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[129.46.96.20]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1b503191a43sm614392c88.10.2026.11.12.10.25.16 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 12 Nov 2026 10:25:17 -0800 (PST) From: To: "'Jakub Kicinski'" Cc: , , , , , , References: <20261108075727.2031331-1-subash.a.kasiviswanathan@oss.qualcomm.com> <20261112083311.641a2216@kernel.org> In-Reply-To: <20261112083311.641a2216@kernel.org> Subject: RE: [PATCH net v4] net: qualcomm: rmnet: Update MTU handling during format changes Date: Thu, 12 Nov 2026 11:25:16 -0700 Message-ID: <000001dd72d3$2b06ba30$81142e90$@oss.qualcomm.com> X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Outlook 16.0 Thread-Index: AQFkeIhnkKVssrYvBGDElDQ/wtA9kAHp7JEquA1kPmA= Content-Language: en-us X-Proofpoint-GUID: 6Rceq854ogjw9Hr8AtojbSIbpZlZ-k8B X-Proofpoint-Spam-Info: AW1haW4tMjYxMTEyMDA3MyBTYWx0ZWRfXyXQF+ts2ChNo E5pIPyYg6x4pOQgda0e4PEzO1ABSQkHwsbCICH+LZhFHstSa/CCOYyuXstNzfmdDGHwkJb3iyE7 tKvM4afV3Lwh2rVtbK0YTStVQj1jgPQ= X-Proofpoint-ORIG-GUID: 6Rceq854ogjw9Hr8AtojbSIbpZlZ-k8B X-Authority-Analysis: v=2.4 cv=d49gWhjE c=1 sm=1 tr=0 ts=6af6048f cx=c_pps a=kVLUcbK0zfr7ocalXnG1qA==:117 a=ouPCqIW2jiPt+lZRy3xVPw==:17 a=kj9zAlcOel0A:10 a=zJRp6_cAMcgA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=YMgV9FUhrdKAYTUUvYB2:22 a=VwQbUJbxAAAA:8 a=EUspDBNiAAAA:8 a=J1Y8HTJGAAAA:8 a=20KFwNOVAAAA:8 a=mXP6K7Sk1cvqIwA962kA:9 a=CjuIK1q_8ugA:10 a=vr4QvYf-bLy2KjpDp97w:22 a=y1Q9-5lHfBjTkpIzbSAN:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMTEyMDA3MyBTYWx0ZWRfX5LpPH9EiCdzz 2ZjL5Mmc23PUqsNaFXRK4cs9My2Fm9K7M6QWMwlqQoVpQCmnI3OPabzw89SJkIvoDuDlofuXQbN S+KlhNx5mwNjPWXTAIurJLsKzs0688AYFNoQ44UaN0ik54rlSaVGeJauRlEr7X6TZVFgsnpA9i6 F8Y+4Wt7Qg5sE3XgIQMRjlO8myIjeZFRy93d0F2fdGL4gX8Avp/btgM+vkCz92NN4rmRzrNo3m2 bjf5fMuaFu+x6hsIYhLesRtj65MzulyRt8au2XGRdt+xy8P1MVKGrgORkBfEotqIwXv6vUHH6rB qk1v7qTgXy5rR+J2tlDD0cngYPgKAG0dwDrXzedBHm7fK6j4hrGY3XsxSFx1C04iBp/FpJr+rbi wTsJRPK2GMtS6W8hN7dWpz8VPZPlrAWj3vqViXh13GWLe8/b7vZljo9oOZzR4j4t+J5RCakr07s GDBRHMnwJN9pwv/jfUg== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.138,FMLib:17.12.100.49 definitions=2026-11-12_02,2026-11-11_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 spamscore=0 malwarescore=0 clxscore=1015 suspectscore=0 adultscore=0 lowpriorityscore=0 impostorscore=0 bulkscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2611040001 definitions=main-2611120073 > -----Original Message----- > From: Jakub Kicinski > Sent: Thursday, November 12, 2026 9:33 AM > To: Subash Abhinov Kasiviswanathan > > Cc: sean.tranchetti@oss.qualcomm.com; andrew+netdev@lunn.ch; > davem@davemloft.net; edumazet@kernel.org; pabeni@redhat.com; > netdev@vger.kernel.org; linux-kernel@vger.kernel.org > Subject: Re: [PATCH net v4] net: qualcomm: rmnet: Update MTU handling > during format changes > > On Sat, 7 Nov 2026 23:57:27 -0800 Subash Abhinov Kasiviswanathan wrote: > > rmnet derives the MTU of its devices from the real device MTU minus > > the headroom needed by the egress data format. Several problems exist > > in how this is handled when the data format is set or changed: > > > > - The headroom only accounts for the V4 egress checksum header and > > ignores the V5 one, so devices using V5 checksum offload get an MTU > > that is too large for the real device. > > - rmnet_newlink() sizes the first device from the port's data format > > before the requested IFLA_RMNET_FLAGS have been applied, so the MTU > > does not match the format that ends up being used. > > - A real device MTU smaller than the headroom underflows the unsigned > > subtraction, and a real device with a jumbo MTU makes the creation of > > the first device fail while resizing an existing one clamps it. > > - Existing endpoints are shrunk by writing dev->mtu directly. No MTU > > notifiers run and userspace gets no link notification. The helper > > also returns -1, and changelink flattens every failure into -EINVAL. > > - rmnet_changelink() publishes the new data format before resizing the > > endpoints and reverts it on failure, so the datapath can observe a > > format whose headers do not fit the MTUs. A failed resize can also > > leave some endpoints shrunk, and a mux_id change requested in the > > same call is kept even though the call returned an error. > > > > Fix these by calculating the headroom from the requested data format, > > These should probably be 5 separate fixes in a patch series? Sure, I'll split the patch and send it as a series.