Messages in this thread | | | Date | Fri, 20 Dec 2019 10:11:31 +0100 | From | Petr Mladek <> | Subject | Re: [PATCH v2] printk: Fix preferred console selection with multiple matches |
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On Fri 2019-12-20 08:48:24, Benjamin Herrenschmidt wrote: > On Thu, 2019-12-19 at 14:50 +0100, Petr Mladek wrote: > > The code really need simplification. I would prefer to take the risk > > and reduce the amount of added conditions as much as possible. > > I have an idea, see below. > > I wanted you to say that :-) I'll rework along those lines. Just a nit > or two: > > > > > > > --- a/kernel/printk/printk.c > > > +++ b/kernel/printk/printk.c > > > @@ -2542,6 +2545,53 @@ static int __init keep_bootcon_setup(char *str) > > > > > > early_param("keep_bootcon", keep_bootcon_setup); > > > > > > +enum con_match { > > > + con_matched, > > > + con_matched_preferred, > > > + con_braille, > > > + con_failed, > > > + con_no_match, > > > +}; > > > > Please, replace this with int, where: > > > > + con_matched -> 0 > > + con_matched_preferred -> 0 and make "has_preferred" global variable > > + con_braile -> 0 later check for CON_BRL flag > > + con_failed -> -EFAULT > > + con_no_match -> -ENOENT > > Not fan of using -EFAULT here, it's a detail since it's rather kernel > internal, but I'd rather use -ENXIO for no match and -EIO for failed > (or pass the original error code up if any). That said it's really bike > shed painting at this point :-)
Sigh, either variant is somehow confusing.
I think that -ENOENT is a bit better than -EIO. It is abbreviation of "No entry or No entity" which quite fits here. Also the device might exist but it is not used when not requested.
I do not mind about -EFAULT vs -EIO. Well, -EIO might actually better describe the reality.
That said, I do not want to spend much time on bikesheding. Feel free to use whatever looks better to you.
> > > @@ -2615,41 +2664,19 @@ void register_console(struct console *newcon) > > /* Prefer command line over platform specific defaults. */ > > err = try_match_new_console(newcon, true); > > if (err = -ENOENT) > > err = try_match_new_console(newcon, false); > > > > /* printk() messages are not printed to Braille consoles. */ > > if (err || console->flags | CON_BRL) > > return; > > So this changes the existing behaviour in one way that may or may not > matter, I don't know: > > If setup() fails, the existing code will not exit. That means that if > the console has CON_ENABLED already set (some do set it statically or > set it from outside this function, I haven't looked into details the > various circumstances this can happen), the existing code will still > insert it. Your patch will make us not insert it.
Great catch! There is still a lot to learn about this code.
It seems that, for example, pstore and netconsole are not added into console_cmdline and do not match. They relly on the explicitely set CON_ENABLED.
I would prefer to hide this into the new "shorter" function. I would rename it to try_enable_new_console() and add the following at the end:
/* * For example, pstore, netconsole, are enabled even * without matching. */ if (console->flags & CON_ENABLED) return 0;
Best Regards, Petr
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