[PATCH v1 2/7] pc-bios/s390-ccw: Add dynamic net header size handling

The virtio-net device used a fixed header size that did not account for
the num_buffers field used in VirtIO 1.0 or for the mergeable receive
buffers feature.

Use dynamic header sizing: 10 bytes for legacy mode and 12 bytes for
VirtIO 1.0 or when VIRTIO_NET_F_MRG_RXBUF is enabled. This ensures
correct packet handling across different VirtIO configurations.

Signed-off-by: Zhuoying Cai <[email protected]>
---
 pc-bios/s390-ccw/virtio-net.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/pc-bios/s390-ccw/virtio-net.c b/pc-bios/s390-ccw/virtio-net.c
index 0ee51653ab..3a9ae789cf 100644
--- a/pc-bios/s390-ccw/virtio-net.c
+++ b/pc-bios/s390-ccw/virtio-net.c
@@ -20,6 +20,7 @@
 #include "s390-ccw.h"
 #include "virtio.h"
 #include "virtio-ccw.h"
+#include "virtio-pci.h"
 #include "s390-time.h"
 #include "helper.h"
 
@@ -28,10 +29,15 @@
 #endif
 
 #define VIRTIO_NET_F_MAC_BIT  (1 << 5)
+#define VIRTIO_NET_F_MRG_RXBUF_BIT (1 << 15)
 
 #define VQ_RX 0         /* Receive queue */
 #define VQ_TX 1         /* Transmit queue */
 
+/* Header sizes for different modes */
+#define VIRTIO_NET_HDR_SIZE_LEGACY  10  /* Without num_buffers */
+#define VIRTIO_NET_HDR_SIZE_V1      12  /* With num_buffers */
+
 struct VirtioNetHdr {
     uint8_t flags;
     uint8_t gso_type;
@@ -39,11 +45,12 @@ struct VirtioNetHdr {
     uint16_t gso_size;
     uint16_t csum_start;
     uint16_t csum_offset;
-    /*uint16_t num_buffers;*/ /* Only with VIRTIO_NET_F_MRG_RXBUF or VIRTIO1 */
+    uint16_t num_buffers; /* Only with VIRTIO_NET_F_MRG_RXBUF or VIRTIO1 */
 };
 typedef struct VirtioNetHdr VirtioNetHdr;
 
 static uint16_t rx_last_idx;  /* Last index in receive queue "used" ring */
+static int virtio_net_hdr_size;
 
 int virtio_net_init(void *mac_addr)
 {
@@ -62,12 +69,17 @@ int virtio_net_init(void *mac_addr)
         return -1;
     }
 
+    virtio_net_hdr_size = ((vdev->guest_features[1] & VIRTIO_F_VERSION_1) ||
+                           (vdev->guest_features[0] & VIRTIO_NET_F_MRG_RXBUF_BIT))
+                          ? VIRTIO_NET_HDR_SIZE_V1
+                          : VIRTIO_NET_HDR_SIZE_LEGACY;
+
     memcpy(mac_addr, vdev->config.net.mac, ETH_ALEN);
 
     for (i = 0; i < 64; i++) {
-        buf = malloc(ETH_MTU_SIZE + sizeof(VirtioNetHdr));
+        buf = malloc(ETH_MTU_SIZE + virtio_net_hdr_size);
         IPL_assert(buf != NULL, "Can not allocate memory for receive buffers");
-        vring_send_buf(rxvq, buf, ETH_MTU_SIZE + sizeof(VirtioNetHdr),
+        vring_send_buf(rxvq, buf, ETH_MTU_SIZE + virtio_net_hdr_size,
                        VRING_DESC_F_WRITE);
     }
     vring_notify(rxvq);
@@ -82,9 +94,9 @@ int send(int fd, const void *buf, int len, int flags)
     VRing *txvq = &vdev->vrings[VQ_TX];
 
     /* Set up header - we do not use anything special, so simply clear it */
-    memset(&tx_hdr, 0, sizeof(tx_hdr));
+    memset(&tx_hdr, 0, virtio_net_hdr_size);
 
-    vring_send_buf(txvq, &tx_hdr, sizeof(tx_hdr), VRING_DESC_F_NEXT);
+    vring_send_buf(txvq, &tx_hdr, virtio_net_hdr_size, VRING_DESC_F_NEXT);
     vring_send_buf(txvq, (void *)buf, len, VRING_HIDDEN_IS_CHAIN);
     while (!vr_poll(txvq)) {
         yield();
@@ -108,13 +120,13 @@ int recv(int fd, void *buf, int maxlen, int flags)
         return 0;
     }
 
-    len = rxvq->used->ring[rx_last_idx % rxvq->num].len - sizeof(VirtioNetHdr);
+    len = rxvq->used->ring[rx_last_idx % rxvq->num].len - virtio_net_hdr_size;
     if (len > maxlen) {
         puts("virtio-net: Receive buffer too small");
         len = maxlen;
     }
     id = rxvq->used->ring[rx_last_idx % rxvq->num].id % rxvq->num;
-    pkt = (uint8_t *)(rxvq->desc[id].addr + sizeof(VirtioNetHdr));
+    pkt = (uint8_t *)(rxvq->desc[id].addr + virtio_net_hdr_size);
 
 #if DEBUG_VIRTIO_NET   /* Dump packet */
     int i;
-- 
2.55.0