[RFC,BlueZ,3/9] bap: add and use chainable future abstraction

Multi-part operations will need to postpone things like DBus replies
until all parts are complete. Make this a bit simpler with a chainable
future.
---
 profiles/audio/bap.c | 136 +++++++++++++++++++++++++++++++++----------
 1 file changed, 105 insertions(+), 31 deletions(-)

Hi Pauli,

On Sat, Mar 1, 2025 at 10:58 AM Pauli Virtanen <pav@iki.fi> wrote:
>
> Multi-part operations will need to postpone things like DBus replies
> until all parts are complete. Make this a bit simpler with a chainable
> future.
> ---
>  profiles/audio/bap.c | 136 +++++++++++++++++++++++++++++++++----------
>  1 file changed, 105 insertions(+), 31 deletions(-)
>
> diff --git a/profiles/audio/bap.c b/profiles/audio/bap.c
> index 37168e58c..8b9b89c70 100644
> --- a/profiles/audio/bap.c
> +++ b/profiles/audio/bap.c
> @@ -80,7 +80,7 @@ struct bap_setup {
>         struct iovec *metadata;
>         unsigned int id;
>         struct iovec *base;
> -       DBusMessage *msg;
> +       struct future *qos_done;
>         void (*destroy)(struct bap_setup *setup);
>  };
>
> @@ -114,6 +114,17 @@ struct bap_data {
>         void *user_data;
>  };
>
> +typedef void (*future_func_t)(int err, const char *err_msg, void *data);
> +
> +struct future {
> +       unsigned int step, steps;
> +       const char *name;
> +       future_func_t func;
> +       void *data;
> +       int err;
> +       const char *err_msg;
> +};

This I'm not convinced is the right direction, it will be sort of hard
to make it generic enough besides I think this should actually be
handled directly by bt_bap instead, it is actually weird that the
testing spec doesn't capture stream reconfiguration from streaming
state for example, in any case we can come up with our on tests for it
to ensure the stream is properly released and CIS is closed before we
attempt reconfigure it for example.

