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McKenney" , Peter Zijlstra , Shakeel Butt , Tejun Heo , Thomas Gleixner , Thomas =?iso-8859-1?Q?Wei=DFschuh?= Subject: Re: [PATCH v2] init/main.c: Wrap long kernel cmdline when printing to logs Message-ID: <20251022092947.14504A78-hca@linux.ibm.com> References: <20251021173939.v2.1.I095f1e2c6c27f9f4de0b4841f725f356c643a13f@changeid> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=EJELElZC c=1 sm=1 tr=0 ts=68f8a412 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=kj9zAlcOel0A:10 a=x6icFKpwvdMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=cm27Pg_UAAAA:8 a=FjV1DHKLklVSAG7hgsgA:9 a=CjuIK1q_8ugA:10 a=nl4s5V0KI7Kw-pW0DWrs:22 a=pHzHmUro8NiASowvMSCR:22 a=xoEH_sTeL_Rfw54TyV31:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMDE4MDAyMiBTYWx0ZWRfX1mWYlSkJEKs0 0zlGdnl10eTJxwIg3cdrnZlYWyjiFzwnQsepEjfeNTMLP9Y4ncVdzRWxJ/uQU+nEI63Z0a+74mL yfqVqr5dvKFMbGX+0BRiy78XU9Dfo8ruo81i5sT453Tk33mir9lTdobrziN+OTpjkG6cfeyb0eA ce1gT6f222fQ5GOvdEa3e5dsN0k0K5W1fHAgSfG8DLL0BCEBU/YNmoDegJlxx09noe09bZsvCze OELLvGWoHlKHw2Wk8vWPQmgwSY0j4Vv8xO9MioFfmp3BdkFGAOqj7v0ap5rAtT9zcH0nC4OO8Mw VZjUbgKHAEN+HDHJOnPtYxuGxfaOd6OyxZAO3U5mhLiFIUQOxthpPYiGYHFpjlgKECavkkCvXdi klVMLU2yh7xBRe+anYFlSrbV3UyRvQ== X-Proofpoint-GUID: zZD3nkoHjh7LVE_ZMh22w963104QWy1Y X-Proofpoint-ORIG-GUID: FzfTzG1qWiiZHe3oCnKICL44RCkP09-J X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-10-22_03,2025-10-13_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 priorityscore=1501 suspectscore=0 bulkscore=0 spamscore=0 malwarescore=0 phishscore=0 adultscore=0 lowpriorityscore=0 clxscore=1015 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510020000 definitions=main-2510180022 On Wed, Oct 22, 2025 at 11:16:06AM +0200, Geert Uytterhoeven wrote: > Hi Douglas, > > On Wed, 22 Oct 2025 at 02:41, Douglas Anderson wrote: > > The kernel cmdline length is allowed to be longer than what printk can > > handle. When this happens the cmdline that's printed to the kernel > > ring buffer at bootup is cutoff and some kernel cmdline options are > > "hidden" from the logs. This undercuts the usefulness of the log > > message. > > > > Specifically, grepping for COMMAND_LINE_SIZE shows that 2048 is common > > and some architectures even define it as 4096. s390 allows a > > CONFIG-based maximum up to 1MB (though it's not expected that anyone > > will go over the default max of 4096 [1]). > > Of course (unless the kernel crashes) you can also look at /proc/cmdline > later. However, that seems to be limited to a single page, too, > as fs/proc/cmdline.c:cmdline_proc_show() uses seq_puts*(). proc seq_files are not PAGE_SIZE limited. If the output doesn't fit into a single page the size of the buffer is doubled, until the output fits into the buffer. See the while(1) loop in seq_read_iter().