASSERT_WITH_MSG(!packet_check_range(p, data->iov[i].iov_base,
diff --git a/packet.h b/packet.h
index e51cbd1..ba8d5c2 100644
--- a/packet.h
+++ b/packet.h
@@ -37,7 +37,7 @@ void packet_add_do(struct pool *p, struct iov_tail *data,
 		   const char *func, int line);
 bool packet_get_do(const struct pool *p, const size_t idx,
 		   struct iov_tail *data, const char *func, int line);
-bool pool_full(const struct pool *p);
+bool pool_can_fit(const struct pool *p, struct iov_tail *data);
 void pool_flush(struct pool *p);
 
 #define packet_add(p, data)					\
diff --git a/tap.c b/tap.c
index 5e0173b..7ba6399 100644
--- a/tap.c
+++ b/tap.c
@@ -1103,14 +1103,14 @@ void tap_add_packet(struct ctx *c, struct iov_tail *data,
 	switch (ntohs(eh->h_proto)) {
 	case ETH_P_ARP:
 	case ETH_P_IP:
-		if (pool_full(pool_tap4)) {
+		if (!pool_can_fit(pool_tap4, data)) {
 			tap4_handler(c, pool_tap4, now);
 			pool_flush(pool_tap4);
 		}
 		packet_add(pool_tap4, data);
 		break;
 	case ETH_P_IPV6:
-		if (pool_full(pool_tap6)) {
+		if (!pool_can_fit(pool_tap6, data)) {
 			tap6_handler(c, pool_tap6, now);
 			pool_flush(pool_tap6);
 		}