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 A45962E2EF3 for ; Fri, 19 Sep 2025 08:17:17 +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=1758269837; cv=none; b=kJUPE97Pl8WY5HiGRI4dX8IFWTxZxcDGp3jocP1k60iqGz7NEjbLDb+M4EWqkZTS//J48riRv0/tyqoGy7Hzn2EZiNnQFnVhwgF/Sng7c+V1nLnUxeheR5kAnvIEivzDKeMPHA4pg1p7tL/xxaN9DvDQrKvbniSZd5/AwVblk8E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758269837; c=relaxed/simple; bh=i3/RzkO3B8rc15ZliOkwEOYBS4cPZFpT6JGYgtdm5P0=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=RuzgWzXJilR1/hjVOsvcWS3JxwmPyTqMEHf8HrlTtFtUifMwR8N8ke7T6xScsPSyzMljwUJJUV5RipFeZBw9k2MLthk/NagghI6W43bEhYFEwAEhCdA56djWyRLb0YXQoirYoUlupZvZq2QJWZNAY86/l5pyQ4WtdLeW4v5pEXU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=G11O1c4B; 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="G11O1c4B" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A63ABC4CEF0; Fri, 19 Sep 2025 08:17:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1758269837; bh=i3/RzkO3B8rc15ZliOkwEOYBS4cPZFpT6JGYgtdm5P0=; h=Date:Subject:To:References:From:In-Reply-To:From; b=G11O1c4BZkZ25lo6hxUViav/VL8giUr/VfobWB91gekTPufCmTWSxK5VN1RbFSxyK ctIr+oNpwKUT76lW3kHSzoALeZlmQbNxfDNqw2YPFrVOqdwA256Lh+U9N6vloHDfs3 EfRJ3/cv6sLEIas1UeSA829TVjGuWEIXaCSJydPzukuUH9HfrNa6bhLDnmuwEpBrkZ wTW2ZU/ukgIG7gujrX9g13a6oFtWu7mBhkcIXR++EZUVnrYDfE5A0cRv7rTi5/kuIo nmsnzFcOwmCdsBv5KhfZA3QbBfUTLdVsME9xzw1A8bndmcB7T+hz2XYfvLVtyEk5FD fCvqTX7JkyCJQ== Message-ID: <77711101-541d-4d12-b377-74faf088c40f@kernel.org> Date: Fri, 19 Sep 2025 10:17:15 +0200 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-net v2 1/2] mptcp: pm: in-kernel: usable client side with C-flag Content-Language: en-GB, fr-BE To: Geliang Tang , MPTCP Upstream References: <20250916-pm-c-flag-client-default-v2-0-3be2c5bc4d6a@kernel.org> <20250916-pm-c-flag-client-default-v2-1-3be2c5bc4d6a@kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Geliang, On 19/09/2025 05:01, Geliang Tang wrote: > Hi Matt, > > Thanks for this v2. > > On Tue, 2025-09-16 at 13:01 +0200, Matthieu Baerts (NGI0) wrote: >> When servers set the C-flag in their MP_CAPABLE to tell clients not >> to >> create subflows to the initial address and port, clients will likely >> not >> use their other endpoints. That's because the in-kernel path-manager >> uses the 'subflow' endpoints to create subflows only to the initial >> address and port. >> >> If the limits have not been modified to accept ADD_ADDR, the client >> doesn't try to establish new subflows. If the limits accept ADD_ADDR, >> the routing routes will be used to select the source IP. >> >> The C-flag is typically set when the server is operating behind a >> legacy >> Layer 4 load balancer, or using anycast IP address. Clients having >> their >> different 'subflow' endpoints setup, don't end up creating multiple >> subflows as expected, and causing some deployment issues. >> >> A special case is then added here: when servers set the C-flag in the >> MPC and directly sends an ADD_ADDR, this single ADD_ADDR is accepted. >> The 'subflows' endpoints will then be used with this new remote IP >> and >> port. This exception is only allowed when the ADD_ADDR is sent >> immediately after the 3WHS, and makes the client switching to the >> 'fully >> established' mode. After that, 'select_local_address()' will not be >> able >> to find any subflows, because 'id_avail_bitmap' will be filled in >> mptcp_pm_create_subflow_or_signal_addr(), when switching to 'fully >> established' mode. >> >> Fixes: df377be38725 ("mptcp: add deny_join_id0 in >> mptcp_options_received") >> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/536 >> Signed-off-by: Matthieu Baerts (NGI0) >> --- >> Notes: >> - I tried to find a simple solution that can hopefully be backported >> to >>   cover the 'CDN' use-case. >> - I tried to find a solution respecting the 'accepted add addr' >> limit, >>   but I don't see how to... That's why here I limit the exception a >>   maximum: when this limit is 0 (default case), only the first >> ADD_ADDR, >>   etc. Feel free to share what