Re: [Qemu-devel] [PATCH for-3.0 2/9] migration: loosen recovery check when load vm

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Peter Xu (peterx@redhat.com) wrote:
> We were checking against -EIO, assuming that it will cover all IO
> failures.  But actually it is not.  One example is that in
> qemu_loadvm_section_start_full() we can have tons of places that will
> return -EINVAL even if the error is caused by IO failures on the
> network.

I suspect we should fix those; but OK; I think the only cases
in there that could hit that are the get_counted_string and the
check_section_footer; they could both be fixed to return an errno
like the other cases.

> Let's loosen the recovery check logic here to cover all the error cases
> happened by removing the explicit check against -EIO.  After all we
> won't lose anything here if any other failure happened.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  migration/savevm.c | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 851d74e8b6..efcc795071 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -2276,18 +2276,14 @@ out:
>          qemu_file_set_error(f, ret);
>  
>          /*
> -         * Detect whether it is:
> -         *
> -         * 1. postcopy running (after receiving all device data, which
> -         *    must be in POSTCOPY_INCOMING_RUNNING state.  Note that
> -         *    POSTCOPY_INCOMING_LISTENING is still not enough, it's
> -         *    still receiving device states).
> -         * 2. network failure (-EIO)
> -         *
> -         * If so, we try to wait for a recovery.
> +         * If we are during an active postcopy, then we pause instead
> +         * of bail out to at least keep the VM's dirty data.  Note
> +         * that POSTCOPY_INCOMING_LISTENING stage is still not enough,
> +         * during which we're still receiving device states and we
> +         * still haven't yet started the VM on destination.
>           */
>          if (postcopy_state_get() == POSTCOPY_INCOMING_RUNNING &&
> -            ret == -EIO && postcopy_pause_incoming(mis)) {
> +            postcopy_pause_incoming(mis)) {

Hmm, OK; It does make me a bit nervous we might trigger this
too often, but I see the other cases where we're missing stuff
we should trigger it.  We might find we need to go the other way
and blacklist some errors.


Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

>              /* Reset f to point to the newly created channel */
>              f = mis->from_src_file;
>              goto retry;
> -- 
> 2.17.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK