tap: Use different io vector bases depending on tap type

Currently tap_send_frames() expects the frames it is given to include the
vnet_len field, even in pasta mode which doesn't use it (although it need
not be initialized in that case).  To match, tap_iov_base() and
tap_iov_len() construct the frame in that way.

This will inconvenience future changes, so alter things to set the buffers
to include just the frame needed by the tap backend type.

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

2 files changed, 6 insertions, 5 deletions

diff --git a/tap.c b/tap.c
index d0dd72c..5ec6b70 100644
--- a/tap.c
+++ b/tap.c
@@ -317,8 +317,7 @@ static void tap_send_frames_pasta(struct ctx *c,
 	size_t i;
 
 	for (i = 0; i < n; i++) {
-		if (write(c->fd_tap, (char *)iov->iov_base + 4,
-			  iov->iov_len - 4) < 0) {
+		if (write(c->fd_tap, (char *)iov->iov_base, iov->iov_len) < 0) {
 			debug("tap write: %s", strerror(errno));
 			if (errno != EAGAIN && errno != EWOULDBLOCK)
 				tap_handler(c, c->fd_tap, EPOLLERR, NULL);
@@ -383,7 +382,7 @@ void tap_send_frames(struct ctx *c, const struct iovec *iov, size_t n)
 	else
 		tap_send_frames_pasta(c, iov, n);
 
-	pcap_multiple(iov, n, sizeof(uint32_t));
+	pcap_multiple(iov, n, c->mode == MODE_PASST ? sizeof(uint32_t) : 0);
 }
 
 /**
diff --git a/tap.h b/tap.h
index 8fe460a..40cf480 100644
--- a/tap.h
+++ b/tap.h
@@ -20,8 +20,10 @@ struct tap_hdr {
 
 static inline size_t tap_hdr_len_(const struct ctx *c)
 {
-	(void)c;
-	return sizeof(struct tap_hdr);
+	if (c->mode == MODE_PASST)
+		return sizeof(struct tap_hdr);
+	else
+		return sizeof(struct ethhdr);
 }
 
 /**