you think about that. >> - I have some additional code doing some cleanup, and I started to >> look >>   at #503, which is a bit linked to that. >> - v2: move conditions to new helper (Geliang) + rename var, squash >> comm. >> --- >>  net/mptcp/pm.c        |  7 +++++-- >>  net/mptcp/pm_kernel.c | 37 +++++++++++++++++++++++++++++++++++++ >>  net/mptcp/protocol.h  |  7 +++++++ >>  3 files changed, 49 insertions(+), 2 deletions(-) >> >> diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c >> index >> 02dfb379417e2843301f121039ec0d370b040ef7..edaf93fe6f86b32aee8e9bb8831 >> 8b1dc2a7fcb5e 100644 >> --- a/net/mptcp/pm.c >> +++ b/net/mptcp/pm.c >> @@ -637,9 +637,12 @@ void mptcp_pm_add_addr_received(const struct >> sock *ssk, >>   } else { >>   __MPTCP_INC_STATS(sock_net((struct sock >> *)msk), MPTCP_MIB_ADDADDRDROP); >>   } >> - /* id0 should not have a different address */ >> + /* - id0 should not have a different address >> + * - special case for C-flag: linked to >> fill_local_addresses_vec() >> + */ >>   } else if ((addr->id == 0 && >> !mptcp_pm_is_init_remote_addr(msk, addr)) || >> -    (addr->id > 0 && !READ_ONCE(pm->accept_addr))) { >> +    (addr->id > 0 && !READ_ONCE(pm->accept_addr) && >> +     !mptcp_pm_add_addr_c_flag_case(msk))) { >>   mptcp_pm_announce_addr(msk, addr, true); >>   mptcp_pm_add_addr_send_ack(msk); >>   } else if (mptcp_pm_schedule_work(msk, >> MPTCP_PM_ADD_ADDR_RECEIVED)) { >> diff --git a/net/mptcp/pm_kernel.c b/net/mptcp/pm_kernel.c >> index >> f30df8e884a0b3de9fb092e5774cafe08f6350ce..d7cd89fa6a11a1ea7703edbfbdf >> 2bbe86a6a3054 100644 >> --- a/net/mptcp/pm_kernel.c >> +++ b/net/mptcp/pm_kernel.c >> @@ -389,10 +389,12 @@ static unsigned int >> fill_local_addresses_vec(struct mptcp_sock *msk, >>   struct mptcp_addr_info mpc_addr; >>   struct pm_nl_pernet *pernet; >>   unsigned int subflows_max; >> + bool c_flag_case; >>   int i = 0; >>   >>   pernet = pm_nl_get_pernet_from_msk(msk); >>   subflows_max = mptcp_pm_get_subflows_max(msk); >> + c_flag_case = remote->id && >> mptcp_pm_add_addr_c_flag_case(msk); >>   >>   mptcp_local_address((struct sock_common *)msk, &mpc_addr); >>   >> @@ -409,6 +411,10 @@ static unsigned int >> fill_local_addresses_vec(struct mptcp_sock *msk, >>   locals[i].flags = entry->flags; >>   locals[i].ifindex = entry->ifindex; >>   >> + if (c_flag_case) >> + __clear_bit(locals[i].addr.id, >> +     msk- >>> pm.id_avail_bitmap); >> + >>   /* Special case for ID0: set the correct ID >> */ >>   if (mptcp_addresses_equal(&locals[i].addr, >> &mpc_addr, locals[i].addr.port)) >>   locals[i].addr.id = 0; >> @@ -419,6 +425,37 @@ static unsigned int >> fill_local_addresses_vec(struct mptcp_sock *msk, >>   } >>   rcu_read_unlock(); >>   >> + /* Special case: peer sets the C flag, accept one ADD_ADDR >> if default >> + * limits are used -- accepting no ADD_ADDR -- and use >> subflow endpoints >> + */ >> + if (!i && c_flag_case) { >> + unsigned int local_addr_max = >> mptcp_pm_get_local_addr_max(msk); >> + >> + while (msk->pm.local_addr_used < local_addr_max && >> +        msk->pm.subflows < subflows_max) { >> + struct mptcp_pm_local *local = &locals[i]; >> + >> + if (!select_local_address(pernet, msk, >> local)) >> + break; >> + >> + __clear_bit(local->addr.id, msk- >>> pm.id_avail_bitmap); >> + >> + if (!mptcp_pm_addr_families_match(sk, >> &local->addr, >> +   remote)) >> + continue; >> + >> + if (mptcp_addresses_equal(&local->addr, >> &mpc_addr, >> +   local->addr.port)) >> + continue; >> + >> + msk->pm.local_addr_used++; >> + msk->pm.subflows++; >> + i++; >> + } >> + >> + return i; >> + } > > In the subsequent patches, this was refactored into a separate helper. > I think that change is well-implemented and could be directly squashed > into this patch. We can define this fill_local_addresses_vec_c_flag > here directly within this patch. WDYT? I think it would be better not to add this new helper in this patch, and keep it as it is: it will be easier to backport that, and probably easier to review. Cheers, Matt -- Sponsored by the NGI0 Core fund.