[PULL 12/23] pc-bios/s390-ccw: Add dynamic net header size handling

[Eric Farman <farman@linux.ibm.com>]

From: Zhuoying Cai <zycai@linux.ibm.com>

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

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

The VirtioNetHdr and VirtioNetHdrMrgRxbuf structures replicate the
same field layout as struct virtio_net_hdr and struct
virtio_net_hdr_mrg_rxbuf defined in include/uapi/linux/virtio_net.h.

Signed-off-by: Zhuoying Cai <zycai@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: Jared Rossi <jrossi@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20260924222949.147720-3-zycai@linux.ibm.com
Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
 pc-bios/s390-ccw/virtio-net.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/pc-bios/s390-ccw/virtio-net.c b/pc-bios/s390-ccw/virtio-net.c
index f58f7ffc55..7bb3f8f551 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"
 
@@ -39,11 +40,21 @@ 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 */
 };
 typedef struct VirtioNetHdr VirtioNetHdr;
 
+struct VirtioNetHdrMrgRxbuf {
+    struct VirtioNetHdr hdr;
+    uint16_t num_buffers; /* Only with VIRTIO_NET_F_MRG_RXBUF or VIRTIO1 */
+};
+typedef struct VirtioNetHdrMrgRxbuf VirtioNetHdrMrgRxbuf;
+
+/* Header sizes for different modes */
+#define VIRTIO_NET_HDR_SIZE_LEGACY  sizeof(VirtioNetHdr)
+#define VIRTIO_NET_HDR_SIZE_V1      sizeof(VirtioNetHdrMrgRxbuf)
+
 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 +73,16 @@ int virtio_net_init(void *mac_addr)
         return -1;
     }
 
+    virtio_net_hdr_size = vdev->guest_features[1] & VIRTIO_F_VERSION_1
+                          ? 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);
@@ -77,14 +92,14 @@ int virtio_net_init(void *mac_addr)
 
 int send(int fd, const void *buf, int len, int flags)
 {
-    VirtioNetHdr tx_hdr;
+    VirtioNetHdrMrgRxbuf tx_hdr;
     VDev *vdev = virtio_get_device();
     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));
 
-    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 +123,13 @@ 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