From patchwork Wed Nov 15 10:29:27 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tomas Mudrunka X-Patchwork-Id: 744398 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id F25FFC07548 for ; Wed, 15 Nov 2023 10:29:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234420AbjKOK3m (ORCPT ); Wed, 15 Nov 2023 05:29:42 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33622 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234680AbjKOK3l (ORCPT ); Wed, 15 Nov 2023 05:29:41 -0500 Received: from harvie.cz (harvie.cz [77.87.242.242]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id A4F07F5 for ; Wed, 15 Nov 2023 02:29:38 -0800 (PST) Received: from anemophobia.amit.cz (unknown [31.30.84.130]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by harvie.cz (Postfix) with ESMTPSA id 513B7180354; Wed, 15 Nov 2023 11:29:33 +0100 (CET) From: Tomas Mudrunka To: jirislaby@kernel.org Cc: corbet@lwn.net, gregkh@linuxfoundation.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, rdunlap@infradead.org, tomas.mudrunka@gmail.com Subject: [PATCH v8] /proc/sysrq-trigger: accept multiple keys at once Date: Wed, 15 Nov 2023 11:29:27 +0100 Message-ID: <20231115102927.192841-1-tomas.mudrunka@gmail.com> X-Mailer: git-send-email 2.42.1 In-Reply-To: <670993bf-a8ef-4561-8213-6a37d0598d83@kernel.org> References: <670993bf-a8ef-4561-8213-6a37d0598d83@kernel.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org Just for convenience. This way we can do: `echo _reisub > /proc/sysrq-trigger` Instead of: `for i in r e i s u b; do echo "$i" > /proc/sysrq-trigger; done;` This can be very useful when trying to execute sysrq combo remotely or from userspace. When sending keys in multiple separate writes, userspace can be killed before whole combo is completed. Therefore putting all keys in single write is more robust approach. Signed-off-by: Tomas Mudrunka --- V7 -> V8: Added this list of changes V6 -> V7: Fixed english in documentation V5 -> V6: Documentation now has notice about undefined behavior V4 -> V5: Added this list of changes V3 -> V4: Bulk is now bool instead of char (and fixed typo) V2 -> V3: Fixed code styling (and introduced typo) V1 -> V2: Bulk mode only activated by underscore now, added docs Documentation/admin-guide/sysrq.rst | 11 ++++++++++- drivers/tty/sysrq.c | 18 +++++++++++++++--- 2 files changed, 25 insertions(+), 4 deletions(-) diff --git a/Documentation/admin-guide/sysrq.rst b/Documentation/admin-guide/sysrq.rst index 51906e473..fbe79d314 100644 --- a/Documentation/admin-guide/sysrq.rst +++ b/Documentation/admin-guide/sysrq.rst @@ -75,10 +75,19 @@ On other submit a patch to be included in this section. On all - Write a character to /proc/sysrq-trigger. e.g.:: + Write single character to /proc/sysrq-trigger. + Only the first character is processed, the rest of string is ignored. + However, it is not recommended to write any extra characters + as the behavior is undefined and might change in the future versions. + E.g.:: echo t > /proc/sysrq-trigger + Alternatively, write multiple characters prepended by underscore. + This way, all characters will be processed. E.g.:: + + echo _reisub > /proc/sysrq-trigger + The :kbd:`` is case sensitive. What are the 'command' keys? diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index 6b4a28bcf..5411351e4 100644 --- a/drivers/tty/sysrq.c +++ b/drivers/tty/sysrq.c @@ -1150,16 +1150,28 @@ EXPORT_SYMBOL(unregister_sysrq_key); #ifdef CONFIG_PROC_FS /* * writing 'C' to /proc/sysrq-trigger is like sysrq-C + * Normally only the first character written is processed. + * If first character is underscore, all characters are processed. */ static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf, size_t count, loff_t *ppos) { - if (count) { + bool bulk = false; + size_t i; + + for (i = 0; i < count; i++) { char c; - if (get_user(c, buf)) + if (get_user(c, buf + i)) return -EFAULT; - __handle_sysrq(c, false); + + if (c == '_') + bulk = true; + else + __handle_sysrq(c, false); + + if (!bulk) + break; } return count;