Re: [PATCH 10/12] kvm: qemu: Add a -net tap,fd=X,vnet_hdr=on option

[Anthony Liguori <anthony@codemonkey.ws>]

Mark McLoughlin wrote:
> Some management apps like libvirt creates a tap interface,
> adds it to a bridge and then passes the fd to qemu-kvm.
>
> Since we have no way of querying whether the IFF_VNET_HDR
> flag has been enabled on the interface, the app needs to
> tell us if has enabled it.
>   

Sounds like we should just patch the kernel to add a mechanism to query 
the IF_VNET_HDR flag.

Regards,

Anthony Liguori

> Signed-off-by: Mark McLoughlin <markmc@redhat.com>
> ---
>  qemu/vl.c |   11 ++++++++++-
>  1 files changed, 10 insertions(+), 1 deletions(-)
>
> diff --git a/qemu/vl.c b/qemu/vl.c
> index 14a66e0..499d6f9 100644
> --- a/qemu/vl.c
> +++ b/qemu/vl.c
> @@ -5487,10 +5487,19 @@ int net_client_init(const char *device, const char *p)
>          int fd;
>          vlan->nb_host_devs++;
>          if (get_param_value(buf, sizeof(buf), "fd", p) > 0) {
> +            int vnet_hdr = 0;
>              fd = strtol(buf, NULL, 0);
>              fcntl(fd, F_SETFL, O_NONBLOCK);
> +            if (get_param_value(buf, sizeof(buf), "vnet_hdr", p) > 0) {
> +                if (strcmp(buf, "on") == 0) {
> +                    vnet_hdr = 1;
> +                } else if (strcmp(buf, "off") != 0) {
> +                    fprintf(stderr, "qemu: '%s' invalid vnet_hdr option\n", buf);
> +                    return 0;
> +                }
> +            }
>              ret = -1;
> -            if (net_tap_fd_init(vlan, fd, 0))
> +            if (net_tap_fd_init(vlan, fd, vnet_hdr))
>                  ret = 0;
>          } else {
>              if (get_param_value(ifname, sizeof(ifname), "ifname", p) <= 0) {
>