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[PATCH] tracing: Add saved_tgids file to show cached pid to tgid mappings

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  [PATCH] tracing: Add saved_tgids file to show cached pid to tgid  mappings Michael Sartain <mikesart@fastmail.com> - 2017-06-30 19:20 +0200
    Re: [PATCH] tracing: Add saved_tgids file to show cached pid to  tgid mappings Steven Rostedt <rostedt@goodmis.org> - 2017-07-01 00:00 +0200
      Re: [PATCH] tracing: Add saved_tgids file to show cached pid to tgid mappings Joel Fernandes <joelaf@google.com> - 2017-07-01 01:40 +0200
      Re: [PATCH] tracing: Add saved_tgids file to show cached pid to tgid  mappings Michael Sartain <mikesart@fastmail.com> - 2017-07-01 02:40 +0200
    Re: [PATCH] tracing: Add saved_tgids file to show cached pid to tgid  mappings kbuild test robot <lkp@intel.com> - 2017-07-02 03:50 +0200

#1679013 — [PATCH] tracing: Add saved_tgids file to show cached pid to tgid mappings

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 ]

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;
 
 	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;
 }
 
+static int saved_tgids_show(struct seq_file *m, void *v)
+{
+	unsigned int *pid = v;
+
+	seq_printf(m, "%d %d\n", *pid, trace_find_tgid(*pid));
+	return 0;
+}
+
 static const struct seq_operations tracing_saved_cmdlines_seq_ops = {
 	.start		= saved_cmdlines_start,
 	.next		= saved_cmdlines_next,
@@ -4750,12 +4765,45 @@ static const struct seq_operations tracing_saved_cmdlines_seq_ops = {
 	.show		= saved_cmdlines_show,
 };
 
+static const struct seq_operations tracing_saved_tgids_seq_ops = {
+	.start		= saved_cmdlines_start,
+	.next		= saved_cmdlines_next,
+	.stop		= saved_cmdlines_stop,
+	.show		= saved_tgids_show,
+};
+
 static int tracing_saved_cmdlines_open(struct inode *inode, struct file *filp)
 {
+	int ret;
+
+	if (tracing_disabled)
+		return -ENODEV;
+
+	ret = seq_open(filp, &tracing_saved_cmdlines_seq_ops);
+	if (!ret) {
+		struct seq_file *m = filp->private_data;
+
+		m->private = (void *) 0; /* Do not check for valid tgids */
+	}
+
+	return ret;
+}
+
+static int tracing_saved_tgids_open(struct inode *inode, struct file *filp)
+{
+	int ret;
+
 	if (tracing_disabled)
 		return -ENODEV;
 
-	return seq_open(filp, &tracing_saved_cmdlines_seq_ops);
+	ret = seq_open(filp, &tracing_saved_tgids_seq_ops);
+	if (!ret) {
+		struct seq_file *m = filp->private_data;
+
+		m->private = (void *) 1; /* Check for valid tgids */
+	}
+
+	return ret;
 }
 
 static const struct file_operations tracing_saved_cmdlines_fops = {
@@ -4765,6 +4813,13 @@ static const struct file_operations tracing_saved_cmdlines_fops = {
 	.release	= seq_release,
 };
 
+static const struct file_operations tracing_saved_tgids_fops = {
+	.open		= tracing_saved_tgids_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
 static ssize_t
 tracing_saved_cmdlines_size_read(struct file *filp, char __user *ubuf,
 				 size_t cnt, loff_t *ppos)
@@ -7933,6 +7988,9 @@ static __init int tracer_init_tracefs(void)
 	trace_create_file("saved_cmdlines_size", 0644, d_tracer,
 			  NULL, &tracing_saved_cmdlines_size_fops);
 
+	trace_create_file("saved_tgids", 0444, d_tracer,
+			NULL, &tracing_saved_tgids_fops);
+
 	trace_eval_init();
 
 	trace_create_eval_file(d_tracer);
-- 
2.11.0

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#1679153 — Re: [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;
>  }
>  

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#1679214 — Re: [PATCH] tracing: Add saved_tgids file to show cached pid to tgid mappings

On Fri, Jun 30, 2017 at 2:50 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> On Fri, 30 Jun 2017 11:17:50 -0600
[..]
>>
>> 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.

I agree with Steven, this patch should be rewritten to use separate
functions and not reuse the other ones as its otherwise really
confusing and not good design.

Thanks,
Joel

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#1679222

On Fri, Jun 30, 2017 at 05:50:57PM -0400, Steven Rostedt wrote:
> 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.

Ah, thank you. I saw it used in the previous cmdline patch and used it
as a reference.

> > 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.

Will do. Joel was also kind enough to send me feedback about RFCs and
merge windows, etc. so I apologize - wasn't trying to get anything by
anyone, just that this is my first real patch and I've obviously got a
lot to learn here. Thank you for the comments. I'll fix and resubmit
next week.
 -Mike

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#1679417

[Multipart message — attachments visible in raw view] — view raw

Hi Michael,

[auto build test ERROR on trace/for-next]
[also build test ERROR on next-20170630]
[cannot apply to tip/perf/core linus/master v4.12-rc7]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Michael-Sartain/tracing-Add-saved_tgids-file-to-show-cached-pid-to-tgid-mappings/20170702-092448
base:   https://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git for-next
config: i386-randconfig-x070-07010433 (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All errors (new ones prefixed by >>):

   kernel//trace/trace.c: In function 'saved_cmdlines_next':
>> kernel//trace/trace.c:4612:22: error: implicit declaration of function 'trace_find_tgid' [-Werror=implicit-function-declaration]
      if (tgid_check && !trace_find_tgid(*ptr))
                         ^~~~~~~~~~~~~~~
   kernel//trace/trace.c: In function 'saved_cmdlines_start':
>> kernel//trace/trace.c:4627:21: error: 'tgid_map' undeclared (first use in this function)
     if (tgid_check && !tgid_map)
                        ^~~~~~~~
   kernel//trace/trace.c:4627:21: note: each undeclared identifier is reported only once for each function it appears in
   cc1: some warnings being treated as errors

vim +/trace_find_tgid +4612 kernel//trace/trace.c

  4606		(*pos)++;
  4607	
  4608		for (; ptr < &savedcmd->map_cmdline_to_pid[savedcmd->cmdline_num];
  4609		     ptr++) {
  4610			if (*ptr == -1 || *ptr == NO_CMDLINE_MAP)
  4611				continue;
> 4612			if (tgid_check && !trace_find_tgid(*ptr))
  4613				continue;
  4614	
  4615			return ptr;
  4616		}
  4617	
  4618		return NULL;
  4619	}
  4620	
  4621	static void *saved_cmdlines_start(struct seq_file *m, loff_t *pos)
  4622	{
  4623		void *v;
  4624		loff_t l = 0;
  4625		long tgid_check = (long) m->private;
  4626	
> 4627		if (tgid_check && !tgid_map)
  4628			return NULL;
  4629	
  4630		preempt_disable();

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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