From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from dediextern.your-server.de (dediextern.your-server.de [85.10.215.232]) (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 AFEF928628E; Wed, 19 Feb 2025 14:47:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=85.10.215.232 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739976464; cv=none; b=Bis4ajilexR0VPzPhl+2YxXti7SiGpRdovsvvyxqSowrTL+rDfSHtaIVtoewsb3gkG56ng5KZby8lKcHGMv0P/vaHmjPqJvUZMkyom4AHzbAvJW38OiBIndWDCSORlVZ4jzq643gCO03F4RbyNlWh7EMBzC/HtYgjAVxIbIZfvk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739976464; c=relaxed/simple; bh=bVhdQ6db7vpeRW96FXxkda9FROiCv9l+LI7ZCrTmn6U=; h=Message-ID:Date:MIME-Version:To:Cc:References:From:Subject: In-Reply-To:Content-Type; b=iSHtV5agESVmDmnDyeK4D68gKU22WGZR/iSl3mHaB171hh6lg3HAjJBI9CGD+c4z981yJUpHXboN/mJ26Kx+8ZgVPQxIcXMagKnUE7O70+I/HpaZtAn2N7f58ZJjLk4pcCAQG5ja0qUc59+JMaVnCzBWn0xU5yJFWPgyMx9C9M8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=hetzner-cloud.de; spf=pass smtp.mailfrom=hetzner-cloud.de; arc=none smtp.client-ip=85.10.215.232 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=hetzner-cloud.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=hetzner-cloud.de Received: from sslproxy05.your-server.de ([78.46.172.2]) by dediextern.your-server.de with esmtpsa (TLS1.3) tls TLS_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1tklLz-000ADq-88; Wed, 19 Feb 2025 15:47:11 +0100 Received: from [2a0d:3344:1523:1f10:f118:b2d4:edbb:54af] by sslproxy05.your-server.de with esmtpsa (TLS1.3) tls TLS_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1tklLy-0008aU-39; Wed, 19 Feb 2025 15:47:11 +0100 Message-ID: Date: Wed, 19 Feb 2025 15:47:09 +0100 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: Willem de Bruijn , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: jasowang@redhat.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, mykolal@fb.com, shuah@kernel.org, hawk@kernel.org References: <20250217172308.3291739-1-marcus.wichelmann@hetzner-cloud.de> <20250217172308.3291739-3-marcus.wichelmann@hetzner-cloud.de> <67b3e6b6b9dc6_c0e2529482@willemb.c.googlers.com.notmuch> Content-Language: en-US From: Marcus Wichelmann Autocrypt: addr=marcus.wichelmann@hetzner-cloud.de; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated-Sender: marcus.wichelmann@hetzner-cloud.de X-Virus-Scanned: Clear (ClamAV 1.0.7/27554/Wed Feb 19 10:50:24 2025) Am 18.02.25 um 02:47 schrieb Willem de Bruijn: > Marcus Wichelmann wrote: >> [...] >> + metasize = max(xdp->data - xdp->data_meta, 0); > > Can xdp->data_meta ever be greater than xdp->data? When an xdp_buff has no metadata support, then this is marked by setting xdp->data_meta to xdp->data + 1. See xdp_prepare_buff or xdp_set_data_meta_invalid. In the case of tun_xdp_one, the xdp_buff is externally created by another driver and passed to the tun driver using sendmsg and TUN_MSG_PTR. For now, the vhost_net driver is the only driver doing that, and xdp->data_meta is set to xdp->data there, marking support for metadata. So knowing that vhost_net is currently the only driver passing xdp_buffs to tun_sendmsg, the check is not strictly necessary. But other drivers may use this API as well in the future. That's why I'd like to not make the assumption that other drivers always create the xdp_buffs with metadata support, when they pass them to tun_sendmsg. Or am I just to careful about this? What do you think? > This is pointer comparison, which is tricky wrt type. It likely is > ptrdiff_t and thus signed. But may want to use max_t(long int, ..) to > make this explicit. Ah, I see, good point. So like that? metasize = max_t(long int, xdp->data - xdp->data_meta, 0); if (metasize) skb_metadata_set(skb, metasize); Alternatively, there is also xdp_data_meta_unsupported(xdp_buff) which could be used to make this check very explicit, but I don't see it being used in network drivers elsewhere. Not sure why. >> + if (metasize) >> + skb_metadata_set(skb, metasize); >> + > > Not strictly needed. As skb_metadata_clear is just > skb_metadata_set(skb, 0). But also not wrong, so fine to keep. Oh, haven't seen that. I'm following a common pattern here that I've seen in many other network drivers (grep for "skb_metadata_set"): unsigned int metasize = xdp->data - xdp->data_meta; [...] if (metasize) skb_metadata_set(skb, metasize); Marcus