lkml.org 
[lkml]   [2017]   [Jun]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] tracing: Add saved_tgids file to show cached pid to tgid mappings
On Fri, 30 Jun 2017 11:17:50 -0600
Michael Sartain <mikesart@fastmail.com> wrote:

> Export the cached pid / tgid mappings to userspace. This allows user
> apps to translate the pids from a trace to their respective thread
> group.
>
> Example saved_tgids file with pid / tgid values separated by ' ':
>
> # cat saved_tgids
> 1048 1048
> 1047 1047
> 7 7
> 1049 1047
> 1054 1047
> 1053 1047
>
> [ Impact: let userspace apps reading binary buffer know tgid's ]

Impact line? Linus put a kibosh on this a while ago...

https://lkml.org/lkml/2009/4/15/296

Although, I will admit that this line is actually useful. Just remove
the brackets.

>
> Signed-off-by: Michael Sartain <mikesart@fastmail.com>
> ---
> kernel/trace/trace.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 59 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 68c214b..ca84c97 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -4692,6 +4692,7 @@ static const struct file_operations tracing_readme_fops = {
> static void *saved_cmdlines_next(struct seq_file *m, void *v, loff_t *pos)
> {
> unsigned int *ptr = v;
> + long tgid_check = (long) m->private;

I really don't like the subtle use of having m->private != NULL mean
this is for tgid listing.

In fact, I don't see the purpose of reusing the seq code. The cmdlines
and tgid map are quite different. Just create its own functions. I
don't see the benefit of trying to reuse this except for making the
code more complex.

-- Steve

>
> if (*pos || m->count)
> ptr++;
> @@ -4702,6 +4703,8 @@ static void *saved_cmdlines_next(struct seq_file *m, void *v, loff_t *pos)
> ptr++) {
> if (*ptr == -1 || *ptr == NO_CMDLINE_MAP)
> continue;
> + if (tgid_check && !trace_find_tgid(*ptr))
> + continue;
>
> return ptr;
> }
> @@ -4713,6 +4716,10 @@ static void *saved_cmdlines_start(struct seq_file *m, loff_t *pos)
> {
> void *v;
> loff_t l = 0;
> + long tgid_check = (long) m->private;
> +
> + if (tgid_check && !tgid_map)
> + return NULL;
>
> preempt_disable();
> arch_spin_lock(&trace_cmdline_lock);
> @@ -4743,6 +4750,14 @@ static int saved_cmdlines_show(struct seq_file *m, void *v)
> return 0;
> }
>

\
 
 \ /
  Last update: 2017-06-30 23:51    [W:0.046 / U:8.604 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site