From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-dy1-f182.google.com (mail-dy1-f182.google.com [74.125.82.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DBC8430ACF1 for ; Mon, 12 Oct 2026 04:58:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.82.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791781091; cv=none; b=ToaFcBx5BYas9DHgIQEo8ZD/fqYmZ6aoFQVCBdcS5YLVFNRvgWv7qON335HyCScf0hBbpY9ummgyngyDxWyy5DiN9x1w6qMOx/zS2stDXHOZ+7+6vTt711ySXTCiRqVNp9/dEO7wA/D/lIceeSa6UOhkO023dFH/BG9EIPPW9dE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791781091; c=relaxed/simple; bh=unQ8Kv3Fy+buE9N5m0DeZVnQ6loHexCxxXoC2t0MmFo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=k7boYM7xKL8oyk5HV0FnrN0NSogSIwwEJ/jkABNP81X5lJ9ebq3Jy+caBBQEeUsCn2xIn5JifHvPyucm6tOyWu8r8snctSZ8ZTwuOaMeC8tGUslpgnzklaW8R6kEjc8fKf/7bRrbVQyv3iWI99dht/pNtmIRsEaGwHeMyaZW/to= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=Yp2cRVit; arc=none smtp.client-ip=74.125.82.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Yp2cRVit" Received: by mail-dy1-f182.google.com with SMTP id 5a478bee46e88-35943f55c06so1027485eec.0 for ; Sun, 11 Oct 2026 21:58:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1791781089; x=1792385889; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to:content-type; bh=OPxwWFgnfVFbchTbdw0or35TN+U5yCxRRFvUU5bcKZM=; b=Yp2cRVitNSlNqdGxhTzqznvtp50R0HC7g+MqHapP8Ur7R4J95+RCUhOHeSqa1dduR+ cwmCQVTQOReAMbHovTYBraiOTXwNIPy0LUAssjdFTGlEU3Ua0eAxrnFrAHj/+IweXkIl ScF+9p23+ZkQa8+wno0ExUprSKDWdElK8Qa101YL1KWsMsJkdpr6i95nXKeCE8evhtKv O8SksGt9Q2SwJ6w4k3r+Hfs/4kLxq1IdqtGIBvYShFnUWH4wR2ZdNKal1V2NSnAe9eDE G9QweBcpMnAuQYe9U/p5prP9nZoEbnalnX6WL1jiBuYY40BEUP3oe2dGFW87m+t4tgnf vC+g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1791781089; x=1792385889; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to:content-type; bh=OPxwWFgnfVFbchTbdw0or35TN+U5yCxRRFvUU5bcKZM=; b=MFmPpqDhXLDGmrLEpXyNyZCyuwQyoQGJQf4SwwTzejIi9q7N/HLp7pTbI6V2Cyhb9/ DwS24yDuwObNMK1Ae7NWehVFKnoKR2dMfxHCdmVtGHGUkHBBSvuBD8O1Ql3KdYTgjumr NFtuXUcgjRtWHHKjSOmo5b9B1acEHVzxPb/l2LQkdQB/97ar0qf8MBKQJZHmYnMoy0hb EhIOE8D8CfY9Tyd+VX1ICGnzqmjHZ2NrHFl0X1aC7f7njxrGNgPgksk8+GkxNIdLAQo9 PxhfyW73vjTo/0vGP6YUgXcritFYZhignlPjAyi/aaBgs0GFWk39cQ+ubuuJS1SySCQe +LbA== X-Forwarded-Encrypted: i=1; AKwUvBz/BWosuJX2i0N7SsRc+cUuh3AO3pP+IiNjVSdGKW4+Vk4VlmBJ41JVHZKQDQEfdkoTfUv6oY3l8rx3tWA=@vger.kernel.org X-Gm-Message-State: AFq9FYKtieSSfsJURYAtmPqtIcO+M09Az+2H9Da50jpGg1ye2Vp6BYpa 2dpzDDfoPqGOdhP3oyRT6n9xENVgklGKCgtl3KG1bglfRkNv9K87vC2s X-Gm-Gg: AYBFou1MbKUdUOirW2+XQJnH0bbtZTh8kW0SuISkZkqd04YxGjql1O5+hJAsz8LCgHT elZGW9vBPPjoDm5KdIHqFIiw0ibdgsWxjmldW4SCOl5cLwbNaR+ogY+2iMYQ0XZlYYL7DHkQwhv Pi6tUgyyTp9QfHyCaN89Mji/E9LeD6OdviIsI1TPGuFnQCi7Ru//tZ92BFqAnOlQDqXnxkMIfNy 