Re: [PATCH] dynamic_debug: add wildcard support to filter files/functions/modules

[Jason Baron]

On 07/25/2013 12:47 PM, Joe Perches wrote:
> On Thu, 2013-07-25 at 21:02 +0800, Du, Changbin wrote:
> > From: "Du, Changbin" <changbin.du@xxxxxxxxx>
> >
> > This patch add wildcard '*'(matches zero or more characters) and '?'
> > (matches one character) support when qurying debug flags.
> Seems very useful.  Caveat below.
>
> > diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
> []
> > @@ -127,6 +127,21 @@ static void vpr_info_dq(const struct ddebug_query *query, const char *msg)
> >   		 query->first_lineno, query->last_lineno);
> >   }
> >   
> > +static int match_pattern(char *pat, char *str)
> > +{
> > +	switch (*pat) {
> > +	case '\0':
> > +		return !*str;
> > +	case '*':
> > +		return  match_pattern(pat+1, str) ||
> > +			(*str && match_pattern(pat, str+1));
> > +	case '?':
> > +		return *str && match_pattern(pat+1, str+1);
> > +	default:
> > +		return *pat == *str && match_pattern(pat+1, str 1);
> > +	}
> > +}
> What's the maximum length string used today?
> On a very long pattern, can this recursion cause stack overflow?
>
> Other than that, I like it.

The recursion here is a concern - especially since the 'pat' pointer is 
controlled from userspace. Maybe not at pretty, but this can easily be 
done in userspace. For example, to set all driver/usb* one could do 
something like:

grep "drivers/usb" control | awk -F ":| "  '{ print "file " $1 " line " 
$2 }' | xargs -i -n1 echo {} +p > control

Thanks,

-Jason



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