On Sat, Feb 14, 2026 at 10:46 AM Zhang Chen <[email protected]> wrote:
>
> On Sat, Feb 7, 2026 at 9:47 PM Cindy Lu <[email protected]> wrote:
> >
> > From: Jason Wang <[email protected]>
> >
> > Add a QAPI option 'enable_when_stopped' for filter-redirector that
> > allows it to continue receiving data from netdev when VM is stopped.
> >
> > When enabled, a VM state change handler activates the netdev's
> > read_poll() when VM stops, allowing the netdev to continue reading
> > data and passing it through filter-redirector to the chardev output.
> >
> > This is useful for scenarios where filter-redirector needs to
> > process network traffic even when the VM is paused.
> >
> > Usage:
> > -object filter-redirector,id=f0,netdev=net0,queue=tx,\
> > outdev=chardev0,enable_when_stopped=true
> >
>
> It seems this series is trying to address previous VM migration network
> related issues that Juraj Marcin mentioned.
> Add CC to him.
>
> I've taken a quick look, and this series lacks support for
> filter-reply and filter-rewriter.
> Could there be a reason for this?
>
> Thanks
> Chen
>
Hi Chen
For this RFC, filter-reply and filter-rewriter is not need, I will add
support for them later.
Thanks
cindy
> .
>
>
>
>
> > Signed-off-by: Jason Wang <[email protected]>
> > Signed-off-by: Cindy Lu <[email protected]>
> > ---
> > net/filter-mirror.c | 38 ++++++++++
> > qapi/qom.json | 7 +-
> > tests/qtest/test-filter-redirector.c | 106 +++++++++++++++++++++++++++
> > 3 files changed, 150 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/filter-mirror.c b/net/filter-mirror.c
> > index aa2ab452fd..e1a0650abd 100644
> > --- a/net/filter-mirror.c
> > +++ b/net/filter-mirror.c
> > @@ -21,6 +21,7 @@
> > #include "qemu/iov.h"
> > #include "qemu/sockets.h"
> > #include "block/aio-wait.h"
> > +#include "system/runstate.h"
> >
> > #define TYPE_FILTER_MIRROR "filter-mirror"
> > typedef struct MirrorState MirrorState;
> > @@ -41,6 +42,8 @@ struct MirrorState {
> > CharFrontend chr_out;
> > SocketReadState rs;
> > bool vnet_hdr;
> > + bool enable_when_stopped;
> > + VMChangeStateEntry *vmsentry;
> > };
> >
> > typedef struct FilterSendCo {
> > @@ -251,6 +254,7 @@ static void filter_redirector_cleanup(NetFilterState
> > *nf)
> >
> > qemu_chr_fe_deinit(&s->chr_in, false);
> > qemu_chr_fe_deinit(&s->chr_out, false);
> > + qemu_del_vm_change_state_handler(s->vmsentry);
> > }
> >
> > static void filter_mirror_setup(NetFilterState *nf, Error **errp)
> > @@ -282,6 +286,18 @@ static void redirector_rs_finalize(SocketReadState *rs)
> > redirector_to_filter(nf, rs->buf, rs->packet_len);
> > }
> >
> > +static void filter_redirector_vm_state_change(void *opaque, bool running,
> > + RunState state)
> > +{
> > + NetFilterState *nf = opaque;
> > + MirrorState *s = FILTER_REDIRECTOR(nf);
> > + NetClientState *nc = nf->netdev;
> > +
> > + if (!running && s->enable_when_stopped && nc->info->read_poll) {
> > + nc->info->read_poll(nc, true);
> > + }
> > +}
> > +
> > static void filter_redirector_setup(NetFilterState *nf, Error **errp)
> > {
> > MirrorState *s = FILTER_REDIRECTOR(nf);
> > @@ -331,6 +347,9 @@ static void filter_redirector_setup(NetFilterState *nf,
> > Error **errp)
> > return;
> > }
> > }
> > +
> > + s->vmsentry = qemu_add_vm_change_state_handler(
> > + filter_redirector_vm_state_change, nf);
> > }
> >
> > static void filter_redirector_status_changed(NetFilterState *nf, Error
> > **errp)
