On Fri, 06 Nov 2015 18:45:04 +0100
Greg Kurz <gk...@linux.vnet.ibm.com> wrote:
> 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.
>
> Whether we have to fix vnet headers in userspace now depends on:
>
> virtio_needs_swap(vdev) && n->needs_vnet_hdr_swap
>
> virtio_needs_swap() allows to filter out non cross-endian cases without
> runtime penalty.
>
> 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 <gk...@linux.vnet.ibm.com>
> ---
Bah this one won't build... I'll send a v2 with numbered patches and a cover.
> hw/net/virtio-net.c | 35 +++++++++++++++++++++++++++++++++--
> include/hw/virtio/virtio-net.h | 1 +
> 2 files changed, 34 insertions(+), 2 deletions(-)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index a877614e3e7a..69dc4442e5e2 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++) {
> @@ -957,7 +985,10 @@ 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_needs_swap(vdev) && n->needs_vnet_hdr_swap) {
> + 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 +1198,7 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
> error_report("virtio-net header incorrect");
> exit(1);
> }
> - if (virtio_needs_swap(vdev)) {
> + if (virtio_needs_swap(vdev) && n->needs_vnet_hdr_swap) {
> 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,
>
>
