Re: [Qemu-devel] [PATCH 1/1] RFC: net/slirp: link with libslirp

[Marc-André Lureau]

Hi

On Mon, Feb 11, 2019 at 12:09 PM Daniel P. Berrangé <address@hidden> wrote:
>
> On Fri, Feb 08, 2019 at 07:12:26PM +0100, Marc-André Lureau wrote:
> > Once libslirp has received its first release, we can link with the
> > external libslirp library.
> >
> > The migration data should be compatible with current and older qemu
> > versions (same compatibility as today). See "slirp: add state
> > saving/loading" patch. However, the content should be treated as a
> > blob, as the format may change eventually in the future.
>
> How are we going to manage live migration compat if libslirp changes
> the blob content ?
>
> Bear in mind that we need to support all existing QEMU releases live
> migrating to effectively all future QEMU releases, with all future
> libslirp releases, in *both* directions. ie arbitrarily newer
> libslirp needs to be able to emit a blob format that can be read
> by arbitrarily older slirp inside QEMU.


Right, this is all supported currently with the proposed patch set,
since it is effectively the same code.

So register_savevm_live() get passed slirp_state_version() (currently == 4)

& slirp_state_load() get the version_id from QEMU.

>
> Normally we tie data format changes to the machine type. How are
> we going to achieve such machine type associations with an external
> libslirp ?

Is this relevant for slirp? I don't see any version tied to machine
type. Am I missing something?

thanks

>
> It seems to me that if a libslirp wants to change live migration
> format, it will need to support both the old and new formats
> indefinitely, and the new format must be an opt-in. QEMU can
> then tell libslirp which migraiton format based on the machine
> type.
>
>

ok

>
> Regards,
> Daniel
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