> > @@ -437,6 +456,22 @@ static void filter_redirector_set_vnet_hdr(Object *obj,
> > s->vnet_hdr = value;
> > }
> >
> > +static bool filter_redirector_get_enable_when_stopped(Object *obj, Error
> > **errp)
> > +{
> > + MirrorState *s = FILTER_REDIRECTOR(obj);
> > +
> > + return s->enable_when_stopped;
> > +}
> > +
> > +static void filter_redirector_set_enable_when_stopped(Object *obj,
> > + bool value,
> > + Error **errp)
> > +{
> > + MirrorState *s = FILTER_REDIRECTOR(obj);
> > +
> > + s->enable_when_stopped = value;
> > +}
> > +
> > static void filter_mirror_class_init(ObjectClass *oc, const void *data)
> > {
> > NetFilterClass *nfc = NETFILTER_CLASS(oc);
> > @@ -463,6 +498,9 @@ static void filter_redirector_class_init(ObjectClass
> > *oc, const void *data)
> > object_class_property_add_bool(oc, "vnet_hdr_support",
> > filter_redirector_get_vnet_hdr,
> > filter_redirector_set_vnet_hdr);
> > + object_class_property_add_bool(oc, "enable_when_stopped",
> > +
> > filter_redirector_get_enable_when_stopped,
> > +
> > filter_redirector_set_enable_when_stopped);
> >
> > nfc->setup = filter_redirector_setup;
> > nfc->cleanup = filter_redirector_cleanup;
> > diff --git a/qapi/qom.json b/qapi/qom.json
> > index 6f5c9de0f0..b1fe55944c 100644
> > --- a/qapi/qom.json
> > +++ b/qapi/qom.json
> > @@ -488,13 +488,18 @@
> > # @vnet_hdr_support: if true, vnet header support is enabled
> > # (default: false)
> > #
> > +# @enable_when_stopped: if true, activate netdev's read poll when VM
> > +# stops to allow filter-redirector to continue receiving data
> > +# (default: false)
> > +#
> > # Since: 2.6
> > ##
> > { 'struct': 'FilterRedirectorProperties',
> > 'base': 'NetfilterProperties',
> > 'data': { '*indev': 'str',
> > '*outdev': 'str',
> > - '*vnet_hdr_support': 'bool' } }
> > + '*vnet_hdr_support': 'bool',
> > + '*enable_when_stopped': 'bool' } }
> >
> > ##
> > # @FilterRewriterProperties:
> > diff --git a/tests/qtest/test-filter-redirector.c
> > b/tests/qtest/test-filter-redirector.c
> > index 5540c232c0..fa958bb0a5 100644
> > --- a/tests/qtest/test-filter-redirector.c
> > +++ b/tests/qtest/test-filter-redirector.c
> > @@ -385,6 +385,110 @@ static void test_redirector_init_status_off(void)
> > qtest_quit(qts);
> > }
> >
> > +/*
> > + * Test filter-redirector works when VM is stopped (TX direction).
> > + *
> > + * This test verifies that when VM is stopped, the filter-redirector
> > + * can still receive data from the netdev because the VM state change
> > + * handler activates the netdev's read_poll(). Data flows from netdev
> > + * to filter-redirector and out through the chardev.
> > + *
> > + * Data flow: backend_sock -> netdev (read_poll) -> filter-redirector ->
> > chardev
> > + */
> > +static void test_redirector_with_vm_stop(void)
> > +{
> > + int backend_sock[2], recv_sock;
> > + uint32_t ret = 0, len = 0;
> > + char send_buf[] = "Hello!!";
> > + char sock_path0[] = "filter-redirector0.XXXXXX";
> > + char *recv_buf;
> > + uint32_t size = sizeof(send_buf);
> > + size = htonl(size);
> > + QTestState *qts;
> > + struct timeval tv;
> > + fd_set rfds;
> > +
> > + ret = socketpair(PF_UNIX, SOCK_STREAM, 0, backend_sock);
> > + g_assert_cmpint(ret, !=, -1);
> > +
> > + ret = mkstemp(sock_path0);
> > + g_assert_cmpint(ret, !=, -1);
> > +
> > + /*
> > + * Setup TX path: netdev -> filter-redirector -> chardev
> > + * Data sent to backend_sock[0] will be read by the netdev,
> > + * passed through filter-redirector, and output to sock_path0.
