Re: [PATCH 00/11] [GIT PULL] more updates for the tag format

[Steven Rostedt]

On Wed, 10 Jun 2009, Theodore Tso wrote:

> On Wed, Jun 10, 2009 at 01:11:40PM +0200, Frédéric Weisbecker wrote:
> > Well, indeed I had worries, but I discussed about it with Steven and
> > now I actually
> > think this new tag format is much more powerful than printf style.
> > It brings a cleaner, and much higher level way to control the data exports.
> > 
> > But it would be nice to read some opinions from end users (end
> > developers) of TRACE_EVENT().
> 
> Maybe I'm missing something, but looks like the this new format, while
> simpler and easier to read, doesn't have support for using a more
> complicated C expression as a printk argument.  For example:
> 
> 	TP_printk("dev %s ino %lu mode %d uid %u gid %u blocks %llu",
> 		  jbd2_dev_to_name(__entry->dev), __entry->ino, __entry->mode,
> 		  __entry->uid, __entry->gid, __entry->blocks)
> 
> How should I handle the "jbd2_dev_to_name(__entry->dev)" argument to
> TP_printk?  The whole point of calling jbd2_dev_to_name() at TP_printk
> time is to not bloat the ring buffer with a 32 byte devname.

Understood, and the example you just gave also has the flaw that a 
userspace tool could not parse it, because it would not know what to do 
with "jbd2_dev_to_name()".

This is why I suggested keeping the TP_printk, for cases like this. Since 
it is also currently useless in userspace.

But we really should convert all cases, and I was toying with an idea to 
dynamically make your own data type, and be able to make a way to print 
it. That is you could register:

register_trace_event_data_type(const char *name, 
	(int)(*print_func)(struct trace_seq *s, void *data, int size),
	const char *fmt, ...);

Where the name would be the data type you are making, the print_func is 
how ftrace would print it in debugfs/tracing/trace, and the fmt, ... would 
be who to show the user how to print it.

For example, for the GFP flags we could do something like:

/* helper routine */
unsigned long long trace_get_word(void *p, int len)
{
	unsigned long long val;

        switch (size) {
        case 1:
                val = *(char *)p;
                break;
        case 2:
                val = *(short *)p;
                break;
        case 4:
                val = *(int *)p;
                break;
        case 8:
                val = *(long long *)p;
                break;
        default:
		WARN(1,"length %d not valid word size\n");
                return 0;
        }

        return val;
}

static int test_gfp(unsigned long *gfp, unsigned long mask)
{
	if ((*gfp & mask) == mask) {
		*gfp &= ~mask;
		return 1;
	}
	return 0;
}

#define test_gfp_name(under, name)			\
	if (test_gfp(&gfp, under##GFP_##name)) {	\
		if (first)				\
			first = 0;			\
		else					\
			trace_seq_putc(s, '|');		\
		trace_seq_puts(s, "GFP_" #name);	\
	}


static int print_gfp(struct trace_seq *s, void *data, int len)
{
	unsigned long gfp;

	gfp = trace_get_word(data, len);

	if (!gfp) {
		trace_seq_puts(s, GPF_NOWAIT);
		return 0;
	}

	while (gfp) {
		test_gfp_name(,HIGHUSER_MOVABLE);
		test_gfp_name(,HIGHUSER);
		test_gfp_name(,USER);
		test_gfp_name(,TEMPORARY);
		test_gfp_name(,KERNEL);
		test_gfp_name(,NOFS);
		test_gfp_name(,ATOMIC);
		test_gfp_name(,NOIO);
		test_gfp_name(__,HIGH);
		test_gfp_name(__,WAIT);
		test_gfp_name(__,IO);
		test_gfp_name(__,COLD);
		test_gfp_name(__,NOWARN);
		test_gfp_name(__,REPEAT);
		test_gfp_name(__,NOFAIL);
		test_gfp_name(__,NORETRY);
		test_gfp_name(__,COMP);
		test_gfp_name(__,ZERO);
		test_gfp_name(__,NOMEMALLOC);
		test_gfp_name(__,HARDWALL);
		test_gfp_name(__,THISNODE);
		test_gfp_name(__,RECLAIMABLE);
		test_gfp_name(__,MOVABLE);

}

#define gfp_insert(under, name)	\
		(unsigned long)under##GFP_##name, "GFP_" #name

	register_trace_event_data_type("gfp", print_gfp,
		"mask:\n"
	        " 0=GFP_NOWAIT,"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n"
		" 0x%lx=%s,\n",
		gfp_insert(,HIGHUSER_MOVABLE),
		gfp_insert(,HIGHUSER),
		gfp_insert(,USER),
		gfp_insert(,TEMPORARY),
		gfp_insert(,NOFS),
		gfp_insert(,ATOMIC),
		gfp_insert(,NOIO),
		gfp_insert(__,HIGH),
		gfp_insert(__,WAIT),
		gfp_insert(__,IO),
		gfp_insert(__,COLD),
		gfp_insert(__,NOWARN),
		gfp_insert(__,REPEAT),
		gfp_insert(__,NOFAIL),
		gfp_insert(__,NORETRY),
		gfp_insert(__,COMP),
		gfp_insert(__,ZERO),
		gfp_insert(__,NOMEMALLOC),
		gfp_insert(__,HARDWALL),
		gfp_insert(__,THISNODE),
		gfp_insert(__,RECLAIMABLE),
		gfp_insert(__,MOVEABLE));


And then in the trace format, we could do:

	<data:gfp:field>

And the 'data' will flag us to how to print the data.

For userland, there could be a file in:

	/debug/tracing/events/data_types/gfp/format

That will show that format. Yes we duplicate some of the code, but it 
it would solve these types of issues.

-- Steve