From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> To: Alper Nebi Yasak <alpernebiyasak@gmail.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Jiri Slaby <jslaby@suse.com>, Petr Mladek <pmladek@suse.com>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, linux-serial@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>, Andy Shevchenko <andriy.shevchenko@linux.intel.com>, Arvind Sankar <nivedita@alum.mit.edu>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, "David S. Miller" <davem@davemloft.net>, Feng Tang <feng.tang@intel.com> Subject: Re: [RFC PATCH v2 1/3] printk: Add function to set console to preferred console's driver Date: Fri, 1 May 2020 10:44:54 +0900 [thread overview] Message-ID: <20200501014454.GB288759@jagdpanzerIV.localdomain> (raw) In-Reply-To: <20200430161438.17640-2-alpernebiyasak@gmail.com> On (20/04/30 19:14), Alper Nebi Yasak wrote: > 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. Hmm. Preferred console selection is very fragile, there are too many setups and workarounds that even minor tweaks introduce regressions oftentimes. We have, by the way, a pending patchset which changes the same are - preferred console selection. git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk.git for-5.7-preferred-console [..] > 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); > } I didn't know about this code. > The code above was introduced in commit 9e124fe16ff2 ("xen: Enable > console tty by default in domU if it's not a dummy"). 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. Let me take a look over the weekend. -ss
next prev parent reply other threads:[~2020-05-01 1:44 UTC|newest] Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-04-30 16:14 [RFC PATCH v2 0/3] Prefer working VT console over SPCR and device-tree chosen stdout-path Alper Nebi Yasak 2020-04-30 16:14 ` [RFC PATCH v2 1/3] printk: Add function to set console to preferred console's driver Alper Nebi Yasak 2020-04-30 16:46 ` Andy Shevchenko 2020-05-01 1:44 ` Sergey Senozhatsky [this message] 2020-05-01 11:48 ` Alper Nebi Yasak 2020-05-13 5:35 ` Sergey Senozhatsky 2020-05-24 10:01 ` Daniel Vetter 2020-04-30 16:14 ` [RFC PATCH v2 2/3] vt: Set as preferred console when a non-dummy backend is bound Alper Nebi Yasak 2020-04-30 16:14 ` [RFC PATCH v2 3/3] printk: Preset tty0 as a pseudo-preferred console Alper Nebi Yasak 2020-04-30 16:44 ` [RFC PATCH v2 0/3] Prefer working VT console over SPCR and device-tree chosen stdout-path Andy Shevchenko 2020-04-30 19:32 ` Alper Nebi Yasak 2020-05-01 1:30 ` Sergey Senozhatsky 2020-05-01 11:08 ` Alper Nebi Yasak 2020-05-01 13:16 ` Andy Shevchenko 2020-05-01 15:07 ` Alper Nebi Yasak 2020-05-13 14:37 ` Petr Mladek 2020-05-13 22:22 ` Benjamin Herrenschmidt 2020-05-15 19:27 ` Alper Nebi Yasak 2020-05-25 13:04 ` Petr Mladek
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