linux-kernel - Re: [Patch 11/11] ftrace plugin for kernel symbol tracing using HW Breakpoint interfaces

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Date:	Sun, 22 Mar 2009 10:35:43 +0100
From:	Pavel Machek <pavel@....cz>
To:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@....ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	maneesh@...ux.vnet.ibm.com, Roland McGrath <roland@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [Patch 11/11] ftrace plugin for kernel symbol tracing using HW
	Breakpoint interfaces - v2

Hi!

> This patch adds an ftrace plugin to detect and profile memory access over
> kernel variables. It uses HW Breakpoint interfaces to 'watch memory
> addresses.


> +static void ksym_trace_print_header(struct seq_file *m)
> +{
> +
> +	seq_puts(m,
> +		 "#       TASK-PID      CPU#      Symbol         Type    "
> +		 "Function         \n");
> +	seq_puts(m,
> +		 "#          |           |          |              |         "
> +		 "|            \n");
> +}
...
> +	trace_assign_type(field, entry);
> +
> +	ret = trace_seq_printf(s, "%-15s %-5d %-3d %-20s ", field->p_name,
> +				entry->pid, iter->cpu, field->ksym_name);
> +	if (!ret)
> +		return TRACE_TYPE_PARTIAL_LINE;
> +
> +	switch (field->ksym_hbp->info.type) {
> +	case HW_BREAKPOINT_WRITE:
> +		ret = trace_seq_printf(s, " W  ");
> +		break;
> +	case HW_BREAKPOINT_RW:
> +		ret = trace_seq_printf(s, " RW ");
> +		break;
> +	default:
> +		return TRACE_TYPE_PARTIAL_LINE;
> +	}
> +#ifdef CONFIG_PROFILE_KSYM_TRACER
> +static int ksym_tracer_stat_headers(struct seq_file *m)
> +{
> +	seq_printf(m, "   Access type    ");
> +	seq_printf(m, "            Symbol                     Counter     \n");
> +	return 0;
> +}
...

> +	switch (access_type) {
> +	case HW_BREAKPOINT_WRITE:
> +		seq_printf(m, "     W     ");
> +		break;
> +	case HW_BREAKPOINT_RW:
> +		seq_printf(m, "     RW    ");
> +		break;
> +	default:
> +		seq_printf(m, "     NA    ");
> +	}
> +
> +	if (lookup_symbol_name(entry->ksym_addr, fn_name) >= 0)
> +		seq_printf(m, "               %s                 ", fn_name);
> +	else
> +		seq_printf(m, "               <NA>                ");
> +
> +	seq_printf(m, "%15lu\n", entry->counter);
> +	return 0;
> +}

Quite as lot of ascii-art here. Is userland expected to parse it? If
so, how? (docs would be nice) What if you'll want to make fields  wider one day?
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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