Re: [RFC PATCH 04/25] migration: Move multifd_recv_setup call

[Peter Xu <peterx@redhat.com>]

On Fri, Dec 26, 2025 at 06:19:06PM -0300, Fabiano Rosas wrote:
> The multifd_recv_setup() call is currently in a place where it will be
> called for every channel that appears. That doesn't make much
> sense.
> 
> It seems it was moved when the channel discovery mechanism was added
> back at commit 6720c2b327 (migration: check magic value for deciding
> the mapping of channels, 2022-12-20). The original place was
> migration_incoming_setup() which would run for just the main channel,
> but it was discovered that the main channel might arrive after a
> multifd channel.
> 
> Move the call back to a place where it will be called only once.
> 
> With respect to cleanup, this new location at
> qemu_start_incoming_migration() has the same issue as the previous
> callsite at migration_ioc_process_incoming(): no cleanup ever happens.
> 
> The error message goes from being emitted via error_report_err(), to
> being returned to the qmp_migrate_incoming() incoming command, which
> is arguably better, since this is setup code.

This is not the only and real reason that you moved it, right?

Neither should it be the reason that you want it to be called only exactly
once; after all the function will be no-op in the 2nd+ calls.

I'll keep reading.. I'm guessing I'll find it later, but IMHO it'll always
be good to mention the real motivation in the commit log.

> 
> Signed-off-by: Fabiano Rosas <farosas@suse.de>
> ---
>  migration/migration.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index 71efe945f6..974313944c 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -786,6 +786,10 @@ static void qemu_start_incoming_migration(const char *uri, bool has_channels,
>          return;
>      }
>  
> +    if (multifd_recv_setup(errp) != 0) {
> +        return;
> +    }
> +
>      if (addr->transport == MIGRATION_ADDRESS_TYPE_SOCKET) {
>          SocketAddress *saddr = &addr->u.socket;
>          if (saddr->type == SOCKET_ADDRESS_TYPE_INET ||
> @@ -1065,10 +1069,6 @@ void migration_ioc_process_incoming(QIOChannel *ioc, Error **errp)
>          channel = CH_POSTCOPY;
>      }
>  
> -    if (multifd_recv_setup(errp) != 0) {
> -        return;
> -    }
> -
>      if (channel == CH_MAIN) {
>          f = qemu_file_new_input(ioc);
>          migration_incoming_setup(f);
> -- 
> 2.51.0
> 

-- 
Peter Xu