(03/06/2013 10:49 PM), Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)"<srost...@redhat.com>
>
> When cat'ing the snapshot file, instead of showing an empty trace
> header like the trace file does, show how to use the snapshot
> feature.
>
> Also, this is a good place to show if the snapshot has been allocated
> or not. Users may want to "pre allocate" the snapshot to have a fast
> "swap" of the current buffer. Otherwise, a swap would be slow and might
> fail as it would need to allocate the snapshot buffer, and that might
> fail under tight memory constraints.
>
> Here's what it looked like before:
>
> # tracer: nop
> #
> # entries-in-buffer/entries-written: 0/0 #P:4
> #
> # _-----=> irqs-off
> # / _----=> need-resched
> # | / _---=> hardirq/softirq
> # || / _--=> preempt-depth
> # ||| / delay
> # TASK-PID CPU# |||| TIMESTAMP FUNCTION
> # | | | |||| | |
>
> Here's what it looks like now:
>
> # tracer: nop
> #
> #
> # * Snapshot is freed *
> #
> # Snapshot commands:
> # echo 0 > snapshot : Clears and frees snapshot buffer
> # echo 1 > snapshot : Allocates snapshot buffer, if not already allocated.
> # Takes a snapshot of the main buffer.
> # echo 2 > snapshot : Clears snapshot buffer (but does not allocate)
> # (Doesn't have to be '2' works with any number that
> # is not a '0' or '1')
>
> Cc: Hiraku Toyooka<hiraku.toyooka...@hitachi.com>
> Signed-off-by: Steven Rostedt<rost...@goodmis.org>
> ---
Acked-by: Hiraku Toyooka <hiraku.toyooka...@hitachi.com>
> kernel/trace/trace.c | 25 ++++++++++++++++++++++++-
> 1 file changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index c2e2c23..9e3120b 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2400,6 +2400,27 @@ static void test_ftrace_alive(struct seq_file *m)
> seq_printf(m, "# MAY BE MISSING FUNCTION EVENTS\n");
> }
>
> +#ifdef CONFIG_TRACER_MAX_TRACE
> +static void print_snapshot_help(struct seq_file *m, struct trace_iterator
> *iter)
> +{
> + if (iter->trace->allocated_snapshot)
> + seq_printf(m, "#\n# * Snapshot is allocated *\n#\n");
> + else
> + seq_printf(m, "#\n# * Snapshot is freed *\n#\n");
> +
> + seq_printf(m, "# Snapshot commands:\n");
> + seq_printf(m, "# echo 0 > snapshot : Clears and frees snapshot
> buffer\n");
> + seq_printf(m, "# echo 1 > snapshot : Allocates snapshot buffer, if not
> already allocated.\n");
> + seq_printf(m, "# Takes a snapshot of the main
> buffer.\n");
> + seq_printf(m, "# echo 2 > snapshot : Clears snapshot buffer (but does
> not allocate)\n");
> + seq_printf(m, "# (Doesn't have to be '2' works
> with any number that\n");
> + seq_printf(m, "# is not a '0' or '1')\n");
> +}
> +#else
> +/* Should never be called */
> +static inline void print_snapshot_help(struct seq_file *m, struct
> trace_iterator *iter) { }
> +#endif
> +
> static int s_show(struct seq_file *m, void *v)
> {
> struct trace_iterator *iter = v;
> @@ -2411,7 +2432,9 @@ static int s_show(struct seq_file *m, void *v)
> seq_puts(m, "#\n");
> test_ftrace_alive(m);
> }
> - if (iter->trace && iter->trace->print_header)
> + if (iter->snapshot && trace_empty(iter))
> + print_snapshot_help(m, iter);
> + else if (iter->trace && iter->trace->print_header)
> iter->trace->print_header(m);
> else
> trace_default_header(m);
> -- 1.7.10.4 .
>
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