From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 997BAC54FD5 for ; Wed, 25 Mar 2020 12:03:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 65C9C20771 for ; Wed, 25 Mar 2020 12:03:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727457AbgCYMD5 (ORCPT ); Wed, 25 Mar 2020 08:03:57 -0400 Received: from mx2.suse.de ([195.135.220.15]:50392 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727389AbgCYMD5 (ORCPT ); Wed, 25 Mar 2020 08:03:57 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 55705AC1D; Wed, 25 Mar 2020 12:03:54 +0000 (UTC) From: Vlastimil Babka To: Luis Chamberlain , Kees Cook , Iurii Zaikin Cc: linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-mm@kvack.org, Ivan Teterevkov , Michal Hocko , David Rientjes , Matthew Wilcox , "Eric W . Biederman" , "Guilherme G . Piccoli" , Vlastimil Babka Subject: [RFC v2 1/2] kernel/sysctl: support setting sysctl parameters from kernel command line Date: Wed, 25 Mar 2020 13:03:44 +0100 Message-Id: <20200325120345.12946-1-vbabka@suse.cz> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org A recently proposed patch to add vm_swappiness command line parameter in addition to existing sysctl [1] made me wonder why we don't have a general support for passing sysctl parameters via command line. Googling found only somebody else wondering the same [2], but I haven't found any prior discussion with reasons why not to do this. Settings the vm_swappiness issue aside (the underlying issue might be solved in a different way), quick search of kernel-parameters.txt shows there are already some that exist as both sysctl and kernel parameter - hung_task_panic, nmi_watchdog, numa_zonelist_order, traceoff_on_warning. A general mechanism would remove the need to add more of those one-offs and might be handy in situations where configuration by e.g. /etc/sysctl.d/ is impractical. Also after 61a47c1ad3a4 ("sysctl: Remove the sysctl system call") the only way to set sysctl is via procfs, so this would eventually allow small systems to be built without CONFIG_PROC_SYSCTL and still be able to change sysctl parameters. Hence, this patch adds a new parse_args() pass that looks for parameters prefixed by 'sysctl.' and searches for them in the sysctl ctl_tables. When found, the respective proc handler is invoked. The search is just a naive linear one, to avoid using the whole procfs layer. It should be acceptable, as the cost depends on number of sysctl. parameters passed. The main limitation of avoiding the procfs layer is however that sysctls dynamically registered by register_sysctl_table() or register_sysctl_paths() cannot currently be set by this method. The processing is hooked right before the init process is loaded, as some handlers might be more complicated than simple setters and might need some subsystems to be initialized. At the moment the init process can be started and eventually execute a process writing to /proc/sys/ then it should be also fine to do that from the kernel. [1] https://lore.kernel.org/linux-doc/BL0PR02MB560167492CA4094C91589930E9FC0@BL0PR02MB5601.namprd02.prod.outlook.com/ [2] https://unix.stackexchange.com/questions/558802/how-to-set-sysctl-using-kernel-command-line-parameter Signed-off-by: Vlastimil Babka --- v2: - handle any nesting level of parameter name - add Documentation/admin-guide/kernel-parameters.txt blurb - alias support for legacy one-off parameters, with first conversion (patch 2) - still no support for dynamically registed sysctls .../admin-guide/kernel-parameters.txt | 9 +++ include/linux/sysctl.h | 1 + init/main.c | 21 +++++++ kernel/sysctl.c | 62 +++++++++++++++++++ 4 files changed, 93 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index c07815d230bc..5076e288f93f 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4793,6 +4793,15 @@ switches= [HW,M68k] + sysctl.*= [KNL] + Set a sysctl parameter right before loading the init + process, as if the value was written to the respective + /proc/sys/... file. Currently a subset of sysctl + parameters is supported that is not registered + dynamically. Unrecognized parameters and invalid values + are reported in the kernel log. + Example: sysctl.vm.swappiness=40 + sysfs.deprecated=0|1 [KNL] Enable/disable old style sysfs layout for old udev on older distributions. When this option is enabled diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h index 02fa84493f23..62ae963a5c0c 100644 --- a/include/linux/sysctl.h +++ b/include/linux/sysctl.h @@ -206,6 +206,7 @@ struct ctl_table_header *register_sysctl_paths(const struct ctl_path *path, void unregister_sysctl_table(struct ctl_table_header * table); extern int sysctl_init(void); +int process_sysctl_arg(char *param, char *val, const char *unused, void *arg); extern struct ctl_table sysctl_mount_point[]; diff --git a/init/main.c b/init/main.c index ee4947af823f..74a094c6b8b9 100644 --- a/init/main.c +++ b/init/main.c @@ -1345,6 +1345,25 @@ void __weak free_initmem(void) free_initmem_default(POISON_FREE_INITMEM); } +static void do_sysctl_args(void) +{ +#ifdef CONFIG_SYSCTL + size_t len = strlen(saved_command_line) + 1; + char *command_line; + + command_line = kzalloc(len, GFP_KERNEL); + if (!command_line) + panic("%s: Failed to allocate %zu bytes\n", __func__, len); + + strcpy(command_line, saved_command_line); + + parse_args("Setting sysctl args", command_line, + NULL, 0, -1, -1, NULL, process_sysctl_arg); + + kfree(command_line); +#endif +} + static int __ref kernel_init(void *unused) { int ret; @@ -1367,6 +1386,8 @@ static int __ref kernel_init(void *unused) rcu_end_inkernel_boot(); + do_sysctl_args(); + if (ramdisk_execute_command) { ret = run_init_process(ramdisk_execute_command); if (!ret) diff --git a/kernel/sysctl.c b/kernel/sysctl.c index ad5b88a53c5a..18c7f5606d55 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -1980,6 +1980,68 @@ int __init sysctl_init(void) return 0; } +/* Set sysctl value passed on kernel command line. */ +int process_sysctl_arg(char *param, char *val, + const char *unused, void *arg) +{ + size_t count; + char *remaining; + int err; + loff_t ppos = 0; + struct ctl_table *ctl, *found = NULL; + + if (strncmp(param, "sysctl.", sizeof("sysctl.") - 1)) + return 0; + + param += sizeof("sysctl.") - 1; + + remaining = param; + ctl = &sysctl_base_table[0]; + + while(ctl->procname != 0) { + int len = strlen(ctl->procname); + if (strncmp(remaining, ctl->procname, len)) { + ctl++; + continue; + } + if (ctl->child) { + if (remaining[len] == '.') { + remaining += len + 1; + ctl = ctl->child; + continue; + } + } else { + if (remaining[len] == '\0') { + found = ctl; + break; + } + } + ctl++; + } + + if (!found) { + pr_warn("Unknown sysctl param '%s' on command line", param); + return 0; + } + + if (!(found->mode & 0200)) { + pr_warn("Cannot set sysctl '%s=%s' from command line - not writable", + param, val); + return 0; + } + + count = strlen(val); + err = found->proc_handler(found, 1, val, &count, &ppos); + + if (err) + pr_warn("Error %d setting sysctl '%s=%s' from command line", + err, param, val); + + pr_debug("Set sysctl '%s=%s' from command line", param, val); + + return 0; +} + #endif /* CONFIG_SYSCTL */ /* -- 2.25.1