From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xie He Subject: [PATCH v2] drivers/net/wan/lapbether: Use needed_headroom instead of hard_header_len Date: Thu, 30 Jul 2020 00:37:02 -0700 Message-ID: <20200730073702.16887-1-xie.he.0141@gmail.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=K+Oo0bHEpODF7XLQBQ6GDyIq38DUDAb0nnpXubPm0uI=; b=gcQTdkUwMvU1FPhnUFLPP+UPLAy2jxmTogTN2emcrLTfrpzcy5xxre8T4B4/PeTPEJ /Mz40YKCWv+F52Z6VI00Fcf+4FmiJBl4341OILo+enlqoGli0586/XSBRTjL6//WiKwP vKPo3NFq1H1Or6BHlxSLKDq/odvYSy39q+pTv6ZY/3p1D/RnFpPm0exZGMgVTUO3AWmm IpYo5g1xmDgnp4nPd+y0n7W/3HY7rCx8MW5Ac65Xl3gUOsq/mD2nLfPhJfxahNzeBgFS lZ5uTeDWusdNq07HOOiqipYsL1aL/A6NsaThNpZkivIqJfZp/sCT7q1zWe0NQ6CTry2K 8kjA== Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" To: "David S. Miller" , Jakub Kicinski , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-x25@vger.kernel.org Cc: Xie He In net/packet/af_packet.c, the function packet_snd first reserves a headroom of length (dev->hard_header_len + dev->needed_headroom). Then if the socket is a SOCK_DGRAM socket, it calls dev_hard_header, which calls dev->header_ops->create, to create the link layer header. If the socket is a SOCK_RAW socket, it "un-reserves" a headroom of length (dev->hard_header_len), and assumes the user to provide the appropriate link layer header. So according to the logic of af_packet.c, dev->hard_header_len should be the length of the header that would be created by dev->header_ops->create. However, this driver doesn't provide dev->header_ops, so logically dev->hard_header_len should be 0. So we should use dev->needed_headroom instead of dev->hard_header_len to request necessary headroom to be allocated. Signed-off-by: Xie He --- Patch v2 has no difference from v1. I re-submitted it because I want to find new reviewers, and I want to free new reviewers from the burden of reading the lengthy discussion and explanations in the v1 email threads. Summary of v1 discussion: Cong Wang referred me to Brian Norris, who did a similar change before. Brian Norris agreed with me on "hard_header_len vs needed_headroom", but was unfamiliar with X.25 drivers. --- drivers/net/wan/lapbether.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c index b2868433718f..34cf6db89912 100644 --- a/drivers/net/wan/lapbether.c +++ b/drivers/net/wan/lapbether.c @@ -305,6 +305,7 @@ static void lapbeth_setup(struct net_device *dev) dev->netdev_ops = &lapbeth_netdev_ops; dev->needs_free_netdev = true; dev->type = ARPHRD_X25; + dev->hard_header_len = 0; dev->mtu = 1000; dev->addr_len = 0; } @@ -331,7 +332,8 @@ static int lapbeth_new_device(struct net_device *dev) * then this driver prepends a length field of 2 bytes, * then the underlying Ethernet device prepends its own header. */ - ndev->hard_header_len = -1 + 3 + 2 + dev->hard_header_len; + ndev->needed_headroom = -1 + 3 + 2 + dev->hard_header_len + + dev->needed_headroom; lapbeth = netdev_priv(ndev); lapbeth->axdev = ndev; -- 2.25.1