From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 D282737A83D for ; Fri, 31 Jul 2026 21:40:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785534035; cv=none; b=kHIo8kqWOexk7HoTGJ7+I7X3q4W2FTgDafs0FzdGfPE3OjTfs0yID7nw/rQO3J9/Hp0wcCb8rCTweefyixVsYiEZpsafXI4U6KXwjF+ocOCmAVpRXpqI0oL/CAzzDK/15Mcg/ouozPWwJ2DKEC4PpPX/6PCkOwmDsRKgQT+iuTU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785534035; c=relaxed/simple; bh=PbIiAuOFzstU7Cec1rWWvaUvsgfLnbF47nUhljR9eAg=; h=From:Subject:To:Cc:In-Reply-To:References:Content-Type:Date: Message-Id; b=NoH4AY/4zbMPOZrFxHY6M3Muem+Aw+4uSOmR1FIZUqfBJrWe0X0Udk9EGjQ1cveTxesXuZzXdWGlW/gulFRlXycGuc+BlCIuJpIkC3zR26Q6U6jzL/ni5YBrhCwmAU9Q6vYqJBEjcdJegivfcHJgg4PDYIjzcal+sEnvWoPb9Bs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=koo5ES/H; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="koo5ES/H" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A42B71F00AC4; Fri, 31 Jul 2026 21:40:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785534033; bh=gyFC39/rSlAZ2vn0IfwJ4n40wVL2/PEoZ9JURnsOTyM=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=koo5ES/H0Va5I9+IV4dS2dI25tuFyUdcemN7bbyZEsZUT4kTIgd82dNecd76GQIRp ct/JMaJAJ57MBhQUsme/5hKHOjs0xzzW5hy8HOR+1Qw5DbNVfgYPaz4+K0Z3ltjAcL bWlIKlHAdTp8s21omjw7E7chR4WyO4/DiLfo/0sHVYVCqDrS4QufkyDIBeGPG0CybH gYiSME7F3I24LbAsCZvPoVWWELY1xy00cGwjztWuS0Id/vUvYujKSziydQW027HBLt kkwcRWAfWwujKc2q+VWwHB8/Fth+jConFjwX1TLcyWf0f6seClI8fbJ7AIZg+ppzhK iX9UZuOPa0xyA== From: sashiko-bot@kernel.org Subject: Re: [PATCH net-next v13 1/5] tun/tap: add IFF_BACKPRESSURE flag Reply-To: sashiko-reviews@lists.linux.dev To: "Simon Schippers" Cc: kvm@vger.kernel.org In-Reply-To: <20260730213639.726381-2-simon.schippers@tu-dortmund.de> References: <20260730213639.726381-1-simon.schippers@tu-dortmund.de> <20260730213639.726381-2-simon.schippers@tu-dortmund.de> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Fri, 31 Jul 2026 21:40:33 +0000 Message-Id: <20260731214033.A42B71F00AC4@smtp.kernel.org> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Thank you for your contribution! Sashiko AI review found 1 potential issue(= s) to consider: - [Medium] Premature UAPI exposure of `IFF_BACKPRESSURE` flag breaks featur= e detection. -- --- Patch [1]: [PATCH net-next v13 1/5] tun/tap: add IFF_BACKPRESSURE flag = --- commit 43e4cc9000a7c476758fd2aa10db82e86b3c41ca Author: Simon Schippers tun/tap: add IFF_BACKPRESSURE flag This commit adds the IFF_BACKPRESSURE flag to the tun/tap UAPI headers and enables it in TUN_FEATURES. The flag is intended to gate qdisc backpressure logic added in subsequent patches. > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c [ ... ] > @@ -98,7 +98,8 @@ static void tun_default_link_ksettings(struct net_devic= e *dev, > #define TUN_FASYNC IFF_ATTACH_QUEUE > =20 > #define TUN_FEATURES (IFF_NO_PI | IFF_ONE_QUEUE | IFF_VNET_HDR | \ > - IFF_MULTI_QUEUE | IFF_NAPI | IFF_NAPI_FRAGS) > + IFF_MULTI_QUEUE | IFF_NAPI | IFF_NAPI_FRAGS | \ > + IFF_BACKPRESSURE) [Severity: Medium] Does adding this flag to TUN_FEATURES before the implementation is present break userspace feature detection during a git bisect? If userspace calls ioctl(TUNGETFEATURES) at this specific commit, it will see IFF_BACKPRESSURE as supported and might set it via TUNSETIFF. However, because the actual backpressure logic is delegated to later patches in the series, the kernel will silently drop packets instead of exerting backpressure. Would it be safer to introduce the UAPI flag definitions early in the series, but wait to add IFF_BACKPRESSURE to TUN_FEATURES until the final patch when the implementation is fully in place? --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20260730213639.7263= 81-1-simon.schippers@tu-dortmund.de?part=3D1