>  static struct queue *sessions;
>
>  /* Structure holding the parameters for Periodic Advertisement create sync.
> @@ -155,6 +166,94 @@ struct bt_iso_qos bap_sink_pa_qos = {
>         }
>  };
>
> +static void future_clear(struct future **p, int err, const char *err_msg)
> +{
> +       struct future *h = *p;
> +
> +       if (!h)
> +               return;
> +
> +       DBG("future %p (%s) 0x%02x (%s) step %u/%u", h, h->name ? h->name : "",
> +               err, (err && err_msg) ? err_msg : "", h->step + 1, h->steps);
> +
> +       *p = NULL;
> +
> +       if (err && !h->err) {
> +               h->err = err;
> +               h->err_msg = err_msg;
> +       }
> +
> +       if (++h->step < h->steps)
> +               return;
> +
> +       h->func(h->err, h->err_msg, h->data);
> +       free(h);
> +}
> +
> +static void future_dbus_callback_func(int err, const char *err_msg, void *data)
> +{
> +       DBusMessage *msg = data;
> +       DBusMessage *reply;
> +
> +       if (err && !err_msg)
> +               err_msg = strerror(err);
> +
> +       switch (err) {
> +       case 0:
> +               reply = dbus_message_new_method_return(msg);
> +               break;
> +       case EINVAL:
> +               reply = btd_error_invalid_args_str(msg, err_msg);
> +               break;
> +       default:
> +               reply = btd_error_failed(msg, err_msg);
> +               break;
> +       }
> +
> +       g_dbus_send_message(btd_get_dbus_connection(), reply);
> +
> +       dbus_message_unref(msg);
> +}
> +
> +static void future_init(struct future **p, const char *name, future_func_t func,
> +                                                               void *data)
> +{
> +       struct future *h;
> +
> +       future_clear(p, ECANCELED, NULL);
> +
> +       h = new0(struct future, 1);
> +       h->steps = 1;
> +       h->name = name;
> +       h->func = func;
> +       h->data = data;
> +
> +       DBG("future %p (%s) init", h, h->name ? h->name : "");
> +
> +       *p = h;
> +}
> +
> +static void future_init_dbus_reply(struct future **p, const char *name,
> +                                                       DBusMessage *msg)
> +{
> +       future_init(p, name, future_dbus_callback_func, dbus_message_ref(msg));
> +}
> +
> +__attribute__((unused))
> +static void future_init_chain(struct future **p, struct future *h)
> +{
> +       future_clear(p, ECANCELED, NULL);
> +
> +       if (h) {
> +               h->steps++;
> +
> +               DBG("future %p (%s) init step %u", h, h->name ? h->name : "",
> +                                                               h->steps);
> +       }
> +
> +       *p = h;
> +}
> +
>  static bool bap_data_set_user_data(struct bap_data *data, void *user_data)
>  {
>         if (!data)
> @@ -740,24 +839,12 @@ static void qos_cb(struct bt_bap_stream *stream, uint8_t code, uint8_t reason,
>                                         void *user_data)
>  {
>         struct bap_setup *setup = user_data;
> -       DBusMessage *reply;
>
>         DBG("stream %p code 0x%02x reason 0x%02x", stream, code, reason);
>
>         setup->id = 0;
>
> -       if (!setup->msg)
> -               return;
> -
> -       if (!code)
> -               reply = dbus_message_new_method_return(setup->msg);
> -       else
> -               reply = btd_error_failed(setup->msg, "Unable to configure");
> -
> -       g_dbus_send_message(btd_get_dbus_connection(), reply);
> -
> -       dbus_message_unref(setup->msg);
> -       setup->msg = NULL;
> +       future_clear(&setup->qos_done, code ? EIO : 0, "Unable to configure");
>  }
>
>  static void config_cb(struct bt_bap_stream *stream,
> @@ -765,7 +852,6 @@ static void config_cb(struct bt_bap_stream *stream,
>                                         void *user_data)
>  {
>         struct bap_setup *setup = user_data;
> -       DBusMessage *reply;
>
>         DBG("stream %p code 0x%02x reason 0x%02x", stream, code, reason);
>
> @@ -786,14 +872,7 @@ static void config_cb(struct bt_bap_stream *stream,
>                 return;
>         }
>
> -       if (!setup->msg)
> -               return;
> -
> -       reply = btd_error_failed(setup->msg, "Unable to configure");
> -       g_dbus_send_message(btd_get_dbus_connection(), reply);
> -
> -       dbus_message_unref(setup->msg);
> -       setup->msg = NULL;
> +       future_clear(&setup->qos_done, EIO, "Unable to configure");
>  }
>
>  static void setup_io_close(void *data, void *user_data)
> @@ -872,7 +951,6 @@ static struct bap_setup *setup_new(struct bap_ep *ep)
>  static void setup_free(void *data)
>  {
>         struct bap_setup *setup = data;
> -       DBusMessage *reply;
>
>         DBG("%p", setup);
>
> @@ -881,12 +959,7 @@ static void setup_free(void *data)
>                 setup->id = 0;
>         }
>
> -       if (setup->msg) {
> -               reply = btd_error_failed(setup->msg, "Canceled");
> -               g_dbus_send_message(btd_get_dbus_connection(), reply);
> -               dbus_message_unref(setup->msg);
> -               setup->msg = NULL;
> -       }
> +       future_clear(&setup->qos_done, ECANCELED, NULL);
>
>         if (setup->ep)
>                 queue_remove(setup->ep->setups, setup);
> @@ -1038,7 +1111,8 @@ static DBusMessage *set_configuration(DBusConnection *conn, DBusMessage *msg,
>
>         switch (bt_bap_stream_get_type(setup->stream)) {
>         case BT_BAP_STREAM_TYPE_UCAST:
> -               setup->msg = dbus_message_ref(msg);
> +               future_init_dbus_reply(&setup->qos_done, "set_configuration",
> +                                                                       msg);
>                 break;
>         case BT_BAP_STREAM_TYPE_BCAST:
>                 /* No message sent over the air for broadcast */
> --
> 2.48.1
>
>