From: Petr Mladek <pmladek@suse.com>
To: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Chris Down <chris@chrisdown.name>,
linux-kernel@vger.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
John Ogness <john.ogness@linutronix.de>,
Johannes Weiner <hannes@cmpxchg.org>,
Andrew Morton <akpm@linux-foundation.org>,
Steven Rostedt <rostedt@goodmis.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Kees Cook <keescook@chromium.org>,
kernel-team@fb.com
Subject: Re: [PATCH v5] printk: Userspace format enumeration support
Date: Mon, 19 Apr 2021 11:16:43 +0200 [thread overview]
Message-ID: <YH1Kex8NOr89BJXq@alley> (raw)
In-Reply-To: <e9f74575-1ba0-0c06-b370-59d151c72ed6@rasmusvillemoes.dk>
On Mon 2021-04-19 09:27:43, Rasmus Villemoes wrote:
> On 16/04/2021 15.56, Chris Down wrote:
> > Hey Petr, Rasmus,
>
> >> This is great point! There are many other subsystem specific wrappers,
> >> e,g, ata_dev_printk(), netdev_printk(), snd_printk(), dprintk().
> >> We should make it easy to index them as well.
> >
> > These would be nice to have, but we should agree about how we store
> > things internally.
> >
> > For example, in printk we typically store the level inline as part of
> > the format string at compile time. However, for `dev_printk`, it's
> > passed entirely separately from the format string after preprocessing is
> > already concluded (or at least, not in a way we can easily parse it the
> > same way we do for printk()):
> >
> > void dev_printk(const char *level, const struct device *dev, const
> > char *fmt, ...)
>
> Hm, yeah, for "naked" dev_printk() calls there's no easy way to grab the
> level, for dev_err and friends it's somewhat easier as you could just
> hook into the definition of the dev_err macro. I'm not saying you need
> to handle everything at once, but doing dev_err and netdev_err would get
> you a very long way
It is true that there are many messages printed using
dev_printk(). For example, these rough numbers:
$> git grep pr_err | wc -l
19885
$> git grep dev_err | wc -l
58153
> > One (ugly) way to handle this would be to have a new "level" field in
> > the printk index entry, with semantics that if it's some sentinel value,
> > look at the format itself for the format, otherwise if it's some other
> > value, the level field itself is the level.
> >
> > This will work, but it's pretty ugly. Any better suggestions? :-)
We should use the same algorithm that is used in parse_prefix() called
from vprintk_store(). parse_prefix() updates @level only when
the current value is LOGLEVEL_DEFAULT.
We should set the new field in the printk index entry to
LOGLEVEL_DEFAULT by default. It should be set to a particular level
when it is defined by an extra parameter, like in dev_printk().
> Well, that was more or less exactly what I suggested when I wrote
>
> > One could also record the function a format is being used with - without
> > that, the display probably can't show a reasonable <level> for those
> > dev_* function.
>
> But, I think the real question is, why are we/you interested in the
> level at all? Isn't the format string itself enough for the purpose of
> tracking which printks have come and gone? IOW, what about, on the
> display side, simply skipping over some KERN_* prefix if present?
Messages are filtered on consoles by console_loglevel. The loglevel
might be important to decide whether the message is visible or not.
Best Regards,
Petr
next prev parent reply other threads:[~2021-04-19 9:16 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-10 2:30 [PATCH v5] printk: Userspace format enumeration support Chris Down
2021-03-10 6:20 ` kernel test robot
2021-03-10 6:50 ` Greg Kroah-Hartman
2021-03-10 12:12 ` Chris Down
2021-03-10 12:16 ` Greg Kroah-Hartman
2021-03-11 9:34 ` Petr Mladek
2021-03-11 9:43 ` Greg Kroah-Hartman
2021-03-10 12:17 ` Chris Down
2021-03-11 9:20 ` Petr Mladek
2021-03-10 12:31 ` kernel test robot
2021-03-12 11:14 ` Petr Mladek
2021-03-12 13:53 ` Chris Down
2021-03-15 10:02 ` Petr Mladek
2021-03-15 12:20 ` Chris Down
2021-03-16 11:39 ` Petr Mladek
2021-03-16 13:27 ` Chris Down
2021-03-16 14:12 ` Rasmus Villemoes
2021-03-16 14:28 ` Chris Down
2021-03-17 8:40 ` Petr Mladek
2021-03-17 10:03 ` Rasmus Villemoes
2021-03-18 10:46 ` Petr Mladek
2021-03-18 11:31 ` Rasmus Villemoes
2021-03-19 11:43 ` Petr Mladek
2021-04-16 13:56 ` Chris Down
2021-04-16 14:09 ` Joe Perches
2021-04-16 14:29 ` Chris Down
2021-04-19 7:27 ` Rasmus Villemoes
2021-04-19 9:16 ` Petr Mladek [this message]
2021-04-19 9:53 ` Greg Kroah-Hartman
2021-04-19 11:02 ` Joe Perches
2021-04-21 13:14 ` Chris Down
2021-04-22 12:36 ` Joe Perches
2021-04-22 14:59 ` Chris Down
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