Re: [PATCH V2 13/13] migration: cpr-transfer mode

[Peter Xu <peterx@redhat.com>]

On Tue, Oct 08, 2024 at 03:12:32PM -0400, Steven Sistare wrote:
> > This is slightly tricky part and would be nice to be documented somewhere,
> > perhaps starting from in the commit message.
> 
> I will extend the block comment in qmp_migrate:
> 
>     /*
>      * For cpr-transfer, the target may not be listening yet on the migration
>      * channel, because first it must finish cpr_load_state.  The target tells
>      * us it is listening by closing the cpr-state socket.  Wait for that HUP
>      * event before connecting in qmp_migrate_finish.
>      *
>      * The HUP could occur because the target fails while reading CPR state,
>      * in which case the target will not listen for the incoming migration
>      * connection, so qmp_migrate_finish will fail to connect, and then recover.
>      */

Yes this is better, thanks.

> 
> > Then the error will say "failed to connect to destination QEMU" hiding the
> > real failure (cpr save/load failed), right?  That's slightly a pity.
> 
> Yes, but destination qemu will also emit a more specific message.

True.

> 
> > I'm OK with the HUP as of now, but if you care about accurate CPR-stage
> > error reporting, then feel free to draft something else in the next post.
> 
> I'll think about it, but to get cpr into 9.2, this will probably need to be
> deferred as a future enhancement.

Yep that's OK.

-- 
Peter Xu