[2/4] net: add net_is_tap_client()

From: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

The vhost-net code interacts closely with the net/tap.c backend so that
it can pass the underlying file descriptor to the vhost_net.ko driver.
We need a check that confirms a NetClientState is indeed a tap backend
(and not something else like slirp or socket).

Formalize this in the new net_is_tap_client() function.  This way
callers do not reach inside net internals to check the type.

Note that I've added this function to net/tap.c but named it
net_is_tap_client().  Ideally it should be in net.c but I want to keep
the code where the tap net client is defined.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
---
 hw/vhost_net.c  | 5 ++---
 hw/virtio-net.c | 9 +++++----
 net/tap.c       | 5 +++++
 net/tap.h       | 1 +
 4 files changed, 13 insertions(+), 7 deletions(-)

Il 18/10/2012 16:56, Stefan Hajnoczi ha scritto:
> From: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
> 
> The vhost-net code interacts closely with the net/tap.c backend so that
> it can pass the underlying file descriptor to the vhost_net.ko driver.
> We need a check that confirms a NetClientState is indeed a tap backend
> (and not something else like slirp or socket).

Could you use object_dynamic_cast(OBJECT(backend), TYPE_TAP_NET_CLIENT)
instead?

Paolo

> Formalize this in the new net_is_tap_client() function.  This way
> callers do not reach inside net internals to check the type.
> 
> Note that I've added this function to net/tap.c but named it
> net_is_tap_client().  Ideally it should be in net.c but I want to keep
> the code where the tap net client is defined.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
> ---
>  hw/vhost_net.c  | 5 ++---
>  hw/virtio-net.c | 9 +++++----
>  net/tap.c       | 5 +++++
>  net/tap.h       | 1 +
>  4 files changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/vhost_net.c b/hw/vhost_net.c
> index 6737600..d60da6a 100644
> --- a/hw/vhost_net.c
> +++ b/hw/vhost_net.c
> @@ -82,10 +82,9 @@ void vhost_net_ack_features(struct vhost_net *net, unsigned features)
>  
>  static int vhost_net_get_fd(NetClientState *backend)
>  {
> -    switch (backend->info->type) {
> -    case NET_CLIENT_OPTIONS_KIND_TAP:
> +    if (net_is_tap_client(backend)) {
>          return tap_get_fd(backend);
> -    default:
> +    } else {
>          fprintf(stderr, "vhost-net requires tap backend\n");
>          return -EBADFD;
>      }
> diff --git a/hw/virtio-net.c b/hw/virtio-net.c
> index 8342391..6668ff2 100644
> --- a/hw/virtio-net.c
> +++ b/hw/virtio-net.c
> @@ -108,7 +108,7 @@ static void virtio_net_vhost_status(VirtIONet *n, uint8_t status)
>      if (!n->nic->nc.peer) {
>          return;
>      }
> -    if (n->nic->nc.peer->info->type != NET_CLIENT_OPTIONS_KIND_TAP) {
> +    if (!net_is_tap_client(n->nic->nc.peer)) {
>          return;
>      }
>  
> @@ -205,8 +205,9 @@ static int peer_has_vnet_hdr(VirtIONet *n)
>      if (!n->nic->nc.peer)
>          return 0;
>  
> -    if (n->nic->nc.peer->info->type != NET_CLIENT_OPTIONS_KIND_TAP)
> +    if (!net_is_tap_client(n->nic->nc.peer)) {
>          return 0;
> +    }
>  
>      n->has_vnet_hdr = tap_has_vnet_hdr(n->nic->nc.peer);
>  
> @@ -249,7 +250,7 @@ static uint32_t virtio_net_get_features(VirtIODevice *vdev, uint32_t features)
>      }
>  
>      if (!n->nic->nc.peer ||
> -        n->nic->nc.peer->info->type != NET_CLIENT_OPTIONS_KIND_TAP) {
> +        !net_is_tap_client(n->nic->nc.peer)) {
>          return features;
>      }
>      if (!tap_get_vhost_net(n->nic->nc.peer)) {
> @@ -288,7 +289,7 @@ static void virtio_net_set_features(VirtIODevice *vdev, uint32_t features)
>                          (features >> VIRTIO_NET_F_GUEST_UFO)  & 1);
>      }
>      if (!n->nic->nc.peer ||
> -        n->nic->nc.peer->info->type != NET_CLIENT_OPTIONS_KIND_TAP) {
> +        !net_is_tap_client(n->nic->nc.peer)) {
>          return;
>      }
>      if (!tap_get_vhost_net(n->nic->nc.peer)) {
> diff --git a/net/tap.c b/net/tap.c
> index df89caa..22f8de7 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -304,6 +304,11 @@ static void tap_poll(NetClientState *nc, bool enable)
>      tap_write_poll(s, enable);
>  }
>  
> +bool net_is_tap_client(NetClientState *nc)
> +{
> +    return nc->info->type == NET_CLIENT_OPTIONS_KIND_TAP;
> +}
> +
>  int tap_get_fd(NetClientState *nc)
>  {
>      TAPState *s = DO_UPCAST(TAPState, nc, nc);
> diff --git a/net/tap.h b/net/tap.h
> index d44d83a..4a9431b 100644
> --- a/net/tap.h
> +++ b/net/tap.h
> @@ -50,6 +50,7 @@ int tap_probe_has_ufo(int fd);
>  void tap_fd_set_offload(int fd, int csum, int tso4, int tso6, int ecn, int ufo);
>  void tap_fd_set_vnet_hdr_len(int fd, int len);
>  
> +bool net_is_tap_client(NetClientState *nc);
>  int tap_get_fd(NetClientState *nc);
>  
>  struct vhost_net;
>

On Thu, Oct 18, 2012 at 05:05:51PM +0200, Paolo Bonzini wrote:
> Il 18/10/2012 16:56, Stefan Hajnoczi ha scritto:
> > From: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
> > 
> > The vhost-net code interacts closely with the net/tap.c backend so that
> > it can pass the underlying file descriptor to the vhost_net.ko driver.
> > We need a check that confirms a NetClientState is indeed a tap backend
> > (and not something else like slirp or socket).
> 
> Could you use object_dynamic_cast(OBJECT(backend), TYPE_TAP_NET_CLIENT)
> instead?

Yes.

Stefan