> > + * Enable enable_when_stopped to activate read_poll when VM stops.
> > + */
> > + qts = qtest_initf(
> > + "-nic socket,id=qtest-bn0,fd=%d "
> > + "-chardev socket,id=redirector0,path=%s,server=on,wait=off "
> > + "-object filter-redirector,id=qtest-f0,netdev=qtest-bn0,"
> > + "queue=tx,outdev=redirector0,enable_when_stopped=true ",
> > + backend_sock[1], sock_path0);
> > +
> > + recv_sock = unix_connect(sock_path0, NULL);
> > + g_assert_cmpint(recv_sock, !=, -1);
> > +
> > + /* Ensure connection is established */
> > + qtest_qmp_assert_success(qts, "{ 'execute' : 'query-status'}");
> > +
> > + struct iovec iov[] = {
> > + {
> > + .iov_base = &size,
> > + .iov_len = sizeof(size),
> > + }, {
> > + .iov_base = send_buf,
> > + .iov_len = sizeof(send_buf),
> > + },
> > + };
> > +
> > + /*
> > + * Stop the VM - this triggers our vm_state_change handler
> > + * which should activate the netdev's read_poll()
> > + */
> > + qtest_qmp_assert_success(qts, "{ 'execute' : 'stop'}");
> > +
> > + /* Wait for VM to actually stop */
> > + qtest_qmp_eventwait(qts, "STOP");
> > +
> > + /*
> > + * Send data to backend socket while VM is stopped.
> > + * The netdev should still read the data (because read_poll is
> > + * activated by our vm_state_change handler), pass it through
> > + * filter-redirector, and output to the chardev.
> > + */
> > + ret = iov_send(backend_sock[0], iov, 2, 0, sizeof(size) +
> > sizeof(send_buf));
> > + g_assert_cmpint(ret, ==, sizeof(send_buf) + sizeof(size));
> > +
> > + /*
> > + * Data should arrive at recv_sock even with VM stopped,
> > + * because read_poll is activated.
> > + */
> > + FD_ZERO(&rfds);
> > + FD_SET(recv_sock, &rfds);
> > + tv.tv_sec = 5;
> > + tv.tv_usec = 0;
> > + ret = select(recv_sock + 1, &rfds, NULL, NULL, &tv);
> > + g_assert_cmpint(ret, ==, 1); /* Data should arrive */
> > +
> > + ret = recv(recv_sock, &len, sizeof(len), 0);
> > + g_assert_cmpint(ret, ==, sizeof(len));
> > + len = ntohl(len);
> > +
> > + g_assert_cmpint(len, ==, sizeof(send_buf));
> > + recv_buf = g_malloc(len);
> > + ret = recv(recv_sock, recv_buf, len, 0);
> > + g_assert_cmpint(ret, ==, len);
> > + g_assert_cmpstr(recv_buf, ==, send_buf);
> > +
> > + g_free(recv_buf);
> > + close(recv_sock);
> > + close(backend_sock[0]);
> > + unlink(sock_path0);
> > + qtest_quit(qts);
> > +}
> > +
> > static void test_redirector_rx_event_opened(void)
> > {
> > int backend_sock[2], send_sock;
> > @@ -489,5 +593,7 @@ int main(int argc, char **argv)
> > test_redirector_init_status_off);
> > qtest_add_func("/netfilter/redirector_rx_event_opened",
> > test_redirector_rx_event_opened);
> > + qtest_add_func("/netfilter/redirector_with_vm_stop",
> > + test_redirector_with_vm_stop);
> > return g_test_run();
> > }
> > --
> > 2.52.0
> >
>
