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Re: [Qemu-devel] [PATCH 0/2] migration/channel errors and cancelling
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH 0/2] migration/channel errors and cancelling |
Date: |
Tue, 19 Dec 2017 10:14:08 +0000 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
* Peter Xu (address@hidden) wrote:
> On Fri, Dec 15, 2017 at 05:16:53PM +0000, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <address@hidden>
> >
> > Hi,
> > Where a channel fails asynchronously during connect, call
> > back through the migration code so it can clean up.
> > In particular this causes the transition of a 'cancelling' state
> > to 'cancelled' in the case of:
> >
> > migrate -d tcp:deadhost:port
> > <host tries to connect>
> > migrate_cancel
> >
> > previously the status would get stuck in cancelling because
> > the final cleanup didn't happen.
> >
> > This is the second part of the fix for:
> > https://bugzilla.redhat.com/show_bug.cgi?id=1525899
>
> IIUC this series tries to deliver the connection error a long way
> until migrate_fd_connect() to handle it. But, haven't we already have
> a function migrate_fd_error() to do that (which is faster, and
> simpler)?
>
> void migrate_fd_error(MigrationState *s, const Error *error)
> {
> trace_migrate_fd_error(error_get_pretty(error));
> assert(s->to_dst_file == NULL);
> migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
> MIGRATION_STATUS_FAILED);
> migrate_set_error(s, error);
> notifier_list_notify(&migration_state_notifiers, s);
> block_cleanup_parameters(s);
> }
>
> I think it's not handling the case when cancelling. If we let it to
> handle the cancelling case well, would it be a simpler fix?
>
> Moreover, I think this is another good example that migration is not
> handling the cleanup "cleanly" in general... I really hope we can do
> this better in 2.12. I'll see whether I can give it a shot, but in
> all cases it'll be after the merging of existing patches since there
> are already quite a lot of dangling patches.
No, I think migrate_fd_error is the cause of the problem here, not the
answer.
If we stick to the simple rule that a migration must always call
migrate_fd_cleanup then the cancellation problems are fixed - I think
that's how we make migration 'clean' - a single cleanup routine
that always gets called.
Dave
> Thanks,
>
> --
> Peter Xu
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK