Vladimir Sementsov-Ogievskiy <[email protected]> writes: > Support transferring of TAP state (including open fd). > > Add new property "x-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 is enabled by global "local" migration > parameter, 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 > - "x-local-migration-supported" TAP option set to true (the > default, starting from 11.2 QEMU Machine Types)
Is the machine type part still accurate? The description in the QAPI schema has (default: false, since 11.2). > > 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 "x-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 "x-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]> > Reviewed-by: Ben Chaney <[email protected]> [...] > diff --git a/qapi/net.json b/qapi/net.json > index acb8594c952..e6921912e12 100644 > --- a/qapi/net.json > +++ b/qapi/net.json > @@ -437,6 +437,29 @@ > # @poll-us: maximum number of microseconds that could be spent on busy > # polling for tap (since 2.7) > # > +# @x-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 @x-local-migration-supporeted > +# parameter set) will simply fail. Either have a a blank line here so you actually get two paragraphs, or refill the entire description to avoid the illusion of two paragraphs. > +# Moreover, when QEMU is in incoming migration state, migration > +# parameter @local is set and @x-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 @downscript > +# explicitly disabled (empty strings or "no"). "no" is deprecated [PATCH 3]. We'll have to remember deleting 'or "no"' here when remove it. Easy to forget. Delete it now? Maybe # Additionally, @script and @downscript must be explicitly disabled # then. > +# (default: false, since 11.2) > +# > +# Features: > +# > +# @unstable: Member @x-local-migration-supported is experimental. > +# > # Since: 1.2 > ## > { 'struct': 'NetdevTapOptions', > @@ -455,7 +478,9 @@ > '*vhostfds': 'str', > '*vhostforce': 'bool', > '*queues': 'uint32', > - '*poll-us': 'uint32'} } > + '*poll-us': 'uint32', > + '*x-local-migration-supported': { > + 'type': 'bool', 'features' : [ 'unstable'] } } } > > ## > # @NetdevSocketOptions: Naming is hard... "Supported" sounds like a property of the QEMU process. That's not what this is. It's an on/off switch that happens to be in series with another on/off switch, namely migration parameter @local. Maybe @permit-local-migration: permit local migration for this TAP backend. When set, local migration is enabled/disabled by migration parameter @local for this TAP backend. ...
