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SubjectRe: [PATCH v3] tracing: kdb: Allow ftdump to skip all but the last few lines
On Fri, 15 Mar 2019 10:45:28 -0700
Douglas Anderson <dianders@chromium.org> wrote:


> Changes in v3:
> - Optimize counting as per Steven Rostedt.
> - Down to 1 patch since patch #1 from v2 landed.
>
> kernel/trace/trace_kdb.c | 38 +++++++++++++++++++++++++++++---------
> 1 file changed, 29 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/trace/trace_kdb.c b/kernel/trace/trace_kdb.c
> index 810d78a8d14c..cc6ca6c0d6de 100644
> --- a/kernel/trace/trace_kdb.c
> +++ b/kernel/trace/trace_kdb.c
> @@ -17,7 +17,7 @@
> #include "trace.h"
> #include "trace_output.h"
>
> -static void ftrace_dump_buf(int skip_lines, long cpu_file)
> +static int ftrace_dump_buf(int skip_lines, long cpu_file, bool quiet)

Not quite what I wanted you to do.


> {
> /* use static because iter can be a bit big for the stack */
> static struct trace_iterator iter;
> @@ -39,8 +39,6 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file)
> /* don't look at user memory in panic mode */
> tr->trace_flags &= ~TRACE_ITER_SYM_USEROBJ;
>
> - kdb_printf("Dumping ftrace buffer:\n");
> -
> /* reset all but tr, trace, and overruns */
> memset(&iter.seq, 0,
> sizeof(struct trace_iterator) -
> @@ -55,6 +53,9 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file)
> cpu, GFP_ATOMIC);
> ring_buffer_read_start(iter.buffer_iter[cpu]);
> tracing_iter_reset(&iter, cpu);
> +
> + cnt +=
> + ring_buffer_entries_cpu(iter.trace_buffer->buffer, cpu);

BTW, 80 char limit is a guideline not a rule. Don't break a line to
make it look worse. But that doesn't matter because this isn't the
change I meant.

> }
> } else {
> iter.cpu_file = cpu_file;
> @@ -63,13 +64,21 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file)
> cpu_file, GFP_ATOMIC);
> ring_buffer_read_start(iter.buffer_iter[cpu_file]);
> tracing_iter_reset(&iter, cpu_file);
> +
> + cnt += ring_buffer_entries_cpu(iter.trace_buffer->buffer,
> + cpu_file);
> }
>
> - while (trace_find_next_entry_inc(&iter)) {
> - if (!cnt)
> - kdb_printf("---------------------------------\n");
> - cnt++;
> + if (quiet)
> + goto out;
> +
> + kdb_printf("Dumping ftrace buffer (skipping %d lines):\n",
> + skip_lines);
> +
> + if (cnt)
> + kdb_printf("---------------------------------\n");
>
> + while (trace_find_next_entry_inc(&iter)) {
> if (!skip_lines) {
> print_trace_line(&iter);
> trace_printk_seq(&iter.seq);
> @@ -99,6 +108,8 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file)
> iter.buffer_iter[cpu] = NULL;
> }
> }
> +
> + return cnt;
> }
>
> /*
> @@ -109,6 +120,7 @@ static int kdb_ftdump(int argc, const char **argv)
> int skip_lines = 0;
> long cpu_file;
> char *cp;
> + int cnt;
>
> if (argc > 2)
> return KDB_ARGCOUNT;
> @@ -129,7 +141,14 @@ static int kdb_ftdump(int argc, const char **argv)
> }
>
> kdb_trap_printk++;
> - ftrace_dump_buf(skip_lines, cpu_file);
> +
> + /* A negative skip_lines means skip all but the last lines */
> + if (skip_lines < 0) {
> + cnt = ftrace_dump_buf(0, cpu_file, true);

Actually, you can add a function in trace.c that exposes
get_total_entries:

unsigned long trace_total_entries(struct trace_array *tr)
{
unsigned long total, entries;

if (!tr)
tr = &global_trace;

get_total_entries(tr->trace_buffer, &total, &entries);

return entries;
}

and then do:
cnt = trace_total_entries(NULL);

Don't modify ftrace_dump_buf()

-- Steve

> + skip_lines = max(cnt + skip_lines, 0);
> + }
> +
> + ftrace_dump_buf(skip_lines, cpu_file, false);
> kdb_trap_printk--;
>
> return 0;
> @@ -138,7 +157,8 @@ static int kdb_ftdump(int argc, const char **argv)
> static __init int kdb_ftrace_register(void)
> {
> kdb_register_flags("ftdump", kdb_ftdump, "[skip_#lines] [cpu]",
> - "Dump ftrace log", 0, KDB_ENABLE_ALWAYS_SAFE);
> + "Dump ftrace log; -skip dumps last #lines", 0,
> + KDB_ENABLE_ALWAYS_SAFE);
> return 0;
> }
>

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