From: Petr Mladek <pmladek@suse.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 5/5] console: Introduce ->exit() callback
Date: Thu, 30 Jan 2020 14:22:46 +0100 [thread overview]
Message-ID: <20200130132246.qesf6bupt4m3jnue@pathway.suse.cz> (raw)
In-Reply-To: <20200129142558.GF32742@smile.fi.intel.com>
On Wed 2020-01-29 16:25:58, Andy Shevchenko wrote:
> On Wed, Jan 29, 2020 at 10:41:41PM +0900, Sergey Senozhatsky wrote:
> > On (20/01/28 11:44), Andy Shevchenko wrote:
> > > > If the console was not registered (hence not enabled) is it still required
> > > > to call ->exit()? Is there a requirement that ->exit() should handle such
> > > > cases?
> > >
> > > This is a good point. The ->exit() purpose is to keep balance for whatever
> > > happened at ->setup().
> > >
> > > But ->setup() is being called either when we have has_preferred == false or
> > > when we got no matching we call it for all such consoles, till it returns an
> > > error (can you elaborate the logic behind it?).
> >
> > ->match() does alias matching and ->setup(). If alias matching failed,
> > exact name match takes place. We don't call ->setup() for all consoles,
> > but only for those that have exact name match:
> >
> > if (strcmp(c->name, newcon->name) != 0)
> > continue;
> >
> > As to why we don't stop sooner in that loop - I need to to do some
> > archaeology. We need to have CON_CONSDEV at proper place, which is
> > IIRC the last matching console.
> >
> > Pretty much every time we tried to change the logic we ended up
> > reverting the changes.
>
> I understand. Seems the ->setup() has to be idempotent. We can tell the same
> for ->exit() in some comment.
I believe that ->setup() can succeesfully be called only once.
It is tricky like hell:
1st piece:
if (!has_preferred || bcon || !console_drivers)
has_preferred = preferred_console >= 0;
note:
+ "has_preferred" is updated here only when it was not "true" before.
+ "has_preferred" is set to "true" here only when "preferred_console"
is set in __add_preferred_console()
2nd piece:
+ __add_preferred_console() is called for console defined on
the command line. "preferred_console" points to the console
defined by the last "console=" parameter.
3rd piece:
+ "has_preferred" is set to "true" later in register_console() when
a console with tty binding gets enabled.
4th piece:
+ The code:
/*
* See if we want to use this console driver. If we
* didn't select a console we take the first one
* that registers here.
*/
if (!has_preferred)
... try to enable the given console
The comment is a bit unclear. The code is used as a fallback
when no console was defined on the command line.
Note that "has_preferred" is always true when "preferred_console"
was defined via command line, see 2nd piece above.
By other words:
+ The fallback code (4th piece) is called only when
"preferred_console" was not defined on the command line.
+ The cycle below matches the given console only when
it was defined on the command line.
As a result, I believe that ->setup() could never be called
in both paths for the same console. Especially I think that
fallback code should not be used when the console was defined on
the command line.
I am not 100% sure but I am ready to risk this. Anyway, I think
that many ->setup() callbacks are not ready to be successfully
called twice.
(Sigh, I have started to clean up this code two years ago.
But I have never found time to finish the patchset. It is
such a huge mess.)
> Can you describe, btw, struct console in kernel doc format?
> It will be very helpful!
>
> > > In both cases we will get the console to have CON_ENABLED flag set.
> >
> > And there are sneaky consoles that have CON_ENABLED before we even
> > register them.
>
> So, taking into consideration my comment to the previous patch, what would be
> suggested guard here?
>
> For a starter something like this?
>
> if ((console->flags & CON_ENABLED) && console->exit)
> console->exit(console);
I would do:
if (!res && console->exit)
console->exit(console);
I mean. I would call ->exit() only when console->setup() succeeded in
register_console(). In this case, the console was later added to
the console_drivers list.
Best Regards,
Petr
next prev parent reply other threads:[~2020-01-30 13:22 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-27 11:47 [PATCH v3 1/5] console: Don't perform test for CON_BRL flag Andy Shevchenko
2020-01-27 11:47 ` [PATCH v3 2/5] console: Drop double check for console_drivers being non-NULL Andy Shevchenko
2020-01-29 13:24 ` Petr Mladek
2020-01-27 11:47 ` [PATCH v3 3/5] console: Use for_each_console() helper in unregister_console() Andy Shevchenko
2020-01-29 14:11 ` Petr Mladek
2020-01-27 11:47 ` [PATCH v3 4/5] console: Avoid positive return code from unregister_console() Andy Shevchenko
2020-01-28 4:43 ` Sergey Senozhatsky
2020-01-28 9:22 ` Andy Shevchenko
2020-01-28 9:25 ` Sergey Senozhatsky
2020-01-28 9:37 ` Sergey Senozhatsky
2020-01-28 9:52 ` Andy Shevchenko
2020-01-30 9:04 ` Petr Mladek
2020-01-30 9:58 ` Andy Shevchenko
2020-01-30 12:22 ` Petr Mladek
2020-01-30 13:13 ` Andy Shevchenko
2020-01-27 11:47 ` [PATCH v3 5/5] console: Introduce ->exit() callback Andy Shevchenko
2020-01-28 5:17 ` Sergey Senozhatsky
2020-01-28 9:44 ` Andy Shevchenko
2020-01-29 13:41 ` Sergey Senozhatsky
2020-01-29 14:25 ` Andy Shevchenko
2020-01-29 15:12 ` Sergey Senozhatsky
2020-01-29 16:50 ` Sergey Senozhatsky
2020-01-30 13:14 ` Andy Shevchenko
2020-01-30 13:22 ` Petr Mladek [this message]
2020-01-30 13:39 ` Andy Shevchenko
2020-01-30 9:09 ` Petr Mladek
2020-01-30 10:01 ` Andy Shevchenko
2020-01-29 12:29 ` [PATCH v3 1/5] console: Don't perform test for CON_BRL flag Petr Mladek
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200130132246.qesf6bupt4m3jnue@pathway.suse.cz \
--to=pmladek@suse.com \
--cc=andriy.shevchenko@linux.intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=rostedt@goodmis.org \
--cc=sergey.senozhatsky.work@gmail.com \
--cc=sergey.senozhatsky@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).