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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