[Qemu-devel] [PATCH 0/5] Network traffic dumping via netfilter

[Qemu-devel] [PATCH 0/5] Network traffic dumping via netfilter

[Thomas Huth]

The "-net dump" option only works with the "-net" option. So far, it
is not possible to dump network traffic with the "-netdev" option yet.
This patch series now fixes this ugliness by enabling dumping for the
netdev devices via the new netfilter infrastructure from Yang Hongyang
(integration into that infrastructure was pretty easy, so thanks for
this great work!)
The dumping filter can be used like this for example:

 ppc64-softmmu/qemu-system-ppc64 -device virtio-net,netdev=mynet \
     -netdev user,id=mynet,tftp=/tmp/tftp,bootfile=zImage \
     -object filter-dump,id=f0,netdev=mynet,file=/tmp/dumpfile.dat

The patches have to be applied on top of the Jason's net branch
(since the netfilter patches have not been pulled into master yet).

Thomas Huth (5):
  net/dump: Add support for receive_iov function
  net/dump: Rework net-dump init functions
  net/dump: Separate the NetClientState from the DumpState
  net/dump: Provide the dumping facility as a net filter
  net/dump: Add documentation

 net/dump.c      | 228 ++++++++++++++++++++++++++++++++++++++++++++++++--------
 qemu-options.hx |   8 ++
 vl.c            |   8 +-
 3 files changed, 212 insertions(+), 32 deletions(-)

-- 
1.8.3.1

[Qemu-devel] [PATCH 1/5] net/dump: Add support for receive_iov function

[Thomas Huth]

Adding a proper receive_iov function to the net dump module.
This will make it easier to support the dump filter feature for
the -netdev option in later patches.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 net/dump.c | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/net/dump.c b/net/dump.c
index 02c8064..f8afb83 100644
--- a/net/dump.c
+++ b/net/dump.c
@@ -25,6 +25,7 @@
 #include "clients.h"
 #include "qemu-common.h"
 #include "qemu/error-report.h"
+#include "qemu/iov.h"
 #include "qemu/log.h"
 #include "qemu/timer.h"
 #include "hub.h"
@@ -57,12 +58,15 @@ struct pcap_sf_pkthdr {
     uint32_t len;
 };
 
-static ssize_t dump_receive(NetClientState *nc, const uint8_t *buf, size_t size)
+static ssize_t dump_receive_iov(NetClientState *nc, const struct iovec *iov,
+                                int cnt)
 {
     DumpState *s = DO_UPCAST(DumpState, nc, nc);
     struct pcap_sf_pkthdr hdr;
     int64_t ts;
     int caplen;
+    size_t size = iov_size(iov, cnt);
+    struct iovec dumpiov[cnt + 1];
 
     /* Early return in case of previous error. */
     if (s->fd < 0) {
@@ -76,8 +80,12 @@ static ssize_t dump_receive(NetClientState *nc, const uint8_t *buf, size_t size)
     hdr.ts.tv_usec = ts % 1000000;
     hdr.caplen = caplen;
     hdr.len = size;
-    if (write(s->fd, &hdr, sizeof(hdr)) != sizeof(hdr) ||
-        write(s->fd, buf, caplen) != caplen) {
+
+    dumpiov[0].iov_base = &hdr;
+    dumpiov[0].iov_len = sizeof(hdr);
+    cnt = iov_copy(&dumpiov[1], cnt, iov, cnt, 0, caplen);
+
+    if (writev(s->fd, dumpiov, cnt + 1) != sizeof(hdr) + caplen) {
         qemu_log("-net dump write error - stop dump\n");
         close(s->fd);
         s->fd = -1;
@@ -86,6 +94,15 @@ static ssize_t dump_receive(NetClientState *nc, const uint8_t *buf, size_t size)
     return size;
 }
 
+static ssize_t dump_receive(NetClientState *nc, const uint8_t *buf, size_t size)
+{
+    struct iovec iov = {
+        .iov_base = (void *)buf,
+        .iov_len = size
+    };
+    return dump_receive_iov(nc, &iov, 1);
+}
+
 static void dump_cleanup(NetClientState *nc)
 {
     DumpState *s = DO_UPCAST(DumpState, nc, nc);
@@ -97,6 +114,7 @@ static NetClientInfo net_dump_info = {
     .type = NET_CLIENT_OPTIONS_KIND_DUMP,
     .size = sizeof(DumpState),
     .receive = dump_receive,
+    .receive_iov = dump_receive_iov,
     .cleanup = dump_cleanup,
 };
 
-- 
1.8.3.1

[Qemu-devel] [PATCH 2/5] net/dump: Rework net-dump init functions

[Thomas Huth]

Move the creation of the dump client from net_dump_init() into
net_init_dump(), so we can later use the former function for
dump via netfilter, too. Also rename net_dump_init() to
net_dump_state_init() to make it easier distinguishable from
net_init_dump().

