From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BDC9DC433E0 for ; Wed, 27 May 2020 15:38:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8F54420776 for ; Wed, 27 May 2020 15:38:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="E3tC5aAQ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727890AbgE0Piy (ORCPT ); Wed, 27 May 2020 11:38:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55268 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726807AbgE0Pix (ORCPT ); Wed, 27 May 2020 11:38:53 -0400 Received: from mail-ot1-x32a.google.com (mail-ot1-x32a.google.com [IPv6:2607:f8b0:4864:20::32a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9CC3BC05BD1E for ; Wed, 27 May 2020 08:38:52 -0700 (PDT) Received: by mail-ot1-x32a.google.com with SMTP id g25so19442697otp.13 for ; Wed, 27 May 2020 08:38:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=WxfTPJMG0B7j7zZi7li0uvVMY8W3X3q/OTBuYRSk/CI=; b=E3tC5aAQqDHGy/iMn7mC28/A1D9QNAU8A3at4bE3eP7fON5QOH5NL0NjrwOcKVFsTF K8aUiSUQ0IjDnlqoAdKmI3mHcu9Ir2jcnf8cTioB9mtEt0MdCVX1z3CdJ3NIvQnuFoBh pHBgu58QSD/rT3jtoh6inrxPR/Tpe1VmFPGTfoG5W4BMDrehuq5Ya6ZFk4VAlWXkXGQ3 rLXRns8ydMo9/WwAUUYvwczX7HcN8S2hrYXLLtbfCHukd0B0FAXLnrSQh6bbwX9boRo4 /zTzGT2H3hJGLqvzXG1b0t5oIVe0bgQd/VA4q53FPAKxJ79E8NBdvpY60s0mLKrTtQZs aiXA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=WxfTPJMG0B7j7zZi7li0uvVMY8W3X3q/OTBuYRSk/CI=; b=dvCikQ7CnlVoHT3FerR7NoGoe4TWrCqH20hQVzrUNpUSmMcYFuyMHRtgpGQO5VUyOY hX9OLr9jZqVPLTcwp+ZCZ5NchJFT1eK+xYRvpdmCr4EqSO4QsNz1ds0eiTIDwgXjM6N+ hLz7J4mmLtTjNQBsQCMpa+ImwmMM91WcqWlCwp5A/rPRLChsMaWhXzHmM5OQzog6U0Qo U4PUXXCss0gaTP2CCRRAeU2eA1FoWrS1P7Dy+fgsLvo80O6ehpa025EuEuboUA8U4oR4 TibPWZ66FhxPdRKt41JPtKoPEo7ni9rxj/+FHdrc6c90phmspm2G9vJGCQikPGL+aM9r OBgw== X-Gm-Message-State: AOAM5304TRexgES0gMTxUbj4QBUqpL1ILvDW9Zm/EdH2D4NNFhrWl6Yx HDa5XWjndvw1Pck/ehhWYJrI0urMUQiy3QOyuQo= X-Google-Smtp-Source: ABdhPJyi8X6IeWrw7hreSuP0QVQ6ujc2GVU2GOupRjWJw/iWxGtrGRc16on0bQk8F2B8enKZYlCG3qcPlro7b7gNwAw= X-Received: by 2002:a05:6830:310c:: with SMTP id b12mr5205706ots.11.1590593931942; Wed, 27 May 2020 08:38:51 -0700 (PDT) MIME-Version: 1.0 References: <11527909.O9o76ZdvQC@ix> In-Reply-To: <11527909.O9o76ZdvQC@ix> From: Luiz Augusto von Dentz Date: Wed, 27 May 2020 08:38:38 -0700 Message-ID: Subject: Re: Comments on the ConnectDevice API function To: Szymon Janc Cc: Martin Woolley , "Linux-bluetooth@vger.kernel.org" Content-Type: text/plain; charset="UTF-8" Sender: linux-bluetooth-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-bluetooth@vger.kernel.org Hi Szymon, On Wed, May 27, 2020 at 7:10 AM Szymon Janc wrote: > > Hi Martin, > > On Wednesday, 27 May 2020 15:41:12 CEST Martin Woolley wrote: > > Hi Luiz > > > > thanks for your response. Much appreciated. I must confess this is the first > > time I've used the BlueZ APIs directly (via D-Bus). > > > I'm all for hiding implementation details where possible in APIs and making > > the API itself take care of conditional aspects if possible, but these were > > just my $0.02, no more than that. I wasn't aware of the background or the > > philosophy, so thanks for that insight as well. > > > Having the API take care of the AlreadyExists error by providing a > > connection to the already discovered device, transparently does seem a nice > > touch for the application developer but certainly not essential. > > This API was added only for qualification purposes (there are some GAP tests > specified in a way that upper tester is not doing discovery) and it shouldn't > be used for 'normal' usage. Btw, we could perhaps have a different flag from such API e.g. qualification-only or perhaps add an entry on main.conf would be better in this regard since it may mean that we never really adopt them as stable APIs. > > > > All the best > > > > Martin > > > > -----Original Message----- > > From: Luiz Augusto von Dentz > > Sent: 22 May 2020 18:49 > > To: Martin Woolley > > Cc: Linux-bluetooth@vger.kernel.org > > Subject: Re: Comments on the ConnectDevice API function > > > > Hi Martin, > > > > On Fri, May 22, 2020 at 1:25 AM Martin Woolley > > wrote: > > > > > > > > > Hello > > > > > > > > > > > > I've recently been working with BlueZ via D-Bus and have a situation which > > > requires me to be able to connect to a device whose Bluetooth device > > > address is known, but without first scanning. This is a link layer state > > > transition with the specification allows. > > > > > > > > > > > BlueZ currently supports this via an API adapter function called > > > ConnectDevice, whose status is currently "experimental". From my > > > experience of using this function, it seems to behave like this: > > > > > > > > > > > If the BlueZ instance has not scanned yet, so that the target device is > > > not known to it, the ConnectDevice call results in scanning taking place > > > and then if the target device is found, it is connected to. Success! > > > > > > > > > > > But if scanning has previously been performed, regardless of the state of > > > the actual device (e.g. advertising and ready to accept connections), an > > > exception is thrown with a message whose text value is "Already Exists". > > > > > > > > > > > I was wondering if I could influence the design of the API before the > > > ConnectDevice experimental status is removed? > > > > > > > > > > > I would like to suggest that there should be no need for a special API to > > > connect directly to a device without first scanning. Why burden the > > > application developer needing to call it just in case this condition > > > applies, catching the BlueZ exception ("Already Exists") and responding > > > by then calling the normal Connect API? > > > > I guess the intention was to have the application use the intended API for > > devices already present _before_ calling ConnectDevice, so before entering > > the address manually the application would enumerate the existing devices > > and figure out if that was already present. > > > > > > An alternative would be to accommodate this special case (not scanned > > > before) in the implementation of the standard device Connect(bdaddr) > > > function or if that makes no sense because Device objects must correspond > > > to previously discovered, physical devices, then at least the adapter > > > ConnectDevice function could take care of the two possible paths and > > > simplify matters for the application developer. > > > > I guess you probably know this but just in case someone look at the archives > > it is better that we make some things clearer, while the core spec allows > > connecting without scanning D-Bus are intend to be a higher level API thus > > why ConnectDevice was not really necessary for a long time and we just > > introduced it for qualification purpose or when there are multiple adapter > > where one acts as scanner. Also ever since the introduction of privacy > > (random addresses) APIs that takes addresses becomes rather complicated to > > be used directly, and there exists ways to scan for a specific address with > > pattern filtering: > > https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.kerne > > l.org%2Fpub%2Fscm%2Fbluetooth%2Fbluez.git%2Ftree%2Fdoc%2Fadapter-api.txt%23n > > 122&data=02%7C01%7C%7Cfafcb0f940054867612508d7fe7866fb%7Ce4e0fec5fc6c4dd > > 6ae374bdb30e156b9%7C0%7C0%7C637257665400787125&sdata=Iy%2FwWkxs%2FyW3gL2 > > 39FLWdoDRGa0apb63WxMhYwRoneM%3D&reserved=0 > > That said I don't oppose to remove Already Exists error, but we should be > > very clear that the use of such API should only be recommended with users > > input and does not substitute the likes of Device.Connect. > > > -- > > Luiz Augusto von Dentz > > > -- > pozdrawiam > Szymon Janc > > -- Luiz Augusto von Dentz