linux-kernel - Re: [PATCH v2 13/24] dyndbg: combine flags & mask into a struct, use that

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Date:   Tue, 16 Jun 2020 13:34:43 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     jim.cromie@...il.com
Cc:     Jason Baron <jbaron@...mai.com>,
        LKML <linux-kernel@...r.kernel.org>, akpm@...uxfoundation.org,
        Greg KH <gregkh@...uxfoundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v2 13/24] dyndbg: combine flags & mask into a struct, use
 that

On Mon 2020-06-15 23:47:26, jim.cromie@...il.com wrote:
> On Mon, Jun 15, 2020 at 9:14 AM Petr Mladek <pmladek@...e.com> wrote:
> >
> > On Sat 2020-06-13 09:57:27, Jim Cromie wrote:
> > > combine flags & mask into a struct, and replace those 2 parameters in
> > > 3 functions: ddebug_change, ddebug_parse_flags, ddebug_read_flags,
> > > altering the derefs in them accordingly.
> > >
> > > This simplifies the 3 function sigs, preparing for more changes.
> > > We dont yet need mask from ddebug_read_flags, but will soon.
> > > ---
> > >  lib/dynamic_debug.c | 46 +++++++++++++++++++++++----------------------
> > >  1 file changed, 24 insertions(+), 22 deletions(-)
> > >
> > > diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
> > > index 93c627e9c094..8dc073a6e8a4 100644
> > > --- a/lib/dynamic_debug.c
> > > +++ b/lib/dynamic_debug.c
> > > +struct flagsettings {
> > > +     unsigned int flags;
> > > +     unsigned int mask;
> > > +};
> >
> > static int ddebug_change(const struct ddebug_query *query,
> > > -                     unsigned int pflags, unsigned int mask)
> > > +                      struct flagsettings *mods)
> >
> > > -static int ddebug_read_flags(const char *str, unsigned int *flags)
> > > +static int ddebug_read_flags(const char *str, struct flagsettings *f)
> >
> > > -static int ddebug_parse_flags(const char *str, unsigned int *flagsp,
> > > -                            unsigned int *maskp)
> > > +static int ddebug_parse_flags(const char *str, struct flagsettings *mods)
> >
> > What "mods" stands for, please?
> >
> modifying_flags, or modifiers.
> the original flags & mask bundled together
> ie the pfmlt in
>    echo +pfmlt > control

Honestly, storing flags and mask is a hack that makes the code
tricky like hell.

IMHO, it would be much easier to define something like:

struct flags_operation {
	unsinged int flags;
	enum flags_operation_type op;
}

Where the opration would be:

enum flags_operation_type {
	DD_FLAGS_SET,		/* for '=' */
	DD_FLAGS_ADD,		/* for '+' */
	DD_FLAGS_DEL,		/* for '-' */
	DD_FLAGS_FILTER_MATCH,
	DD_FLAGS_FILTER_NON_MATCH,
};

Then you could define

     struct flags_operation fop_change;
     struct flags_operation fop_filter;

Then you could do in ddebug_change():

	if (fop_filter) {
		switch(fop_filter->op) {
			case DD_FLAGS_FILTER_MATCH:
				if ((dp->flags & fop_filter->flags) != fop_filter->flags)
					continue;
				break;
			case: DD_FLAGS_FILTER_NON_MATCH:
				if ((dp->flags & fop_filter->flags)
					continue;
				break;
			default:
				// warn error;
		}
	}

	switch (fop_change->op) {
		case DD_FLAGS_SET:
			dp->flags = fop_change->flags;
			break;
		case DD_FLAGS_ADD:
			dp->flags |= fop_change->flags;
			break;
		case DD_FLAGS_DEL:
			dp->flgas &= ^(fop_change->flgas);
			break;
		default:
			// error;
	}


It might be more lines. But the bit operations will become straightforward.
and the code self-explaining,


> does the above help ?
> I could go with modifying_flags
> keep in mind the name has to suit all + - = operations
> 
> I'll review all the new names. I recall you didnt like filterflags either,
> so I wasnt sufficently clear there either.
> Im mulling a better explanation.


The above would make the code manageable. Another question is the user
interface.

I still wonder if it is worth it.
What is the motivation for this fitlering?
Is it requested by users?
Or is it just a prerequisite for the user-specific filters?

We need to be really careful. User interface is hard to change
or remove later.

Best Regards,
Petr