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 net/dump.c | 27 +++++++++++++--------------
 1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/net/dump.c b/net/dump.c
index f8afb83..27083d4 100644
--- a/net/dump.c
+++ b/net/dump.c
@@ -118,13 +118,10 @@ static NetClientInfo net_dump_info = {
     .cleanup = dump_cleanup,
 };
 
-static int net_dump_init(NetClientState *peer, const char *device,
-                         const char *name, const char *filename, int len,
-                         Error **errp)
+static int net_dump_state_init(DumpState *s, const char *filename,
+                               int len, Error **errp)
 {
     struct pcap_file_hdr hdr;
-    NetClientState *nc;
-    DumpState *s;
     struct tm tm;
     int fd;
 
@@ -148,13 +145,6 @@ static int net_dump_init(NetClientState *peer, const char *device,
         return -1;
     }
 
-    nc = qemu_new_net_client(&net_dump_info, peer, device, name);
-
-    snprintf(nc->info_str, sizeof(nc->info_str),
-             "dump to %s (len=%d)", filename, len);
-
-    s = DO_UPCAST(DumpState, nc, nc);
-
     s->fd = fd;
     s->pcap_caplen = len;
 
@@ -167,10 +157,11 @@ static int net_dump_init(NetClientState *peer, const char *device,
 int net_init_dump(const NetClientOptions *opts, const char *name,
                   NetClientState *peer, Error **errp)
 {
-    int len;
+    int len, rc;
     const char *file;
     char def_file[128];
     const NetdevDumpOptions *dump;
+    NetClientState *nc;
 
     assert(opts->kind == NET_CLIENT_OPTIONS_KIND_DUMP);
     dump = opts->dump;
@@ -200,5 +191,13 @@ int net_init_dump(const NetClientOptions *opts, const char *name,
         len = 65536;
     }
 
-    return net_dump_init(peer, "dump", name, file, len, errp);
+    nc = qemu_new_net_client(&net_dump_info, peer, "dump", name);
+    snprintf(nc->info_str, sizeof(nc->info_str),
+             "dump to %s (len=%d)", file, len);
+
+    rc = net_dump_state_init(DO_UPCAST(DumpState, nc, nc), file, len, errp);
+    if (rc) {
+        qemu_del_net_client(nc);
+    }
+    return rc;
 }
-- 
1.8.3.1

[Qemu-devel] [PATCH 3/5] net/dump: Separate the NetClientState from the DumpState

[Thomas Huth]

With the upcoming dumping-via-netfilter patch, the DumpState
should not be related to NetClientState anymore, so move the
related information to a new struct called DumpNetClient.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 net/dump.c | 74 +++++++++++++++++++++++++++++++++++++++++---------------------
 1 file changed, 49 insertions(+), 25 deletions(-)

diff --git a/net/dump.c b/net/dump.c
index 27083d4..afff78e 100644
--- a/net/dump.c
+++ b/net/dump.c
@@ -31,7 +31,6 @@
 #include "hub.h"
 
 typedef struct DumpState {
-    NetClientState nc;
     int64_t start_ts;
     int fd;
     int pcap_caplen;
@@ -58,10 +57,8 @@ struct pcap_sf_pkthdr {
     uint32_t len;
 };
 
-static ssize_t dump_receive_iov(NetClientState *nc, const struct iovec *iov,
-                                int cnt)
+static ssize_t dump_receive_iov(DumpState *s, const struct iovec *iov, int cnt)
 {
-    DumpState *s = DO_UPCAST(DumpState, nc, nc);
     struct pcap_sf_pkthdr hdr;
     int64_t ts;
     int caplen;
@@ -94,30 +91,12 @@ static ssize_t dump_receive_iov(NetClientState *nc, const struct iovec *iov,
     return size;
 }
 
