Re: [PATCH] net: Strip virtio-net header when dumping

[Philippe Mathieu-Daudé]

On 13/1/23 14:08, Akihiko Odaki wrote:
> filter-dump specifiees Ethernet as PCAP LinkType, which does not expect
> virtio-net header. Having virtio-net header in such PCAP file breaks
> PCAP unconsumable. Unfortunately currently there is no LinkType for
> virtio-net so for now strip virtio-net header to convert the output to
> Ethernet.
>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
>   include/net/net.h |  6 ++++++
>   net/dump.c        | 11 +++++++----
>   net/net.c         | 18 ++++++++++++++++++
>   net/netmap.c      |  1 +
>   net/tap.c         | 16 ++++++++++++++++
>   5 files changed, 48 insertions(+), 4 deletions(-)
>
> diff --git a/include/net/net.h b/include/net/net.h
> index dc20b31e9f..4b2d72b3fc 100644
> --- a/include/net/net.h
> +++ b/include/net/net.h
> @@ -56,8 +56,10 @@ typedef RxFilterInfo *(QueryRxFilter)(NetClientState *);
>   typedef bool (HasUfo)(NetClientState *);
>   typedef bool (HasVnetHdr)(NetClientState *);
>   typedef bool (HasVnetHdrLen)(NetClientState *, int);
> +typedef bool (GetUsingVnetHdr)(NetClientState *);
>   typedef void (UsingVnetHdr)(NetClientState *, bool);
>   typedef void (SetOffload)(NetClientState *, int, int, int, int, int);
> +typedef int (GetVnetHdrLen)(NetClientState *);
>   typedef void (SetVnetHdrLen)(NetClientState *, int);
>   typedef int (SetVnetLE)(NetClientState *, bool);
>   typedef int (SetVnetBE)(NetClientState *, bool);
> @@ -84,8 +86,10 @@ typedef struct NetClientInfo {
>       HasUfo *has_ufo;
>       HasVnetHdr *has_vnet_hdr;
>       HasVnetHdrLen *has_vnet_hdr_len;
> +    GetUsingVnetHdr *get_using_vnet_hdr;

[*]

>       UsingVnetHdr *using_vnet_hdr;
>       SetOffload *set_offload;
> +    GetVnetHdrLen *get_vnet_hdr_len;
>       SetVnetHdrLen *set_vnet_hdr_len;
>       SetVnetLE *set_vnet_le;
>       SetVnetBE *set_vnet_be;
> @@ -183,9 +187,11 @@ void qemu_format_nic_info_str(NetClientState *nc, uint8_t 
> macaddr[6]);
>   bool qemu_has_ufo(NetClientState *nc);
>   bool qemu_has_vnet_hdr(NetClientState *nc);
>   bool qemu_has_vnet_hdr_len(NetClientState *nc, int len);
> +bool qemu_get_using_vnet_hdr(NetClientState *nc);
>   void qemu_using_vnet_hdr(NetClientState *nc, bool enable);
>   void qemu_set_offload(NetClientState *nc, int csum, int tso4, int tso6,
>                         int ecn, int ufo);

> @@ -153,8 +154,10 @@ static ssize_t filter_dump_receive_iov(NetFilterState *nf, 
> NetClientState *sndr,
>                                          int iovcnt, NetPacketSent *sent_cb)
>   {
>       NetFilterDumpState *nfds = FILTER_DUMP(nf);
> +    int offset = qemu_get_using_vnet_hdr(nf->netdev) ?
> +                 qemu_get_vnet_hdr_len(nf->netdev) : 0;
>   
> -    dump_receive_iov(&nfds->ds, iov, iovcnt);
> +    dump_receive_iov(&nfds->ds, iov, iovcnt, offset);
>       return 0;
>   }
>   
> diff --git a/net/net.c b/net/net.c
> index 2d01472998..3a95c3ba6a 100644
> --- a/net/net.c
> +++ b/net/net.c
> @@ -513,6 +513,15 @@ bool qemu_has_vnet_hdr_len(NetClientState *nc, int len)
>       return nc->info->has_vnet_hdr_len(nc, len);
>   }
>   
> +bool qemu_get_using_vnet_hdr(NetClientState *nc)
> +{
> +    if (!nc || !nc->info->get_using_vnet_hdr) {
> +        return false;
> +    }
> +
> +    return nc->info->get_using_vnet_hdr(nc);

Per [*], is get_using_vnet_hdr() really useful? Can't we just
check for using_vnet_hdr != NULL as:

       return nc->info->using_vnet_hdr != NULL;

> +}
> +
>   void qemu_using_vnet_hdr(NetClientState *nc, bool enable)
>   {
>       if (!nc || !nc->info->using_vnet_hdr) {
> @@ -532,6 +541,15 @@ void qemu_set_offload(NetClientState *nc, int csum, int 
> tso4, int tso6,
>       nc->info->set_offload(nc, csum, tso4, tso6, ecn, ufo);
>   }
>   
> +int qemu_get_vnet_hdr_len(NetClientState *nc)
> +{
> +    if (!nc || !nc->info->get_vnet_hdr_len) {
> +        return -ENOSYS;

Does -ENOSYS provides any value? Otherwise we could return 0.

> +    }
> +
> +    return nc->info->get_vnet_hdr_len(nc);
> +}

> diff --git a/net/netmap.c b/net/netmap.c
> index 9e0cec58d3..ed9c7ec948 100644
> --- a/net/netmap.c
> +++ b/net/netmap.c
> @@ -393,6 +393,7 @@ static NetClientInfo net_netmap_info = {
>       .has_ufo = netmap_has_vnet_hdr,
>       .has_vnet_hdr = netmap_has_vnet_hdr,
>       .has_vnet_hdr_len = netmap_has_vnet_hdr_len,
> +    .get_using_vnet_hdr = netmap_get_using_vnet_hdr,

On what is this patch based? I don't have netmap_get_using_vnet_hdr().

>       .using_vnet_hdr = netmap_using_vnet_hdr,
>       .set_offload = netmap_set_offload,
>       .set_vnet_hdr_len = netmap_set_vnet_hdr_len,