[Qemu-devel] [PATCH v2 1/2] virtio-net: use the backend cross-endian capabilities

[Greg Kurz]

When running a fully emulated device in cross-endian conditions, including
a virtio 1.0 device offered to a big endian guest, we need to fix the vnet
headers. This is currently handled by the virtio_net_hdr_swap() function
in the core virtio-net code but it should actually be handled by the net
backend.

With this patch, virtio-net now tries to configure the backend to do the
endian fixing when the device starts. If the backend cannot support the
requested endiannes, we have to fall back on virtio_net_hdr_swap(): this
is recorded in the needs_vnet_hdr_swap flag.

The current vhost-net code also tries to configure net backends. This will
be no more needed and will be addressed in a subsequent patch.

Signed-off-by: Greg Kurz <address@hidden>
---
v2: - introduced virtio_net_needs_hdr_swap() to consolidate the logic in one
      place
---
 hw/net/virtio-net.c            |   43 ++++++++++++++++++++++++++++++++++++++--
 include/hw/virtio/virtio-net.h |    1 +
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index a877614e3e7a..a10f7a0b4d28 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -152,6 +152,33 @@ static void virtio_net_vhost_status(VirtIONet *n, uint8_t 
status)
     }
 }
 
+static int peer_has_vnet_hdr(VirtIONet *n);
+
+static void virtio_net_vnet_status(VirtIONet *n, uint8_t status)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(n);
+    NetClientState *peer = qemu_get_queue(n->nic)->peer;
+
+    if (virtio_net_started(n, status)) {
+        int r;
+
+        if (virtio_is_big_endian(vdev)) {
+            r = qemu_set_vnet_be(peer, true);
+        } else {
+            r = qemu_set_vnet_le(peer, true);
+        }
+
+        n->needs_vnet_hdr_swap = !!r;
+    } else if (virtio_net_started(n, vdev->status) &&
+               !virtio_net_started(n, status)) {
+        if (virtio_is_big_endian(vdev)) {
+            qemu_set_vnet_be(peer, false);
+        } else {
+            qemu_set_vnet_le(peer, false);
+        }
+    }
+}
+
 static void virtio_net_set_status(struct VirtIODevice *vdev, uint8_t status)
 {
     VirtIONet *n = VIRTIO_NET(vdev);
@@ -159,6 +186,7 @@ static void virtio_net_set_status(struct VirtIODevice 
*vdev, uint8_t status)
     int i;
     uint8_t queue_status;
 
+    virtio_net_vnet_status(n, status);
     virtio_net_vhost_status(n, status);
 
     for (i = 0; i < n->max_queues; i++) {
@@ -949,6 +977,14 @@ static void work_around_broken_dhclient(struct 
virtio_net_hdr *hdr,
     }
 }
 
+static bool virtio_net_needs_hdr_swap(VirtIONet *n)
+{
+    /* virtio_needs_swap() is constant for fixed endian targets: call it
+     * first to filter them out without penalty.
+     */
+    return virtio_needs_swap(VIRTIO_DEVICE(n)) && n->needs_vnet_hdr_swap;
+}
+
 static void receive_header(VirtIONet *n, const struct iovec *iov, int iov_cnt,
                            const void *buf, size_t size)
 {
@@ -957,7 +993,10 @@ static void receive_header(VirtIONet *n, const struct 
iovec *iov, int iov_cnt,
         void *wbuf = (void *)buf;
         work_around_broken_dhclient(wbuf, wbuf + n->host_hdr_len,
                                     size - n->host_hdr_len);
-        virtio_net_hdr_swap(VIRTIO_DEVICE(n), wbuf);
+
+        if (virtio_net_needs_hdr_swap(n)) {
+            virtio_net_hdr_swap(VIRTIO_DEVICE(n), wbuf);
+        }
         iov_from_buf(iov, iov_cnt, 0, buf, sizeof(struct virtio_net_hdr));
     } else {
         struct virtio_net_hdr hdr = {
@@ -1167,7 +1206,7 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
                 error_report("virtio-net header incorrect");
                 exit(1);
             }
-            if (virtio_needs_swap(vdev)) {
+            if (virtio_net_needs_hdr_swap(n)) {
                 virtio_net_hdr_swap(vdev, (void *) &mhdr);
                 sg2[0].iov_base = &mhdr;
                 sg2[0].iov_len = n->guest_hdr_len;
diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
index f3cc25feca2b..27bc868fbc7d 100644
--- a/include/hw/virtio/virtio-net.h
+++ b/include/hw/virtio/virtio-net.h
@@ -94,6 +94,7 @@ typedef struct VirtIONet {
     uint64_t curr_guest_offloads;
     QEMUTimer *announce_timer;
     int announce_counter;
+    bool needs_vnet_hdr_swap;
 } VirtIONet;
 
 void virtio_net_set_netclient_name(VirtIONet *n, const char *name,