Support transferring of TAP state (including open fd).
Add new property "local-migration-supported", which defines
whether local-migration is actually supported for this TAP device.
Starting from 11.2 QEMU Machine Types it's enabled by default.
Note that local-migration (including migrating opened FDs
through migration channel, which must be UNIX socket) is
enabled by global "local" migration parameters. But individual
devices may have additional options to enable/disable it
per device.
The tricky thing is that we need to know whether to call open/connect in
TAP initialization code, i.e. we need to know the value of migration
parameter "local" when creating the TAP device. For incoming migration,
we can know only for TAP devices created with QMP after setting the
migration parameter with QMP.
So the full picture is:
On source, to start outgoing "local" migration you need:
- migration parameter "local" set to true
- "local-migration-supported" TAP option set to true (the
default, starting from 11.2 QEMU Machine Types)
If at least one of these options is not set, TAP backend
doesn't participate in migration.
On target, things are more difficult:
Same, you need both "local" and "local-migration-supported"
be set. And same, if one of them is not set, TAP backend
is initialized as usual, and doesn't accept any incoming
state.
Additionally, if you are going to set "local", it must be
set before creating the TAP device. If TAP device created
with "local" unset, it initializes as usual. If you enable
"local" after it and start incoming migration, it will fail
in .pre_load handler of TAP backend.
Moreover, there are interface restrictions: if you create TAP
device when QEMU is in INCOMING state, and both "local"
and "local-migration-supported" set, most of TAP options are
not allowed, and script/downscript are required to be explicitly
unset (set to "" or "no").
Signed-off-by: Vladimir Sementsov-Ogievskiy <[email protected]>
---
net/tap.c | 165 ++++++++++++++++++++++++++++++++++++++++++++++++--
qapi/net.json | 22 ++++++-
2 files changed, 180 insertions(+), 7 deletions(-)
diff --git a/net/tap.c b/net/tap.c
index 2bd4b089573..4162820bcee 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -38,12 +38,17 @@
#include "monitor/monitor.h"
#include "system/runstate.h"
#include "system/system.h"
+#include "migration/misc.h"
#include "qapi/error.h"
#include "qemu/cutils.h"
#include "qemu/error-report.h"
#include "qemu/main-loop.h"
#include "qemu/sockets.h"
#include "hw/virtio/vhost.h"
+#include "hw/core/vmstate-if.h"
+#include "migration/vmstate.h"
+#include "qom/object.h"
+#include "qom/compat-properties.h"
#include "net/tap.h"
#include "net/util.h"
@@ -71,6 +76,8 @@ static const int kernel_feature_bits[] = {
OBJECT_DECLARE_SIMPLE_TYPE(TAPState, TAP_NETDEV)
+static const VMStateDescription vmstate_tap;
+
struct TAPState {
Object parent_obj;
@@ -95,6 +102,7 @@ struct TAPState {
int queue_index;
bool read_poll_detached;
VMChangeStateEntry *vmstate;
+ bool local_migration_supported;
};
static void launch_script(const char *setup_script, const char *ifname,
@@ -409,6 +417,8 @@ static void tap_cleanup(NetClientState *nc)
tap_write_poll(s, false);
close(s->fd);
s->fd = -1;
+
+ vmstate_unregister(VMSTATE_IF(s), &vmstate_tap, s);
}
static void tap_poll(NetClientState *nc, bool enable)
@@ -445,6 +455,76 @@ static VHostNetState *tap_get_vhost_net(NetClientState *nc)
return s->vhost_net;
}
+static bool tap_is_wait_incoming(NetClientState *nc)
+{
+ TAPState *s = container_of(nc, TAPState, nc);
+ assert(nc->info->type == NET_CLIENT_DRIVER_TAP);
+ return s->fd == -1;
+}
+
+static bool tap_pre_load(void *opaque, Error **errp)
+{
+ TAPState *s = opaque;
+
+ if (s->fd != -1) {
+ error_setg(errp,
+ "TAP is already initialized and cannot receive "
+ "incoming fd. For local migration, 'local' "
+ "migration parameter must be set _before_ "
+ "creating TAP device.");
