Re: [PATCH 2/2] trace-cmd: Add an option to set saved_cmdlines_size

[Vincent Donnefort <vincent.donnefort@arm.com>]

On Mon, Nov 11, 2019 at 05:52:03PM -0500, Steven Rostedt wrote:
> On Thu,  7 Nov 2019 10:51:06 +0000
> vincent.donnefort@arm.com wrote:
>
> > From: Vincent Donnefort <vincent.donnefort@arm.com>
> >
> > The tracing file saved_cmdlines_size allows setting the number of entries
> > that saved_cmdlines will contain. The latter is then dumped into the
> > trace.dat file to map PIDs with comm. The default value is 128.
> >
> > Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com>
> >
> > diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
> > index 7260d27..a4e10a4 100644
> > --- a/tracecmd/trace-record.c
> > +++ b/tracecmd/trace-record.c
> > @@ -229,6 +229,7 @@ struct common_record_context {
> >     int topt;
> >     int do_child;
> >     int run_command;
> > +   int saved_cmdlines_size;
> >  };
> >
> >  static void add_reset_file(const char *file, const char *val, int prio)
> > @@ -1810,6 +1811,39 @@ static void set_options(void)
> >     }
> >  }
> >
> > +static void set_saved_cmdlines_size(struct common_record_context *ctx)
> > +{
> > +   char *path, *str;
> > +   int fd, len, ret;
> > +
> > +   if (!ctx->saved_cmdlines_size)
> > +           return;
> > +
> > +   path = tracecmd_get_tracing_file("saved_cmdlines_size");
> > +   if (!path)
> > +           goto err;
> > +
> > +   reset_save_file(path, RESET_DEFAULT_PRIO);
> > +
> > +   fd = open(path, O_WRONLY);
> > +   tracecmd_put_tracing_file(path);
> > +   if (fd < 0)
> > +           goto err;
> > +
> > +   len = asprintf(&str, "%d", ctx->saved_cmdlines_size);
> > +   if (len < 0)
> > +           die("%s couldn't allocate memory", __func__);
> > +
> > +   if (write(fd, str, len) > 0)
> > +           ret = 0;
> > +
> > +   close(fd);
> > +   free(str);
> > +err:
> > +   if (ret)
> > +           warning("Couldn't set saved_cmdlines_size");
> > +}
> > +
> >  static int trace_check_file_exists(struct buffer_instance *instance, char *file)
> >  {
> >     struct stat st;
> > @@ -5480,7 +5514,7 @@ static void parse_record_options(int argc,
> >             if (IS_EXTRACT(ctx))
> >                     opts = "+haf:Fp:co:O:sr:g:l:n:P:N:tb:B:ksiT";
> >             else
> > -                   opts = "+hae:f:FA:p:cC:dDGo:O:s:r:vg:l:n:P:N:tb:R:B:ksSiTm:M:H:q";
> > +                   opts = "+hae:f:FA:p:cC:dDGo:O:s:r:vg:l:n:P:N:tb:R:B:kK:sSiTm:M:H:qK";
> >             c = getopt_long (argc-1, argv+1, opts, long_options, &option_index);
> >             if (c == -1)
> >                     break;
> > @@ -5741,6 +5775,9 @@ static void parse_record_options(int argc,
> >             case 'k':
> >                     keep = 1;
> >                     break;
> > +           case 'K':
> > +                   ctx->saved_cmdlines_size = atoi(optarg);
> > +                   break;
>
> Perhaps we should make this a long variable --cmdline-size(?), and not
> yet give it a short option.

Hi Steve,

Thank you for your review. I also thought that we could avoid having a new
option and try to write /proc/sys/kernel/threads-max into saved_cmdlines_size,
before recording the trace. Do you think that would be a more suitable
solution?

--
Vincent

>
> >             case 'i':
> >                     ignore_event_not_found = 1;
> >                     break;
> > @@ -5990,6 +6027,7 @@ static void record_trace(int argc, char **argv,
> >                     enable_events(instance);
> >     }
> >
> > +   set_saved_cmdlines_size(ctx);
> >     set_buffer_size();
> >     update_plugins(type);
> >     set_options();
> > diff --git a/tracecmd/trace-usage.c b/tracecmd/trace-usage.c
> > index b5788f7..ddfb480 100644
> > --- a/tracecmd/trace-usage.c
> > +++ b/tracecmd/trace-usage.c
> > @@ -47,6 +47,7 @@ static struct usage_help usage_help[] = {
> >             "          -b change kernel buffersize (in kilobytes per CPU)\n"
> >             "          -B create sub buffer and following events will be enabled here\n"
> >             "          -k do not reset the buffers after tracing.\n"
> > +           "          -K change kernel saved_cmdlines_size\n"
>
> We would also want to update the man pages too.
>
> Thanks!
>
> -- Steve
>
> >             "          -i do not fail if an event is not found\n"
> >             "          -q print no output to the screen\n"
> >             "          --quiet print no output to the screen\n"
>
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