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

From: Akihiko Odaki <akihiko.odaki@daynix.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>,
	Dmitry Fleytman <dmitry.fleytman@gmail.com>,
	Thomas Huth <thuth@redhat.com>,
	Laurent Vivier <lvivier@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	qemu-devel@nongnu.org, qemu-ppc@nongnu.org,
	Yan Vugenfirer <yvugenfi@redhat.com>,
	Yuri Benditovich <yuri.benditovich@daynix.com>,
	Sriram Yagnaraman <sriram.yagnaraman@est.tech>,
	Alexander Bulekov <alxndr@bu.edu>
Subject: Re: [PATCH v4 20/28] net: Strip virtio-net header when dumping
Date: Tue, 31 Jan 2023 00:36:38 +0900	[thread overview]
Message-ID: <2b7d65e9-5928-8038-34f2-03fc2ee6a819@daynix.com> (raw)
In-Reply-To: <20230130101211-mutt-send-email-mst@kernel.org>

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.

> 
>> ---
>>   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
> 