-static ssize_t dump_receive(NetClientState *nc, const uint8_t *buf, size_t size)
-{
-    struct iovec iov = {
-        .iov_base = (void *)buf,
-        .iov_len = size
-    };
-    return dump_receive_iov(nc, &iov, 1);
-}
-
-static void dump_cleanup(NetClientState *nc)
+static void dump_cleanup(DumpState *s)
 {
-    DumpState *s = DO_UPCAST(DumpState, nc, nc);
-
     close(s->fd);
+    s->fd = -1;
 }
 
-static NetClientInfo net_dump_info = {
-    .type = NET_CLIENT_OPTIONS_KIND_DUMP,
-    .size = sizeof(DumpState),
-    .receive = dump_receive,
-    .receive_iov = dump_receive_iov,
-    .cleanup = dump_cleanup,
-};
-
 static int net_dump_state_init(DumpState *s, const char *filename,
                                int len, Error **errp)
 {
@@ -154,6 +133,49 @@ static int net_dump_state_init(DumpState *s, const char *filename,
     return 0;
 }
 
+/* Dumping via VLAN netclient */
+
+struct DumpNetClient {
+    NetClientState nc;
+    DumpState ds;
+};
+typedef struct DumpNetClient DumpNetClient;
+
+static ssize_t dumpclient_receive(NetClientState *nc, const uint8_t *buf,
+                                  size_t size)
+{
+    DumpNetClient *dc = DO_UPCAST(DumpNetClient, nc, nc);
+    struct iovec iov = {
+        .iov_base = (void *)buf,
+        .iov_len = size
+    };
+
+    return dump_receive_iov(&dc->ds, &iov, 1);
+}
+
+static ssize_t dumpclient_receive_iov(NetClientState *nc,
+                                      const struct iovec *iov, int cnt)
+{
+    DumpNetClient *dc = DO_UPCAST(DumpNetClient, nc, nc);
+
+    return dump_receive_iov(&dc->ds, iov, cnt);
+}
+
+static void dumpclient_cleanup(NetClientState *nc)
+{
+    DumpNetClient *dc = DO_UPCAST(DumpNetClient, nc, nc);
+
+    dump_cleanup(&dc->ds);
+}
+
+static NetClientInfo net_dump_info = {
+    .type = NET_CLIENT_OPTIONS_KIND_DUMP,
+    .size = sizeof(DumpNetClient),
+    .receive = dumpclient_receive,
+    .receive_iov = dumpclient_receive_iov,
+    .cleanup = dumpclient_cleanup,
+};
+
 int net_init_dump(const NetClientOptions *opts, const char *name,
                   NetClientState *peer, Error **errp)
 {
@@ -162,6 +184,7 @@ int net_init_dump(const NetClientOptions *opts, const char *name,
     char def_file[128];
     const NetdevDumpOptions *dump;
     NetClientState *nc;
+    DumpNetClient *dnc;
 
     assert(opts->kind == NET_CLIENT_OPTIONS_KIND_DUMP);
     dump = opts->dump;
@@ -195,7 +218,8 @@ int net_init_dump(const NetClientOptions *opts, const char *name,
     snprintf(nc->info_str, sizeof(nc->info_str),
              "dump to %s (len=%d)", file, len);
 
-    rc = net_dump_state_init(DO_UPCAST(DumpState, nc, nc), file, len, errp);
+    dnc = DO_UPCAST(DumpNetClient, nc, nc);
+    rc = net_dump_state_init(&dnc->ds, file, len, errp);
     if (rc) {
         qemu_del_net_client(nc);
     }
-- 
1.8.3.1

[Qemu-devel] [PATCH 4/5] net/dump: Provide the dumping facility as a net filter

[Thomas Huth]

