Re: [PATCH] migration/rdma: Fix return-path case

[Peter Xu]

On Tue, Mar 14, 2023 at 05:15:58PM +0000, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> The RDMA code has return-path handling code, but it's only enabled
> if postcopy is enabled; if the 'return-path' migration capability
> is enabled, the return path is NOT setup but the core migration
> code still tries to use it and breaks.
> 
> Enable the RDMA return path if either postcopy or the return-path
> capability is enabled.
> 
> bz: https://bugzilla.redhat.com/show_bug.cgi?id=2063615
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Acked-by: Peter Xu <peterx@redhat.com>

> @@ -3373,7 +3373,8 @@ static int qemu_rdma_accept(RDMAContext *rdma)
>       * initialize the RDMAContext for return path for postcopy after first
>       * connection request reached.
>       */
> -    if (migrate_postcopy() && !rdma->is_return_path) {
> +    if ((migrate_postcopy() || migrate_use_return_path())
> +        && !rdma->is_return_path) {
>          rdma_return_path = qemu_rdma_data_init(rdma->host_port, NULL);
>          if (rdma_return_path == NULL) {
>              rdma_ack_cm_event(cm_event);

It's not extremely clear to me yet on when we should use migrate_postcopy()
and when to use migrate_postcopy_ram().  I think it's because I don't know
enough on the dirty-bitmaps capability.  Do we have some good documentation
somewhere?

Not much I get from the qapi doc..

# @dirty-bitmaps: If enabled, QEMU will migrate named dirty bitmaps.
#                 (since 2.12)

Thanks,

-- 
Peter Xu