2jpK7ROu+xviaVed5EXMQUCzuyK47MoetXuLa7siVPt191LB1tn9RpT8PrAiG7qjWpOSRkhRT+6 yMSF8Sz8FlQJzIJhDN9Y2Z86m0tN7uKIJlFNChcbe6nWDAUvh0Nw5sC5sMICNJNmAs3fxzNkA9V GmCPpXhebmM1BbE+YmUcCgeOSqNEWQ72QtEnVRitpXfIbNnYdtpphHFAgJsmmHISnjan9Kol+iY mTETjeJLhBuMNdqXUT2igMnZGnrS9eS9w3SWRa/Eq4VUIWV6vP5VnQOQ2NaBWf0TRY3cEEl8eAv OuCGIZuxIsM0mKEwhwgIhvLv337YMtDyKEXS2qxm5s03WE7VOqn5QlDuNQtOMsSPnIF9RX8nTaD UZ9NJqn32JTvgAu3JhEwmjqH/1sRjwcFYb6pi/SW9ZPgPTxM4AJYy9wChUb659y8PPK1bJwZkOp AdLgSB23TRtp6peyeK00Sct/tpzJmLErfoP6aYDo5NY9DeipYDQLwSSE= X-Received: by 2002:a05:7300:fb8a:b0:353:82a3:eb86 with SMTP id 5a478bee46e88-35382a3ef76mr16701172eec.0.1791781088584; Sun, 11 Oct 2026 21:58:08 -0700 (PDT) Received: from FT6N242TWK ([223.181.119.248]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3537c841648sm32829284eec.3.2026.10.11.21.58.05 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sun, 11 Oct 2026 21:58:08 -0700 (PDT) From: Shashank Mohan Jain To: Eric Dumazet , Neal Cardwell , Jakub Kicinski , Paolo Abeni , "David S. Miller" Cc: Kuniyuki Iwashima , Simon Horman , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net] tcp: keep the route window metric when SO_RCVBUF is set before connect Date: Mon, 12 Oct 2026 10:28:02 +0530 Message-ID: <20261012045802.47339-1-jain.sm@gmail.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Sun, Oct 11, 2026, Eric Dumazet wrote: > Note that we ask to not top post on netdev@ mailing list. Understood, replying inline from here on. > 1) "TCP_WINDOW_CLAMP 4096" only holds until the first data segment. > ... What the patch really restores is the SYN/SYN-ACK window and the > window scale. Please say so. Agreed, presenting the clamp as persistent was wrong. v2 says the patch restores the window and window scale advertised in the SYN / SYN-ACK, and notes that since a2cbb1603943 ("tcp: Update window clamping condition") tcp_measure_rcv_mss() recomputes window_clamp from sk_rcvbuf once the scaling ratio changes, independent of this change. > 2) "no window scaling" is not accurate: we still send the option, > with a shift of 0. Right; changed to "wscale 0 (the window scale option is still sent, with a shift of 0)". > 3) This also fixes TCP_WINDOW_CLAMP being overwritten by a later > SO_RCVBUF on a not yet connected socket or a listener. ... worth > mentioning. Done - v2 leads with the SO_RCVBUF-before-connect / listener case as the common one, with the route metric as a second effect. > A packetdrill test covering the SYN window and wscale would be nice. I'll add a packetdrill test for the SYN window and wscale, with and without SO_RCVBUF set before connect, in v2. > It seems to be a net-next candidate ... Will repost as [PATCH net-next]. Reposted as v2: https://lore.kernel.org/all/20261011111606.14753-1-jain.sm@gmail.com/ Thanks for the review. Shashank