Use the net filter infrastructure to provide the dumping
functions for netdev devices, too.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 net/dump.c | 129 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 vl.c       |   8 +++-
 2 files changed, 134 insertions(+), 3 deletions(-)

diff --git a/net/dump.c b/net/dump.c
index afff78e..5904f58 100644
--- a/net/dump.c
+++ b/net/dump.c
@@ -28,7 +28,8 @@
 #include "qemu/iov.h"
 #include "qemu/log.h"
 #include "qemu/timer.h"
-#include "hub.h"
+#include "qapi/visitor.h"
+#include "net/filter.h"
 
 typedef struct DumpState {
     int64_t start_ts;
@@ -225,3 +226,129 @@ int net_init_dump(const NetClientOptions *opts, const char *name,
     }
     return rc;
 }
+
+/* Dumping via filter */
+
+#define TYPE_FILTER_DUMP "filter-dump"
+
+#define FILTER_DUMP(obj) \
+    OBJECT_CHECK(NetFilterDumpState, (obj), TYPE_FILTER_DUMP)
+
+struct NetFilterDumpState {
+    NetFilterState nfs;
+    DumpState ds;
+    char *filename;
+    uint32_t maxlen;
+};
+typedef struct NetFilterDumpState NetFilterDumpState;
+
+static ssize_t filter_dump_receive_iov(NetFilterState *nf, NetClientState *sndr,
+                                       unsigned flags, const struct iovec *iov,
+                                       int iovcnt, NetPacketSent *sent_cb)
+{
+    NetFilterDumpState *nfds = FILTER_DUMP(nf);
+
+    dump_receive_iov(&nfds->ds, iov, iovcnt);
+    return 0;
+}
+
+static void filter_dump_cleanup(NetFilterState *nf)
+{
+    NetFilterDumpState *nfds = FILTER_DUMP(nf);
+
+    dump_cleanup(&nfds->ds);
+}
+
+static void filter_dump_setup(NetFilterState *nf, Error **errp)
+{
+    NetFilterDumpState *nfds = FILTER_DUMP(nf);
+
+    if (!nfds->filename) {
+        error_setg(errp, "dump filter needs 'file' property set!");
+        return;
+    }
+
+    net_dump_state_init(&nfds->ds, nfds->filename, nfds->maxlen, errp);
+}
+
+static void filter_dump_get_maxlen(Object *obj, Visitor *v, void *opaque,
+                                   const char *name, Error **errp)
+{
+    NetFilterDumpState *nfds = FILTER_DUMP(obj);
+    uint32_t value = nfds->maxlen;
+
+    visit_type_uint32(v, &value, name, errp);
+}
+
+static void filter_dump_set_maxlen(Object *obj, Visitor *v, void *opaque,
+                                   const char *name, Error **errp)
+{
+    NetFilterDumpState *nfds = FILTER_DUMP(obj);
+    Error *local_err = NULL;
+    uint32_t value;
+
+    visit_type_uint32(v, &value, name, &local_err);
+    if (local_err) {
+        goto out;
+    }
+    if (value == 0) {
+        error_setg(&local_err, "Property '%s.%s' doesn't take value '%u'",
+                   object_get_typename(obj), name, value);
+        goto out;
+    }
+    nfds->maxlen = value;
+
+out:
+    error_propagate(errp, local_err);
+}
+
+static char *file_dump_get_filename(Object *obj, Error **errp)
+{
+    NetFilterDumpState *nfds = FILTER_DUMP(obj);
+
+    return g_strdup(nfds->filename);
+}
+
+static void file_dump_set_filename(Object *obj, const char *value, Error **errp)
+{
+   NetFilterDumpState *nfds = FILTER_DUMP(obj);
+
+    g_free(nfds->filename);
+    nfds->filename = g_strdup(value);
+}
+
+static void filter_dump_instance_init(Object *obj)
+{
+    NetFilterDumpState *nfds = FILTER_DUMP(obj);
+
+    nfds->maxlen = 65536;
+
+    object_property_add(obj, "maxlen", "int", filter_dump_get_maxlen,
+                        filter_dump_set_maxlen, NULL, NULL, NULL);
+    object_property_add_str(obj, "file", file_dump_get_filename,
+                            file_dump_set_filename, NULL);
+}
+
+static void filter_dump_class_init(ObjectClass *oc, void *data)
+{
+    NetFilterClass *nfc = NETFILTER_CLASS(oc);
+
+    nfc->setup = filter_dump_setup;
+    nfc->cleanup = filter_dump_cleanup;
+    nfc->receive_iov = filter_dump_receive_iov;
+}
+
+static const TypeInfo filter_dump_info = {
+    .name = TYPE_FILTER_DUMP,
+    .parent = TYPE_NETFILTER,
+    .class_init = filter_dump_class_init,
+    .instance_init = filter_dump_instance_init,
+    .instance_size = sizeof(NetFilterDumpState),
+};
+
+static void filter_dump_register_types(void)
+{
+    type_register_static(&filter_dump_info);
+}
+
+type_init(filter_dump_register_types);
diff --git a/vl.c b/vl.c
index 9be4d22..aa99ef3 100644
--- a/vl.c
+++ b/vl.c
@@ -2761,8 +2761,12 @@ static bool object_create_initial(const char *type)
         return false;
     }
 
