Vladimir Sementsov-Ogievskiy <[email protected]> writes:
> 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.");
>From error_setg()'s contract:
* The resulting message should be a single phrase, with no newline or
* trailing punctuation.
Suggest something like
error_setg(errp,
"TAP is already initialized and cannot receive "
"incoming fd");
error_append_hint(errp,
"Migration parameter 'local' must be set"
" _before_ creating the TAP device.");
Requires ERRP_GUARD().
> + return false;
> + }
> +
> + return true;
> +}
[...]
> diff --git a/qapi/net.json b/qapi/net.json
> index ada0329ef9d..d0d6e303b0d 100644
> --- a/qapi/net.json
> +++ b/qapi/net.json
> @@ -435,6 +435,25 @@
> # @poll-us: maximum number of microseconds that could be spent on busy
> # polling for tap (since 2.7)
> #
> +# @local-migration-supported: enable local migration for this TAP
> +# backend. When set, local migration is enabled/disabled by
> +# migration parameter @local for this TAP backend. When unset,
> +# migration parameter @local is ignored for this TAP backend.
> +# To be able to do incoming local migration of a TAP backend,
> +# migration parameter @local must be set _before_ creating the
> +# TAP backend. Otherwise, TAP backend is initialized as usual,
> +# opening/creating TAP devices in kernel. In this case further
> +# local incoming migration (with migration parameter @local set
> +# after creating TAP backend with @local-migration-supporeted
> +# parameter set) will simply fail.
> +# Moreover, when QEMU is in incoming migration state, migration
> +# parameter @local is set and @local-migration-supported is set,
> +# the following options are not supported and must not be set:
> +# @fd, @fds, @helper, @br, @ifname, @sndbuf, @vnet_hdr.
> +# Additionally in this case @script and @downscipt must be
> +# explicitly disabled (empty strings or "no").
> +# (Since 11.2)
Default?
> +#
> # Since: 1.2
> ##
> { 'struct': 'NetdevTapOptions',
> @@ -453,7 +472,8 @@
> '*vhostfds': 'str',
> '*vhostforce': 'bool',
> '*queues': 'uint32',
> - '*poll-us': 'uint32'} }
> + '*poll-us': 'uint32',
> + '*local-migration-supported': 'bool' } }
>
> ##
> # @NetdevSocketOptions:
