From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A2B7C20551B for ; Thu, 9 Jan 2025 12:20:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736425209; cv=none; b=bkzlkN7PinzfLfk6xIHKv4OSouHVQtcSsW8L2uJF82gmLOdXwhUGf2Jeshvj0SmYqJARexop5QYmUXb9+df5Qf7gBS7iTmIHmJzKoG6fweE1Ia5DOSy84bdOsOz8QdZQn3KTRwNbAEKbYenxw6HB0j6baporc5SwgwcHJccEoyc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736425209; c=relaxed/simple; bh=oSZkhDcy/wTygWRX3ru3pofK6WXLe/kAWxM/Pv4sbAY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ICZJ7T0fqqqt62JxR/5gay4F7hkj2p71c9q8EA4P1C0QEBEau8KqefCOGZO79o5RlFsBhczzJsJi4Lqjp7zX8PSdjLjqQAoFjRDjguK6RljqJO58dTK5gb5HSfm+cjB8mR6QpzrVtRm03beEP3eBohE1ZjBQbPlM10+d7NI4+q4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=E9wKVNNY; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="E9wKVNNY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5B8FEC4CED6; Thu, 9 Jan 2025 12:20:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1736425209; bh=oSZkhDcy/wTygWRX3ru3pofK6WXLe/kAWxM/Pv4sbAY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=E9wKVNNY8ps/aKnD/HFcsYR4RVI1y7eD6evSYnjIN2ye4m0n8MmDBPk9G9N6ziJok kLsC9BgfKKg8t4zW2onMdCwgovRm9TQZfOqtSJA5LLHX3ibGrFRTk5PzWXh0Hqw7kd j/vK/bDiPGhWZ5DHcblIM31AmaefkTBh1UaElVlID65QKSVTRRdp3kDvL6Mu85O4eD kFnRsvCBTw/0tieJj9xUKvMfM1ebGhExTdJO5X2fIOZdQIpZIJG+bzFUzAwiC8foRt DaJ+4uTRZJKdmg8xQFnBSfqQx5ZoDf38EkJkL+ncBzyV8txsjJO9wIsDfpmceCRzCS da7w5Y8hQVofA== Message-ID: <9f8c7031-4f5d-4195-93de-e23491799367@kernel.org> Date: Thu, 9 Jan 2025 13:20:06 +0100 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH mptcp-next v3 5/8] mptcp: userspace pm set_flags id support Content-Language: en-GB To: Geliang Tang , mptcp@lists.linux.dev Cc: Geliang Tang References: <30061158e34c4fbf9063150e6aec40c0eed42b6b.1736308884.git.tanggeliang@kylinos.cn> <3284b879-8844-4324-ae92-970c4fe5d686@kernel.org> <51c240cd267760b883bd2749e0a01be5854f62a9.camel@kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Geliang, Thank you for your reply! On 09/01/2025 04:40, Geliang Tang wrote: > Hi Matt, > > Thanks for the review! > > On Wed, 2025-01-08 at 19:51 +0100, Matthieu Baerts wrote: >> On 08/01/2025 19:47, Matthieu Baerts wrote: >>> Hi Geliang, >>> >>> On 08/01/2025 05:21, Geliang Tang wrote: >>>> From: Geliang Tang >>>> >>>> Similar to in-kernel PM, this patch adds address ID support to >>>> set_flags() >>>> interface of userspace PM, allowing it to work with either an >>>> address or >>>> an address ID. >>>> >>>> When an address ID is used, >>>> mptcp_userspace_pm_lookup_addr_by_id() helper >>>> is used to look up the address entry in the local address list >>>> instead of >>>> using mptcp_userspace_pm_lookup_addr(). >>> >>> Mmh, I'm still not sure about that. As I was saying in [1], if I'm >>> not >>> mistaken, with the userspace PM, it is possible not to find any >>> entries >>> here, e.g.: if a subflow using this address has not been added or >>> the >>> address has not been announced. (I guess the initial address is not >>> there then). > > The previous version (in [1]) did have this issue and userspace_pm.sh > tests would fail because of it, but this new version has fixed it. > > mptcp_pm_nl_mp_prio_send_ack(msk, > entry ? &entry->addr : &local->addr, > remote, bkup); > > When the entry is not found, we continue to pass local->addr to ensure > the same behavior as before. Yes indeed, the tests are fixed, but if 'entry' is NULL, the address you will give will be empty, so it will not be able to find any subflow to send the MP_PRIO, right? >>> Do you think this patch is worth it? Setting by ID for the in- >>> kernel PM >>> makes sense: unique ID for the netns, easier to type the ID than >>> the >>> full address. While for the userspace PM, it will be managed by a >>> daemon >>> that will have to track addresses anyway. > > I think it's still useful to extend this functionality while the > original behavior is not affected, at least it doesn't hurt. I'm sorry, I think it is not that simple: if we extend this functionality, it means we will have to maintain it. Here, the interface looks buggy because it will not work with all addresses: the initial ones, the ones not announced but implicitly used, etc. If the interface does not always work, I don't think we will recommend using it, then why do we need to maintain it? > We cannot assume that userspace PM is always managed by a daemon. We > have exported its interfaces to BPF. We allow users to customize path > managers. That means we also allow users to use their own userspace PM > in any way. I think the BPF PM is different: it is a different interface. To interact with the userspace PM, it is required to monitor the MPTCP events sent via Netlink, e.g. to get the token. When a new subflow is created, the userspace will know which addresses (including the ID) it is linked to. In this case, why only setting the ID in the address structure if it doesn't always work, while setting the address will always work as expected. > Another consideration is that we need to maintain the consistency > between in-kernel PM and userspace PM. Not really: when they can do the same thing, yes, but the two interfaces are different. We don't have to keep the consistency if it doesn't make sense to do so. > For ease of maintenance, we need > to make these two PMs use the same code as much as possible, and only > abstract their differences through PM interfaces such as get_addr, > dump_addr, set_flags, etc. Yes but there are some limits: if some code is shared between multiple interfaces, it is important not to break one of them when changing the code. In other words, if the behaviour is very similar (e.g. get_addr), that's fine. But if they start to be too different, you have complex common code where you need to think "OK, this one acts like that, but the other one like that", and complexity is not good for the maintenance. In this case, it sounds better to keep them separated. > At present, the biggest difference between > the two is that they use different linked lists (pernet- >> local_addr_list vs. msk->pm.userspace_pm_local_addr_list) to store > address entries, so we only need to put the code for operating the > linked lists into the interfaces of each PM. This is also the goal of > adjusting the pm interfaces in this series. Yes, but that's not the only difference, because the interfaces are different. With the in-kernel PM, we act per netns, while with the userspace PM, it is per connection. Because of that, addresses lists are managed differently, leading to different concept, e.g. the list not having all addresses, the addresses not having ID 0 in one, but OK in the other, etc. With shared code that acts for both of them, you need to keep thinking about these differences when reading or writing code, and that's a source of error I think. >>> Or in other words, do you have a use-case for this? To me, it looks >>> like >>> "yes, you can only set the ID, but it might not always work". Then >>> maybe >>> better to always set the full address, no? > > If you're worried that this functionality isn't covered by tests, I've > added a test that covers it in BPF path manager selftests: > > err = userspace_pm_set_flags(token, addr, "backup"); > if (!ASSERT_OK(err, "userspace_pm_set_flags backup")) > goto close_accept; > > ... > > err = userspace_pm_set_flags_by_id(token, 100, "nobackup"); > if (!ASSERT_OK(err, "userspace_pm_set_flags_by_id nobackup")) > goto close_accept; I would need to check the BPF PM interface, but for me the userspace PM and BPF PM interfaces don't have to be the same, e.g. why having a dump if the BPF PM can directly access data from the kernel? Same here for the ID: it depends if all IDs are tracked in the corresponding list, e.g. it might not be the case with an "announced" list. But also yes, if something is exposed to userspace (via Netlink), it should be covered by a test (using the userspace Netlink interface) >>> >>> [1] >>> https://lore.kernel.org/mptcp/d01d0e8a-5606-4152-aabe-32e4402adeeb@kernel.org/ >> >> Note: if we drop this patch (I think it is better), maybe patch 8/8 >> is >> not worth it: not to have a "common" section with plenty of 'if >> (token)', no? Or do you really need them for the BPF PM? > > Here we are only adjusting set_flags interface of in-kernel PM and > userspace PM, which has nothing to do with the BPF PM implementation. > > It seems that moving the code in mptcp_pm_nl_set_flags_doit() to > mptcp_pm_set_flags() can remove these 'if (token)': > > int mptcp_pm_nl_set_flags_doit(struct sk_buff *skb, struct genl_info > *info) > { > return mptcp_pm_set_flags(info); I'm not sure whether it is useful to have one function simply calling another function that is only used once. > } > > static int mptcp_pm_set_flags(struct genl_info *info) > { > struct mptcp_pm_addr_entry loc = { .addr = { .family = > AF_UNSPEC }, }; > struct mptcp_addr_info rem = { .family = AF_UNSPEC, }; > struct nlattr *attr_loc, *attr_rem; > int ret; > > if (GENL_REQ_ATTR_CHECK(info, MPTCP_PM_ATTR_ADDR)) > return -EINVAL; > > attr_loc = info->attrs[MPTCP_PM_ATTR_ADDR]; > ret = mptcp_pm_parse_entry(attr_loc, info, false, &loc); > if (ret < 0) > return ret; > > if (info->attrs[MPTCP_PM_ATTR_TOKEN]) { > if (GENL_REQ_ATTR_CHECK(info, > MPTCP_PM_ATTR_ADDR_REMOTE)) > return -EINVAL; > > attr_rem = info->attrs[MPTCP_PM_ATTR_ADDR_REMOTE]; > ret = mptcp_pm_parse_addr(attr_rem, info, &rem); > if (ret < 0) > return ret; > > if (rem.family == AF_UNSPEC) { > NL_SET_ERR_MSG_ATTR(info->extack, attr_rem, > "invalid remote address > family"); > return -EINVAL; > } > > return mptcp_userspace_pm_set_flags(&loc, &rem, info); > } The problem is the same: ↑ is specific to the userspace PM, why moving the code here in the common section then? Same for the code ↓. So at the end, the only common code is the parsing of the local address, so just GENL_REQ_ATTR_CHECK(MPTCP_PM_ATTR_ADDR) and mptcp_pm_parse_entry(MPTCP_PM_ATTR_ADDR). Is it worth it? So if we want to share code, all we can get I think is this: int mptcp_pm_nl_set_flags_doit(...) { (...) if (GENL_REQ_ATTR_CHECK(info, MPTCP_PM_ATTR_ADDR)) return -EINVAL; attr_loc = info->attrs[MPTCP_PM_ATTR_ADDR]; ret = mptcp_pm_parse_entry(attr_loc, info, false, &loc); if (ret < 0) return ret; if (info->attrs[MPTCP_PM_ATTR_TOKEN]) return mptcp_userspace_pm_set_flags(&loc, info); return mptcp_pm_nl_set_flags(&loc, info); } Not a lot to share, but at least there is nothing PM specific here, except to pick the interface to continue with. And yes, that's something that could be done, but that's not much... > > if (loc.addr.family == AF_UNSPEC) { > if (!loc.addr.id) { > NL_SET_ERR_MSG_ATTR(info->extack, attr_loc, > "missing address ID"); > return -EOPNOTSUPP; > } > } > > return mptcp_pm_nl_set_flags(&loc, info); > } > > WDYT? > > -Geliang > >> >> Cheers, >> Matt > Cheers, Matt -- Sponsored by the NGI0 Core fund.