-    /* return false for concrete netfilters */
-    if (g_str_equal(type, "filter-buffer")) {
+    /*
+     * return false for concrete netfilters since
+     * they depend on netdevs already existing
+     */
+    if (g_str_equal(type, "filter-buffer") ||
+        g_str_equal(type, "filter-dump")) {
         return false;
     }
 
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH 4/5] net/dump: Provide the dumping facility as a net filter

[Yang Hongyang]

The filter interface part looks good to me, thanks!

On 09/24/2015 03:22 PM, Thomas Huth wrote:
> Use the net filter infrastructure to provide the dumping
> functions for netdev devices, too.
>
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>   net/dump.c | 129 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>   vl.c       |   8 +++-
>   2 files changed, 134 insertions(+), 3 deletions(-)
>
> diff --git a/net/dump.c b/net/dump.c
> index afff78e..5904f58 100644
> --- a/net/dump.c
> +++ b/net/dump.c
> @@ -28,7 +28,8 @@
>   #include "qemu/iov.h"
>   #include "qemu/log.h"
>   #include "qemu/timer.h"
> -#include "hub.h"
> +#include "qapi/visitor.h"
> +#include "net/filter.h"
>
>   typedef struct DumpState {
>       int64_t start_ts;
> @@ -225,3 +226,129 @@ int net_init_dump(const NetClientOptions *opts, const char *name,
>       }
>       return rc;
>   }
> +
> +/* Dumping via filter */
> +
> +#define TYPE_FILTER_DUMP "filter-dump"
> +
> +#define FILTER_DUMP(obj) \
> +    OBJECT_CHECK(NetFilterDumpState, (obj), TYPE_FILTER_DUMP)
> +
> +struct NetFilterDumpState {
> +    NetFilterState nfs;
> +    DumpState ds;
> +    char *filename;
> +    uint32_t maxlen;
> +};
> +typedef struct NetFilterDumpState NetFilterDumpState;
> +
> +static ssize_t filter_dump_receive_iov(NetFilterState *nf, NetClientState *sndr,
> +                                       unsigned flags, const struct iovec *iov,
> +                                       int iovcnt, NetPacketSent *sent_cb)
> +{
> +    NetFilterDumpState *nfds = FILTER_DUMP(nf);
> +
> +    dump_receive_iov(&nfds->ds, iov, iovcnt);
> +    return 0;
> +}
> +
> +static void filter_dump_cleanup(NetFilterState *nf)
> +{
> +    NetFilterDumpState *nfds = FILTER_DUMP(nf);
> +
> +    dump_cleanup(&nfds->ds);
> +}
> +
> +static void filter_dump_setup(NetFilterState *nf, Error **errp)
> +{
> +    NetFilterDumpState *nfds = FILTER_DUMP(nf);
> +
> +    if (!nfds->filename) {
> +        error_setg(errp, "dump filter needs 'file' property set!");
> +        return;
> +    }
> +
> +    net_dump_state_init(&nfds->ds, nfds->filename, nfds->maxlen, errp);
> +}
> +
> +static void filter_dump_get_maxlen(Object *obj, Visitor *v, void *opaque,
> +                                   const char *name, Error **errp)
> +{
> +    NetFilterDumpState *nfds = FILTER_DUMP(obj);
> +    uint32_t value = nfds->maxlen;
> +
> +    visit_type_uint32(v, &value, name, errp);
> +}
> +
> +static void filter_dump_set_maxlen(Object *obj, Visitor *v, void *opaque,
> +                                   const char *name, Error **errp)
> +{
> +    NetFilterDumpState *nfds = FILTER_DUMP(obj);
> +    Error *local_err = NULL;
> +    uint32_t value;
> +
> +    visit_type_uint32(v, &value, name, &local_err);
> +    if (local_err) {
> +        goto out;
> +    }
> +    if (value == 0) {
> +        error_setg(&local_err, "Property '%s.%s' doesn't take value '%u'",
> +                   object_get_typename(obj), name, value);
> +        goto out;
> +    }
> +    nfds->maxlen = value;
> +
> +out:
> +    error_propagate(errp, local_err);
> +}
> +
> +static char *file_dump_get_filename(Object *obj, Error **errp)
> +{
> +    NetFilterDumpState *nfds = FILTER_DUMP(obj);
> +
> +    return g_strdup(nfds->filename);
> +}
> +
> +static void file_dump_set_filename(Object *obj, const char *value, Error **errp)
> +{
> +   NetFilterDumpState *nfds = FILTER_DUMP(obj);
> +
> +    g_free(nfds->filename);
> +    nfds->filename = g_strdup(value);
> +}
> +
> +static void filter_dump_instance_init(Object *obj)
> +{
> +    NetFilterDumpState *nfds = FILTER_DUMP(obj);
> +
> +    nfds->maxlen = 65536;
> +
> +    object_property_add(obj, "maxlen", "int", filter_dump_get_maxlen,
> +                        filter_dump_set_maxlen, NULL, NULL, NULL);
> +    object_property_add_str(obj, "file", file_dump_get_filename,
> +                            file_dump_set_filename, NULL);
> +}
> +
> +static void filter_dump_class_init(ObjectClass *oc, void *data)
> +{
> +    NetFilterClass *nfc = NETFILTER_CLASS(oc);
> +
> +    nfc->setup = filter_dump_setup;
> +    nfc->cleanup = filter_dump_cleanup;
> +    nfc->receive_iov = filter_dump_receive_iov;
> +}
> +
> +static const TypeInfo filter_dump_info = {
> +    .name = TYPE_FILTER_DUMP,
> +    .parent = TYPE_NETFILTER,
> +    .class_init = filter_dump_class_init,
> +    .instance_init = filter_dump_instance_init,
> +    .instance_size = sizeof(NetFilterDumpState),
> +};
> +
> +static void filter_dump_register_types(void)
> +{
> +    type_register_static(&filter_dump_info);
> +}
> +
> +type_init(filter_dump_register_types);
> diff --git a/vl.c b/vl.c
> index 9be4d22..aa99ef3 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -2761,8 +2761,12 @@ static bool object_create_initial(const char *type)
>           return false;
>       }
>
> -    /* return false for concrete netfilters */
> -    if (g_str_equal(type, "filter-buffer")) {
> +    /*
> +     * return false for concrete netfilters since
> +     * they depend on netdevs already existing
> +     */
> +    if (g_str_equal(type, "filter-buffer") ||
> +        g_str_equal(type, "filter-dump")) {
>           return false;
>       }
>
>

