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Mon, 23 Mar 2020 03:48:46 -0700 (PDT) Subject: [RFC PATCH 1/3] printk: Add function to set console to preferred console's driver To: Greg Kroah-Hartman , Jiri Slaby , Petr Mladek , Sergey Senozhatsky References: <44156595-0eee-58da-4376-fd25b634d21b@gmail.com> From: Alper Nebi Yasak Message-ID: Date: Mon, 23 Mar 2020 13:48:41 +0300 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <44156595-0eee-58da-4376-fd25b634d21b@gmail.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200323_034850_025202_C344BFB3 X-CRM114-Status: GOOD ( 20.81 ) X-Spam-Score: -0.2 (/) X-Spam-Report: SpamAssassin version 3.4.3 on bombadil.infradead.org summary: Content analysis details: (-0.2 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at https://www.dnswl.org/, no trust [2a00:1450:4864:20:0:0:0:143 listed in] [list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider [alpernebiyasak[at]gmail.com] -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Steven Rostedt Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org Currently, add_preferred_console sets a preferred console, but doesn't actually change /dev/console to match it. That part is handled within register_device, where a newly registered console driver will be set as /dev/console if it matches the preferred console. However, if the relevant driver is already registered, the only way to set it as /dev/console is by un-registering and re-registering it. An example is the xenfb_make_preferred_console() function: console_lock(); for_each_console(c) { if (!strcmp(c->name, "tty") && c->index == 0) break; } console_unlock(); if (c) { unregister_console(c); c->flags |= CON_CONSDEV; c->flags &= ~CON_PRINTBUFFER; /* don't print again */ register_console(c); } The code above was introduced in commit 9e124fe16ff2. In short, it's aim is to set VT as the preferred console only after a working framebuffer is registered and thus VT is not the dummy device. This patch introduces an update_console_to_preferred function that handles the necessary /dev/console change. With this change, the example above can be replaced with: console_lock(); add_preferred_console("tty", 0, NULL); update_console_to_preferred(); console_unlock(); More importantly, these two calls can be moved to vt.c in order to bump its priority when a non-dummy backend for it is introduced, solving that problem in general. Signed-off-by: Alper Nebi Yasak --- include/linux/console.h | 1 + kernel/printk/printk.c | 56 +++++++++++++++++++++++++++++++++++++++++ 2 files changed, 57 insertions(+) diff --git a/include/linux/console.h b/include/linux/console.h index 75dd20650fb..4b3fa34be24 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -172,6 +172,7 @@ enum con_flush_mode { }; extern int add_preferred_console(char *name, int idx, char *options); +extern int update_console_to_preferred(void); extern void register_console(struct console *); extern int unregister_console(struct console *); extern struct console *console_drivers; diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index ad460623454..6b16c973587 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2212,12 +2212,68 @@ __setup("console=", console_setup); * be used by arch-specific code either to override the user or more * commonly to provide a default console (ie from PROM variables) when * the user has not supplied one. + * + * Preferences set by this function don't take effect until the next + * time a matching driver for the preferred console is registered. If a + * matching driver was already registered, @update_console_to_preferred + * function can be used to set that as the preferred console driver. */ int add_preferred_console(char *name, int idx, char *options) { return __add_preferred_console(name, idx, options, NULL, false); } +/** + * update_console_to_preferred - set console to the preferred console's driver. + * + * Updates console_drivers and CON_CONSDEV flags so that an already + * registered and enabled console driver matching the preferred console + * is used as /dev/console. + * + * Must be called within console_lock();. + */ +int update_console_to_preferred(void) +{ + struct console_cmdline *c = NULL; + struct console *con = NULL; + struct console *tmp = NULL; + + if (preferred_console >= 0) + c = &console_cmdline[preferred_console]; + + if (!c || !c->name[0]) + return 0; + + for_each_console(con) { + if (!con->next || !(con->next->flags & CON_ENABLED)) + continue; + if (strcmp(c->name, con->next->name) != 0) + continue; + if (con->next->index >= 0 && + con->next->index != c->index) + continue; + break; + } + + if (!con) + return -ENODEV; + + pr_info("switching to console [%s%d]\n", + con->next->name, con->next->index); + + tmp = con->next; + con->next = con->next->next; + tmp->next = console_drivers; + console_drivers = tmp; + + if (console_drivers->next) + console_drivers->next->flags &= ~CON_CONSDEV; + console_drivers->flags |= CON_CONSDEV; + has_preferred_console = true; + + return 0; +} + bool console_suspend_enabled = true; EXPORT_SYMBOL(console_suspend_enabled);