Re: [PATCH 09/16] tracing: export trace formats to user space

[Frederic Weisbecker <fweisbec@gmail.com>]

On Thu, Mar 12, 2009 at 10:37:13PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@redhat.com>
> 
> The binary printk saves a pointer to the format string in the ring buffer.
> On output, the format is processed. But if the user is reading the
> ring buffer through a binary interface, the pointer is meaningless.
> 
> This patch creates a file called printk_formats that maps the pointers
> to the formats.
> 
>  # cat /debug/tracing/printk_formats
> 0xffffffff80713d40 : "irq_handler_entry: irq=%d handler=%s\n"
> 0xffffffff80713d48 : "lock_acquire: %s%s%s\n"
> 0xffffffff80713d50 : "lock_release: %s\n"
> 
> Signed-off-by: Steven Rostedt <srostedt@redhat.com>
> ---
>  kernel/trace/trace_printk.c |  119 +++++++++++++++++++++++++++++++++++++++++--
>  1 files changed, 114 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/trace/trace_printk.c b/kernel/trace/trace_printk.c
> index f307a11..4867852 100644
> --- a/kernel/trace/trace_printk.c
> +++ b/kernel/trace/trace_printk.c
> @@ -4,18 +4,19 @@
>   * Copyright (C) 2008 Lai Jiangshan <laijs@cn.fujitsu.com>
>   *
>   */
> +#include <linux/seq_file.h>
> +#include <linux/debugfs.h>
> +#include <linux/uaccess.h>
>  #include <linux/kernel.h>
>  #include <linux/ftrace.h>
>  #include <linux/string.h>
> +#include <linux/module.h>
> +#include <linux/marker.h>
> +#include <linux/mutex.h>
>  #include <linux/ctype.h>
>  #include <linux/list.h>
> -#include <linux/mutex.h>
>  #include <linux/slab.h>
> -#include <linux/module.h>
> -#include <linux/seq_file.h>
>  #include <linux/fs.h>
> -#include <linux/marker.h>
> -#include <linux/uaccess.h>
>  
>  #include "trace.h"
>  
> @@ -153,6 +154,114 @@ int __ftrace_vprintk(unsigned long ip, const char *fmt, va_list ap)
>  }
>  EXPORT_SYMBOL_GPL(__ftrace_vprintk);
>  
> +static void *
> +t_next(struct seq_file *m, void *v, loff_t *pos)
> +{
> +	const char **fmt = m->private;
> +	const char **next = fmt;
> +
> +	(*pos)++;
> +
> +	if ((unsigned long)fmt >= (unsigned long)__stop___trace_bprintk_fmt)
> +		return NULL;
> +
> +	next = fmt;
> +	m->private = ++next;
> +
> +	return fmt;
> +}
> +
> +static void *t_start(struct seq_file *m, loff_t *pos)
> +{
> +	return t_next(m, NULL, pos);
> +}
> +
> +static int t_show(struct seq_file *m, void *v)
> +{
> +	const char **fmt = v;
> +	const char *str = *fmt;
> +	int i;
> +
> +	seq_printf(m, "0x%lx : \"", (unsigned long)fmt);
> +
> +	/*
> +	 * Tabs and new lines need to be converted.
> +	 */
> +	for (i = 0; str[i]; i++) {
> +		switch (str[i]) {
> +		case '\n':
> +			seq_puts(m, "\\n");
> +			break;
> +		case '\t':
> +			seq_puts(m, "\\t");
> +			break;
> +		case '\\':
> +			seq_puts(m, "\\");
> +			break;
> +		case '"':
> +			seq_puts(m, "\\\"");
> +			break;
> +		default:
> +			seq_putc(m, str[i]);
> +		}
> +	}
> +	seq_puts(m, "\"\n");
> +
> +	return 0;
> +}
> +
> +static void t_stop(struct seq_file *m, void *p)
> +{
> +}
> +
> +static const struct seq_operations show_format_seq_ops = {
> +	.start = t_start,
> +	.next = t_next,
> +	.show = t_show,
> +	.stop = t_stop,
> +};
> +
> +static int
> +ftrace_formats_open(struct inode *inode, struct file *file)
> +{
> +	int ret;
> +
> +	ret = seq_open(file, &show_format_seq_ops);
> +	if (!ret) {
> +		struct seq_file *m = file->private_data;
> +
> +		m->private = __start___trace_bprintk_fmt;
> +	}
> +	return ret;
> +}
> +
> +static const struct file_operations ftrace_formats_fops = {
> +	.open = ftrace_formats_open,
> +	.read = seq_read,
> +	.llseek = seq_lseek,
> +	.release = seq_release,
> +};
> +
> +static __init int init_trace_printk_function_export(void)
> +{
> +	struct dentry *d_tracer;
> +	struct dentry *entry;
> +
> +	d_tracer = tracing_init_dentry();
> +	if (!d_tracer)
> +		return 0;
> +
> +	entry = debugfs_create_file("printk_formats", 0444, d_tracer,
> +				    NULL, &ftrace_formats_fops);
> +	if (!entry)
> +		pr_warning("Could not create debugfs "
> +			   "'printk_formats' entry\n");
> +
> +	return 0;
> +}
> +
> +fs_initcall(init_trace_printk_function_export);
> +
>  static __init int init_trace_printk(void)
>  {
>  	return register_module_notifier(&module_trace_bprintk_format_nb);
> -- 
> 1.6.1.3
> 
> -- 

If I remember well, a very similar patch as in the first bprintk serie sent by Lai
in december. I should have include it. Anyway it's too late :)