Re: [Qemu-devel] [PATCH v6 for-2.7 10/28] migration: add reporting of errors for outgoing migration

[Juan Quintela <quintela@redhat.com>]

"Daniel P. Berrange" <berrange@redhat.com> wrote:
> Currently if an application initiates an outgoing migration,
> it may or may not, get an error reported back on failure. If
> the error occurs synchronously to the 'migrate' command
> execution, the client app will see the error message. This
> is the case for DNS lookup failures. If the error occurs
> asynchronously to the monitor command though, the error
> will be thrown away and the client left guessing about
> what went wrong. This is the case for failure to connect
> to the TCP server (eg due to wrong port, or firewall
> rules, or other similar errors).
>
> In the future we'll be adding more scope for errors to
> happen asynchronously with the TLS protocol handshake.
> TLS errors are hard to diagnose even when they are well
> reported, so discarding errors entirely will make it
> impossible to debug TLS connection problems.
>
> Management apps which do migration are already using
> 'query-migrate' / 'info migrate' to check up on progress
> of background migration operations and to see their end
> status. This is a fine place to also include the error
> message when things go wrong.
>
> This patch thus adds an 'error-desc' field to the
> MigrationInfo struct, which will be populated when
> the 'status' is set to 'failed':
>
> (qemu) migrate -d tcp:localhost:9001
> (qemu) info migrate
> capabilities: xbzrle: off rdma-pin-all: off auto-converge: off zero-blocks: off compress: off events: off x-postcopy-ram: off
> Migration status: failed (Error connecting to socket: Connection refused)
> total time: 0 milliseconds
>
> In the HMP, when doing non-detached migration, it is
> also possible to display this error message directly
> to the app.
>
> (qemu) migrate tcp:localhost:9001
> Error connecting to socket: Connection refused
>
> Or with QMP
>
>   {
>     "execute": "query-migrate",
>     "arguments": {}
>   }
>   {
>     "return": {
>       "status": "failed",
>       "error-desc": "address resolution failed for myhost:9000: No address associated with hostname"
>     }
>   }
>
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> ---

Reviewed-by: Juan Quintela <quintela@redhat.com>