Re: [RFC 4/6] migration: Deprecate -incoming <uri>

[Juan Quintela <quintela@redhat.com>]

Peter Xu <peterx@redhat.com> wrote:
> On Mon, Jun 12, 2023 at 10:51:08PM +0200, Juan Quintela wrote:
>> Peter Xu <peterx@redhat.com> wrote:
>> > On Mon, Jun 12, 2023 at 09:33:42PM +0200, Juan Quintela wrote:
>> >> Only "defer" is recommended.  After setting all migation parameters,
>> >> start incoming migration with "migrate-incoming uri" command.
>> >> 
>> >> Signed-off-by: Juan Quintela <quintela@redhat.com>
>> >> ---
>> >>  docs/about/deprecated.rst | 7 +++++++
>> >>  softmmu/vl.c              | 2 ++
>> >>  2 files changed, 9 insertions(+)
>> >> 
>> >> diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
>> >> index 47e98dc95e..518672722d 100644
>> >> --- a/docs/about/deprecated.rst
>> >> +++ b/docs/about/deprecated.rst
>> >> @@ -447,3 +447,10 @@ The new way to modify migration is using migration parameters.
>> >>  ``blk`` functionality can be acchieved using
>> >>  ``migrate_set_parameter block-incremental true``.
>> >>  
>> >> +``-incoming uri`` (since 8.1)
>> >> +'''''''''''''''''''''''''''''
>> >> +
>> >> +Everything except ``-incoming defer`` are deprecated.  This allows to
>> >> +setup parameters before launching the proper migration with
>> >> +``migrate-incoming uri``.
>> >> +
>> >> diff --git a/softmmu/vl.c b/softmmu/vl.c
>> >> index b0b96f67fa..7fe865ab59 100644
>> >> --- a/softmmu/vl.c
>> >> +++ b/softmmu/vl.c
>> >> @@ -2651,6 +2651,8 @@ void qmp_x_exit_preconfig(Error **errp)
>> >>      if (incoming) {
>> >>          Error *local_err = NULL;
>> >>          if (strcmp(incoming, "defer") != 0) {
>> >> +            warn_report("-incoming %s is deprecated, use -incoming defer and "
>> >> +                        " set the uri with migrate-incoming.", incoming);
>> >
>> > I still use uri for all my scripts, alongside with "-global migration.xxx"
>> > and it works.
>> 
>> You know what you are doing (TM).
>> And remember that we don't support -gobal migration.x-foo.
>> Yes, I know, we should drop the "x-" prefixes.
>
> I hope they'll always be there. :) They're pretty handy for tests, when we
> want to boot a VM without the need to script the sequences of qmp cmds.
>
> Yes, we probably should just always drop the x-.  We can always declare
> debugging purpose for all -global migration.* fields.
>
>> 
>> > Shall we just leave it there?  Or is deprecating it helps us in any form?
>> 
>> See the patches two weeks ago when people complained that lisen(.., num)
>> was too low.  And there are other parameters that work the same way
>> (that I convenientely had forgotten).  So the easiest way to get things
>> right is to use "defer" always.  Using -incoming "uri" should only be
>> for people that "know what they are doing", so we had to ways to do it:
>> - review all migration options and see which ones work without defer
>>   and document it
>> - deprecate everything that is not defer.
>> 
>> Anything else is not going to be very user unfriendly.
>> What do you think.
>
> IIRC Wei Wang had a series just for that, so after that patchset applied we
> should have fixed all issues cleanly?

No, what he does is using always a very big value for listen.  But that
is it.  Anyways, I don't know how to change the backlog listen value
without restarting the listen call.

> Is there one more thing that's not
> working right there?

Compression has other problems.  But independentely of that, they have
the problem that we need to set the parameters before we call incoming.

>> PD.  This series are RFC for multiple reasons O:-)
>
> Happy to know the rest (besides which I know will break my script :).

Thanks, Juan.