Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751953AbdI2Aob (ORCPT ); Thu, 28 Sep 2017 20:44:31 -0400 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:43716 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751692AbdI2Ao1 (ORCPT ); Thu, 28 Sep 2017 20:44:27 -0400 Smtp-Origin-Hostprefix: devbig From: Calvin Owens Smtp-Origin-Hostname: devbig337.prn1.facebook.com To: Petr Mladek , Sergey Senozhatsky , Steven Rostedt CC: , , , , Calvin Owens Smtp-Origin-Cluster: prn1c29 Subject: [PATCH 2/3] printk: Add /sys/consoles/ interface Date: Thu, 28 Sep 2017 17:43:56 -0700 Message-ID: X-Mailer: git-send-email 2.9.5 In-Reply-To: <08c1dc1a96afd6b6aecc5ff3c7c0e62c36670893.1506644730.git.calvinowens@fb.com> References: <08c1dc1a96afd6b6aecc5ff3c7c0e62c36670893.1506644730.git.calvinowens@fb.com> X-FB-Internal: Safe MIME-Version: 1.0 Content-Type: text/plain X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-09-28_08:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5485 Lines: 193 This adds a new sysfs interface that contains a directory for each console registered on the system. Each directory contains a single "loglevel" file for reading and setting the per-console loglevel. We can let kobject destruction race with console removal: if it does, loglevel_{show,store}() will safely fail with -ENODEV. This is a little weird, but avoids embedding the kobject and therefore needing to totally refactor the way we handle console struct lifetime. Cc: Petr Mladek Cc: Steven Rostedt Cc: Sergey Senozhatsky Signed-off-by: Calvin Owens --- (V1: https://lkml.org/lkml/2017/4/4/784) Changes in V2: * Honor minimum_console_loglevel when setting loglevels * Added entry in Documentation/ABI/testing Documentation/ABI/testing/sysfs-consoles | 13 +++++ include/linux/console.h | 1 + kernel/printk/printk.c | 88 ++++++++++++++++++++++++++++++++ 3 files changed, 102 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-consoles diff --git a/Documentation/ABI/testing/sysfs-consoles b/Documentation/ABI/testing/sysfs-consoles new file mode 100644 index 0000000..6a1593e --- /dev/null +++ b/Documentation/ABI/testing/sysfs-consoles @@ -0,0 +1,13 @@ +What: /sys/consoles/ +Date: September 2017 +KernelVersion: 4.15 +Contact: Calvin Owens +Description: The /sys/consoles tree contains a directory for each console + configured on the system. These directories contain the + following attributes: + + * "loglevel" Set the per-console loglevel: the kernel uses + max(system_loglevel, perconsole_loglevel) when + deciding whether to emit a given message. The + default is 0, which means max() always yields + the system setting in the kernel.printk sysctl. diff --git a/include/linux/console.h b/include/linux/console.h index a5b5d79..76840be 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -148,6 +148,7 @@ struct console { void *data; struct console *next; int level; + struct kobject *kobj; }; /* diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 3f1675e..488bda3 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -105,6 +105,8 @@ enum devkmsg_log_masks { static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT; +static struct kobject *consoles_dir_kobj; + static int __control_devkmsg(char *str) { if (!str) @@ -2371,6 +2373,82 @@ static int __init keep_bootcon_setup(char *str) early_param("keep_bootcon", keep_bootcon_setup); +static ssize_t loglevel_show(struct kobject *kobj, struct kobj_attribute *attr, + char *buf) +{ + struct console *con; + ssize_t ret = -ENODEV; + + console_lock(); + for_each_console(con) { + if (con->kobj == kobj) { + ret = sprintf(buf, "%d\n", con->level); + break; + } + } + console_unlock(); + + return ret; +} + +static ssize_t loglevel_store(struct kobject *kobj, struct kobj_attribute *attr, + const char *buf, size_t count) +{ + struct console *con; + ssize_t ret; + int tmp; + + ret = kstrtoint(buf, 10, &tmp); + if (ret < 0) + return ret; + + if (tmp < LOGLEVEL_EMERG) + return -ERANGE; + + /* + * Mimic the behavior of /dev/kmsg with respect to minimum_loglevel + */ + if (tmp < minimum_console_loglevel) + tmp = minimum_console_loglevel; + + ret = -ENODEV; + console_lock(); + for_each_console(con) { + if (con->kobj == kobj) { + con->level = tmp; + ret = count; + break; + } + } + console_unlock(); + + return ret; +} + +static const struct kobj_attribute console_loglevel_attr = + __ATTR(loglevel, 0644, loglevel_show, loglevel_store); + +static void console_register_sysfs(struct console *newcon) +{ + /* + * We might be called very early from register_console(): in that case, + * printk_late_init() will take care of this later. + */ + if (!consoles_dir_kobj) + return; + + newcon->kobj = kobject_create_and_add(newcon->name, consoles_dir_kobj); + if (WARN_ON(!newcon->kobj)) + return; + + WARN_ON(sysfs_create_file(newcon->kobj, &console_loglevel_attr.attr)); +} + +static void console_unregister_sysfs(struct console *oldcon) +{ + kobject_put(oldcon->kobj); +} + /* * The console driver calls this routine during kernel initialization * to register the console printing procedure with printk() and to @@ -2495,6 +2573,7 @@ void register_console(struct console *newcon) * By default, the per-console minimum forces no messages through. */ newcon->level = LOGLEVEL_EMERG; + newcon->kobj = NULL; /* * Put this console in the list - keep the @@ -2531,6 +2610,7 @@ void register_console(struct console *newcon) */ exclusive_console = newcon; } + console_register_sysfs(newcon); console_unlock(); console_sysfs_notify(); @@ -2597,6 +2677,7 @@ int unregister_console(struct console *console) console_drivers->flags |= CON_CONSDEV; console->flags &= ~CON_ENABLED; + console_unregister_sysfs(console); console_unlock(); console_sysfs_notify(); return res; @@ -2672,6 +2753,13 @@ static int __init printk_late_init(void) ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "printk:online", console_cpu_notify, NULL); WARN_ON(ret < 0); + + consoles_dir_kobj = kobject_create_and_add("consoles", NULL); + WARN_ON(!consoles_dir_kobj); + + for_each_console(con) + console_register_sysfs(con); + return 0; } late_initcall(printk_late_init); -- 2.9.5