-- 
Thanks,
Yang.

[Qemu-devel] [PATCH 5/5] net/dump: Add documentation

[Thomas Huth]

Add a short description for the filter-dump command line options.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 qemu-options.hx | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/qemu-options.hx b/qemu-options.hx
index b09f97f..347ee28 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2011,6 +2011,7 @@ qemu -m 512 -object memory-backend-file,id=mem,size=512M,mem-path=/hugetlbfs,sha
 Dump network traffic on VLAN @var{n} to file @var{file} (@file{qemu-vlan0.pcap} by default).
 At most @var{len} bytes (64k by default) per packet are stored. The file format is
 libpcap, so it can be analyzed with tools such as tcpdump or Wireshark.
+Note: For devices created with '-netdev', use '-object filter-dump,...' instead.
 
 @item -net none
 Indicate that no network devices should be configured. It is used to
@@ -3660,6 +3661,13 @@ chain @var{all|in|out} is an option that can be applied to any netfilter, defaul
 
 @option{out} means this filter will receive packets sent from the netdev
 
+@item -object filter-dump,id=@var{id},netdev=@var{dev},file=@var{filename}][,maxlen=@var{len}]
+
+Dump the network traffic on netdev @var{dev} to the file specified by
+@var{filename}. At most @var{len} bytes (64k by default) per packet are stored.
+The file format is libpcap, so it can be analyzed with tools such as tcpdump
+or Wireshark.
+
 @end table
 
 ETEXI
-- 
1.8.3.1