Re: [PATCH v4 20/28] net: Strip virtio-net header when dumping

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jan 30, 2023 at 10:47:07PM +0900, 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>

Probably means you need to calculate checksums and split gso too right?

> ---
>  include/net/net.h |  6 ++++++
>  net/dump.c        | 11 +++++++----
>  net/net.c         | 18 ++++++++++++++++++
>  net/tap.c         | 16 ++++++++++++++++
>  4 files changed, 47 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);
> +int qemu_get_vnet_hdr_len(NetClientState *nc);
>  void qemu_set_vnet_hdr_len(NetClientState *nc, int len);
>  int qemu_set_vnet_le(NetClientState *nc, bool is_le);
>  int qemu_set_vnet_be(NetClientState *nc, bool is_be);
> diff --git a/net/dump.c b/net/dump.c
> index 6a63b15359..7d05f16ca7 100644
> --- a/net/dump.c
> +++ b/net/dump.c
> @@ -61,12 +61,13 @@ struct pcap_sf_pkthdr {
>      uint32_t len;
>  };
>  
> -static ssize_t dump_receive_iov(DumpState *s, const struct iovec *iov, int cnt)
> +static ssize_t dump_receive_iov(DumpState *s, const struct iovec *iov, int cnt,
> +                                int offset)
>  {
>      struct pcap_sf_pkthdr hdr;
>      int64_t ts;
>      int caplen;
> -    size_t size = iov_size(iov, cnt);
> +    size_t size = iov_size(iov, cnt) - offset;
>      struct iovec dumpiov[cnt + 1];
>  
>      /* Early return in case of previous error. */
> @@ -84,7 +85,7 @@ static ssize_t dump_receive_iov(DumpState *s, const struct iovec *iov, int cnt)
>  
>      dumpiov[0].iov_base = &hdr;
>      dumpiov[0].iov_len = sizeof(hdr);
> -    cnt = iov_copy(&dumpiov[1], cnt, iov, cnt, 0, caplen);
> +    cnt = iov_copy(&dumpiov[1], cnt, iov, cnt, offset, caplen);
>  
>      if (writev(s->fd, dumpiov, cnt + 1) != sizeof(hdr) + caplen) {
>          error_report("network dump write error - stopping dump");
> @@ -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..03f17de5fc 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);
> +}
> +
>  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 0;
> +    }
> +
> +    return nc->info->get_vnet_hdr_len(nc);
> +}
> +
>  void qemu_set_vnet_hdr_len(NetClientState *nc, int len)
>  {
>      if (!nc || !nc->info->set_vnet_hdr_len) {
> diff --git a/net/tap.c b/net/tap.c
> index 7d7bc1dc5f..1bf085d422 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -255,6 +255,13 @@ static bool tap_has_vnet_hdr_len(NetClientState *nc, int len)
>      return !!tap_probe_vnet_hdr_len(s->fd, len);
>  }
>  
> +static int tap_get_vnet_hdr_len(NetClientState *nc)
> +{
> +    TAPState *s = DO_UPCAST(TAPState, nc, nc);
> +
> +    return s->host_vnet_hdr_len;
> +}
> +
>  static void tap_set_vnet_hdr_len(NetClientState *nc, int len)
>  {
>      TAPState *s = DO_UPCAST(TAPState, nc, nc);
> @@ -268,6 +275,13 @@ static void tap_set_vnet_hdr_len(NetClientState *nc, int len)
>      s->host_vnet_hdr_len = len;
>  }
>  
> +static bool tap_get_using_vnet_hdr(NetClientState *nc)
> +{
> +    TAPState *s = DO_UPCAST(TAPState, nc, nc);
> +
> +    return s->using_vnet_hdr;
> +}
> +
>  static void tap_using_vnet_hdr(NetClientState *nc, bool using_vnet_hdr)
>  {
>      TAPState *s = DO_UPCAST(TAPState, nc, nc);
> @@ -372,8 +386,10 @@ static NetClientInfo net_tap_info = {
>      .has_ufo = tap_has_ufo,
>      .has_vnet_hdr = tap_has_vnet_hdr,
>      .has_vnet_hdr_len = tap_has_vnet_hdr_len,
> +    .get_using_vnet_hdr = tap_get_using_vnet_hdr,
>      .using_vnet_hdr = tap_using_vnet_hdr,
>      .set_offload = tap_set_offload,
> +    .get_vnet_hdr_len = tap_get_vnet_hdr_len,
>      .set_vnet_hdr_len = tap_set_vnet_hdr_len,
>      .set_vnet_le = tap_set_vnet_le,
>      .set_vnet_be = tap_set_vnet_be,
> -- 
> 2.39.1