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

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

On Tue, Jan 31, 2023 at 12:36:38AM +0900, Akihiko Odaki wrote:
> On 2023/01/31 0:12, Michael S. Tsirkin wrote:
> > 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?
> 
> It was not necessary in my case as I used Wireshark and it tolerates wrong
> checksums and large packets (it even says "Checksum incorrect [maybe caused
> by 'TCP checksum offload'?]"). It was even more helpful to have raw packets
> instead of transformed packets for debugging purposes. Perhaps an option to
> transform packets may be added later if a need arises.

I think we should add LINKTYPE_VIRTIO. Very useful to debug a host of
checksum/segmentation issues. Want to hack it up?

> > 
> > > ---
> > >   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
> >