Messages in this thread | | | Date | Mon, 19 Apr 2021 11:16:43 +0200 | From | Petr Mladek <> | Subject | Re: [PATCH v5] printk: Userspace format enumeration support |
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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
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