[ovs-dev] [RFC] ovsdb-idl: improved error handling for non-existent db

[Ben Pfaff]

On Wed, Jan 27, 2016 at 02:46:07PM -0500, Lance Richardson wrote:
> A common error scenario with OVN is to attempt to use ovn-nbctl when
> the OVN databases have not been created:
>    1. ovn-nbctl sends "get_schema" request for OVN db to ovsdb-server.
>    2. ovsdb-server fails to lookup requested db, sends error response
>       to ovn-nbctl.
>    3. ovn-nbctl received the error response in ovsdb_idl_run(), but
>       takes no specific action in this case.
>    4. ovn-nbctl hangs forever in IDL_S_SCHEMA_REQUESTED state (assuming
>       a timeout wasn't requested on the command line).
> 
> Here is an RFC patch to start the discussion about how handling of this
> particular error can be improved.
> 
> Signed-off-by: Lance Richardson <lrichard at redhat.com>
> ---
>  lib/ovsdb-idl.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/lib/ovsdb-idl.c b/lib/ovsdb-idl.c
> index 7e84138..3f4be51 100644
> --- a/lib/ovsdb-idl.c
> +++ b/lib/ovsdb-idl.c
> @@ -453,6 +453,16 @@ ovsdb_idl_run(struct ovsdb_idl *idl)
>                  ovsdb_idl_send_monitor_request(idl);
>                  idl->state = IDL_S_MONITOR_REQUESTED;
>              }
> +        } else if (msg->type == JSONRPC_ERROR
> +                   && idl->state == IDL_S_SCHEMA_REQUESTED
> +                   && idl->request_id
> +                   && json_equal(idl->request_id, msg->id)) {
> +                json_destroy(idl->request_id);
> +                idl->request_id = NULL;
> +                VLOG_ERR("%s: requested schema not found",
> +                         jsonrpc_session_get_name(idl->session));
> +                ovsdb_idl_destroy(idl);
> +                exit(EXIT_FAILURE);

I think that logging the problem is a good place to start, but the IDL
definitely shouldn't kill the process.  The IDL's clients include
long-running daemons that can and should reasonably recover from this
kind of error.