Vladimir Sementsov-Ogievskiy <vsement...@yandex-team.ru> writes:
> To migrate TAP device (including open fds) locally, user should:
>
> 1. enable local-tap migration capability both on source and target
> 2. use additional local-incoming=true option for tap on target
>
> Why capability is not enough? We need an option to modify early
> initialization of TAP, to avoid opening new fds. The capability
> may not be set at the moment of netdev initialization.
Bummer. No way around that?
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@yandex-team.ru>
[...]
> diff --git a/qapi/migration.json b/qapi/migration.json
> index 2387c21e9c..992a5b1e2b 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -517,6 +517,12 @@
> # each RAM page. Requires a migration URI that supports seeking,
> # such as a file. (since 9.0)
> #
> +# @local-tap: Migrate TAPs locally, keeping backend alive. Open file
> +# descriptors and TAP-related state are migrated. Only may be
> +# used when migration channel is unix socket. For target device
> +# also @local-incoming option must be specified (since 10.2)
> +# (since 10.2)
> +#
> # Features:
> #
> # @unstable: Members @x-colo and @x-ignore-shared are experimental.
Missing here: local-tap is also experimental.
> @@ -536,7 +542,8 @@
> { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] },
> 'validate-uuid', 'background-snapshot',
> 'zero-copy-send', 'postcopy-preempt', 'switchover-ack',
> - 'dirty-limit', 'mapped-ram'] }
> + 'dirty-limit', 'mapped-ram',
> + { 'name': 'local-tap', 'features': [ 'unstable' ] } ] }
>
> ##
> # @MigrationCapabilityStatus:
> diff --git a/qapi/net.json b/qapi/net.json
> index 78bcc9871e..8f53549d58 100644
> --- a/qapi/net.json
> +++ b/qapi/net.json
> @@ -353,6 +353,15 @@
> # @poll-us: maximum number of microseconds that could be spent on busy
> # polling for tap (since 2.7)
> #
> +# @local-incoming: Do load open file descriptor for that TAP
> +# on incoming migration. May be used only if QEMU is started
> +# for incoming migration. Will work only together with local-tap
> +# migration capability enabled (default: false) (Since: 10.2)
Scratch "Do".
Re "Maybe be used only": what happens when you use it without incoming
migration or when local-tap is off?
Does "local-incoming": false count as invalid use then?
Two spaces between sentences for consistency, please.
> +#
> +# Features:
> +#
> +# @unstable: Member @local-incoming is experimental
Period at the end for consistency, please.
> +#
> # Since: 1.2
> ##
> { 'struct': 'NetdevTapOptions',
> @@ -371,7 +380,8 @@
> '*vhostfds': 'str',
> '*vhostforce': 'bool',
> '*queues': 'uint32',
> - '*poll-us': 'uint32'} }
> + '*poll-us': 'uint32',
> + '*local-incoming': { 'type': 'bool', 'features': [ 'unstable' ] } } }
>
> ##
> # @NetdevSocketOptions:
