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

Frederic Weisbecker
2009-03-13T15:03:20Z

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 :)